Plasma coating is the process of utilizing plasma flames in order to spray various coating materials onto metal substrates. The definition of flame that is used in reference of plasma is as a stream of gas that is made luminous, or resembles flames, as a result of heat. The requirement of heat makes plasma coating fall under the category of a thermal spray coating process.
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Categorized by the method used to achieve coating rather than the materials that are used to coat or the substrate being coated, plasma coating processes can use a variety of materials including ceramics, stainless steel, aluminum oxides and carbide. In addition, plasma coating is used in a broad spectrum of heavy-duty applications and industries such as: electronics, in which plasma coatings serve as excellent means of electrical insulation; industrial manufacturing, for the coating of various components such as pumps, pipes, valves and more; aerospace, in order to coat many component parts to meet industry standards for spaceflight and aviation; and architecture, which utilizes plasma coatings for both protective and decorative applications. Common materials that undergo the plasma coating process in order to achieve strength, corrosion-resistance and durability include titanium, aluminum and magnesium.
The plasma that is utilized in plasma spraying processes most commonly utilizes one or more of the following gases: argon, helium, nitrogen and hydrogen. As a gas, argon is the most typically used in plasma spraying processes since it is the easiest gas to form into plasma. Helium, on the other hand, is most often used as a secondary gas with argon as the primary. For nitrogen, it is commonly used as the primary gas and although it is not as easy to form into plasma as argon, it is the least expensive of the gases to use. Lastly, hydrogen is also primarily used as a secondary gas in this process, offering benefits such as effective heat transfer and anti-oxidant properties. The process is slightly different than other spray methods of coating services since temperatures can reach up to twenty thousand K (35,540ºF). Using a spray gun comprising of an anode and a cathode, both of which have been cooled by water, the plasma coating process begins as the plasma gas flows around the spray gun's cathode and through the anode (which is shaped into a nozzle). A direct current (DC) arc forms between the cathode and anode, and the resistance heating resulting from the arc enables the plasma gas to reach such high temperatures. Thus, the plasma gas leaves the nozzle as a flame and is then transferred to the surface that needs to be coated.
