A meteorite is a meteoroid (a solid piece of debris from such sources as asteroids or comets) originating in outer space that survives impact with the Earth’s surface. A meteorite’s size can range from small to extremely large. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids. When a meteoroid enters the atmosphere, frictional, pressure, and chemical interactions with the atmospheric gasses cause the body to heat up and emit light, thus forming a fireball, also known as a meteor or shooting/falling star. The term bolide refers to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface.
The Tunguska event was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 07:14 KRAT (00:14 UT) on June 30 [O.S. June 17], 1908. The explosion, having the epicentre (60.886°N, 101.894°E), is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometres (3–6 mi) above the Earth’s surface. Different studies have yielded widely varying estimates of the object’s size, on the order of 100 metres (330 ft). It is the largest impact event on or near Earth in recorded history. The number of scholarly publications on the problem of the Tunguska explosion since 1908 may be estimated at about 1,000 (mainly in Russian). Many scientists have participated in Tunguska studies, the best-known of them being Leonid Kulik, Yevgeny Krinov, Kirill Florensky, Nikolai Vladimirovich Vasiliev, and Wilhelm Fast.
Although the Richter scale was not yet invented, the explosion is estimated to have created the effects of a magnitude 5.0 earthquake, causing buildings to shake, windows to break, and people to be knocked off their feet even at 40 miles away. The blast, centered in a desolate and forested area near the Podkamennaya Tunguska River in Russia, is estimated to have been a thousand times more powerful than the bomb dropped on Hiroshima. The explosion leveled an estimated 80 million trees over an 830 square-mile area in a radial pattern from the blast zone. Dust from the explosion hovered over Europe, reflecting light that was bright enough for Londoners to read at night by it.
At around 07:17 local time, Evenks natives and Russian settlers in the hills northwest of Lake Baikal observed a column of bluish light, nearly as bright as the Sun, moving across the sky. About 10 minutes later, there was a flash and a sound similar to artillery fire. Eyewitnesses closer to the explosion reported the sound source moving east to north. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away. The majority of witnesses reported only the sounds and the tremors, not the sighting of the explosion. Eyewitness accounts differ as to the sequence of events and their overall duration.
The explosion registered on seismic stations across Eurasia. In some places the shock wave would have been equivalent to an earthquake of 5.0 on the Richter scale. It also produced fluctuations in atmospheric pressure strong enough to be detected in Great Britain. Over the next few days, night skies in Asia and Europe were aglow; it has been theorized that this was due to light passing through high-altitude ice particles formed at extremely low temperatures, a phenomenon that occurred again when the Space Shuttle re-entered the Earth’s atmosphere. In the United States, the Smithsonian Astrophysical Observatory and the Mount Wilson Observatory observed a decrease in atmospheric transparency that lasted for several months, from suspended dust.
In the decades since this huge explosion, scientists and others have attempted to explain the cause of this mysterious event. The most commonly accepted scientific explanation is that either a meteor or a comet entered the Earth’s atmosphere and exploded a couple of miles above the ground (this explains the lack of impact crater). Other explanations have ranged from the possible to the ludicrous, including a natural gas leak escaped from the ground and exploded, a UFO spaceship crashed, the effects of a meteor destroyed by a UFO’s laser in an attempt to save Earth, a black hole that touched Earth, and an explosion caused by scientific tests done by Nikola Tesla. Over a hundred years later, the Tunguska Event remains a mystery. However, if the blast was caused by a comet or meteor entering the Earth’s atmosphere, it poses the serious possibility that in the future a similar meteor could once again enter Earth’s atmosphere, but this time, land on a populated area. The result would be catastrophic. Researchers continue to study the area to find answers to their many questions.
US researchers have found a new way to weld together metal nanowires – simply by bathing them in white light. The finding could offer a new way to fabricate transparent nanowire meshes for electronic applications in areas such as touchscreens and organic photovoltaics.Erik Garnett and colleagues at Stanford University used a technique called the polyol process to synthesise silver nanowires 30-80nm in diameter and 3-10µm long. The process results in nanowires that are coated in a molecular sheath of polyvinylpyrrolidine (PVP). The nanowires were deposited on a surface randomly by dropping or spraying. This resulted in many of the wires lying over one another in a criss-cross pattern. Due to the layer of PVP where the nanowires cross, a gap of about 2nm exists between them.
Researchers at the University of Sheffield in the UK have now demonstrated the ability to reliably weld individual nanowires and nanoobjects into complex geometries with controllable junctions. This represents a significant breakthrough for the current and future bottom-up localized assembly, integration, and repair of micro- and nanodevices.
“Most everyday joining techniques cannot be applied at the nanoscale, where nano-objects are easily destroyed by heat,” Dr. Beverley Inkson tells Nanowerk. “Scientists have developed many ways to make individual nano-objects, but not many ways to securely join them together. But now we have reached a point where the ability to weld individual nanoscale objects such as nanowires and nanoparticles together is becoming vitally important for nanotechnology applications such as nanosensors and nanoelectronics.” Inkson is a Reader in Nanostructured Materials at the University of Sheffield’s NanoLAB and Chair of the UK NanoFIB network. As part of the RCUK Basic Technology programme in Nanorobotics, where Inkson is project director, she and her team (post doc researcher Yong Peng and Professor Tony Cullis) have developed a new way to weld together individual nanowires and nano-objects using tiny blobs of metal solder less than 250 atoms across.
This nanoscale electrical welding technique radically improves the spatial resolution, flexibility, and controllability of welds between individual nanowires and nanoobjects. Inkson notes that the key advance is to avoid detrimental current flow though the nanoobjects to be joined and instead to locally deposit nanoscale volumes of a chosen metal at the weld site by Joule heating a sacrificial nanowire.
The new nanowelding technique can be used to join nano-objects with a wide range of shapes and chemistries, and so could be used in the future as part of a 3D nanoscale fabrication line. Nanosolder can also rejoin things that have come apart during use, such as interconnect wires in computer chips which often fail by the formation of holes (by ‘electromigration’). Nanosolder has immediate research and industrial applications including fabrication of multifunctional nanosensors and nanoelectronics constructed from a small number of nanoobjects, and repair of interconnects and failed nanoscale electronics.
The 20th century has produced the greatest advancement in ceramics and materials technology since humans have been capable of conceptive thought. As the limits of metal-based systems are surpassed, new materials capable of operating under higher temperatures, higher speeds, longer life factors and lower maintenance costs are required to maintain pace with technological advancements. Metals, by virtue of their unique properties: ductility, tensile strength, abundance, simple chemistry, relatively low cost of production, case of forming, case of joining, etc. have occupied the vanguard position in regard to materials development. This combination enables large shapes to be made; the Space Shuttle is a typical example of the application of advanced materials and an excellent example of the capability of advanced materials.
It is only during the last 30 years or so, with the advances of understanding in ceramic chemistry, crystallography and the more extensive knowledge gained in regard to the production of advanced and engineered ceramics that the potential for these materials has been realised. This advancement changed the way ceramic systems were viewed.
Techniques previously applied to metals were now considered applicable to ceramic systems. Phase transformations, alloying, quenching and tempering techniques were applied to a range of ceramic systems. Significant improvements to the fracture toughness, ductility and impact resistance of ceramics were realised and thus the gap in physical properties between ceramics and metals began to close. More recent developments in non-oxide and tougher ceramics (e.g. nitride ceramics) have closed the gap even further.
Ceramics for today’s engineering applications can be considered to be non-traditional. Traditional ceramics are the older and more generally known types, such as: porcelain, brick, earthenware, etc. The new and emerging family of ceramics are referred to as advanced, new or fine, and utilise highly refined materials and new forming techniques. These “new” or “advanced” ceramics, when used as an engineering material, posses several properties which can be viewed as superior to metal-based systems.
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous. Technical Ceramics can also be classified into three distinct material categories:
Oxidation resistant, chemically inert, electrically insulating, generally low thermal conductivity, slightly complex manufacturing and low cost for alumina, more complex manufacturing and higher cost for zirconia.
Low oxidation resistance, extreme hardness, chemically inert, high thermal conductivity, and electrically conducting, difficult energy dependent manufacturing and high cost.
Toughness, low and high oxidation resistance (type related), variable thermal and electrical conductivity, complex manufacturing processes, high cost.
Forging is one of the oldest known metalworking processes. Traditionally, forging was performed by a smith using hammer and anvil, and though the use of water power in the production and working of iron dates to the 12th century, the hammer and anvil are not obsolete. The smithy or forge has evolved over centuries to become a facility with engineered processes, production equipment, tooling, raw materials and products to meet the demands of modern industry.
In modern times, industrial forging is done either with presses or with hammers powered by compressed air, electricity, hydraulics or steam. These hammers may have reciprocating weights in the thousands of pounds. Smaller power hammers, 500 lb (230 kg) or less reciprocating weight, and hydraulic presses are common in art smithies as well. Some steam hammers remain in use, but they became obsolete with the availability of the other, more convenient, power sources. Forging can produce a piece that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics.
Some metals may be forged cold, but iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forging, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are generally more economical and more controllable. Alloys that are amenable to precipitation hardening, such as most aluminium alloys and titanium, can be hot forged, followed by hardening. Production forging involves significant capital expenditure for machinery, tooling, facilities and personnel. In the case of hot forging, a high-temperature furnace (sometimes referred to as the forge) is required to heat ingots or billets. Owing to the massiveness of large forging hammers and presses and the parts they can produce, as well as the dangers inherent in working with hot metal, a special building is frequently required to house the operation. In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer. Most forging operations use metal-forming dies, which must be precisely machined and carefully heat-treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved.
Press Forgings: Press forging use a slow squeezing action of a press, to transfer a great amount of compressive force to the workpiece. Unlike an open-die forging where multiple blows transfer the compressive energy to the outside of the product, press forging transfers the force uniformly to the bulk of the material. This results in uniform material properties and is necessary for large weight forgings. Parts made with this process can be quite large as much as 125 kg (260 lb) and 3m (10 feet) long.
Upset Forgings: Upset forging increases cross-section by compressing the length, this is used in making heads on bolts and fasteners, valves and other similar parts.
Roll Forgings: In roll forging, a bar stock, round or flat is placed between die rollers which reduces the cross-section and increases the length to form parts such as axles, leaf springs etc. This is essentially a form of draw forging.
Swaging: Swaging – a tube or rod is forced inside a die and the diameter is reduced as the cylindrical object is fed. The die hammers the diameter and causes the metal to flow inward causing the outer diameter of the tube or the rod to take the shape of the die.
Net Shape / Near-Net Shape Forging: In net shape or near-net shape forging, forging results in wastage of material in the form of material flash and subsequent machining operations. This wastage can be as high as 70 % for gear blanks, and even 90+ % in the case of aircraft structural parts. Net-shape and near-net-shape processes minimize the waste by making precision dies, producing parts with very little draft angle (less than 1º). These types of processes often eliminate or reduce machining. The processes are quite expensive in terms of tooling and the capital expenditure required. Thus, these processes can be only justified for current processes that are very wasteful where the material savings will pay for the significant increase in tooling costs.
Ferrite also known as alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body-centered cubic crystal structure. It is this crystalline structure which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material. Practically speaking, it can be considered pure iron. It has a strength of 280 N/mm2 and a hardness of approximately 80 Brinell.
Ferrites are chemical compounds consisting of ceramic materials with iron(III) oxide (Fe2O3) as their principal component. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.
Mild steel (carbon steel with up to about 0.2 wt% C) consist mostly of ferrite, with increasing amounts of pearlite (a fine lamellar structure of ferrite and cementite) as the carbon content is increased. Since bainite (shown as ledeburite on the diagram at the bottom of this page) and pearlite each have ferrite as a component, any iron-carbon alloy will contain some amount of ferrite if it is allowed to reach equilibrium at room temperature. The exact amount of ferrite will depend on the cooling processes the iron-carbon alloy undergoes as it cools from liquid state.
Ferrites are usually non-conductive ferrimagnetic ceramic compounds derived from iron oxides such as hematite (Fe2O3) or magnetite (Fe3O4) as well as oxides of other metals. Ferrites are, like most other ceramics, hard and brittle. In terms of their magnetic properties, the different ferrites are often classified as “soft” or “hard”, which refers to their low or high magnetic coercivity.
In pure iron, ferrite is stable below 910 °C (1,670 °F). Above this temperature the face-centred cubic form of iron, austenite (gamma-iron) is stable. Above 1,390 °C (2,530 °F), up to the melting point at 1,539 °C (2,802 °F), the body-centred cubic crystal structure is again the more stable form of delta-ferrite. Ferrite above the critical temperature A2 (Curie temperature) of 771 °C (1,044 K; 1,420 °F), where it is paramagnetic rather than ferromagnetic, is beta ferrite or beta iron.
Only a very small amount of carbon can be dissolved in ferrite; the maximum solubility is about 0.02 wt% at 723 °C (1,333 °F) and 0.005% carbon at 0 °C (32 °F). This is because carbon dissolves in iron interstitially, with the carbon atoms being about twice the diameter of the interstitial “holes”, so that each carbon atom is surrounded by a strong local strain field. Hence the enthalpy of mixing is positive (unfavourable), but the contribution of entropy to the free energy of solution stabilises the structure for low carbon content. 723 °C (1,333 °F) also is the minimum temperature at which iron-carbon austenite (0.8 wt% C) is stable; at this temperature there is a eutectoid reaction between ferrite, austenite and cementite.
Ferrite cores are used in electronic inductors, transformers, and electromagnets where the high electrical resistance of the ferrite leads to very low eddy current losses. They are commonly seen as a lump in a computer cable, called a ferrite bead, which helps to prevent high frequency electrical noise (radio frequency interference) from exiting or entering the equipment. Early computer memories stored data in the residual magnetic fields of hard ferrite cores, which were assembled into arrays of core memory. Ferrite powders are used in the coatings of magnetic recording tapes. One such type of material is iron (III) oxide.
Ferrite particles are also used as a component of radar-absorbing materials or coatings used in stealth aircraft and in the absorption tiles lining the rooms used for electromagnetic compatibility measurements. Most common radio magnets, including those used in loudspeakers, are ferrite magnets. Ferrite magnets have largely displaced Alnico magnets in these applications. It is a common magnetic material for electromagnetic instrument pickups. Ferrite nanoparticles exhibit superparamagnetic properties.
Liquid crystals (LCs) are matter in a state that has properties between those of conventional liquid and those of solid crystal. Liquid crystal materials are unique in their properties and uses. As research into this field continues and as new applications are developed, liquid crystals will play an important role in modern technology. This tutorial provides an introduction to the science and applications of these materials. For instance, an LC may flow like a liquid, but its molecules may be orientated in a crystal-like way. There are many different types of LC phases, which can be distinguished by their different optical properties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures. The contrasting areas in the textures correspond to domains where the LC molecules are oriented in different directions. Within a domain, however, the molecules are well ordered. LC materials may not always be in an LC phase (just as water may turn into ice or steam).
Liquid crystal materials were first discovered in 1888 by an Austrian botanist, F. Renitzer. However those liquid crystals were not suitable for any commercial usage, and it is only 25 years ago since the first material suitable for electronically driven displays, was developed. The first room-temperature nematic liquid crystal was observed in the late 1960s. Unfortunately this crystal had quite a short temperature range as it was affected by impurities. Occasionally in homologous series the temperature range could reach from –40 to +100 degrees Celsius. Unfortunately these mixtures were very unstable and they possessed a negative dielectric anisotropy not useful in the twist cell.
The major breakthrough came when cyanobiphenyl materials were discovered a few years later. The more stable phase had a large positive dielectric anisotropy as well as a strong birefringence nearly ideal for the twist cell. During the 1970s and 1980s several liquid crystal compounds and phases were discovered, primarily by the industry, but also in several research programs on liquid crystal materials in colleges and universities around the world.
The ferroelectric chiral smecic (FLC) phase was discovered in 1975 and proved to have a unique form of ferroelectricity. The first display based on the FLC phase was actually patented in 1980. Another example of new liquid crystal phases also discovered during this intense research period, are the forms of polymer dispersions. Also a new effect, the electroclinic effect, was discovered during this period and is now being carefully studied for possible future display applications. Lately several new materials has been discovered such as the retardation film which is extremely important for the supertwisted nematic (STN) and twisted nematic (TN) displays.
Most of this research is situated in Japan due to strong manufacturing capability and high research funds. The most frequently used liquid crystalline phase used today in display devices is the nematic phase. The phase is used both in the TN cell as well as in the active matrix (AM) TN cell. About 60 % of all nematic materials supplied by Merck-Japan, which is the biggest producer of such materials, goes to these applications. The active matrix TN cell is expected to grow substantially during the next 5 years as this technology dominates the manufacturing industry today. Other types of rapidly growing display types are the electrically controlled birefringence (ECB) and polymer-dispersed liquid crystals (PDLCs). Due to the relatively recent technology discovered in producing these cells, they have not yet reached a fully commercial usage.
Liquid crystal displays (LCD’s) offer several advantages over traditional cathode-ray tube displays. LCD’s are flat, and they use only a fraction of the power required by CRT’s. They are easier to read and more pleasant to work with for long periods of time than most ordinary video monitors. One should also now that there are several tradeoffs, such as limited view angel, brightness, and contrast, not to mention high manufacturing costs. As research continues, this limitations are slowly becoming less significant. Today’s LCD’s come mostly in two flavors passive and active. The less expensive passive matrix displays trade off picture quality, view angel, and response time with power requirements and manufacturing costs. Active matrix displays have superior picture quality and viewing characteristics, but need more power to run and are much more expensive to fabricate.
Liquid crystal displays show great potential for the future and there are improvements to be made. The next question is what are the physical limits of this technology ? To answer this question we need to explain liquid crystal in general to determine what characteristics it has and what makes it so appropriate for use in displays. We need to examine in detail the two common kinds of liquid crystal displays passive and active matrix to see how each works. Liquid crystal is a fourth “state” that certain kinds of matter can enter into under the right conditions. The molecules in solids exhibit both positional and orientational order, in other words the molecules are constrained to point only certain directions and to be only in certain positions with respect to each other. In liquids the molecules do not have any positional or orientational order, the direction the molecules point and positions are random.
The liquid crystal “phase” exists between the solid and liquid phase, the molecules in liquid crystal do not exhibit any positional order, but they do possess a certain degree of orientational order. The molecules do not all point the same direction all the time. They tend to point more in one direction over time than other directions. This direction is referred to as the director of the liquid crystal. The “amount” of order is measured by the order parameter of the liquid crystal. This order parameter is highly dependent on the temperature of the sample. See figure 3.1, a typical order vs. temperature relationship. Tc is the temperature of transition between the liquid crystal and the liquid states.
Mesoporous materials are defined as natural or synthetic materials having a pore diameter of 2-50 nm, halfway between the pore sizes that define micro- and macroporous materials. They have a large surface area and are particularly useful for applications in catalysis, separation, and absorption. A mesoporous material is a material containing pores with diameters between 2 and 50 nm. Porous materials are classified into several kinds by their size. According to IUPAC notation, microporous materials have pore diameters of less than 2 nm and macroporous materials have pore diameters of greater than 50 nm; the mesoporous category thus lies in the middle. Typical mesoporous materials include some kinds of silica and alumina that have similarly-sized fine mesopores.
Mesoporous oxides of niobium, tantalum, titanium, zirconium, cerium and tin have also been reported. According to the IUPAC, a mesoporous material can be disordered or ordered in a mesostructure. A procedure for producing mesoporous materials (silica) was patented around 1970. It went almost unnoticed and was reproduced in 1997. Mesoporous silica nanoparticles (MSNs) were independently synthesized in 1990 by researchers in Japan. They were later produced also at Mobil Corporation laboratories and named Mobil Crystalline Materials, or MCM-41.
Over the past 10 years, the concentration appears to have been on synthesis and structures of mesoporous materials. Methods of synthesis covered in the top 20 papers from this time period include block copolymer templating, oligomeric surfactant synthesis, and triblock copolymer synthesis, among others.
Structures of particular interest include mesoporous materials with hybrid organic/inorganic frameworks and crystalline or semi-crystalline frameworks. Over the past two years, the focus of the most-cited papers turns to applications of mesoporous materials. These applications include magnetic fluorescent delivery vehicles, mercury ion detection, drug-delivery systems, bone-tissue engineering, and other potential applications in the medical and environmental fields. Mesoporous materials are those with pores in the range 20-500Å in diameter. They have huge surface areas, providing a vast number of sites where sorption processes can occur. These materials have numerous applications in catalysis, separation and many other fields. The synthesis of these materials is of considerable interest and is constantly being developed to introduce different properties.
A superconductor is a material that can conduct electricity or transport electrons from one atom to another with no resistance. This means no heat, sound or any other form of energy would be released from the material when it has reached “critical temperature” (Tc), or the temperature at which the material becomes superconductive. Unfortunately, most materials must be in an extremely low energy state (very cold) in order to become superconductive. Research is underway to develop compounds that become superconductive at higher temperatures. Currently, an excessive amount of energy must be used in the cooling process making superconductors inefficient and uneconomical.
Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature.It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics.
Superconductors, materials that have no resistance to the flow of electricity, are one of the last great frontiers of scientific discovery. Not only have the limits of superconductivity not yet been reached, but the theories that explain superconductor behavior seem to be constantly under review. In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University (shown above). When he cooled it to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C), its resistance suddenly disappeared. The Kelvin scale represents an “absolute” scale of temperature. Thus, it was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. Later, in 1913, he won a Nobel Prize in physics for his research in this area.
The next great milestone in understanding how matter behaves at extreme cold temperatures occurred in 1933. German researchers Walther Meissner and Robert Ochsenfeld (above right) discovered that a superconducting material will repel a magnetic field. A magnet moving by a conductor induces currents in the conductor. This is the principle on which the electric generator operates. But, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material – causing the magnet to be repulsed. This phenomenon is known as strong diamagnetism and is today often referred to as the “Meissner effect” (an eponym). The Meissner effect is so strong that a magnet can actually be levitated over a superconductive material.
In subsequent decades other superconducting metals, alloys and compounds were discovered. In 1941 niobium-nitride was found to superconduct at 16 K. In 1953 vanadium-silicon displayed superconductive properties at 17.5 K. And, in 1962 scientists at Westinghouse developed the first commercial superconducting wire, an alloy of niobium and titanium (NbTi). High-energy, particle-accelerator electromagnets made of copper-clad niobium-titanium were then developed in the 1960s at the Rutherford-Appleton Laboratory in the UK, and were first employed in a superconducting accelerator at the Fermilab Tevatron in the US in 1987.
The first widely-accepted theoretical understanding of superconductivity was advanced in 1957 by American physicists John Bardeen, Leon Cooper, and John Schrieffer (above). Their Theories of Superconductivity became know as the BCS theory – derived from the first letter of each man’s last name – and won them a Nobel prize in 1972. The mathematically-complex BCS theory explained superconductivity at temperatures close to absolute zero for elements and simple alloys. However, at higher temperatures and with different superconductor systems, the BCS theory has subsequently become inadequate to fully explain how superconductivity is occurring.
Another significant theoretical advancement came in 1962 when Brian D. Josephson (above), a graduate student at Cambridge University, predicted that electrical current would flow between 2 superconducting materials – even when they are separated by a non-superconductor or insulator. His prediction was later confirmed and won him a share of the 1973 Nobel Prize in Physics. This tunneling phenomenon is today known as the “Josephson effect” and has been applied to electronic devices such as the SQUID, an instrument capabable of detecting even the weakest magnetic fields. The 1980′s were a decade of unrivaled discovery in the field of superconductivity. In 1964 Bill Little of Stanford University had suggested the possibility of organic (carbon-based) superconductors. The first of these theoretical superconductors was successfully synthesized in 1980 by Danish researcher Klaus Bechgaard of the University of Copenhagen and 3 French team members. (TMTSF)2PF6 had to be cooled to an incredibly cold 1.2K transition temperature (known as Tc) and subjected to high pressure to superconduct. But, its mere existence proved the possibility of “designer” molecules – molecules fashioned to perform in a predictable way.
Then, in 1986, a truly breakthrough discovery was made in the field of superconductivity. Alex Müller and Georg Bednorz (above), researchers at the IBM Research Laboratory in Rüschlikon, Switzerland, created a brittle ceramic compound that superconducted at the highest temperature then known: 30 K. What made this discovery so remarkable was that ceramics are normally insulators. They don’t conduct electricity well at all. So, researchers had not considered them as possible high-temperature superconductor candidates. The Lanthanum, Barium, Copper and Oxygen compound that Müller and Bednorz synthesized, behaved in a not-as-yet-understood way. (Original article printed in Zeitschrift für Physik Condensed Matter, April 1986.) The discovery of this first of the superconducting copper-oxides (cuprates) won the 2 men a Nobel Prize the following year. It was later found that tiny amounts of this material were actually superconducting at 58 K, due to a small amount of lead having been added as a calibration standard – making the discovery even more noteworthy.
In recent years, many discoveries regarding the novel nature of superconductivity have been made. In 1997 researchers found that at a temperature very near absolute zero an alloy of gold and indium was both a superconductor and a natural magnet. Conventional wisdom held that a material with such properties could not exist! Since then, over a half-dozen such compounds have been found. Recent years have also seen the discovery of the first high-temperature superconductor that does NOT contain any copper (2000), and the first all-metal perovskite superconductor (2001).
Also in 2001 a material that had been sitting on laboratory shelves for decades was found to be an extraordinary new superconductor. Japanese researchers measured the transition temperature of magnesium diboride at 39 Kelvin – far above the highest Tc of any of the elemental or binary alloy superconductors. While 39 K is still well below the Tc’s of the “warm” ceramic superconductors, subsequent refinements in the way MgB2 is fabricated have paved the way for its use in industrial applications. Laboratory testing has found MgB2 will outperform NbTi and Nb3Sn wires in high magnetic field applications like MRI.
Though a theory to explain high-temperature superconductivity still eludes modern science, clues occasionally appear that contribute to our understanding of the exotic nature of this phenomenon. In 2005, for example, Superconductors.ORG discovered that increasing the weight ratios of alternating planes within the layered perovskites can often increase Tc significantly. This has led to the discovery of more than 50 new high-temperature superconductors, including a candidate for a new world record.
A metal is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable, ductile and shiny. The meaning of the term “metal” differs for various communities for example, astronomers call for convenience metals everything but hydrogen and helium. Many elements and compounds that are not normally classified as metals become metallic under high pressures.
Metals typically consist of close-packed atoms, meaning that the atoms are arranged like closely packed spheres. Two packing motifs are common, one being body-centered cubic wherein each metal atom is surrounded by eight equivalent atoms. The other main motif is face-centered cubic where the metal atoms are surrounded by six neighboring atoms. Several metals adopt both structures, depending on the temperature.The materials are grouped roughly into two categories, these being “Non-metallic” and Metallic”. In respect to metallic materials these are then subsequently grouped into two groups being ferrous and non-ferrous. Each of the materials has their own characteristics and requires different machining techniques. Careful consideration needs to be given to the correct material selection for its application. (Definition: Ferrous as in containing Iron, e.g steel – Non-ferrous as in not containing Iron e.g aluminium, copper) A simple test for ferrous/non-ferrous materials is to use magnet as a magnet will sick to ferrous materials due to its iron content.
In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by de-localized electrons, which are responsible for the conductivity. The solid thus produced is held together by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds.
The transition metals (such as iron, copper, zinc, and nickel) are slower to oxidize because they form passivating layer of oxide that protects the interior. Others, like palladium, platinum and gold, do not react with the atmosphere at all. Some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades (like aluminium, magnesium, some steels, and titanium). The oxides of metals are generally basic, as opposed to those of nonmetals, which are acidic.
Painting, anodizing or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion. Metals in general have high electrical conductivity, high thermal conductivity, and high density. Typically they are malleable and ductile, deforming under stress without cleaving. In terms of optical properties, metals are shiny and lustrous. Sheets of metal beyond a few micrometres in thickness appear opaque, but gold leaf transmits green light.
Although most metals have higher densities than most nonmetals, there is wide variation in their densities, Lithium being the least dense solid element and osmium the densest. The alkali and alkaline earth metals in groups I A and II A are referred to as the light metals because they have low density, low hardness, and low melting points. The high density of most metals is due to the tightly packed crystal lattice of the metallic structure. The strength of metallic bonds for different metals reaches a maximum around the center of the transition metal series, as those elements have large amounts of delocalized electrons in tight binding type metallic bonds. However, other factors (such as atomic radius, nuclear charge, number of bonds orbitals, overlap of orbital energies, and crystal form) are involved as well.
Brass is an alloy which is made from a combination of copper and zinc as the main ingredients. In compared with carbon steel or stainless steel, the machine-ability of brass is good, and it also has good soldering properties.
There are many kinds of Alloys to choose from but often, Aluminium is chosen as it is lightweight (about 2700 kg/m3 density), it is comparatively soft and its process-ability is good. From a machining viewpoint pure aluminium (JIS A1000) greatly differs from Al-Cu alloy (JIS A2000) .
A typical stain less steel is JIS SUS304. The benefits of stainless steel is that it has high strength, great heat-resistance, and and it resists staining e.g rust. Due to its high resistance to heat it makes an ideal material for mechanical parts that are subjected to heating such as a heater of a Stirling engine.
Typical carbon steel materials are JIS S45C and JIS SS400. They are very cheap, excelling in weldability, and they can be subjected to various heat treatments. Since many machine tools are designed to cut mild steel material, it is very rare to encounter problems while machining.
Sodium is a chemical element with the symbol Na (from Latin: natrium) in the periodic table and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. The free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth most abundant element in the Earth’s crust, and exists in numerous minerals such as feldspars, sodalite and rock salt. Many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that chloride and sodium are the most common dissolved elements by weight in the Earth’s bodies of oceanic water.
Sodium is relatively abundant in the sun and other stars. The D lines of sodium are prominent in the solar spectrum. Sodium is the sixth most abundant element on earth. It comprises approximately 2.6% of the earth’s crust. Sodium is the most abundant of the alkali metals. The most common sodium compound is sodium chloride (salt). Sodium occurs in many minerals, such as cryolite, soda niter, zeolite, amphibole, and sodalite. Sodium is not found free in nature. It is obtained commercially by the electrolysis of dry fused sodium chloride.
Many sodium compounds are useful, such as sodium hydroxide (lye) for soapmaking, and sodium chloride for use as a deicing agent and a nutrient (edible salt). Sodium is an essential element for all animals and some plants. In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated. The consequent need of animals for sodium causes it to be classified as a dietary inorganic macro-mineral.
Sodium at standard temperature and pressure is a soft metal that can be readily cut with a knife and is a good conductor of electricity. Freshly exposed, sodium has a bright, silvery luster that rapidly tarnishes, forming a white coating of sodium hydroxide and sodium carbonate. These properties change at elevated pressures: at 1.5 Mbar, the color changes to black, then to red transparent at 1.9 Mbar, and finally clear transparent at 3 Mbar. All of these allotropes are insulators and electrides.
Sodium is generally less reactive than potassium and more reactive than lithium. Like all the alkali metals, it reacts exothermically with water, to the point that sufficiently large pieces melt to a sphere and may explode; this reaction produces caustic sodium hydroxide and flammable hydrogen gas. When burned in dry air, it mainly forms sodium peroxide as well as some sodium oxide. In moist air, sodium hydroxide results. Sodium metal is highly reducing, with the reduction of sodium ions requiring ?2.71 volts but potassium and lithium have even more negative potentials. Hence, the extraction of sodium metal from its compounds (such as with sodium chloride) uses a significant amount of energy.
Sodium chloride is important for animal nutrition. Sodium compounds are used in the glass, soap, paper, textile, chemical, petroleum, and metal industries. Metallic sodium is used in manufacturing of sodium peroxide, sodium cyanide, sodamide, and sodium hydride. Sodium is used in preparing tetraethyl lead. It is used in the reduction of organic esters and preparation of organic compounds. Sodium metal may be used to improve the structure of some alloys, to descale metal, and to purify molten metals. Sodium, as well as NaK, an alloy of sodium with potassium, are important heat transfer agents.
Hydrogen cracking also known as cold cracking or delayed cracking. The main feature of this type of crack is that it occurs in ferritic weldable steels, and generally occurs immediately on welding or after a short time after welding, but usually within 48hrs. The mechanism starts with lone hydrogen atoms diffusing through the metal.
At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible. Austempered iron is also susceptible.
Hydrogen cracks can be usually have the following characteristics :
Cracks, which originate in the HAZ, are usually associated with the coarse grain region. The cracks can be intergranular, transgranular or a mixture. Intergranular cracks are more likely to occur in the harder HAZ structures formed in low alloy and high carbon steels. Transgranular cracking is more often found in C-Mn steel structures. In fillet welding, cracks in the HAZ are usually associated with the weld root and parallel to the weld. In butt welds, the HAZ cracks are normally oriented parallel to the weld bead.
There are three factors, which can cause hydrogen cracking:
In low alloy steels, as the weld metal structure is more susceptible than the HAZ, cracking may be found in the weld bead. There are three factors, which can cause hydrogen cracking :
In C-Mn steels, because there is a greater risk of forming a brittle microstructure in the HAZ, most of the hydrogen cracks are likely to be found in the parent metal. Using the correct choice of electrodes, the weld metal will have a lower carbon content than the parent metal and, hence, a lower carbon equivalent (CE). However, transverse weld metal cracks can occur especially when welding thick sections.
Kevlar is five times stronger than steel but very light weight and half the wieght of fiberglass which made it ideal for making bulletproof vests. It is resistant to impact and abrasion damage. In seawwater its strength is 20 times more than steel which made it excellent for offshore drilling operations. Kevlar is made by Dupont Corporation.Kevlar is a chemical compuned polyparaphenylene terepthalamide which belongs to the class aromatic polyamide is a para-aramid synthetic fibre. Aramides belong to class of nylons. The aramide ring and the para structure is what gives kevlar its high strength and thermal stability. Kevlar was developed in 1965 by Stephanie Kwolek and Roberto Berendt at DuPont Laboratories. Kevlar is a very strong synthetic fiber that can be spun into cloth to make body armor. Kevlar cloth was first used to make body armor in the 1970′s. Kevlar went through a number of government tests until finally a “bullet-resistant” vest was developed.
The marketable vest was crafted from 15 layers of Kevlar cloth and could stop most bullets from common street guns like the 0.38 Special and the 0.22 Long Rifle. The vest was a hit with law enforcement because of its light weight, strength, and ability to wear it under clothes. The Kevlar vest has saved thousands of lives since its invention.
Kevlar wasn’t the first attempt to develop a bulletproof vest. There were a number of other attempts from 1880 on including vests made for many layers of cotton, silk and pressed steel plates. Often these armors were expensive, very heavy and restricted movement, just think of the kid in “Christmas Story” trying to walk to school. Although Kevlar has five times the strength of an equal weight of steel there’s no doubt stronger and lighter armors will be developed as we march into the future. Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires. Typically it is spun into ropes or fabric sheets that can be used as such or as an ingredient in composite material components. As far as body armor is concerned, armor was virtually unchanged for 300 years from 1600ish to the 1920′s. If anything the amount of armor soldiers wore was reduced. The full plate knights of medieval times slowly shed their armor until soldiers in the 1800′s only wore the occasional metal breastplate.
What types of Kevlar are aviailable :
Kevlar 29 – used mostly in body lining , vests and brakes.
Kevlar 49 – Due to its high tenacity it is used in suspension cables in bridges and ropes.
Kevllar 100 – this is colored version.
Kevlar 129 – Used in ballistic applications.
Applications of Kevlar :
It is used in Protection for bulletproof vests,fire blocking fabrics due to it shigh thermal stability.
sports equipments – in paddles and in inner lining of bicylce tires to protect from puncturing easily Music in marching drums and woodwind reeds.
Ropes and cable sheaths
Hoses where the outerlayer is made of kevlar to give reinforcement for added protection against sharp objects
High temperature conditions.
As sometimes happens in the arms and armor race, weapons technologically had far outpaced armor technology. The introduction of guns to Europe, notably the musket, started the slow but steady decline of metal armor. At first the muskets were highly inaccurate, slow reloading, and had poor penetrating power. The knights and men-at-arms would have been standing there laughing at the musketeers poor attack attempts. But unfortunately for the knight, guns were refined and all aspects were improved upon. Soon after bullets reached the point of penetrating the plate armor, armor smiths would have realized to make armor that was bulletproof would be too impractical and cumbersome. Weapon invention had outpaced armor invention. It wouldn’t catch up until almost 300 years later.
The basic premise of most pyrometallurgical operations is simple: high-temperature chemistry is employed to segregate valuable metals in one phase while rejecting gangue and impurities in another phase. In most instances, both phases are molten (such as the matte and slag in a conventional copper smelting operation). The gas phase may also be used to advantage, either as a means of separating valuable volatile constituents or for removing unwanted volatile impurities. These separation techniques form the basis of thermal smelting and refining operations.
Pyrometallurgy is a branch of extractive metallurgy. It consists of the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable metals. Pyrometallurgical treatment may produce saleable products such as pure metals, or intermediate compounds or alloys, suitable as feed for further processing. Examples of elements extracted by pyrometallurgical processes include the oxides of less reactive elements like Fe, Cu, Zn, Chromium, Tin, Manganese.
Pyrometallurgical processes are generally grouped into one or more of the following categories:
Most pyrometallurgical processes require energy input to sustain the temperature at which the process takes place. The energy is usually provided in the form of fossil fuel combustion, exothermic reaction of the material, or from electrical heat. When enough material is present in the feed to sustain the process temperature solely by exothermic reaction (i.e. without the addition of fuel or electrical heat), the process is said to be “autogenous.”
In metal extraction, a vast majority of metallurgical reactions are made to take place at elevated temperatures because than the ore compounds become relatively unstable, facilitating the release of the metal. This is the basis of pyrometallurgy. Pyrometallurgy deals with the methods of extraction of metals from their ores and their refining and is based on physical and chemical changes occurring at high temperatures, i.e. 500-2000°C.
Pyrometallurgical methods of metal production are usually cheaper and suited for large scale productions. Some of the noteworthy advantages of pyrometallurgy are:
Calcining is thermal decomposition of a material. Examples include decomposition of hydrates such as ferric hydroxide to ferric oxide and water vapor, or decomposition of calcium carbonate to calcium oxide and carbon dioxide and or of iron carbonate to iron oxide. Calcination processes are carried out in a variety of furnaces, including shaft furnaces, rotary kilns, and fluidized bed reactors.
Roasting consists of thermal gas-solid reactions, which can include oxidation, reduction, chlorination, sulfation, and pyrohydrolysis. The most common example of roasting is the oxidation of metal sulfide ores. The metal sulfide is heated in the presence of air to a temperature that allows the oxygen in the air to react with the sulfide to form sulfur dioxide gas and solid metal oxide. The solid product from roasting is often called “calcine.” In sulfide roasting, if the temperature and gas conditions are such that the sulfide feed is completely oxidized, the process is known as “dead roasting.” Sometimes, as in the case of pre-treating reverberatory or electric smelting furnace feed, the roasting process is performed with less than the required amount of oxygen to fully oxidize the feed.
In this case, the process is called “partial roasting,” because the sulfur is only partially removed. Finally, if the temperature and gas conditions are controlled such that the sulfides in the feed react to form metal sulfates instead of metal oxides, the process is known as “sulfation roasting.” Sometimes, temperature and gas conditions can be maintained such that a mixed sulfide feed (for instance a feed containing both copper sulfide and iron sulfide) reacts such that one metal forms a sulfate and the other forms an oxide, the process is known as “selective roasting” or “selective sulfation.”
Refining is the removal of impurities from materials by a thermal process. This covers a wide range of processes, involving different kinds of furnace or other plant. The term, ‘refining’ can also refer to certain electrolytic processes. Accordingly, some kinds of pyrometallurgical refining are referred to as ‘fire refining’
Smelting involves thermal reactions in which at least one product is a molten phase. Metal oxides can then be smelted by heating with coke or charcoal (forms of carbon), a reducing agent that liberates the oxygen as carbon dioxide leaving a refined mineral. Concern about the production of carbon dioxide is only a recent worry, following the identification of the enhanced greenhouse effect. Carbonate ores are also smelted with charcoal, but sometimes need to be calcined first. Other materials may need to be added as flux, aiding the melting of the oxide ores and assisting in the formation of a slag, as the flux reacts with impurities, such as silicon compounds.
Eastern Time, hitting the southern coast of New Jersey, with its winds slowing slightly to 80 miles an hour from 90 miles an hour earlier, the National Hurricane Center said. By Monday evening, the super storm had already knocked out power to more than 2 million homes and businesses from North Carolina to New England. And a jogger rounding a corner, or cresting a hill, might suddenly come face to face with the true extent of the damage that Monday night’s historic storm had inflicted: cars displaced by the 13ft storm surge that sluiced through Manhattan’s financial district; dangerously damaged power cables; trees wrenched from the ground by the wind; a 700-tonne tanker run aground on the Staten Island shoreline. A state of emergency was declared for Connecticut, Delaware, Washington, D.C., Maryland, Massachusetts, New Jersey, New York, Pennsylvania, Rhode Island and Virginia.
Even before Sandy made landfall, streets in New York, Maryland and New Jersey were already under water, as winds and water pushed ahead of the hurricane. Swelling water overran barriers in Atlantic City, N.J., where the Boardwalk was reported damaged from the hurricane-force winds that stretched up to 175 miles from the storm’s center. Snow was forecast in several states, with blizzard warnings out for higher elevations in Maryland, West Virginia and Virginia. President Barack Obama canceled campaign events to return to Washington, D.C. to oversee the federal government’s response to Sandy. Obama warned the storm, which killed at least 65 people in the Caribbean, could impact millions across a large piece of the United States. “Do not underestimate this storm, we are talking about surges we have not seen before,” New York Gov. Andrew Cuomo said of anticipated record flooding in low-lying coastal areas.
By mid-morning, the clean-up from Hurricane Sandy – reclassified, late on Monday, as a “superstorm” – was well under way. In Central Park in Manhattan and Prospect Park in Brooklyn, work crews were busy clearing tree limbs; on the Upper West Side, doormen hosed leaves into the gutters; at Ground Zero, a still-gaping hole into which river water gushed on Monday night, the repairs were beginning; John F Kennedy airport was scheduled to reopen on Wednesday.
But at the same time, New Yorkers were still struggling to calculate the true scale of the storm’s impact. Towns in New Jersey and Long Island remained under deep water, while flooding had significantly damaged homes and businesses across New York. The city’s schools were due to stay closed on Wednesday. The New York Stock Exchange remained closed on Tuesday, the first time since 1888 that it had closed for two days running because of the weather.
There is no light in the street, no people in the street,” said Ilona, a 22-year-old student from Russia, as she looked out over the murky water. From time to time an acrid smell of burning drifted by, as short circuits in the electrical grid sparked distant fires. On either side of the island of Manhattan, West Street and the FDR East River Drive were quickly underwater. It had recently been renovated, the New York Times reported, after being damaged in 2011 by Hurricane Irene. The night’s most dramatic rescue story concerned the evacuation of about 200 patients from New York University’s Langone Medical Center, after the hospital’s backup generators failed.
Throughout the night, most people seemed to agree, the region’s most senior politicians – New York mayor Michael Bloomberg, New Jersey’s fleece-clad governor, Chris Christie, and Governor Cuomo – were successful in their efforts to maintain calm and provide essential information. Was the New York Stock Exchange under three feet of water, as CNN, apparently working from internet rumours, reported? Was a hospital on fire in Coney Island, and were a score of power-company workers trapped in a building in Manhattan? New York, Philadelphia, Washington and Baltimore moved to shut down their subways, buses and trains and said schools would be closed on Monday.
As rain from the leading edges of the monster hurricane began to fall over the Northeast, hundreds of thousands of people from Maryland to Connecticut were ordered to evacuate low-lying coastal areas, including 375,000 in lower Manhattan and other parts of New York City, 50,000 in Delaware and 30,000 in Atlantic City, N.J., where the city’s 12 casinos were forced to shut down for only the fourth time ever.
If it’s not the storm, it’ll be the aftermath. Authorities warned that the nation’s biggest city could get hit with a surge of seawater that could swamp parts of lower Manhattan, flood subway tunnels and cripple the network of electrical and communications lines that are vital to the nation’s financial center. As of 8 p.m., it was centered about 485 miles southeast of New York City, moving at 15 mph, with hurricane-force winds extending an incredible 175 miles from its center. The storm could also dump up to 2 feet of snow in Kentucky, North Carolina and West Virginia.
Louis Uccellini, environmental prediction chief for the National Oceanic and Atmospheric Administration, told The Associated Press that given Sandy’s east-to-west track into New Jersey, the worst of the storm surge could be just to the north, in New York City, on Long Island and in northern New Jersey. New York called off school Monday for the city’s 1.1 million students and announced it would suspend all train, bus and subway service Sunday night. The New York Stock Exchange announced it will shut down its trading floor Monday but continue to trade electronically. In Washington, President Barack Obama promised the government would “respond big and respond fast” after the storm hits.
Yield strength is the stress at which a specified amount of permanent deformation of a material occurs. When we apply stress to a material, it deforms. Some of the deformation is plastic and the material can recover when the stress is relieved. But some deformation is permanent and the material cannot recover from it. As we apply more stress, there is more deformation. This plots on a curve in a somewhat linear, or proportional, way. But at some point, a bit more stress results in a lot more deformation, and this is the proportional limit of the material. Stress applied beyond this causes an increasing rate of deformation until the maximum or ultimate strength of the material is reached. Yield strength is the stress at which a specified amount of permanent deformation of a material occurs.
When we apply stress to a material, it deforms. Some of the deformation is plastic and the material can recover when the stress is relieved. But some deformation is permanent and the material cannot recover from it. As we apply more stress, there is more deformation. This plots on a curve in a somewhat linear, or proportional, way. But at some point, a bit more stress results in a lot more deformation, and this is the proportional limit of the material. Stress applied beyond this causes an increasing rate of deformation until the maximum or ultimate strength of the material is reached.
The yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible. In the three-dimensional space of the principal stresses, an infinite number of yield points form together a yield surface.
Knowledge of the yield point is vital when designing a component since it generally represents an upper limit to the load that can be applied. It is also important for the control of many materials production techniques such as forging, rolling, or pressing. In structural engineering, this is a soft failure mode which does not normally cause catastrophic failure or ultimate failure unless it accelerates buckling.
True elastic limit
The lowest stress at which dislocations move. This definition is rarely used, since dislocations move at very low stresses, and detecting such movement is very difficult.
Up to this amount of stress, stress is proportional to strain (Hooke’s law), so the stress-strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material.
Elastic limit (yield strength)
Beyond the elastic limit, permanent deformation will occur. The lowest stress at which permanent deformation can be measured. This requires a manual load-unload procedure, and the accuracy is critically dependent on equipment and operator skill. For elastomers, such as rubber, the elastic limit is much larger than the proportionality limit. Also, precise strain measurements have shown that plastic strain begins at low stresses.
The point in the stress-strain curve at which the curve levels off and plastic deformation begins to occur.
Offset yield point (proof stress)
When a yield point is not easily defined based on the shape of the stress-strain curve an offset yield point is arbitrarily defined. The value for this is commonly set at 0.1 or 0.2% of the strain. The offset value is given as a subscript, e.g., Rp0.2=310 MPa. High strength steel and aluminum alloys do not exhibit a yield point, so this offset yield point is used on these materials.
Upper yield point and lower yield point
Some metals, such as mild steel, reach an upper yield point before dropping rapidly to a lower yield point. The material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value. If a metal is only stressed to the upper yield point, and beyond, Lüders bands can develop.
Thin film materials are high purity materials and chemicals used to form or modify thin film deposits and substrates. Examples include precursor gases, sputtering targets, and evaporation filaments. A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction.
Thin films play an important role in many technological applications including microelectronic devices, magnetic storage media and surface coatings. A familiar application of thin films is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface.
The performance of optical coatings (e.g. antireflective, or AR, coatings) are typically enhanced when the thin film coating consists of multiple layers having varying thicknesses and refractive indices. Similarly, a periodic structure of alternating thin films of different materials may collectively form a so-called superlattice which exploits the phenomenon of quantum confinement by restricting electronic phenomena to two-dimensions. Work is being done with ferromagnetic and ferroelectric thin films for use as computer memory.
It is also being applied to pharmaceuticals, via thin film drug delivery. Thin-films are used to produce thin-film batteries. Thin film application also be adopted on Dye-sensitized solar cell. Ceramic thin films are in wide use. The relatively high hardness and inertness of ceramic materials make this type of thin coating of interest for protection of substrate materials against corrosion, oxidation and wear. In particular, the use of such coatings on cutting tools can extend the life of these items by several orders of magnitude.
Here, a fluid precursor undergoes a chemical change at a solid surface, leaving a solid layer. An everyday example is the formation of soot on a cool object when it is placed inside a flame. Since the fluid surrounds the solid object, deposition happens on every surface, with little regard to direction; thin films from chemical deposition techniques tend to be conformal, rather than directional.
Chemical deposition is further categorized by the phase of the precursor :
Research is being done on a new class of thin film inorganic oxide materials, called amorphous heavy-metal cation multicomponent oxides, which could be used to make transparent transistors that are inexpensive and stable. Any technique that deposits a thin film material onto a substrate or previously deposited layers is considered thin-film deposition. “Thin” generally implies micro, nano, or atomic scales for characterizing deposited layers. Thin-film deposition can be specified as either chemical or physical deposition depending on the means by which the layer is deposited.
Thin film materials function in a variety of ways. Using a precursor gas method involves providing a metal-containing precursor to an activation zone, and activating the metal-containing precursor to form an activated precursor. The activated precursor gas is moved to a reaction chamber, and a film is deposited on a substrate using a cyclical deposition process, wherein the activated precursor gas and a reducing gas are alternately adsorbed onto the substrate.
Physical deposition uses mechanical, electromechanical or thermodynamic means to produce a thin film of solid. An everyday example is the formation of frost. Since most engineering materials are held together by relatively high energies, and chemical reactions are not used to store these energies, commercial physical deposition systems tend to require a low-pressure vapor environment to function properly most can be classified as physical vapor deposition (PVD).
The material to be deposited is placed in an energetic, entropic environment, so that particles of material escape its surface. Facing this source is a cooler surface which draws energy from these particles as they arrive, allowing them to form a solid layer. The whole system is kept in a vacuum deposition chamber, to allow the particles to travel as freely as possible. Since particles tend to follow a straight path, films deposited by physical means are commonly directional, rather than conformal.
Examples of physical deposition include :
In the sputtering target process, argon plasma is ignited in a vacuum chamber and argon ions are accelerated towards a negatively charged cathode by means of an electrical field. The argon ions infuse the target with high kinetic energy, resulting in the emission of atoms of the target material. The atoms diffuse through a vacuum chamber and condense as a thin layer on a substrate.
An evaporation filament has the advantages of efficient outgassing, easy reloading of metal charges, and automatic termination of evaporation before less volatile impurities can be evaporated. A falling evaporator film can be operated with very low temperature differences between the heating media and the boiling liquid. A falling evaporator film also has very short product contact times, typically just a few seconds per pass. These characteristics make a falling evaporator film particularly suitable for heat-sensitive products, and are the most frequently used type of film evaporator.
Copper (Cu) Nanoparticles are black brown spherical high surface area metal particles. Nanoscale Copper Particles are typically 10-30 nanometers (nm) with specific surface area (SSA) in the 30 – 70 m2/g range and also available in with an average particle size of 70 -100 nm range with a specific surface area of approximately 5 – 10 m2/g.
Nano Copper Particles are also available in passivated and in Ultra high purity and high purity and carbon coated and dispersed forms. They are also available as a nanofluid through the AE Nanofluid production group. Nanofluids are generally defined as suspended nanoparticles in solution either using surfactant or surface charge technology. Nanofluid dispersion and coating selection technical guidance is also available.
Other nanostructures include nanorods, nanowhiskers, nanohorns, nanopyramids and other nanocomposites. Surface functionalized nanoparticles allow for the particles to be preferentially adsorbed at the surface interface using chemically bound polymers. Development research is underway in Nano Electronics and Photonics materials, such as MEMS and NEMS, Bio Nano Materials, such as Biomarkers, Bio Diagnostics & Bio Sensors, and Related Nano Materials, for use in Polymers, Textiles, Fuel Cell Layers, Composites and Solar Energy materials.
Nanopowders are analyzed for chemical composition by ICP, particle size distribution (PSD) by laser diffraction, and for Specific Surface Area (SSA) by BET multi-point correlation techniques. Novel nanotechnology applications also include Quantum Dots. High surface areas can also be achieved using solutions and using thin film by sputtering targets and evaporation technology using pellets, rod and foil.
Applications for copper nanocrystals include as an anti-microbial, anti-biotic and anti-fungal (fungicide) agent when incorporated in coatings, plastics and textiles, in copper diet supplements, in the interconnect for micro and integrated circuits, for its ability to absorb radioactive cesium and in super strong metals and alloys and in nanowire, nanofiber and and in certain alloy and catalyst applications.
Cysteine coated gold nanoparticles for copper detection. The presence of copper sees a change in colour from red to blue due to particle aggregation with more aggregation the greater the concentration of Cu(II) in solution. TEM images show the unaggregated particles (left) before any exposure to Cu(II) and the aggregated particles (right) after the addition of Cu(II)
In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size : in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized between 2,500 and 100 nanometers. Ultrafine particles, or nanoparticles are sized between 100 and 1 nanometers. The reason for this double name of the same object is that, during the 1970-80′s, when the first thorough fundamental studies were running with “nanoparticles” in the USA (by Granqvist and Buhrman) and Japan, (within an ERATO Project) they were called “ultrafine particles” (UFP).
However, during the 1990s before the National Nanotechnology Initiative was launched in the USA, the new name, “nanoparticle” had become fashionable. Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials. Although the size of most molecules would fit into the above outline, individual molecules are usually not referred to as nanoparticles. Nanoclusters have at least one dimension between 1 and 10 nanometers and a narrow size distribution. Nanopowders are agglomerates of ultrafine particles, nanoparticles, or nanoclusters. Nanometer-sized single crystals, or single-domain ultrafine particles, are often referred to as nanocrystals.
Copper is a Block D, Group 11, Period 4 element. The number of electrons in each of Copper’s shells is 2, 8, 18, 1 and its electronic configuration is 3d10 4s1. In its elemental form copper’s CAS number is 7440-50-8. The copper atom has a radius of 127.8 .pm and it’s Van der Waals radius is 140.pm. Due to its high electrical conductivity, large amounts of copper are used by the electrical industry for wire. Of all pure metals, only silver has a higher electrical conductivity. Copper is also resistant to corrosion caused by moisture, making it a widely used material in pipes, coins, and jewelry.
Copper is often too soft for its applications, so it is incorporated in numerous alloys. For example, brass is a copper-zinc alloy, and bronze is a copper-tin alloy. Copper sulfate (CuSO 4·H2O), also known as blue vitrol, is the most well-known copper compound. It is used as an agricultural poison, an algicide, and as a pigment for inks. Cuprous chloride (CuCl) is a powder used to absorb carbon dioxide (CO2). Copper cyanide (CuCN) is often used in electroplating applications. Copper is available as metal and compounds with purities from 99% to 99.9999% (ACS grade to ultra-high purity) metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder.
Scrap is a term used to describe recyclable and other materials left over from every manner of product consumption, such as parts of vehicles, building supplies, and surplus materials. Scrap metal originates just as frequently between businesses and homes as well. The proper disposal and recycling of scrap metal is typically done by a business or service. Typically a “scrapper” will advertise his services to conveniently remove scrap metal for people who don’t need it, or need to get rid of it.
The scrap industry contributed $65 billion in 2006 and is one of the few contributing positively to the U.S. balance of trade, exporting $15.7 billion in scrap commodities in 2006. This imbalance of trade has resulted in rising scrap prices during 2007 and 2008 within the United States. Scrap recycling also helps reduce greenhouse gas emissions and conserves energy and natural resources.
For example, scrap recycling diverts 145,000,000 short tons (129,464,286 long tons; 131,541,787 t) of materials away from landfills. Recycled scrap is a raw material feedstock for 2 out of 3 pounds of steel made in the U.S., for 60% of the metals and alloys produced in the U.S., for more than 50% of the U.S. paper industry’s needs, and for 33% of U.S. aluminum. Recycled scrap helps keep air and water cleaner by removing potentially hazardous materials and keeping them out of landfills.
Scrap is often taken to a wrecking yard (also known as a scrapyard, junkyard, or breaker’s yard), where it is processed for later melting into new products. A wrecking yard, depending on its location, may allow customers to browse their lot and purchase items before they are sent to the smelters although many scrap yards that deal in large quantities of scrap usually do not, often selling entire units such as engines or machinery by weight with no regard to their functional status.
Customers are typically required to supply all of their own tools and labor to extract parts, and some scrapyards may first require waiving liability for personal injury before entering. Many scrapyards also sell bulk metals (stainless steel, etc.) by weight, often at prices substantially below the retail purchasing costs of similar pieces.
In contrast to wreckers, scrapyards typically sell everything by weight, rather than by item. To the scrapyard, the primary value of the scrap is what the smelter will give them for it, rather than the value of whatever shape the metal may be in.
An auto wrecker, on the other hand, would price exactly the same scrap based on what the item does, regardless of what it weighs. Typically, if a wrecker cannot sell something above the value of the metal in it, they would then take it to the scrapyard and sell it by weight.
Equipment containing parts of various metals can often be purchased at a price below that of either of the metals, due to saving the scrapyard the labor of separating the metals before shipping them to be recycled. As an example, a scrapyard in Arcata, California sells automobile engines for $0.25 per pound, while aluminum, of which the engine is mostly made, sells for $1.25 per pound.
Scrap prices are reported in a handful of U.S. publications, including American Metal Market, based on confirmed sales. Non-US domiciled publications, such as The Steel Index, also report on the US scrap price, which has become increasingly important to global export markets.
The metal recycling industry encompasses a wide range of metals. The more frequently recycled metals are scrap steel, iron (ISS), lead, aluminum, copper, stainless steel and zinc. There are two main categories of metals: ferrous and nonferrous.
Metals which contain iron in them are known as Ferrous where metals without iron are nonferrous. (ISRI Common nonferrous metals are copper, brass, aluminum, zinc, magnesium, tin, nickel, and lead. Nonferrous metals also include precious and exotic metals.
Precious metals are metals with a high market value in any form, such as gold, silver, and platinum. Exotic metals contain rare elements such as cobalt, mercury, titanium, tungsten, arsenic, beryllium, bismuth, cerium, cadmium, niobium, indium, gallium, germanium, lithium, selenium, tantalum, tellurium, vanadium, and zirconium. Some types ofmetals are radioactive. Thesemay be “naturally-occurring” ormay be formed as by-products of nuclear reactions.Metals that have been exposed to radioactive sourcesmay also become radioactive in settings such asmedical environments, research laboratories, or nuclear power plants.
Titanium and most titanium alloys are readily weldable, using several welding processes. Properly made welds in the as-welded condition are ductile and, in most environments, are as corrosion resistant as base metal. Improper welds, on the other hand, might be embrittled and less corrosion-resistant compared to base metal.
Commercially pure titanium and most titanium alloys are readily welded by a number of welding processes being used today. The most common method of joining titanium is the gas tungsten-arc (GTAW) process and, secondarily, the gas metal-arc (GMAW) process. Others include electron beam and more recently laser welding as well as solid state processes such as friction welding and diffusion bonding. Titanium and its alloys also can be joined by resistance welding and by brazing.
The techniques and equipment used in welding titanium are similar to those required for other high-performance materials, such as stainless steels or nickel-base alloys. Titanium, however, demands greater attention to cleanliness and to the use of auxiliary inert gas shielding than these materials. Molten titanium weld metal must be totally protected from contamination by air. Also, hot heat-affected zones and root side of titanium welds must be shielded until temperatures drop below 800°F (427°C).
Reaction of titanium with gases and fluxes makes common welding processes such as gas welding, shielded metal arc, flux cored arc, and submerged arc welding unsuitable.Likewise, welding titanium to most dissimilar metals is not feasible, because titanium forms brittle compounds with most other metals; however, titanium can be welded to zirconium, tantalum and niobium.
The techniques for welding titanium resemble those employed with nickel alloys and stainless steels. Molten titanium reacts readily with oxygen, nitrogen and hydrogen and exposure to these elements in air or in surface contaminants during welding can adversely affect titanium weld metal properties. As a consequence, certain welding processes such as shielded metal arc, flux cored arc and submerged arc are unsuitable for welding titanium. In addition, titanium cannot be welded to most other metals because of formation of embrittling metallic compounds that lead to weld cracking.
While chamber or glove box welding of titanium is still in use today, the vast majority of welding is done in air using inert gas shielding. Conventional welding power supplies are used both for gas tungsten arc and for gas metal arc welding. Tungsten arc welding is done using DC straight polarity (DCSP) while reverse polarity (DCRP) is used with the metallic arc. Field welding is common. Wherever the welding is done, a clean environment is necessary in which to weld titanium. A separate area, specifically set aside for the welding of titanium, aids in making quality welds.
An essential requirement for successfully arc welding titanium is proper gas shielding. Care must be taken to ensure that inert atmosphere protection is maintained until the weld metal temperature cools below 426Â°C (800Â°F). The first or primary shield gas stream issues from the torch and shields the molten puddle and adjacent surfaces. The secondary or trailing gas shield protects the solidified weld metal and heat-affected zone during cooling. The third or backup shield protects the weld underside during welding and cooling. The backup shield can take many forms. One commonly used for straight seam welds is a copper backing bar with gas ports serving as a heat sink and shielding gas source. During GTA and GMA welding, argon or helium shielding gases of welding grade with dewpoint of -50°F (-46°C) or lower are used to provide the necessary protection. Separate gas supplies are needed for : 1. Primary shielding of the molten weld puddle. 2. Secondary shielding of cooling weld deposit and associated heat affected zones. 3. Backup shielding of the backside of weld and associated heat affected zones.
Primary shielding of the molten weld puddle is provided by proper selection of the welding torch. Standard water-cooled welding torches equipped with large (3/4 or 1-inch) ceramic cups and gas lenses, are suitable for titanium. The gas lens provides uniform, nonturbulent inert gas flow. Manufacturer’s recommended gas flow rates to the torch should be used. Excess flow to the torch may cause turbulence and loss of shielding. The effectiveness of primary shielding should be evaluated prior to production welding.
Secondary shielding is most commonly provided by trailing shields. The function of the trailing shield is to protect the solidified titanium weld metal and associated heat-affected zones until temperature reaches 800°F (427°C) or lower. Trailing shields are generally custom-made to fit a particular torch and a particular welding operation. Design of the trailing shield should be compact and allow for uniform distribution of inert gas within the device. The possible need for water-cooling should also be considered, particularly for large shields. Porous bronze diffusers have provided even and nonturbulent flow of inert gas from the shield to the weld.
Titanium and its alloys are most often welded with the gas tungsten-arc (GTA or TIG) and gas metal-arc (GMA or MIG) welding processes. Resistance, plasma arc, electron beam and friction welding are also used on titanium to a limited extent. All of these processes offer advantages for specific situations. However, the following discussion will be concerned primarily with GTA and GMA welding. Many of the principles discussed are applicable to all processes.
Before welding, it is essential that the weld joint surfaces be free of any contamination and that they remain clean during the entire welding operation. Weld joint designs for titanium are similar to those for other metals. The joint design selected for titanium however, must permit proper inert gas shielding of both root and face during welding as well as post-weld inspection of both sides of the weld. Good joint fit-up is important for titanium. Maintenance of joint opening during welding is important. Clamping to prevent joint movement during welding is recommended. Any cracked or contaminated tack welds must be removed before final welding.
The GTA process can be used to make butt joints without filler metal in titanium base sheet of up to about 1/8-inch thickness. Heavier sections generally require the use of filler metal and grooved joints. Either the GTA or GMA welding process can be used, although GMA welding is more economical for sections heavier than about one-half inch. If the GTA process is used, care should be exercised to prevent contact of the tungsten electrode with the molten puddle, thereby preventing tungsten pickup.
A conventional power supply, connected D.C. straight polarity (DCSP), is used for GTA welding of titanium. Reverse polarity (DCRP) is used for GMA welding of titanium. A remote controlled contactor allows the arc to be broken without removal of the torch from the cooling weld metal, thereby maintaining inert gas shielding. Foot operated current and contactor control, high frequency arc starting and shielding gas timers are other desirable features.
A water-cooled welding torch, equipped with a 3/4-inch ceramic cup and a gas lens, is recommended for GTA welding of titanium. A one-inch cup may be required for GMA welding. Thoriated tungsten electrodes (usually 2% thoria) are recommended for GTA welding of titanium. Pointed electrodes (end blunted) help to control arc characteristics. The smallest diameter electrode which can carry the required current should be used.
Before welding titanium, it is important that weld joints and weld wire be free of mill scale, dirt, dust, grease, oil, moisture and other potential contaminants. Inclusion of these foreign substances in titanium weld metal could degrade properties and corrosion resistance. Weld wire is clean as packaged by the manufacturer. All joint surfaces and surfaces of base plate for a distance of at least an inch back from the joint need to be cleaned. Solvent cleaning should be followed by wire brushing, using a new stainless steel brush.
Titanium welding wire is covered by AWS A5.16-70 Specification (“Titanium and Titanium-Alloy Bare Welding Rods and Electrodes”). It is generally good practice to select a filler metal matching the properties and composition of the titanium base metal grade. However, for both commercially pure grades and alloys, selecting a weld wire one strength level below the base metal is also done. Special situations may require a different grade of filler wire to give desired combination of joint properties.
In addition to clean joints and weld wire, proper parameters, and proper inert gas shielding, welder technique requires attention when titanium is being welded. Improper technique can be a source of weld contamination. Before starting an arc in welding titanium, it is good practice to prepurge the torch, trailing shield and backup shield to be sure all air is removed. Whenever possible, high frequency arc starting should be used. Scratch starting with tungsten electrodes is a source of tungsten inclusions in titanium welds. On extinguishing the arc, the use of current downslope and a contactor, controlled by a single foot pedal, is encouraged. Torch shielding should be continued until the weld metal cools below 800°F (427°C).
Prior to making production welds on titanium, procedures and techniques should be closely evaluated. For pressure vessel construction, the ASME Boiler and Pressure Vessel Code, Section IX (Welding Qualification), details procedure and performance tests which must be met. Tensile and bend tests on trial welds made under conditions intended for production are the acceptance criteria. Impact or notch tensile tests may also be required, particularly for low temperature applications. Once good procedures are established, as evidenced by tensile and bend tests, they should be strictly followed in subsequent production welding.
Bend tests evaluate ductility. For this reason, the bend test made on preproduction trial welds or on extensions of production welds made for that purpose, provides a good evaluation of weld quality. A bend sample in which the weld is positioned perpendicular to the bend axis assures uniform straining of weld metal and heat-affected zones, thereby giving more meaningful results.
The supercapacitor, also known as ultracapacitor or double-layer capacitor, differs from a regular capacitor in that it has a very high capacitance. A capacitor stores energy by means of a static charge as opposed to an electrochemical reaction. Applying a voltage differential on the positive and negative plates charges the capacitor. This is similar to the buildup of electrical charge when walking on a carpet. Touching an object releases the energy through the finger.
An electric double-layer capacitor (EDLC), also known as supercapacitor, supercondenser, electrochemical double layer capacitor, or ultracapacitor, is an electrochemical capacitor with relatively high energy density. Their energy density is typically hundreds of times greater than conventional electrolytic capacitors. They also have a much higher power density than batteries or fuel cells. A typical D-cell-sized electrolytic capacitor may have capacitance of up to tens of millifarads. The same size EDLC might reach several farads, an improvement of two orders of magnitude. As of 2011 EDLCs had a maximum working voltage of a few volts (standard electrolytics can work at hundreds of volts) and capacities of up to 5,000 farads. In 2010 the highest available EDLC specific energy was 30 Wh/kg (0.1 MJ/kg). The amount of energy stored per unit of mass is called Specific energy, which is often measured in Watt-hour per kilogram (Wh/kg) or MegaJoules per kilogram (MJ/kg). Up to 85 Wh/kg has been achieved at room temperature in the lab, lower than rapid-charging lithium-titanate batteries.
Engineers at General Electric first experimented with the electric double-layer capacitor, which led to the development of an early type of supercapacitor in 1957. There were no known commercial applications then. In 1966, Standard Oil rediscovered the effect of the double-layer capacitor by accident while working on experimental fuel cell designs. The company did not commercialize the invention but licensed it to NEC, which in 1978 marketed the technology as “supercapacitor” for computer memory backup. It was not until the 1990s that advances in materials and manufacturing methods led to improved performance and lower cost.
The modern supercapacitor is not a battery per se but crosses the boundary into battery technology by using special electrodes and electrolyte. Several types of electrodes have been tried and we focuse on the double-layer capacitor (DLC) concept. It is carbon-based, has an organic electrolyte that is easy to manufacture and is the most common system in use today. General Electric engineers experimenting with devices using porous carbon electrodes first observed the EDLC effect in 1957. They believed that the energy was stored in the carbon pores and the device exhibited “exceptionally high capacitance”, although the mechanism was unknown at that time. General Electric did not immediately follow up on this work. In 1966 researchers at Standard Oil of Ohio developed the modern version of the devices, after they accidentally re-discovered the effect while working on experimental fuel cell designs. Their cell design used two layers of activated charcoal separated by a thin porous insulator, and this basic mechanical design remains the basis of most electric double-layer capacitors.
Standard Oil did not commercialize their invention, licensing the technology to NEC, who finally marketed the results as “supercapacitors” in 1978, to provide backup power for maintaining computer memory. The market expanded slowly for a time, but starting around the mid-1990s various advances in materials science and refinement of the existing systems led to rapidly improving performance and an equally rapid reduction in cost. The first trials of supercapacitors in industrial applications were carried out for supporting the energy supply to robots. In 2005 aerospace systems and controls company Diehl Luftfahrt Elektronik GmbH chose supercapacitors to power emergency actuation systems for doors and evacuation slides in airliners, including the new Airbus 380 jumbo jet. In 2005, the ultracapacitor market was between US $272 million and $400 million, depending on the source.
As of 2007 all solid state micrometer-scale electric double-layer capacitors based on advanced superionic conductors had been for low-voltage electronics such as deep-sub-voltage nanoelectronics and related technologies (the 22 nm technological node of CMOS and beyond). Much research is being carried out to improve performance; for example an order of magnitude energy density improvement was achieved in the laboratory in mid-2011. Prices are dropping: a 3,000F capacitor that was US$5,000 ten years before was $50 in 2011. EDLCs are used for energy storage rather than as general-purpose circuit components. They have a variety of commercial applications, notably in “energy smoothing” and momentary-load devices. They have applications as energy-storage and KERS devices used in vehicles, and for smaller applications like home solar energy systems where extremely fast charging is a valuable feature.
In a conventional capacitor, energy is stored by the removal of charge carriers, typically electrons, from one metal plate and depositing them on another. This charge separation creates a potential between the two plates, which can be harnessed in an external circuit. The total energy stored in this fashion increases with both the amount of charge stored and the potential between the plates. The amount of charge stored per unit voltage is essentially a function of the size, the distance, and the material properties of the plates and the material in between the plates (the dielectric), while the potential between the plates is limited by the breakdown field strength of the dielectric. The dielectric controls the capacitor’s voltage. Optimizing the material leads to higher energy density for a given size of capacitor.
EDLCs do not have a conventional dielectric. Rather than two separate plates separated by an intervening insulator, these capacitors use virtual plates that are in fact two layers of the same substrate. Their electrochemical properties, the so-called “electrical double layer”, result in the effective separation of charge despite the vanishingly thin (on the order of nanometers) physical separation of the layers. The lack of need for a bulky layer of dielectric, and the porosity of the material used, permits the packing of plates with much larger surface area into a given volume, resulting in high capacitances in practical-sized packages.
Supercapacitor-battery hybrid energy devices based on nanocomposite units. (a) Schematic of a four-terminal hybrid-energy device showing the arrangement of supercapacitor and battery in parallel configuration. (b) The discharge curve of battery and supercapacitor is plotted as a function of time. The discharge of battery charges the supercapacitor, and subsequently the supercapacitor is discharged. (c) Schematic of a three-terminal hybrid energy device that can act as both supercapacitor and battery. The three terminals are defined, and the battery and supercapacitor segments of the device are shown. (d) The discharge behavior of the battery and subsequent discharge of supercapacitor are shown. The battery is discharged with terminals 1 and 2 shorted. This simultaneously charges the supercapacitor following the double-layer formation at the electrode interface. Subsequently, the supercapacitor is discharged across terminals 1 and 3. An additional separator (glass fibers) is normally added along with the excess cellulose spacer to improve behavior. In an electrical double layer, each layer by itself is quite conductive, but the physics at the interface where the layers are effectively in contact means that no significant current can flow between the layers. However, the double layer can withstand only a low voltage, which means that electric double-layer capacitors rated for higher voltages must be made of matched series-connected individual EDLCs, much like series-connected cells in higher-voltage batteries.
All capacitors have voltage limits. While the electrostatic capacitor can be made to withstand high volts, the supercapacitor is confined to 2.5–2.7V. To achieve higher voltages, several supercapacitors are connected in series. Serial connection reduces the total capacitance, and strings of more than three capacitors require voltage balancing to prevent any cell from going into over-voltage. Although high compared to a regular capacitor, 30Wh/kg is one-fifth that of a consumer Li-ion battery.
In 2006, two commercial bus routes began to use electric double-layer capacitor buses; one of them is route 11 in Shanghai. In 2001 and 2002 VAG, the public transport operator in Nuremberg, Germany tested an hybrid bus that uses a diesel-electric battery drive system with electric double-layer capacitors. Since 2003 Mannheim Stadtbahn in Mannheim, Germany has operated a light-rail vehicle (LRV) that uses EDLCs to store braking energy.
An alloy is a metal composed of more than one element. Engineering alloys include the cast-irons and steels, aluminum alloys, magnesium alloys, titanium alloys, nickel alloys, zinc alloys and copper alloys. For example, brass is an alloy of copper and zinc. An alloy is a metallic substance that is made from the mixture of multiple metals or, sometimes, a metal with some other element such as carbon. Alloys have been around for about nine millennia, but like most other domains in science and technology, the bulk of progress in alloy technology has occurred in the last few decades. In an alloy, the constituent elements are not meant to combine into larger molecules through chemical reactions, but are merely mixed together. When there are different ratios between two or more metals, the alloys produced have slightly different properties. Alloy is a metal made by combining 2 or more metallic elements, especially to give strength or resistance to corroding.
Alloying a metal is done by combining it with one or more other metals or non-metals that often enhance its properties. For example, steel is stronger than iron, its primary element. The physical properties, such as density, reactivity, Young’s modulus, and electrical and thermal conductivity, of an alloy may not differ greatly from those of its elements, but engineering properties such as tensile strength and shear strength may be substantially different from those of the constituent materials. This is sometimes a result of the sizes of the atoms in the alloy, because larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Sometimes alloys may exhibit marked differences in behavior even when small amounts of one element occur. For example, impurities in semi-conducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura.
Some alloys are made by melting and mixing two or more metals. Bronze, an alloy of copper and tin, was the first alloy discovered, during the prehistoric period now known as the bronze age, it was harder than pure copper and originally used to make tools and weapons, but was later superseded by metals and alloys with better properties. In later times bronze has been used for ornaments, bells, statues, and bearings. Brass is an alloy made from copper and zinc. The first metal to be extracted from ore was copper. Shortly thereafter, it was combined with tin to create the stronger bronze, which dominated human technology for thousands of years.
This period is now called the Bronze Age. alloying is a term which describes a material which, when introduced to another material will change its characteristics to make them advantageous to us. they are split into 2 categories, “Matrix’s” and “reinforcement agent”. For example with carbon fibre the matrix is the carbon and the reinforcement agent is a resin. Other metals mixed with copper to form cruder variants of bronze were manganese, aluminum, silicon, and phosphorous. Co-existing for many years with bronze was the weaker iron, which decays quickly into rust. Eventually, historic forces caused iron to supplant bronze in human tools, ushering in the Iron Age around 1000 BCE, though this date varies depending on the civilization and region being considered.
Alloying a metal is done by combining it with one or more other metals or non-metals that often enhance its properties. For example, steel is stronger than iron, its primary element. Bronze, an alloy of copper and tin, was the first alloy discovered, during the prehistoric period now known as the bronze age, it was harder than pure copper and originally used to make tools and weapons, but was later superseded by metals and alloys with better properties. Brass is an alloy made from copper and zinc. The use of alloys by humans started with the use of meteoric iron, a naturally occurring alloy of nickel and iron. The term alloy is used to describe a mixture of atoms in which the primary constituent is a metal. If there is a mixture of only two types of atoms, not counting impurities, such as a copper-nickel alloy, then it is called a binary alloy. If there are three types of atoms forming the mixture, such as iron, nickel and chromium, then it is called a ternary alloy. An alloy with four constituents is a quaternary alloy, while a five-part alloy is termed a quinary alloy. Pig iron, a very hard but brittle alloy of iron and carbon, was being produced in China as early as 1200 BC, but did not arrive in Europe until the Middle Ages.
These metals found little practical use until the introduction of crucible steel around 300 BC. When a molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism. Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms. The smaller atoms become trapped in the spaces between the atoms in the crystal matrix, called the interstices. This is referred to as an interstitial alloy. Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into the interstices, but some of the iron atoms are replaced with nickel and chromium atoms.
Alloys are often made to alter the mechanical properties of the base metal, to induce hardness, toughness, ductility, or other desired properties. While most metals and alloys can be work hardened by inducing defects in their crystal structure, caused by plastic deformation, some alloys can also have their properties altered by heat treatment. At a certain temperature, the base metal of steel, iron, undergoes a change in the arrangement of the atoms in its crystal matrix, called allotropy. This allows the small carbon atoms to enter the interstices of the crystal. For example, 14 karat gold is an alloy of gold with other elements. The term “alloy” is sometimes used in everyday speech as a synonym for a particular alloy. For example, automobile wheels made of an aluminium alloy are commonly referred to as simply “alloy wheels”, although in point of fact steels and most other metals in practical use are also alloys. Mercury dissolves many metals, such as gold, silver, and tin, to form amalgams (an alloy in a soft paste, or liquid form at ambient temperature). Many ancient civilizations alloyed metals for purely aesthetic purposes. In ancient Egypt and Mycenae, gold was often alloyed with copper to produce red-gold, or iron to produce a bright burgundy-gold. Silver was often found alloyed with gold. Because pig iron could be melted, people began to develop processes of reducing the carbon in the liquid pig iron to create steel. The Bessemer process was able to produce the first large scale manufacture of steel. Once the Bessemer process began to gain widespread use, other alloys of steel began to follow, such as mangalloy, an alloy of steel and manganese, which exhibits extreme hardness and toughness.
Zinc Alloys are combinations of zinc with one or more other metals. If zinc is the primary constituent of the alloy, it is a zinc-base alloy. Zinc also is commonly used in varying degrees as an alloying component with other base metals, such as copper, aluminum, and magnesium. A familiar example of the latter is the association of varying amounts of zinc (up to 45%) with copper to produce brass. Zinc, a crystalline metal with moderate strength and ductility, is seldom used alone except as a coating. After iron, aluminium and copper, zinc is usually the fourth-most used metal. There are many wrought alloys with various alloying elements to improve workability and strenght. There are two major Zinc alloy groups for casting. The first is a standard casting alloy that is primarily Zinc in a hypo-eutectic alloy with less than 5% Aluminum. The Second is the newer group of Zinc-Aluminum alloys. These are hyper-eutectic alloys with up to 27% Aluminum. Both groups are primarily used in die casting.
The modern development started during the 80’s with the first alkaline Zn/Fe (99,5%/0,5%) deposits and Zn/Ni (94%/6%) deposits. Recently, the reinforcement of the corrosion specifications of the major European Car Makers and the Directive ELV that banished the use of hexavalent Chromium (CrVI) Conversion Coating required greater use of alkaline Zn/Ni between 12 and 15% of Ni (Zn/Ni 86/14). Only Zn/Ni (86%/14%) is an alloy while lower content of Iron, Cobalt and Nickel leads to co-deposits. Zn/Ni (12%-15%) in Nickel in acidic and alkaline electrolytes is plated as the gamma crystalline phase of the binary diagram Zn-Ni. Wrought zinc and zinc alloys may be obtained as rolled strip, sheet and foil; extruded rod and shapes and drawn rod and wire. These metals exhibit good resistance to corrosion in many types of service, and because the corrosion products that may form on them are white, other materials are not stained by them.
Wrought zinc has chemical characteristics particularly adapted to certain uses, such as dry batteries and photoengraver`s plate, and offers combinations of desirable physical and mechanical properties at relatively low cost. In common with many other metals and alloys, wrought zinc creeps under constant loads that are substantially less than its ultimate strength that is, wrought zinc does not have clearly defined elastic module, and hence creep data from service tests must be used in designing for strength and rigidity under conditions of continuos stress. All severe fabrication of wrought zinc should be done at temperatures above 20°C. Rolled zinc of the proper grade is readily drawn into a great variety of articles such as batter cups, eyelets, meter cases, novelties, flashlight reflectors and fruit-jar caps.
Suitable grades of rolled zinc also are readily rolled, press formed, stamped or spun into items such as plates for addressing machines, buckles, ferrules, ornaments, nameplates, gaskets, weather-stripping and lamp parts. The ordinary grades of wrought zinc can be soldered easily by conventional methods. The usual precautions should be observed regarding proper cleaning and fluxing. The metal must not be overheated to the point where it melts. Pulsed-arc welding may be used for joining; gas welding of zinc is used only for repair work. Wrought zinc is easily machined using standard methods and tools. However, if it is necessary to machine zinc containing exceedingly coarse grains, the metal should be heated to a temperature between 70 and 100°C in order to avoid cleavage of crystals. Wrought zinc has chemical characteristics particularly adapted to certain uses, such as dry batteries and photoengraver`s plate, and offers combinations of desirable physical and mechanical properties at relatively low cost. In common with many other metals and alloys, wrought zinc creeps under constant loads that are substantially less than its ultimate strength. The ordinary grades of wrought zinc can be soldered easily by conventional methods.
Zinc gravity casting alloys can be used for general industrial applications where strength, hardness, wear resistance or good pressure tightness is required. Zinc alloys often are employed to replace cast iron because of their similar properties and higher machinability ratings. The good bearing and wear characteristics of zinc alloys permit them to be used for bearing bushings and flanges. Other applications in which zinc alloys have been successfully substituted for cast iron or copper alloys include fuel-handling components, pulleys, electrical fittings and hardware components.
pure Zinc is never used in casting due to it’s low strength. Today, all Zinc alloys supplied by reputable producers are made from primary of virgin Zinc which conforms to the SHG (super high grade) or Zn 1 brand which is quoted in commodity markets worldwide. The corrosion protection is primarily due to the anodic potential dissolution of zinc versus iron. Zinc is acting as sacrificial anode for protecting iron (steel). While steel is close to -400 mV, depending on alloy composition, electroplated zinc is much more anodic with -980 mV. Steel is preserved from corrosion by cathodic protection. This enhances corrosion protection further. On the opposite Zn/Ni between 12% and 15% of Ni (Zn/Ni 86/14) has a potential around -680 mV closer to Cadmium -640 mV. Thanks to this mechanism of corrosion, this alloy offers much greater protection than all other alloys.
For cost reasons the existing market is dividing between alkaline Zn/Fe (99,5%/0,5%) and alkaline Zn/Ni (86%/14%). The former Zn/Ni (94%/6%) that was a blend between pure zinc and the crystallographic gamma phase of Zn/Ni (86%/14%), was withdrawn from the European specs. A specific advantage of alkaline Zn/Ni (86%/14%) involves the lack of hydrogen embrittlement by plating. This initial layer preventshydrogen from penetrating deep into the steel substrate thus avoiding the serious problems associated with hydrogen embrittlement.
Aluminium alloys are alloys in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate, foils and extrusions. Cast aluminium alloys yield cost effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys. The most important cast aluminium alloy system is Al-Si, where the high levels of silicon (4.0% to 13%) contribute to give good casting characteristics. Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required.
An alloy is a material made up of two or more metals. Alloys have certain specific, desirable characteristics, including strength, formability, and corrosion resistance. Some of the common elements alloyed with aluminum include copper, manganese, silicon, magnesium, and zinc. Typical applications and uses of aluminum alloys include building products (siding and structural), rigid and flexible packaging (foil, food, and beverage cans), and transportation (automobiles, aircraft, and rail cars).
Aluminum is a silverish white metal that has a strong resistance to corrosion and like gold, is rather malleable. It is a relatively light metal compared to metals such as steel, nickel, brass, and copper with a specific gravity of 2.7. Aluminum is easily machinable and can have a wide variety of surface finishes. It also has good electrical and thermal conductivities and is highly reflective to heat and light.
At extremely high temperatures (200-250°C) aluminum alloys tend to lose some of their strength. However, at subzero temperatures, their strength increases while retaining their ductility, making aluminum an extremely useful low-temperature alloy. Aluminum alloys have a strong resistance to corrosion which is a result of an oxide skin that forms as a result of reactions with the atmosphere. This corrosive skin protects aluminum from most chemicals, weathering conditions, and even many acids, however alkaline substances are known to penetrate the protective skin and corrode the metal. Aluminum also has a rather high electrical conductivity, making it useful as a conductor. Copper is the more widely used conductor, having a conductivity of approximately 161% that of aluminum. Aluminum connectors have a tendency to become loosened after repeated usage leading to arcing and fire, which requires extra precaution and special design when using aluminum wiring in buildings.
Aluminum is a very versatile metal and can be cast in any form known. It can be rolled, stamped, drawn, spun, roll-formed, hammered and forged. The metal can be extruded into a variety of shapes, and can be turned, milled, and bored in the machining process. Aluminum can riveted, welded, brazed, or resin bonded. For most applications, aluminum needs no protective coating as it can be finished to look good, however it is often anodized to improve color and strength.
1xxx Unalloyed (pure) >99% Al
2xxx Copper is the principal alloying element, though other elements (Magnesium) may be specified
3xxx Manganese is the principal alloying element
4xxxSilicon is the principal alloying element
5xxxMagnesium is the principal alloying element
6xxxMagnesium and Silicon are principal alloying elements
7xxxZinc is the principal alloying element, but other elements such as Copper, Magnesium, Chromium, and Zirconium may be specified
8xxxOther elements (including Tin and some Lithium compositions)
9xxx Reserved for future use
1xxx Series. These grades of aluminum are characterized by excellent corrosion resistance, high thermal and electrical conductivities, low mechanical properties, and excellent workability. Moderate increases in strength may be obtained by strain hardening. Iron and silicon are the major impurities.
2xxx Series. These alloys require solution heat treatment to obtain optimum properties; in the solution heat-treated condition, mechanical properties are similar to, and sometimes exceed, those of low-carbon steel. In some instances, precipitation heat treatment (aging) is employed to further increase mechanical properties. This treatment increases yield strength, with attendant loss in elongation; its effect on tensile strength is not as great. The alloys in the 2xxx series do not have as good corrosion resistance as most other aluminum alloys, and under certain conditions they may be subject to intergranular corrosion. Alloys in the 2xxx series are good for parts requiring good strength at temperatures up to 150 °C (300 °F). Except for alloy 2219, these alloys have limited weldability, but some alloys in this series have superior machinability.
3xxx Series. These alloys generally are non-heat treatable but have about 20% more strength than 1xxx series alloys. Because only a limited percentage of manganese (up to about 1.5%) can be effectively added to aluminum, manganese is used as major element in only a few alloys.
4xxx Series. The major alloying element in 4xxx series alloys is silicon, which can be added in sufficient quantities (up to 12%) to cause substantial lowering of the melting range. For this reason, aluminum-silicon alloys are used in welding wire and as brazing alloys for joining aluminum, where a lower melting range than that of the base metal is required. The alloys containing appreciable amounts of silicon become dark gray to charcoal when anodic oxide finishes are applied and hence are in demand for architectural applications.
5xxx Series. The major alloying element is Magnesium an when it is used as a major alloying element or with manganese, the result is a moderate-to-high-strength work-hardenable alloy. Magnesium is considerably more effective than manganese as a hardener, about 0.8% Mg being equal to 1.25% Mn, and it can be added in considerably higher quantities. Alloys in this series possess good welding characteristics and relatively good resistance to corrosion in marine atmospheres. However, limitations should be placed on the amount of cold work and the operating temperatures (150 degrees F) permissible for the higher-magnesium alloys to avoid susceptibility to stress-corrosion cracking.
6xxx Series. Alloys in the 6xxx series contain silicon and magnesium approximately in the proportions required for formation of magnesium silicide (Mg2Si), thus making them heat treatable. Although not as strong as most 2xxx and 7xxx alloys, 6xxx series alloys have good formability, weldability, machinability, and relatively good corrosion resistance, with medium strength. Alloys in this heat-treatable group may be formed in the T4 temper (solution heat treated but not precipitation heat treated) and strengthened after forming to full T6 properties by precipitation heat treatment.
7xxx Series. Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series alloys, and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of moderate to very high strength. Usually other elements, such as copper and chromium, are also added in small quantities. 7xxx series alloys are used in airframe structures, mobile equipment, and other highly stressed parts. Higher strength 7xxx alloys exhibit reduced resistance to stress corrosion cracking and are often utilized in a slightly overaged temper to provide better combinations of strength, corrosion resistance, and fracture toughness.
Titanium alloys are metallic materials which contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness (even at extreme temperatures), light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures. However, the high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft, medical devices, connecting rods on expensive sports cars and some premium sports equipment and consumer electronics. Auto manufacturers Porsche and Ferrari also use titanium alloys in engine components due to its durable properties in these high stress engine environments.
Titanium Alloys are generally classified into four main categories :
Generally, beta-phase titanium is stronger yet less ductile and alpha-phase titanium is more ductile. Alpha-beta-phase titanium has a mechanical property which is in between both. Titanium dioxide dissolves in the metal at high temperatures, and its formation is very energetic. These two factors mean that all titanium except the most carefully purified has a significant amount of dissolved oxygen, and so may be considered a Ti-O alloy. Oxide precipitates offer some strength (as discussed above), but are not very responsive to heat treatment and can substantially decrease the alloy’s toughness. Many alloys also contain titanium as a minor additive, but since alloys are usually categorized according to which element forms the majority of the material, these are not usually considered to be “titanium alloys” as such. See the sub-article on titanium applications.
Titanium alone is a strong, light metal. It is as strong as steel, but 45% lighter. It is also twice as strong as aluminium but only 60% heavier. Titanium is not easily corroded by sea water, and thus is used in propeller shafts, rigging and other parts of boats that are exposed to sea water. Titanium and its alloys are used in airplanes, missiles and rockets where strength, low weight and resistance to high temperatures are important. Further, since titanium does not react within the human body, it and its alloys are used to create artificial hips, pins for setting bones, and for other biological implants.
Grade 1-4 are unalloyed and considered commercially pure or “CP”. Generally the tensile and yield strength goes up with grade number for these “pure” grades. The difference in their physical properties is primarily due to the quantity of interstitial elements. They are used for corrosion resistance applications where cost and ease of fabrication and welding are important. Grade 5, also known as Ti6Al4V, Ti-6Al-4V or Ti 6-4, is the most commonly used alloy. It has a chemical composition of 6% aluminium, 4% vanadium, 0.25% (maximum) iron, 0.2% (maximum) oxygen, and the remainder titanium. Grade 5 is used extensively in Aerospace, Medical, Marine, and Chemical Processing. It is used for connecting rods in ICEs. It is significantly stronger than commercially pure titanium while having the same stiffness and thermal properties (excluding thermal conductivity, which is about 60% lower in Grade 5 Ti than in CP Ti). Among its many advantages, it is heat treatable. This grade is an excellent combination of strength, corrosion resistance, weld and fabricability. In consequence, its uses are numerous such as for military aircraft or turbines. It is also used in surgical implants Generally, it is used in applications up to 400 degrees Celsius. Its properties are very similar to those of the 300 stainless steel series, especially 316. It has a density of roughly 4420 kg/m3, Young’s modulus of 110 GPa, and tensile strength of 1000 MPa. By comparison, annealed type 316 stainless steel has a density of 8000 kg/m3, modulus of 193 GPa, and tensile strength of only 570 MPa. And tempered 6061 aluminium alloy has 2700 kg/m3, 69 GPa, and 310 MPa, respectively. Grade 6 contains 5% aluminium and 2.5% tin. It is also known as Ti-5Al-2.5Sn. This alloy is used in airframes and jet engines due to its good weldability, stability and strength at elevated temperatures. Grade 7 contains 0.12 to 0.25% palladium. This grade is similar to Grade 2. The small quantity of palladium added gives it enhanced crevice corrosion resistance at low temperatures and high pH. Grade 7H contains 0.12 to 0.25% palladium. This grade has enhanced corrosion resistance.
Grade 9 contains 3.0% aluminium and 2.5% vanadium. This grade is a compromise between the ease of welding and manufacturing of the “pure” grades and the high strength of Grade 5. It is commonly used in aircraft tubing for hydraulics and in athletic equipment. Grade 11 contains 0.12 to 0.25% palladium. This grade has enhanced corrosion resistance. Grade 12 contains 0.3% molybdenum and 0.8% nickel. Grades 13, 14, and 15 all contain 0.5% nickel and 0.05% ruthenium. Grade 16 contains 0.04 to 0.08% palladium. This grade has enhanced corrosion resistance. Grade 16H contains 0.04 to 0.08% palladium. Grade 17 contains 0.04 to 0.08% palladium. This grade has enhanced corrosion resistance. Grade 18 contains 3% aluminium, 2.5% vanadium and 0.04 to 0.08% palladium. This grade is identical to Grade 9 in terms of mechanical characteristics. The added palladium gives it increased corrosion resistance. Grade 19 contains 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, and 4% molybdenum. Grade 20 contains 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, 4% molybdenum and 0.04% to 0.08% palladium. Grade 21 contains 15% molybdenum, 3% aluminium, 2.7% niobium, and 0.25% silicon. Grade 23 contains 6% aluminium, 4% vanadium, 0.13% (maximum) Oxygen. Improved ductility and fracture toughness with some reduction in strength. Grade 24 contains 6% aluminium, 4% vanadium and 0.04% to 0.08% palladium. Grade 25 contains 6% aluminium, 4% vanadium and 0.3% to 0.8% nickel and 0.04% to 0.08% palladium. Grades 26, 26H, and 27 all contain 0.08 to 0.14% ruthenium. Grade 28 contains 3% aluminium, 2.5% vanadium and 0.08 to 0.14% ruthenium. Grade 29 contains 6% aluminium, 4% vanadium and 0.08 to 0.14% ruthenium. Grades 30 and 31 contain 0.3% cobalt and 0.05% palladium. Grade 32 contains 5% aluminium, 1% tin, 1% zirconium, 1% vanadium, and 0.8% molybdenum. Grades 33 and 34 contain 0.4% nickel, 0.015% palladium, 0.025% ruthenium, and 0.15% chromium . Grade 35 contains 4.5% aluminium, 2% molybdenum, 1.6% vanadium, 0.5% iron, and 0.3% silicon. Grade 36 contains 45% niobium. Grade 37 contains 1.5% aluminium. Grade 38 contains 4% aluminium, 2.5% vanadium, and 1.5% iron. This grade was developed in the 1990s for use as an armor plating. The iron reduces the amount of Vanadium needed as a beta stabilizer. Its mechanical properties are very similar to Grade 5, but has good cold workability similar to grade 9.
Magnesium alloys are mixtures of magnesium with other metals (called an alloy), often aluminium, zinc, manganese, silicon, copper, rare earths and zirconium. Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminum, copper and steel. Therefore magnesium alloys are typically used as cast alloys, but research of wrought alloys has been more extensive since 2003. Cast magnesium alloys are used for many components of modern cars, and magnesium block engines have been used in some high-performance vehicles, die-cast magnesium is also used for camera bodies and components in lenses.
Copper alloys are metal alloys that have copper as their principal component. They have high resistance against corrosion. The best known traditional types are bronze, where tin is a significant addition, and brass, using zinc instead. Both these are imprecise terms, and today the term copper alloy tends to be substituted, especially by museums. The similarity in external appearance of the various alloys, along with the different combinations of elements used when making each alloy, can lead to confusion when categorizing the different compositions. There are as many as 400 different copper and copper-alloy compositions loosely grouped into the categories: copper, high copper alloy, brasses, bronzes, copper nickels, copper–nickel–zinc (nickel silver), leaded copper, and special alloys. The following table lists the principal alloying element for four of the more common types used in modern industry, along with the name for each type. Historical types, such as those that characterize the Bronze Age, are vaguer as the mixtures were generally .
Nickel-base alloys are used in many applications where they are subjected to harsh environments at high temperatures. Nickel-chromium alloys or alloys that contain more than about 15% Cr are used to provide both oxidation and carburization resistance at temperatures exceeding 760°C. Nickel-base alloys offer excellent corrosion resistance to a wide range of corrosive media. However, as with all types of corrosion, many factors influence the rate of attack. The corrosive media itself is the most important factor governing corrosion of a particular metal. Low-Expansion Alloys Nickel was found to have a profound effect on the thermal expansion of iron.Alloys can be designed to have a very low thermal expansion or display uniform and predictable expansion over certain temperature ranges. Iron-36% Ni alloy (Invar) has the lowest expansion of the Fe-Ni alloys and maintains nearly constant dimensions during normal variations in atmospheric temperature.The addition of cobalt to the nickel-iron matrix produces alloys with a low coefficient of expansion, a constant modulus of elasticity, and high strength. Electrical Resistance Alloys. Several alloy systems based on nickel or containing high nickel contents are used in instruments and control equipment to measure and regulate electrical characteristics (resistance alloys) or are used in furnaces and appliances to generate heat (heating alloys).
Alnico is an acronym referring to iron alloys which in addition to iron are composed primarily of aluminium (Al), nickel (Ni) and cobalt (Co), hence al-ni-co, with the addition of copper, and sometimes titanium. Alnico alloys are ferromagnetic, with a high coercivity (resistance to loss of magnetism) and are used to make permanent magnets. Before the development of rare earth magnets in the 1970s, they were the strongest type of magnet. Other trade names for alloys in this family are: Alni, Alcomax, Hycomax, Columax, and Ticonal. The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe. The development of alnico began in 1931, when T. Mishima in Japan discovered that an alloy of iron, nickel, and aluminum had a coercivity of 400 oersted (Oe), double that of the best magnet steels of the time. Alnico alloys make strong permanent magnets, and can be magnetized to produce strong magnetic fields. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500 gauss (0.15 tesla), or about 3000 times the strength of Earth’s magnetic field. Some brands of alnico are isotropic and can be efficiently magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation.
Alumel is an alloy consisting of approximately 95% nickel, 2% manganese, 2% aluminium and 1% silicon. This magnetic alloy is used for thermocouples and thermocouple extension wire. Alumel is a registered trademark of Hoskins Manufacturing Company. Properties of Alumel:
Chromel is an alloy made of approximately 90 percent nickel and 10 percent chromium that is used to make the positive conductors of ANSI Type E (chromel-constantan) and K (chromel-alumel) thermocouples. It can be used up to 1100 °C in oxidizing atmospheres. Chromel is a registered trademark of the Hoskins Manufacturing Company. Chromel A is an alloy containing 80% of nickel and 20% chromium (by weight). It is used for its excellent resistance to high-temperature corrosion and oxidation. It is also commonly called Nichrome 80-20 and used for electric heating elements.
Cupronickel or copper-nickel (sometimes incorrectly referred to as “cupernickel”) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Cupronickel is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater. Because of this, it is used for piping, heat exchangers and condensers in seawater systems as well as marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats. Cupronickel Cupronickel or copper-nickel (sometimes incorrectly referred to as “cupernickel”) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Cupronickel is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater. Because of this, it is used for piping, heat exchangers and condensers in seawater systems as well as marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats.
In 2008, the major ferronickel-producing countries were Japan (301,000 t), New Caledonia (144,000 t) and Colombia (105,000 t). Together, these three countries accounted for about 51% of world production if China is excluded. Ukraine, Indonesia, Greece, and Macedonia, in descending order of gross weight output, all produced between 68,000 t and 90,000 t of ferronickel, accounting for an additional 31%, excluding China. China was excluded from statistics because its industry produced large tonnages of nickel pig iron in addition to a spectrum of conventional ferronickel grades, for an estimated combined output of 590,000 t gross weight. The nickel content of individual Chinese products varied from about 1.6% to as much as 80%, depending upon customer end use.
Nickel silver, also known as German silver, Argentann, paktong, new silver, nickel brass, or alpacca (or alpaca), is a copper alloy with nickel and often zinc. The usual formulation is 60% copper, 20% nickel and 20% zinc. Nickel silver first became popular as a base metal for silver plated cutlery and other silverware, notably the electroplated wares called EPNS (electro-plated nickel silver). It is used in zippers, better-quality keys, costume jewellery, for making musical instruments (e.g., cymbals, saxophones), and is preferred for the track in electrically powered model railway layouts as its oxide is conductive. It is widely used in the production of coins (e.g. GDR marks, Portuguese escudo). Its industrial and technical uses include marine fittings and plumbing fixtures for its corrosion resistance, and heating coils for its high electrical resistance.
Hastelloy is the registered trademark name of Haynes International, Inc. The trademark is applied as the prefix name of a range of twenty two different highly corrosion-resistant metal alloys loosely grouped by the metallurgical industry under the material term “superalloys” or “high-performance alloys”. The predominant alloying ingredient is typically the transition metal nickel. Other alloying ingredients are added to nickel in each of the subcategories of this trademark designation and include varying percentages of the elements molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminum, carbon, and tungsten. The primary function of the Hastelloy super alloys is that of effective survival under high-temperature, high-stress service in a moderately to severely corrosive, and/or erosion prone environment where more common and less expensive iron-based alloys would fail, including the pressure vessels of some nuclear reactors, chemical reactors, distillation equipment and pipes and valves in chemical industry.
Inconel is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium-based superalloys. Inconel alloys are typically used in high temperature applications. It is often referred to in English as “Inco” (or occasionally “Iconel”). Common trade names for Inconel include: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020. Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments.When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where aluminum and steel would succumb to creep as a result of thermally-induced crystal vacancies (see Arrhenius equation). Inconel’s high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy. In age hardening or precipitation strengthening varieties, small amounts of niobium combine with nickel to form the intermetallic compound Ni3Nb or gamma prime. Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures.
Monel is a trademark of Special Metals Corporation for a series of nickel alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements. Monel was created by David H. Browne, chief metallurgist for International Nickel Co. Monel alloy 400 is binary alloy of the same proportions of nickel and copper as is found naturally in the nickel ore from the Sudbury (Ontario) mines. Monel was named for company president Ambrose Monell, and patented in 1906. One L was dropped, because family names were not allowed as trademarks at that time.
Nichrome is a trademark for a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire, produced by the Driver-Harris Company. A common alloy is 80% nickel and 20% chromium, by mass, but there are many others to accommodate various applications. It is silvery-grey in colour, is corrosion-resistant, and has a high melting point of about 1400 °C (2552 °F). Due to its relatively high electrical resistivity and resistance to oxidation at high temperatures, it is widely used in electric heating elements, such as in hair dryers, electric ovens, soldering iron, toasters, and even electronic cigarettes. Typically, Nichrome is wound in coils to a certain electrical resistance, and current is passed through to produce heat.
Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages.Nitinol alloys exhibit two closely related and unique properties: shape memory and superelasticity (also called pseudoelasticity). Shape memory refers to the ability of nitinol to undergo deformation at one temperature, then recover its original, undeformed shape upon heating above its “transformation temperature”. Superelasticity occurs at a narrow temperature range just above its transformation temperature; in this case, no heating is necessary to cause the undeformed shape to recover, and the material exhibits enormous elasticity, some 10-30 times that of ordinary metal.
Nanomaterials are chemical substances or materials that are manufactured and used at a very small scale (down to 10,000 times smaller than the diameter of a human hair). Nanomaterials are developed to exhibit novel characteristics (such as increased strength, chemical reactivity or conductivity) compared to the same material without nanoscale features. Hundreds of products containing nanomaterials are already in use. Examples are batteries, coatings, anti-bacterial clothing etc. Analysts expect markets to grow to hundreds of billions of Euros by 2015. Nano innovation will be seen in many sectors including public health, information society, industry, innovation, environment, energy, transport, security and space Good things come in small packages. the unique properties of nanomaterials and structures on the nanometer scale have sparked the attention of materials developers. Incremental shifts in product performance using these materials–for example, as fillers in plastics, as coatings on surfaces, and as UV-protectants in cosmetics–are already occurring. The technology holds more promise for the future, though, and is expected to bring more disruptive changes to both products and markets.
Nanomaterials is a field that takes a materials science-based approach to nanotechnology. It studies materials with morphological features on the nanoscale, and especially those that have special properties stemming from their nanoscale dimensions. Nanoscale is usually defined as smaller than a one tenth of a micrometer in at least one dimension, though this term is sometimes also used for materials smaller than one micrometer. In comparison to a human hair which is ca. 80,000 nm in diameter, the nanofibers are 1,000 times smaller in diameter. When the characteristic length scale of the microstructure is in the 1- 100 nm range, it becomes comparable with the critical length scales of physical phenomena, resulting in the so-called “size and shape effects.” This leads to unique properties and the opportunity to use such nanostructured materials in novel applications and devices. Phenomena occurring on this length scale are of interest to physicists, chemists, biologists, electrical and mechanical engineers, and computer scientists, making research in nanotechnology a frontier activity in materials science.
The chemical processing and synthesis of high performance technological components for the private, industrial and military sectors requires the use of high purity ceramics, polymers, glass-ceramics and material composites. In condensed bodies formed from fine powders, the irregular sizes and shapes of nanoparticles in a typical powder often lead to non-uniform packing morphologies that result in packing density variations in the powder compact. Nanomaterials can be metals, ceramics, polymeric materials, or composite materials. Their defining characteristic is a very small feature size in the range of 1-100 nanometers (nm). At the nanomaterial level, some material properties are affected by the laws of atomic physics, rather than behaving as traditional bulk materials do.
In the mid-1980s a new class of material – hollow carbon spheres – was discovered. The way a crack grows in a larger-scale, bulk material is likely to be different from crack propagation in a nanomaterial where crack and particle size are comparable. Where proteins are 10-1000 nm in size, and cell walls 1-100 nm thick, their behavior on encountering a nanomaterial may be quite different from that seen in relation to larger-scale materials. In bulk materials, only a relatively small percentage of atoms will be at or near a surface or interface (like a crystal grain boundary). In nanomaterials, the small feature size ensures that many atoms, perhaps half or more in some cases, will be near interfaces. Surface properties such as energy levels, electronic structure, and reactivity can be quite different from interior states, and give rise to quite different material properties. Let us examine in particular nanocomposites based on polymeric materials, keeping in mind that this is but one small division of nanomaterials. Those most humble of materials, clays, have been found to impart amazing properties.
Decrease in material flammability has also been studied, an especially important property for transportation applications where choice of material is influenced by safety concerns. Clay/polymer nanocomposites have been considered as matrix materials for fiber-based composites destined for aerospace components. Some pores and other structural defects associated with density variations have been shown to play a detrimental role in the sintering process by growing and thus limiting end-point densities. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over particle-particle interactions. Monodisperse powders of colloidal silica, for example, may therefore be stabilized sufficiently to ensure a high degree of order in the colloidal crystal orpolycrystalline colloidal solid which results from aggregation. On 18 October 2011, the European Commission adopted the following definition of a nanomaterial : A natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm – 100 nm.
In specific cases and where warranted by concerns for the environment, health, safety or competitiveness the number size distribution threshold of 50% may be replaced by a threshold between 1 and 50%. An important aspect of nanotechnology is the vastly increased ratio of surface area to volume present in many nanoscale materials, which makes possible new quantum mechanical effects. One example is the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes pronounced when the nanometer size range is reached. A certain number of physical properties also alter with the change from macroscopic systems.
Novel mechanical properties of nanomaterials is a subject of nanomechanics research. Catalytic activities also reveal new behaviour in the interaction with biomaterials. The most energetic research probably concerns carbon nanotubes. Nanoparticles of carbon – rods, fibers, tubes with single walls or double walls, open or closed ends, and straight or spiral forms – have been synthesized in the past 10 years. There is good reason to devote so much effort to them: carbon nanotubes have been shown to have unique properties, stiffness and strength higher than any other material, for example, as well as extraordinary electronic properties. Carbon nanotubes are reported to be thermally stable in vacuum up to 2800 degrees Centigrade, to have a capacity to carry an electric current a thousand times better than copper wires, and to have twice the thermal conductivity of diamond (which is also a form of carbon). Carbon nanotubes are used as reinforcing particles in nanocomposites, but also have many other potential applications. They could be the basis for a new era of electronic devices smaller and more powerful than any previously envisioned. Nanocomputers based on carbon nanotubes have already been demonstrated.
Magnesium alloys are mixtures of magnesium with other metals (called an alloy), often aluminium, zinc, manganese, silicon, copper, rare earths and zirconium. Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys. Magnesium is a silvery-white metal that is principally used as an alloy element for aluminum, lead, zinc, and other nonferrous alloys. Magnesium is among the lightest of all the metals, and also the sixth most abundant on earth. Magnesium is ductile and the most machinable of all the metals. Magnesium has a protective film to protect against corrosion, however it is easily corroded by chlorides, sulfates, and other chemicals, therefore magnesium is often anodized to improve its corrosion resistance.
Magnesium alloy developments have traditionally been driven by aerospace industry requirements for lightweight materials to operate under increasingly demanding conditions. Magnesium alloys have always been attractive to designers due to their low density, only two thirds that of aluminium. This has been a major factor in the widespread use of magnesium alloy castings and wrought products. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminum, copper and steel. Therefore magnesium alloys are typically used as cast alloys, but research of wrought alloys has been more extensive since 2003. Cast magnesium alloys are used for many components of modern cars, and magnesium block engines have been used in some high-performance vehicles; die-cast magnesium is also used for camera bodies and components in lenses.
Magnesium is the lightest of the commonly used metals. Its versatility and abundance make it one of the most popular metals, and variations of magnesium alloys are used in almost every major industry because it is strong, easily machined, and stable. Magnesium alloys are also impact and dent resistant, and they have the capacity for damping and low inertia, which makes them effective in high-speed applications. A further requirement in recent years has been for superior corrosion performance and dramatic improvements have been demonstrated for new magnesium alloys. Improvements in mechanical properties and corrosion resistance have led to greater interest in magnesium alloys for aerospace and speciality applications, and alloys are now being specified on programmes such as the McDonnell Douglas MD 500 helicopter.
Due to its light weight, superior machinability and ease of casting, magnesium is used for many purposes such as auto parts, power tools, sporting goods, aerospace equipment, fixtures, and material handling equipment. Automotive applications include gearboxes, valve covers, wheels, clutch housings, and brake pedal brackets. Wrought alloys are available in rod, bar, sheet, plate, forgings, and extrusions. Like the majority of common metals, magnesium is too soft to be used as a structural metal. That is why magnesium alloys feature additions of other metals. These additions increase magnesium’s strength and makes it a more viable commodity. Magnesium is most commonly used in conjunction with aluminum, but there are magnesium alloys that possess other metals, as well.
Magnesium alloys are not difficult to find. Most major distributors carry at least one grade of magnesium alloy. However, the majority of them do not offer a wide range of shapes and sizes, and almost none can provide customized designs using magnesium alloys. All Metals & Forge offers an extensive collection of pre-made shapes of both AZ31B and AZ61A grade magnesium alloys. Magnox (alloy), whose name is an abbreviation for ‘magnesium non-oxidising’, is 99% magnesium and 1% aluminium, and used in the cladding of fuel rods in some nuclear power stations. Magnesium alloys tend to be referred to by short codes (defined in ASTM 275) denoting the approximate chemical composition by weight: for example, AS41 has 4% aluminium and 1% silicon; AZ81 is 7.5% aluminium and 0.7% zinc. If aluminium is present, manganese is almost always also there at about 0.2% by weight to improve grain structure; if aluminium and manganese are absent, zirconium is usually present at about 0.8% for the same purpose.
Magnesium is one of the most abundant elements found on the Earth’s surface. The sheer amount of magnesium that is available has made it one of the most commonly used metals in a wide range of industries. You will find magnesium in everything from luggage and bicycle frames to ski bindings and archery bows. In its purest form, magnesium is too soft for structural use. However, it can be combined with other metals to gain more strength. This expands the use of magnesium and makes magnesium alloys effective tools in foundry work and other applications that require greater strength. Magnesium can also be used to reduce the amounts of sulfur found in other materials, so it has become a mainstay in both iron and steel processing.
Magnesium alloy castings can be produced by nearly all of the conventional casting methods, namely, sand, permanent, and semi permanent mold and shell, investment, and die-casting. The choice of a casting method for a particular part depends upon factors such as the configuration of the proposed design, the application, the properties required, the total number of castings required, and the properties of the alloy. Magnesium castings of all types have found use in many commercial applications, especially where their lightness and rigidity are a major advantage, such as for chain saw bodies, computer components, camera bodies, and certain portable tools and equipment. Magnesium alloy sand castings are used extensively in aerospace components. The amount of available magnesium and the metal’s ability to be machined quickly makes it easier for companies to offer it in a variety of forms. The magnesium bar is incredibly easy to work with, and is priced in a way that makes it possible for companies of all sizes to benefit from its many uses. If you are in the market for magnesium in any form, it is important to work with a distributor that allows you to find the materials that fit your specific needs.
Welding cast iron has proven to be a very difficult task to do. Many professional welders are sweating hard in determining the best way to weld a stubborn cast iron. Many have tried, many have failed, some had succeeded but the realized that their luck will not turn the next time they weld a cast iron. Cast iron is one of the alloys of iron that has a significant content of carbon in it. The content of carbon varies from about 2% to 4%. This carbon content is about 10 times greater than it is found in other alloys like wrought iron or steel. The cast iron manufacturing process is simple as a result of its simple combination. The reason why cast iron is very complicated to weld is the carbon content that is much higher in the cast iron than other regular irons. Carbon is actually the ingredient that is used in steels and allows it to be heated to make real hard but definitely useful things like razor blades, drill bits, tools and ball bearings.
Cast iron is difficult, but not impossible, to weld. In most cases, welding on cast iron involves repairs to castings, not joining casting to other members. The repairs may be made in the foundry where the castings are produced, or may be made to repair casting defects that are discovered after the part is machined. Mis-machined cast iron parts may require repair welding, such as when holes are drilled in the wrong location. Frequently, broken cast iron parts are repaired by welding. Broken cast iron parts are not unusual, given the brittle nature of most cast iron. Cast irons contains about a full three or four percent carbon, which makes it very hard and vulnerable to weld. Carbon content in cast irons makes the cast iron impossible to dissolve into a metal when it is solidifying from a molten state, and the excess carbon can be found lurking in graphite flakes. These graphite flakes are best for engine blocks and some machine components for they will make lubrication possible in worn surfaces like the cylinder walls. But tough carbon in graphite flakes has its use, which is what makes welding a cast iron very hard.
So generally welding cast iron is difficult, and comes close to impossible, but in particular, welding of cast irons can prove to be a task that can be done if a welder will have the wisdom to differentiate the grades of the cast irons. There are actually many grades of a cast iron, and the fact is, some cast irons can be easily welded than other form of cast irons. It is quite a handful in telling which is what apart, and it will take an experienced welder who has been in many years in the business of welding irons. Determining the right grade of a cast iron can truly help a welder in knowing the proper way of welding, for mostly all old timer welders can testify that welding cast irons can never be the same. One method may work in one kind of cast iron, but that method will not work on the next cast iron. Cast irons are mysterious in their own way, and welding it will prove to be an impossible task if the grade will not be determined.
In general, it is preferred to weld cast iron with preheat–and lots of it. But, another way to successfully weld cast iron is to keep it cool–not cold, but cool. Below, both methods will be described. However, once you select a method, stick with it. Keep it hot, or keep it cool, but don’t change horses in the middle of the stream. Preheating the cast iron part before welding will slow the cooling rate of the weld, and the region surround the weld. It is always preferred to heat the entire casting, if possible. Typical preheat temperatures are 500-1200 degrees F. Don’t heat over 1400 degrees F since that will put the material into the critical temperature range. Preheat the part slowly and uniformly. Weld using a low current, to minimize admixture, and residual stresses. In some cases, it may be necessary to restrict the welds to small, approximately 1-inch long segments to prevent the build up of residual stresses that can lead to cracking. Peening of weld beads can be helpful in this regard as well. After welding, allow the part to slowly cool. Wrapping the casting in an insulating blanket, or burying it in dry sand, will help slow cooling rates, and reduce cracking tendencies.
The size of the casting, or other circumstances, may require that the repair be made without preheat. When this is the case, the part needs to be kept cool, but not cold. Raising the casting temperature to 100 degrees F is helpful. If the part is on an engine, it may be possible to run it for a few minutes to obtain this temperature. Never heat the casting so hot that you cannot place your bare hand on it. Because of the nature of cast iron, tiny cracks tend to appear next to the weld even when good procedures are followed. If the casting must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing compound or they may rust shut very soon after being returned to service. One method used to repair major breaks in large castings is to drill and tap holes over the surfaces that have been beveled to receive the repair weld metal.
The most important thing for you to understand is that electric welding on cast iron is actually the very worst decision you could make to attempt to repair your cracked cast iron part. If you want to make a complete mess of your part, go ahead and arc weld it with nickel rod. Cast iron cannot stretch and withstand the contraction and hardening caused by cast welding with preheating below 1200 deg. F. The brand of welding rod does not make a very big difference. It’s the heat that causes the changes to the cast iron itself. Sure the nickel weld is machineable but the cast iron will become as hard as a drill bit or tap and therefore will prevent the proper machining that is often required. 50% of the casting repairs we see have been arc welded on with disastrous results often costing the owner at least twice as much to repair properly. Cast iron welding should not be attempted even by experienced welders without years of high temperature oven welding training. Cast iron requires preheat of at least 900 deg. F. for brazing and 1300 deg. F. for fusion welding. Cast iron usually has a carbon content of 2 to 4 percent which is much greater than in most steels. This causes most cast iron to be brittle and difficult to weld. Most cast iron welding involves repairs to existing castings instead of forming new castings.
Instructions of Welding Cast Iron :
Furthermore, welding cast iron can be done properly if the environmental factors will be considered. Cast irons must be determined if it has been exposed to hot gases, heating and cooling, or had been exposed to burning fuel exhaust. These facts can be helpful in welding, for an exhaust manifolds is the hardest cast iron to weld, because they have been flat impregnated with carbon for years while cast iron old pot belly stove which has not been exposed to hot gases or any elements can be easily weld. Bottomline is, in welding a cast iron, the grade and the environmental factors must be considered and determined to come up with the best and successful method.
Malleable cast iron is produced from white cast iron, which is made from hot liquid iron with certain chemical components. The white cast iron needs to be treated by malleablizing, such as graphitizing or oxidation and decarbonization, then its metallographic structures or chemical components will be changed, so can become into malleable cast iron. Malleable iron is cast as White iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment the brittle as cast structure is transformed. Carbon agglomerates into small roughly speherical aggregates of graphite leaving a matrix of ferrite or pearlite according to the exact heat treat used. Three basic types of malleable iron are recognized within the casting industry, Blackheart malleable iron, Whiteheart malleable iron and Pearlitic malleable iron. Malleable cast iron is a heat-treated iron-carbon alloy, which solidifies in the as-cast condition with a graphite-free structure, i.e. the total carbon content is present in the cementite form (Fe3C). Two groups of malleable cast iron are specified (whiteheart and blackheart malleable cast iron), differentiated by chemical composition, temperature and time cycles of the annealing process, the annealing atmosphere and the properties and microstructure resulting therefrom. The chemical composition of malleable iron generally conforms to the ranges : Small amounts of chromium (0.01 to 0.03%), boron (0.0020%), copper (max 1.0%), nickel (0.5 to 0.8%), and molybdenum (0.35 to 0.5%) are also sometimes present.
Malleable iron starts as a white iron casting that is then heat treated at about 900 °C (1,650 °F). Graphite separates out much more slowly in this case, so that surface tension has time to form it into spheroidal particles rather than flakes. Due to their lower aspect ratio, spheroids are relatively short and far from one another, and have a lower cross section vis-a-vis a propagating crack or phonon. They also have blunt boundaries, as opposed to flakes, which alleviates the stress concentration problems faced by grey cast iron. In general, the properties of malleable cast iron are more like mild steel. There is a limit to how large a part can be cast in malleable iron, since it is made from white cast iron. Like other similar irons with the carbon formed into spherical or nodular shapes, malleable iron exhibits good ductility. Incorrectly considered by some to be an “old” or “dead” material, malleable iron still has a legitimate place in the design engineer’s toolbox. Malleable is a good choice for small castings or castings with thin cross sections (less than 0.25 inch, 6.35 mm). Other nodular irons produced with graphite in the spherical shape can be difficult to produce in these applications due to the formation of carbides from the rapid cooling.
Comparing with the gray cast iron, malleable cast iron has better strength and ductility, especially better impact resistance in low temperatures. Comparing with cast steel, malleable cast iron has better abrasive resistance and shock absorption. Comparing with the ductile iron, both of them have good strength and ductility, but malleable iron has better impact resistance, but ductile iron has better abrasive resistance. Malleable iron also exhibits better fracture toughness properties in low temperature environments than other nodular irons, due to its lower silicon content. The ductile to brittle transformation temperature is lower than many other ductile iron alloys. In order to form properly the spherical-shaped nodules of graphite in the annealing process, during the casting process care must be taken to ensure the iron casting will solidify with an entirely white iron cross section. Heavier sections of a casting will cool slowly and with the slow cooling some primary graphite may form. This graphite will form random flake-like structures and will not transform in heat treatment. When stress is applied to such a casting in application the fracture will be lower than normal and the large particles of primary graphite can be seen. Such iron is said to have a ‘mottled’ appearance. Some countermeasures can be applied to enhance forming the all white structure, but malleable iron foundries often avoid producing heavy sections due to the constraint of slow cooling times causing the formation of the primary graphite. After the casting and heat treat process malleable iron can be shaped through cold working, such as stamping for straightening, bending or coining operations. This is possible due to malleable iron property of being less strain rate sensitive than other materials.
Whiteheart malleable cast iron
The microstructure of whiteheart malleable cast iron depends on section size. Small sections contain pearlite and temper carbon in ferritic substrate. The microstructure shall not contain flake graphite. In the large sections exists three different zones :
Blackheart and pearlitic malleable cast iron
The microstructure of blackheart malleable cast iron has a matrix essentially of ferrite. The microstructure of pearlitic malleable cast iron has a matrix, according to the grade specified, of pearlite or other transformation products of austenite. Graphite is present in the form of temper carbon nodules. The microstructure shall not contain flake graphite.
Black heart malleable cast iron is mainly used to produce the iron casting parts with impact, shake or torsion functions. Normally used to produce rear axle housing castings, spring bracket, low pressure valve body, pipe fittings, tools and wrenches. Black heart malleable cast iron is also called as ferritic malleable cast iron. Pearlite malleable cast iron has higher strength, hardness and abrasive resistance. So, it is mainly used to produce the abrasion resistant parts for motive power machinery and agricultural machinery.
Malleable cast iron designation system
The designation according to ISO 5922 (1981) of malleable cast iron consists of one letter designating the type of iron, two figures designating the tensile strength and two figures designating the minimum elongation.
Letters designating the type of malleable cast iron can be:
For example: The designation of a whiteheart malleable cast iron having a minimum tensile strength of 400 N/mm² and minimum elongation of 5% when measured on a 12 mm diameter test piece, would be W 40-05. Malleable Cast Iron is the traditional material for manufacturing pipe fittings whose characteristics make it as ideal choice. It is an iron-carbon alloy which combines the outstanding properties of cast iron and steel to produce a material which can still be cast but has improved strength and ductility. It also allows the production of complex shapes combined with a thin wall section. In its cast state it is very hard and brittle and unsuitable for most engineering applications. A controlled heat treatment process (annealing) is applied to the cast material which changes the structure and reduces the carbon content. The resulting microstructure gives a material which is less hard, no longer brittle and now has good malleable and ductile properties while retaining a sufficiently high strength.
Annealing is a heat treatment that alters the microstructure of a material causing changes in properties such as strength and hardness and ductility. Annealed metals are relatively soft and can be cut and shaped more easily. They bend easily when pressure is applied. As a rule they are heated and allowed to cool slowly. Annealing is a heat process whereby a metal is heated to a specific temperature and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily. Mild steel, is heated to a red heat and allowed to cool slowly. However, metals such as aluminium will melt if heated for too long. Process Annealing is used to treat work-hardened parts made out of low-Carbon steels (< 0.25% Carbon). This allows the parts to be soft enough to undergo further cold working without fracturing. Process annealing is done by raising the temperature to just below the Ferrite-Austenite region, line A1 on the diagram.
This temperature is about 727 ºC (1341 ºF) so heating it to about 700 ºC (1292 ºF) should suffice. This is held long enough to allow recrystallization of the ferrite phase, and then cooled in still air. Since the material stays in the same phase through out the process, the only change that occurs is the size, shape and distribution of the grain structure. This process is cheaper than either full annealing or normalizing since the material is not heated to a very high temperature or cooled in a furnace. In general, annealing is the opposite of hardening, You anneal metals to relieve internal stresses, soften them, make them more ductile, and refine their grain structures. Annealing consists of heating a metal to a specific temperature, holding it at that temperature for a set length of time, and then cooling the metal to room temperature. The cooling method depends on the metal and the properties desired. Some metals are furnace-cooled, and others are cooled by burying them in ashes, lime, or other insulating materials.
The benefits of annealing are :
Soft annealing is carried out at a temperature of just under Ac1, sometimes also over Ac1 or by fluctuating around Ac1 with subsequent slow cooling to achieve a soft condition (DIN 17022 part 1-5). Through this heat treatment, the cementite lamination of the perlite is transformed to a spherical form – known as granular cementite. This type of microstructure provides the best workability for steels with a C-content of more than approx. 0.5%. Granular cementite provides the condition for best workability for any type of cold working e.g. for cold-heading, drawing, or cold extrusion.
Full annealing is the process of slowly raising the temperature about 50 ºC (90 ºF) above the Austenitic temperature line A3 or line ACM in the case of Hypoeutectoid steels (steels with < 0.77% Carbon) and 50 ºC (90 ºF) into the Austenite-Cementite region in the case of Hypereutectoid steels (steels with > 0.77% Carbon). It is held at this temperature for sufficient time for all the material to transform into Austenite or Austenite-Cementite as the case may be. It is then slowly cooled at the rate of about 20 ºC/hr (36 ºF/hr) in a furnace to about 50 ºC (90 ºF) into the Ferrite-Cementite range. At this point, it can be cooled in room temperature air with natural convection.
Stress Relief Anneal
Stress Relief Anneal is used to reduce residual stresses in large castings, welded parts and cold-formed parts. Such parts tend to have stresses due to thermal cycling or work hardening. Parts are heated to temperatures of up to 600 – 650 ºC (1112 – 1202 ºF), and held for an extended time (about 1 hour or more) and then slowly cooled in still air.
Spheroidization is an annealing process used for high carbon steels (Carbon > 0.6%) that will be machined or cold formed subsequently. This is done by one of the following ways:
All these methods result in a structure in which all the Cementite is in the form of small globules (spheroids) dispersed throughout the ferrite matrix. This structure allows for improved machining in continuous cutting operations such as lathes and screw machines. Spheroidization also improves resistance to abrasion.
Annealing and Spheoridizing
Full annealing is accomplished by heating a hypoeutectoid steel to a temperature above the UCT (Upper Critical Temperature). In practice, the steel is heated to about 100 oF above the UCT. It is then cooled in the furnace very slowly to room temperature. The formation of austenite destroys all structures that have existed before heating. Slow cooling yields the original phases of ferrite and pearlite.
Hypereutectoid steels consist of pearlite and cementite. The cementite forms a brittle network around the pearlite. This presents difficulty in machining the hypereutectoid steels. To improve the machinability of the annealed hypereutectoid steel spheroidize annealing is applied. This process will produce a spheroidal or globular form of a carbide in a ferritic matrix which makes the machining easy. Prolonged time at the elevated temperature will completely break up the pearlitic structure and cementite network. The structure is called spheroidite. This structure is desirable when minimum hardness, maximum ductility and maximum machinability are required.
Low carbon steels are seldom spheroidized for machining, because they are excessively soft and gummy in the spheoridized conditions. The cutting tool will tend to push the material rather than cut it, causing excessive heat and wear on the cutting tip. Stress-Relief Annealing is sometimes called subcritical annealing, is useful in removing residual stresses due to heavy machining or other cold-working processes. It is usually carried out at temperatures below the LCT, which is usually selected around 1000ºF.
Friction welding is a method for making welds in which one component is rotated relative to, and in pressure contact, with the mating component to produce heat at the faying surfaces. The weld is completed by the application of a forge force during or after the cessation of relative motion. Friction welding is a completely mechanical solid-phase process in which heat generated by friction is used to create the ideal conditions for a high integrity welded joint between similar or dissimilar metals. In its simplest form, friction welding involves holding two components in axial alignment. Then rotate them under pressure causing the interface to heat up.
Friction welding (FW) is a class of solid-state welding processes that generates heat through mechanical friction between a moving workpiece and a stationary component, with the addition of a lateral force called “upset” to plastically displace and fuse the materials. Technically, because no melt occurs, friction welding is not actually a welding process in the traditional sense, but a forging technique. However, due to the similarities between these techniques and traditional welding, the term has become common. Friction welding is used with metals and thermoplastics in a wide variety of aviation and automotive applications.
Friction welding is a versatile process, meaning it is suitable for producing a wide variety of part shapes, materials and weld sizes. Applications that can be friction welded include hydraulic piston rods and cylinders, aircraft and aerospace components, cutting tools, drill pipes, tunnelling rods, agricultural machinery, automotive parts such as drive shafts, oil field pieces, air & waste canisters, military equipment, electrical connectors, chemical and pump shafts, swivel pins, track rollers and turbo chargers. Materials which can be friction welded include nickel alloys, low and medium carbon, micro alloyed, case hardened, heat and corrosion resistant, nitriding and carburising steels, and titanium. Friction Welding offers substantial cost savings in numerous applications. The weld strength normally equals or exceeds parent material strength. In friction welding, joining occurs below the melting pints of the metals involved. Two pieces are held in axial alignment, while one is rotated and thrust against the other. This process allows the use of dissimilar metals to be readily joined.
The combination of fast joining times (on the order of a few seconds), and direct heat input at the weld interface, yields relatively small heat-affected zones. Friction welding techniques are generally melt-free, which avoids grain growth in engineered materials, such as high-strength heat-treated steels. Another advantage is that the motion tends to “clean” the surface between the materials being welded, which means they can be joined with less preparation. During the welding process, depending on the method being used, small pieces of the plastic metal will be forced out of the working mass (flash). It is believed that the flash carries away debris and dirt. Another advantage of friction welding is that it allows dissimilar materials to be joined. This is particularly useful in aerospace, where it is used to join lightweight aluminum stock to high-strength steels. Normally the wide difference in melting points of the two materials would make it impossible to weld using traditional techniques, and would require some sort of mechanical connection. Friction welding provides a “full strength” bond with no additional weight. Other common uses for these sorts of bi-metal joins is in the nuclear industry, where copper-steel joints are common in the reactor cooling systems and in the transport of cryogenic fluids, where friction welding has been used to join aluminum alloys to stainless steels and high-nickel-alloy materials for cryogenic-fluid piping and containment vessels.
In the automotive sector the drive to build more fuel efficient vehicles has led to the increased use of aluminium in an effort save weight, which also improves recyclability when the vehicles a scrapped. Friction stir welding is being use increasingly to replace fusion welding techniques when alumnium alloys are involve the main advantage being low distortion and the ability to weld awkward materials material combination The process has already been applied to the manufacture of tail light panels by Marine Aluminium Aanensen in Norway, and SAPA in Sweden have recently taken delivery of a new friction stir welding machine from ESAB for the production of automotive parts. However, the technique has not yet been adopted in production for the fabrication of aluminium tanks for bulk road transport of liquids and powders. Friction welding is also used with thermoplastics, which act in a fashion analogous to metals under heat and pressure. The heat and pressure used on these materials is much lower than metals, but the technique can be used to join metals to plastics with the metal interface being machined. For instance, the technique can be used to join eyeglass frames to the pins in their hinges. The lower energies and pressures used allows for a wider variety of techniques to be used.
Carbon steel is steel where the main interstitial alloying constituent is carbon. The American Iron and Steel Institute (AISI) defines carbon steel as : “Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect when the specified minimum for copper does not exceed 0.40 percent or when the maximum content specified for any of the following elements does not exceed the percentages noted : manganese 1.65, silicon 0.60, copper 0.60″. Carbon Steel is a malleable, iron-based metal containing carbon, small amounts of manganese, and other elements to make the material useful for many different applications. Carbon steels are the base metals widely used in manufacturing today around the world in nearly every industry, including aerospace, aircraft, automotive, chemical, and defense.
Carbon steel, also called plain-carbon steel, is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. The only other alloying elements allowed in plain-carbon steel are: manganese (1.65% max), silicon (0.60% max), and copper (0.60% max). Steel with a low carbon content has the same properties as iron, soft but easily formed. As carbon content rises the metal becomes harder and stronger but less ductile and more difficult to weld. Higher carbon content lowers steel’s melting point and its temperature resistance in general. The term “carbon steel” may also be used in reference to steel which is not stainless steel, in this use carbon steel may include alloy steels. As the carbon content rises, steel has the ability to become harder and stronger through heat treating, but this also makes it less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.
Steel is an alloy formed between the union of iron and smaller amounts of carbon. Carbon seems to the most appropriate material for iron to bond with. Carbon works as a strengthening instrument in steel; it further solidifies the structures inherent in iron. By tinkering with the different amounts of carbon present in the alloy, many variables can be adjusted such as density, hardness and malleability. Increasing the level of carbon present will make the steel more structurally delicate, but also harder at the same time. Steel is more or less classified by its inherent carbon content. High-carbon steel is traditionally used for fashioning cutting tools and dies because one of its distinguishing features is great hardness. Steel with a lower to medium level of carbon will typically be reserved for metal sheeting for use in construction, due to its increased hardness and malleability.
Types of carbon steel
Steel can be heat-treated which allows parts to be fabricated in an easily-formable soft state. If enough carbon is present, the alloy can be hardened to increase strength, wear, and impact resistance. Steels are often wrought by cold-working methods, which is the shaping of metal through deformation at a low equilibrium or metastable temperature. The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength, or impact resistance. Note that the electrical and thermal conductivity are slightly altered. As with most strengthening techniques for steel, Young’s modulus is unaffected.
Steel has a higher solid solubility for carbon in the austenite phase; therefore all heat treatments, except spheroidizing and process annealing, start by heating to an austenitic phase. The rate at which the steel is cooled through the eutectoid reaction affects the rate at which carbon diffuses out of austenite. Generally speaking, cooling swiftly will give a finer pearlite (until the martensite critical temperature is reached) and cooling slowly will give a coarser pearlite. Cooling a hypoeutectoid (less than 0.77 wt% C) steel results in a pearlitic structure with ?-ferrite at the grain boundaries. If it is hypereutectoid (more than 0.77 wt% C) steel then the structure is full pearlite with small grains of cementite scattered throughout.
Grey cast iron is characterized by its graphitic microstructure, which causes fractures of the material to have a grey appearance. It is the most commonly used cast iron and the most widely used cast material based on weight. Most cast irons have a chemical composition of 2.5 to 4.0% carbon, 1 to 3% silicon, and the remainder is iron. Grey cast iron has less tensile strength and shock resistance than steel, but its compressive strength is comparable to low and medium carbon steel. Grey cast iron also known as flake graphite cast iron, is a type of casting iron in which most of the carbon is present as flake graphite .The properties of grey cast iron depends on the distribution, sizs and amount of graphite flakes, and the matrix structure. Casting quality are influenced mainly by the manufacturing conditions, chemical composition, solidification time and rate of cooling in the mould.
Grey cast iron exhibits low to moderate strength, low modulus of elasticity, low notch sensitiviy, high thermal conductivity, moderate resistance of thermal stock , and outstanding castability. It is used for housings where tensile strength is non-critical, such as internal combustion engine cylinder blocks, pump housings, valve bodies, electrical boxes, and decorative castings. Grey cast iron’s high thermal conductivity and specific heat capacity are often exploited to make cast iron cookware and disc brake rotors. Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due to its carbide impurities which allow cracks to pass straight through. Grey cast iron is named after its grey fractured surface, which occurs because the graphitic flakes deflect a passing crack and initiate countless new cracks as the material breaks.
Carbon (C) and silicon (Si) are the main alloying elements, with the amount ranging from 2.1 to 4 wt% and 1 to 3 wt%, respectively. Iron alloys with less carbon content are known as steel. While this technically makes these base alloys ternary Fe-C-Si alloys, the principle of cast iron solidification is understood from the binary iron-carbon phase diagram. Since the compositions of most cast irons are around the eutectic point of the iron-carbon system, the melting temperatures closely correlate, usually ranging from 1,150 to 1,200 °C (2,102 to 2,192 °F), which is about 300 °C (572 °F) lower than the melting point of pure iron. Gray iron is one of the oldest cast ferrous products. In spite of competition from newer materials and their energetic promotion, gray iron is still used for those applications where its properties have proved it to be the most suitable material available. Next to wrought steel, gray iron is the most widely used metallic material for engineering purposes. For 1967, production of gray iron castings was over 14 million tons, or about two and one-half times the volume of all other types of castings combined.
There are several reasons for its popularity and widespread use. It has a number of desirable characteristics not possessed by any other metal and yet is among the cheapest of ferrous materials available to the engineer. Gray iron castings are readily available in nearly all industrial areas and can be produced in foundries representing comparatively modest investments. It is the purpose of this paper to bring to your attention the characteristics of gray iron which make the material so useful. Gray iron is one of the most easily cast of all metals in the foundry. For the majority of applications, gray iron is used in its as-cast condition, thus simplifying production. The resistance of gray iron to scoring and galling with proper matrix and graphite structure is universally recognized. Gray iron castings can be produced by virtually any well-known foundry process. All of the carbon in gray iron, other than that combined with iron to form pearlite in the matrix, is present as graphite in the form of flakes of varying size and shape. It is the presence of these flakes formed on solidification which characterize gray iron. The presence of these flakes also imparts most of the desirable properties to gray iron.
MacKenzie in his 1944 Howe Memorial Lecture referred to cast iron as “steel plus graphite.” Gray iron belongs to a family of high-carbon silicon alloys which include malleable and nodular irons. Detailed discussions of the metallurgy of gray iron may be found in readily available handbooks. Gray iron is commercially produced over a wide range of compositions. The range of compositions which one may find in gray iron castings is as follows: total carbon, 2.75 to 4.00 percent; silicon, 0.75 to 3.00 percent; manganese, 0.25 to 1.50 percent; sulfur, 0.02 to 0.20 percent; phosphorus, 0.02 to 0.75 percent. Carbon is by far the most important element in gray iron. It is possible to produce all grades of iron of ASTM Specification for Gray Iron Castings (A 48-64) by merely adjusting the carbon and silicon content of the iron. It would be impossible to produce gray iron without an appropriate amount of silicon being present. The addition of silicon reduces the solubility of carbon in iron and also decreases the carbon content of the eutectic. The eutectic of iron and carbon is about 4.3 percent. The addition of each 1.00 percent silicon reduces the amount of carbon in the eutectic by 0.33 percent. Since carbon and silicon are the two principal elements in gray iron, the combined effect of these elements in the form of percent carbon plus 1/s percent silicon is termed carbon equivalent (CE). Gray irons having a carbon equivalent value of less than 4.3 percent are designated hypoeutectic irons, and those with more than 4.3 percent carbon equivalent are called hypereutectic irons. For hypoeutectic irons in the automotive and allied industries, each 0.10 percent increase in carbon equivalent value decreases the tensile strength by about 2700 psi. The iron may freeze in the iron-iron carbide metastable system rather than the stable iron-graphite system, which results in hard or chilled edges on castings.
Increasing the silicon content has a greater effect on reduction of hard edges than increasing the carbon content to the same carbon equivalent value. Increasing the silicon content decreases the carbon content of the pearlite and raises the transformation temperature of ferrite plus pearlite to austenite. The most common range for manganese in gray iron is from 0.55 to 0.75 percent. Virtually, all of the sulfur in gray iron is present as manganese sulfide, and the manganese necessary for this purpose is 1.7 times the sulfur content. Up to 0.15 percent, sulfur tends to promote the formation of Type A graphite. The majority of foundries maintain sulfur content below 0.15 percent with 0.09 to 0.12 percent being a common range for cupola melted irons. Collaud and Thieme report that, if the sulfur is decreased to a very low value together with low phosphorus and silicon, tougher irons will result and have been designated as “TG,” or tough graphite irons. The phosphorus content of most high-production gray iron castings is less than 0.15 percent with the current trend toward more steel in the furnace charge; phosphorus contents below 0.10 percent are common. Phosphorus generally occurs as an iron iron-phosphide eutectic, although in some of the higher- carbon irons, the ternary eutectic of iron iron-phosphide iron-carbide may form. Phosphorus contents over 0.10 percent are undesirable in the lower-carbon equivalent irons used for engine heads and blocks and other applications requiring pressure tightness. Copper and nickel behave in a similar manner in cast iron. An austenitic gray iron may be obtained by raising the nickel content to about 15 percent together with about 6 percent copper, or to 20 percent without copper as shown in ASTM Specification for Austenitic Gray Iron Castings (A 436-63).
Chromium is often added to improve hardness and strength of gray iron, and for this purpose the chromium level is raised to 0.20 to 0.35 percent. Chromium improves the elevated temperature properties of gray iron. Molybdenum is widely used for improving the elevated temperature properties of gray iron. Since the modulus of elasticity of molybdenum is quite high, molybdenum additions to gray iron increase its modulus of elasticity. Even in such small amounts, vanadium has a beneficial effect on the elevated temperature properties of gray iron.Increasing the titanium content of gray iron from about 0.05 to 0.14 percent through the use of a titanium bearing pig iron increased the strength of a hypereutectic iron in an ASTM Specification A 48 test bar A (7/8 in. diameter) from 22,000 to 34,000 psi. Gray irons usually contain between 20 and 92 ppm (0.002 to 0.008 percent) nitrogen.
Inconel alloys are generally known for their resistance to oxidation and their ability to maintain their structural integrity in high temperature atmospheres. There are several Inconel alloys that are used in applications that require a material that does not easily succumb to caustic corrosion, corrosion caused by high purity water, and stress-corrosion cracking. While each variation of Inconel has unique traits that make it effective in different circumstances, the majority of the alloys are used frequently in the chemical industry.
Inconel is the trade name for a group of more than 20 metal alloys made by Special Metals Corporation. The alloys are extremely resistant to oxidation and high temperatures. Most of the alloys have applications in the chemical industry. Inconel is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium-based superalloys. Inconel alloys are typically used in high temperature applications. It is often referred to in English as “Inco” (or occasionally “Iconel”). Common trade names for Inconel include : Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020.
Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments. When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where aluminum and steel would succumb to creep as a result of thermally-induced crystal vacancies. Inconel’s high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy. In age hardening or precipitation strengthening varieties, small amounts of niobium combine with nickel to form the intermetallic compound Ni3Nb or gamma prime. Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures.
Inconel alloys Series
Inconel 600 is a nickel-chromium alloy that offers high levels of resistance to a number of corrosive elements. In high-temperature situations, Inconel 600 will not succumb to chloride-ion stress-corrosion cracking or general oxidation. The alloy is also resistant to caustic corrosion and corrosion caused by high purity water. Its ability to withstand corrosion in a variety of forms has made Inconel 600 the perfect alloy for use in furnace components and chemical processing equipment. However, Inconel 600 is also used effectively in the food industry and in nuclear engineering, because it will maintain its structure in applications that would cause permanent, irreversible distortion to other alloys.
Like Inconel 600, Inconel 601 offers resistance to various forms of high-temperature corrosion and oxidization. However, unlike 600, this nickel-chromium alloy has an addition of aluminum. This addition allows it to demonstrate high mechanical properties even in extremely hot environments. Inconel 601′s ability to stave off the strain that would result in many alloys when exposed to high temperatures has led to its use in furnaces and heat treating equipment like retorts and baskets. You will also find Inconel 601 in gas-turbine components and petrochemical processing equipment.
Inconel 625 is the rare alloy that gains strength without having to undergo an extensive strengthening heat treatment. Inconel 625 is a nickel-chromium-molybdenum alloy with an addition of niobium. The niobium reacts with the molybdenum, causing the alloy’s matrix to stiffen and increasing its strength level. Like most Inconel alloys, Inconel 625 has high resistance to a number of corrosive elements. In fact, it can withstand harsh environments that would all but destroy other alloys. It is particularly effective when it comes to staving off crevice corrosion and pitting. Inconel 625 is a versatile alloy that requires less work than most. It is effectively used in the aerospace industry, marine engineering, the chemical and energy industries, and much more.
The Inconel alloys consist mainly of a group of metal alloys that offer high resistance to corrosive materials and environments. Inconel 690 falls into this category. However, unlike some of the other alloys in the group, it is a high-chromium and nickel alloy. The high-chromium element of the alloy gives it a particularly strong resistance to corrosion that occurs in aqueous atmospheres. Generally, this corrosion occurs as oxidizing acids and salts break a material down. Along with its ability to resist these stresses, Inconel 690 can also withstand the sulfidation that takes place at extremely high temperatures.
Inconel 718 possesses the resistance to corrosive elements that are common among Inconel alloys. However, Inconel 718 differs from other alloys in its “family” in structure and response. 718 is a precipitation-hardenable nickel-chromium alloy. It contains substantial levels of iron, molybdenum, and niobium as well as trace amounts of titanium and aluminum.Its makeup allows for an ease of welding that is not matched by the majority of Inconel alloys. It also allows Inconel 718 to combine anti-corrosive elements with a high level of strength and flexibility. Inconel 718 is particularly resistant to post-weld cracking, and it can maintain its structure in both high-temperature and aqueous environments.
Inconel 722 is a nickel-chromium alloy that shares many of the same properties as other Inconel alloys. It demonstrates a high level of resistance to various forms of corrosion. It also has the capacity to remain effective at extremely high temperatures. Inconel 722 can withstand the stress caused by several types of acids, which has made it a common metal in the chemical industry.
Inconel 903 Inconel 903 is part of a family of alloys that are known for their resistance to corrosion caused by a wide range of stresses in a variety of settings. Many Inconel alloys can remain effective in high temperature and aqueous atmospheres. Most are resistant to multiple acids, as well, so they are used regularly in the petrochemical industry. Inconel is a difficult metal to shape and machine using traditional techniques due to rapid work hardening. After the first machining pass, work hardening tends to plastically deform either the workpiece or the tool on subsequent passes. For this reason, age-hardened Inconels such as 718 are machined using an aggressive but slow cut with a hard tool, minimizing the number of passes required.
Alternatively, the majority of the machining can be performed with the workpiece in a solutionised form, with only the final steps being performed after age-hardening. External threads are machined using a lathe to “single point” the threads, or by rolling the threads using a screw machine. Holes with internal threads are made by welding or brazing threaded inserts made of stainless steel. Cutting of plate is often done with a waterjet cutter. Internal threads can also be cut by single point method on lathe, or by threadmilling on a machining center. New whisker reinforced ceramic cutters are also used to machine nickel alloys. They remove material at a rate typically 8 times faster than carbide cutters. 718 Inconel can also be roll threaded after full aging by using induction heat to 1300 degrees F without increasing grain size. Welding inconel alloys is difficult due to cracking and microstructural segregation of alloying elements in the heat affected zone. However, several alloys have been designed to overcome these problems. The most common welding methods are gas tungsten arc welding and electron beam welding.
Inconel is often encountered in extreme environments. It is common in gas turbine blades, seals, and combustors, as well as turbocharger rotors and seals, electric submersible well pump motor shafts, high temperature fasteners, chemical processing and pressure vessels, heat exchanger tubing, steam generators in nuclear pressurized water reactors, natural gas processing with contaminants such as H2S and CO2, firearm sound suppressor blast baffles, and Formula One and NASCAR exhaust systems. Inconel is increasingly used in the boilers of waste incinerators.
The Joint European Torus vessel is made in Inconel. North American Aviation constructed the skin of the X-15 rocket plane out of an Inconel alloy known as “Inconel X”. Rocketdyne used Inconel X-750 for the thrust chamber of the F-1 rocket engine used in the first stage of the Saturn V Booster. Inconel is also used for the lightweight Sport Exhaust of a recent supercar, the McLaren MP4-12C. Rolled Inconel was frequently used as the recording medium by engraving in black box recorders on aircraft. Alternatives to the use of Inconel in chemical applications like scrubber, columns, reactors, and pipes is Hastelloy, perfluoroalkoxy (PFA) lined carbon steel or fiber reinforced plastic.