Tungsten Metal

Chapter 1: Principle of Tungsten Metal

This chapter will discuss what Tungsten metal is, its occurrence, its production, and properties of Tungsten metal.

What is Tungsten?

Tungsten is a rare naturally occurring chemical element on earth. It is known to be one of the toughest metals on the earth. It is usually a tin white or a steel gray metal. Tungsten is common for its high tensile strength and extreme high temperature resistance with a melting point of 6,191 degrees Fahrenheit. It is also a heavy metal known to be usable on the periodic table.

Occurrence of Tungsten Metal

Tungsten is a naturally occurring element that is found in minerals wolframite and scheelite. Wolframite is an iron manganese tungstate with the chemical composition of (FeMn)WO4 and is a solid solution of the two minerals which are ferberite (FeWO4) and hubnerite MnWO4 and scheelite is calcium tungstate (CaWO4). Some other tungsten minerals vary in their level of occurrence and abundance from semi moderate to very rare and have nearly no economic value.

Nomenclature Associated With Tungsten

The following are some of the terms that are associated with the tungsten metal, uses and other description of tungsten alloys.

Alloy Mixture

An alloy refers to the result of the mixture between two or more homogeneous elements or metals. This is done to share the attributes of one metal with the other so that we can obtain the best of both. Common alloys of tungsten are tungsten carbide (tungsten and carbon), Hastelloy (nickel, chrome, molybdenum and tungsten) and some tungsten nickel alloys just to mention a few.

Tungsten is Brittle

Brittle means that it is easily broken down when man handled or put under great stress. Tungsten metal is very easy to fracture when put under stress and therefore it is mixed with other metals to obtain their non brittle characteristics. Mixing tungsten with carbon makes it significantly stronger and allows it to be used in some areas where it would not have been used on its own.

Tungsten Filament

A filament is a tiny metal wire that is used in light bulbs. It is able to convert electric energy to light energy and still be able to withstand the very high temperature without failing or melting.

Melting Point

The melting point of tungsten refers to the temperature at which tungsten will turn from being a solid to a liquid. Tungsten has a very high melting point of 3 422oC or 6 192 Fahrenheits.

Superalloy

A super alloy refers to a metal that has very good properties in terms of tensile strength, corrosion resistance and high melting points.

Tensile Strength

In the field of engineering, this refers to the point at which a metal fails due to applied stress or pressure.

Wolfram or Tungsten

This is the other name used to refer to tungsten. This name is derived from its ore name (wolframite ore) and it is the main source of tungsten.

Properties of Tungsten

The properties of Tungsten include:

Tungsten Chemical Properties

Tungsten is located in the transitional group of the chemistry periodic table and has oxidation states of + 2, + 3, + 4, + 5, and + 6. It has an atomic number of 74 and a relative atomic mass of 183.84. Tungsten is a solid at room temperatures because of a stable isometric crystal formation which can be seen under an x-ray.

Tungsten is very resistant to corrosion by acids and is only vulnerable to nitric acid and hydrofluoric acid. Also, it can be weakened by alkaline oxidizing melts like potassium nitrate or sodium hydroxide. Tungsten is very resistant to corrosion but will combine with oxygen readily at very high temperatures to produce trioxides.

Naturally, the metal is a mixture of 5 stable isotopes namely tungsten-180, tungsten-182, tungsten-183, tungsten-184, and tungsten-186 which have a percentage composition of 0.12%, 26.5%, 14.3%, 30.6% and 28.4% respectively.

Tungsten Physical Properties

Tungsten in its purest form is a shiny white metal that can easily be processed. It does however contain traces of oxygen and carbon within its chemical composition and this makes it very brittle when put under tremendous stress and force.

Tungsten is the heaviest known engineering metal and has a very high density (19.25 g/cm3). This is due to its dense crystal formation. It has a very high melting point of 3 140oC and a boiling point high at 5 700oC. tungsten has the lowest vapor pressure of all metals and has the highest elasticity modulus of all metals at 400 GPa.

It also has a very low thermal expansion coefficient of 4.4×10-6m/m/oC which is about the same as that of borosilicate glass and this is why it is used for glass metal seals.Tungsten is also environmentally friendly and does not decompose or breakdown easily.

Attributes of Tungsten

Since tungsten is a metal, it has all the common properties of all metals. It is a very good electrical conductor due to the presence of localized electrons. Furthermore, tungsten is an excellent thermal conductor. This means it can transmit heat energy throughout its whole structure. All alloys of tungsten also are good electrical and thermal conductors and this makes them very useful in electrical applications.

Tungsten is also a unique metal that is corrosion resistant. Despite the excellent properties it has, tungsten is a very brittle metal in its original state and it can only be worked with if it is combined with other metals and forms a stronger alloy.

Production of Tungsten Metal

Tungsten is extracted and purified from its ore in several stages. The ore is eventually turned into tungsten (VI) oxide (WO3) which is then heated up with a hydrogen or carbon fuel to produce a powdered form of tungsten. The tungsten can not be molded into ingots because it has a very high melting point and melting is rather not commercially feasible.

The powdered tungsten is therefore prepared by mixing it with small amounts of nickel or other precious metals and it is sintered. During the sintering procedure the nickel diffuses and forms a tungsten alloy.

Tungsten can be extracted by hydrogen in the reduction of tungsten fluoride (WF6)

WF6 + 3H2 W + 6HF

To manufacture tungsten products, the manufactures start by sintering and at times molding the created tungsten alloys into billets of solid blocks or bars. These billets are then fabricated into tungsten foils, tungsten bars, tungsten plates, or tungsten sheets. This is done by grounding, drawing, die cutting, or molding. Some of its products require further processing.

Most tungsten products are sold for usage in three different conditions namely black, a form which retains its coating of lubricant, and oxide. The other form is the cleaned form in which the coating has been removed with the use of various chemicals. Lastly there is ground form in which the metal has been fortified with diamond silicon carbide machinery to remove the coating and obtain a specific smoothness and a desired diameter.

Tungsten Products

Materials made out of tungsten can be used to make a variety of products ranging from tungsten electrodes, mineral drilling equipment, light bulbs, industrial machinery components, home tools, military weapons, material coating (boats), X-ray screens, and some common construction equipment.

Alloys of tungsten play an important function in the armaments manufacturing and creation of very reliable heat sinks for the dissipation of heat energy. Turbine blades are also a common alloy that contain tungsten. Tungsten is also common in the manufacture of heavy equipment like weights and ballasts used in the gyms.

Tungsten is resistant to corrosion and therefore is ideal in the manufacture of tools and helps them last longer without tarnishing or losing its value. Tungsten is also used in industries to make tungsten electrodes. They are ideal for this purpose because of their resistance to very high temperatures and can withstand being used in water without rusting or tarnishing.

Tungsten is also used in the manufacture of welding equipment where it is used to transmit large amounts of voltage and electric current to two separate sheets of metal. Other common uses are in electric discharge machines and tungsten gas arc welding.

Chapter 2: Types of Tungsten Alloys

Tungsten has 5 main alloys and these are alloyed tungsten, cemented carbide, tungsten carbide, tungsten-based chemicals, and pure tungsten. The alloys of tungsten are categorized into classes of nominal tungsten weight and the alloy’s ultimate tensile strength.

Tungsten Carbide

Tungsten carbide is a combination of tungsten and carbon at a percentage ratio of 50%: 50%. It is a fine gray powder that can be processed into various and more useful materials.

This alloy is extremely strong and resists wearing due to other chemicals like acids, alkalis, and even the gradual effects of oxygen and water on metals the compound is twice as strong as high-grade steel and is much denser than titanium or steel. There are up to 20 varieties of tungsten carbide powder grades with varying grain sizes, tensile strength, hardness and melting points for different uses.

Tungsten is sintered and pressed into all these kinds of strong and durable products, tools, and parts. Due to its high strength, tungsten carbide is very useful in the mining industry, construction sites, and metalworking. Statistically 60% of all tungsten carbide alloys are made solely for these industries.

Manufacture of Tungsten Carbide

Tungsten carbide alloy is prepared by reacting tungsten with carbon at a very high temperature range of about 1,400 – 2,000oC. Another technique is using a low temperature fluid bed process in which tungsten metal or blue tungsten oxide (WO3) is reacted with carbon dioxide or a carbon monoxide mixture and hydrogen at a temperature of 900 to 1,200oC.

There are some other chemical vapor methods that have been discovered and these are as follows:

• Tungsten hexachloride is reacted with hydrogen as a reducing agent and methane as the source of carbon at a steady temperature of 670oC.

WCl6 + H2 + CH4 ➔ WC + 6HCl

• Tungsten hexafluoride is also reacted with hydrogen as a reducing agent and methanol as a source of carbon at a temperature of 350oC.

WF6 + 2H2 + CH3OH ➔ WC + 6HF + H2O

Properties of Tungsten Carbide

Tungsten carbide has a macrocrystalline type formation that provides it with its strong and tough nature compared to other alloys of tungsten. Tungsten carbide has a lower melting point due to the addition of carbon to tungsten. The alloy is very resistant to acids but readily reacts with some elements at elevated temperatures.

Tungsten carbide is hard and tough and it ranks to 9 on the Mohs scale of hard metals. It has an impressive tensile strength and a favorable compression strength. Tungsten carbide does conduct electricity though not as well as other materials.

Main Uses of Tungsten Carbide

Tungsten carbide is used in the manufacture of cutting and drilling tools because it is very abrasive and resistant to high temperatures. The alloy makes impressive cutting-edge tools that maintain their sharp edges better than steel tools and therefore are favorable.

Another application is ammunition. Tungsten carbide compounds are used in the manufacture of armor piercing rounds. Since the alloy is very tough it is used in the manufacture of heavy grade ammunition rounds capable of piercing through the hardest of surfaces like tanks and retreat bunks.

Mining and drilling through hard surfaces is another common use for the alloy. Tungsten carbide is used in the manufacture of rock drill bits, roller cutters, plow chisels, and tunnel boring machinery.

The alloy is also used as an effective neutron reflector in the nuclear industries. Furthermore, carbide tips are used in sporting gear. Racing shoe studs and trekking poles are made from the alloy. Surgical instruments and some jewelry are made from tungsten carbide because of its high resistance to corrosion.

Health Issues Associated With Tungsten

Inhalation of carbide dust is a serious health concern as it leads to pulmonary diseases like fibrosis.

Cemented Carbide

This is one of the most common alloys of tungsten. It is a tungsten carbide alloy alloyed further with cobalt which is used as a binder which forms the cement. Cobalt strengthens tungsten and counteracts its tendency of being brittle under high pressure and thereby allowing it to be used in critical structural applications.

Composition of Cemented Carbide

Cemented carbides are typically a metallic matrix composition with the carbide atoms acting as the aggregate and with the metal binder acting as the matrix. Its structure is comparable to that of a grinding wheel with smaller abrasive particles.

Hot isostatic pressing is the process of combining the carbide particles with the binder. The binder is made of a liquid and the carbide grains remain solid since it has a much higher melting point. The final product is a matrix composition with distinct material properties.

Properties of Cemented Carbide

The thermal expansion of cemented carbide varies with the amount of cobalt used as a metal binder. Basically, it increases with the increase in cobalt percentage.

Main Uses of Cemented Carbide

Cemented carbide is used as inserts for metal cutting tools. Due to its reinforced structure, cemented carbide is less prone to vibrations and therefore plays an important role in boring and threading equipment.

Cutting tools are known to wear off with time and therefore are coated to extend their lifespan. Five such coatings used are titanium aluminum-nitride, titanium nitride, titanium carbide-nitride, titanium carbide, and aluminum titanium-nitride. The tungsten alloys are used to coat cutting so they last longer in their usage.

Mining and tunneling equipment are usually fitted with cemented carbide tips and they are commonly known as bottom bits. This makes all drilling and digging machinery made from cemented carbide very ideal to be used world wide. Another application is in the manufacture of hot rolls and cold rolls which are used in milling companies. Industrial pump pistons for high performance pumps like in nuclear sites also use this alloy.

Alloyed Tungsten

Alloyed tungsten is a general term that refers to the various alloys made by mixing tungsten with different types of metals. Common examples are copper and iron alloys. The various alloys are useful in both industrial and commercial applications. Tungsten nickel iron is an example of the alloys of tungsten. Nickel adds density, improves strength and improves ductility of the new metal alloy. Tungsten nickel copper is another viable alloy of tungsten that has some unique abilities. The presence of copper in an alloy substantially makes the new alloy non-magnetic. This therefore creates a very strong metal that has no magnetic properties. It is very important for oncology systems and tasks where shielding of electrical sensors is key.

Properties of Alloyed Tungsten

Copper containing alloys of tungsten is uniquely non magnetic. The alloys have a low tensile strength of about 500 to 700 MPa and a decreased ductility. Despite having great strength, the alloy is used as a conductor in the manufacturing of heating coils.

Uses of Alloyed Tungsten

Tungsten alloys with copper are used mainly in manufacturing heating coils because of their tough resistance to high temperatures. Water geysers, kettles, ovens, and some stove plates are made from the alloy.

Heavy Metal Tungsten Alloys

Heavy metal tungsten alloys contain very little amounts of the other metal added to tungsten. Usually the tungsten has a percentage composition of up to 90%. A typical example of such an alloy is when a small amount of thorium oxide, about 2%, is added. Thorium oxide enhances the thermionic electron transmission.

Pure Tungsten

In its purest form, tungsten is an extremely good electrical conductor and is primarily used in electrical applications. In electronics, pure tungsten is used as a connecting medium for components on a circuit panel.

Tungsten Based Chemicals

Tungsten can also be used to make pigment phosphorus, organic dyes, and x-ray screens.

TA-1 Tungstic Acid

It is a tungstic acid and is yellow and is a fine-grained powder with thin grain sizes. It is a very reactive chemical and has a very high chemical purity. It is used mainly as a sintering improver in extremely high temperature ceramics.

ST-0 Sodium Tungstate Dihydrate

This is a chemical known as sodium tungstate dihydrate. It is a white and crystalline powder with a very high chemical purity and dissolves without leaving residues in water.

AMT-0 Ammonium Metatungstate

Another tungsten based chemical is ammonium metatungstate and is a white crystalline powder that is able to dissolve in water and not leave any residues in the water.

TO-0 Tungsten Trioxide

Tungsten trioxide is a yellow and often green powder that has a very high purity and ultra-fine crystals.

TC-1 Tungsten Carbide

This is a tungsten carbide chemical. It is a black and fine-grained powder. It is commonly used for producing a suspension so as to increase the density of SPT-3.

Chapter 3: Applications and Advantages of Tungsten Metal

This chapter will discuss the applications and advantages of Tungsten metal.

Applications of Tungsten Metal

Tungsten is widely used extensively for the manufacture of filaments for incandescent light bulbs. These bulbs are being phased out in most countries as they don’t conserve energy but rather produce more heat energy than light energy. A current is passed through the filament and the filament heats up brightly producing light. Due to its high resistance of high temperatures, the tungsten filament could withstand the heat energy produced and still be able to stay lit.

Some common practical applications of tungsten include manufacturing cutting tools. Tungsten can be made into cutting blades or have it alloyed with other elements like nickel, copper, or carbon to strengthen. Cutting tools made from tungsten or its alloys are very hard and having a very high melting point means that they can be used hours on end without melting or failing.

Another use of tungsten is for drilling and boring equipment. Drill bits and other heavy-duty earth boring machinery are made from the immensely hard metal. Dental drills are also tungsten-based. Cemented carbide is widely used for the manufacture of high speed tools like those in the mine refineries and other hard tools. Because it is a very tough metal, tungsten is also used in the manufacture of jewelry.

Calcium and magnesium tungstate are used in fluorescent lighting. Some catalysts make use of tungsten in the reduction of some complex compounds. Tungsten is also used in the manufacture of magnetrons that are found in microwave ovens. Cathode ray tubes found in those old model television sets make use of tungsten in their build. It is used because with time, the temperature increases inside the system and the tungsten will be able to withstand the high temperature.

Tungsten is also used in areas of applications that require a high density. Typical examples are manufacture of counter weights, ship anchors, tail ballasts for motor engines( rockets, airplanes, etc.).

Tungsten also has some useful military applications. For instance, it is used in manufacturing armor piercing ammunition. Taking advantage of its strong and hard nature, tungsten or its alloys at times is used in the manufacture of missiles, grenades, shells, large rounds meant to take out heavily fortified tanks, or bunks.

Tungsten (IV) sulfide is a lubricant that can withstand very high temperatures and is best used in high speed tools.

Advantages of Using Tungsten

The advantages of using tungsten metal include:

Resistance to High Temperature

Among all metals in their purest forms, tungsten has the highest melting point of 3,244oC. This means that it can be used in areas of high temperatures where other metals cannot be used.

High Density

Tungsten has a very high density at 19 g/cm3 due to its microcrystalline shape. This property makes it useful in areas that require mass in small sizes.

Low Thermal Expansion

Of all pure metals, tungsten has the least coefficient of thermal expansion. Compared to steel, tungsten is very stable at high temperatures and does not alter its form or size.

Electronic Structure

Because of its conductive properties and general inertness, tungsten is mostly used in electrical appliances where there are very high levels of radiation. It is also a perfect metal that can be used as electrodes in the electrolysis of substances.

Corrosion Resistance

Tungsten is very resistant to corrosion and therefore can be used in a wide range of applications where corrosion is common. It can be used outdoors where water and acids are likely and still hold out its function. Common usage of the metal is in fishing lures and building ship bases and some jewelry.

Fabrication Strengthening

Tungsten is a robust metal but it can be drawn into very thin wires without fracturing. A typical example are the bulb filaments which are heated to very high temperatures and still function.

Disadvantages of Tungsten

Brittle Metal

Tungsten in its purest form, is a very fragile metal and can break easily. It cannot be stretched out, compressed or twisted and still hold up its form. This is mainly because of its rigid structure that makes it impossible to be worked about without failing.

Health Concern

Inhaling tungsten irritates the mucous membrane linings and the lungs. It is regarded as a very toxic compound which if left unchecked could pose serious harm to people and the environment.

Tungsten Costs

Tungsten is a very precious metal and it does come with its fair share of expenses. Because of its unique characteristics, tungsten has significantly remained a pricy metal and an increasing demand makes it more expensive.

Weight of Tungsten

Tungsten is a heavy metal. This weight significantly makes it a very difficult metal to work with. For instance, tungsten jewelry is heavy to the extent that the wearer feels uncomfortable wearing it. Yet again, in situations where tungsten is used in the manufacture of earth boring equipment, transporting the machinery is expensive as it is difficult to transport such heavy equipment around.

Economic Value

Despite being a pricy metal, tungsten can not be returned back to its purchase value. Unlike gold which can be made into fancy bracelets and rings and then can be resold at a near similar purchased price, tungsten cannot be resold again.

Comparing Tungsten with other Metals

When compared with other metals, Tungsten has the following applications and uses:

Manufacturing Heavy-Duty Tools

Manufacture of stronghold tools used for cutting and crushing is done using tungsten or other tungsten alloys. Steel does not remain useful over a long period of time. Steel tends to wear out and break when it's cutting tougher substances so therefore tungsten or tungsten alloys is the best choice for heavy duty tools.

Electrical Conductivity

Tungsten is a good electric conductor but is not favorable because of its expensive, heavy, and brittle characteristics. When it comes to conducting electricity copper and other metals like aluminum and steel.

Building Material

When it comes to building material, tungsten is a hard and tough metal but this does not mean it is ideal in the construction industry. Tungsten is a brittle metal and therefore can not be depended upon for large structured buildings. It is wiser to use lightweight and strong metals like reinforced steel.

Conclusion

In summary, tungsten is a naturally occurring metal found on earth. It is a very unique metal as it has a very substantial chemical structure. It has a very high melting and boiling point and is a very dense metal with an over the top weight and density. Despite all these excellent characteristics, tungsten is a very brittle metal and cannot be used as would other metals like copper and iron.