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Concept
Tungsten carbide
Summary
Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in industrial machinery, cutting tools, chisels, abrasives, armor-piercing shells and jewelry.
Tungsten carbide is approximately twice as stiff as steel, with a Young's modulus of approximately 530–700 GPa, and is double the density of steel. It is comparable with corundum (α-aluminium oxideAl2O3) in hardness and can be polished and finished only with abrasives of superior hardness such as cubic boron nitride and diamond powder, wheels and compounds.
Historically referred to as Wolfram, Wolf Rahm, wolframite ore was then later carburized and cemented with a binder creating a composite now called "tungsten carbide". Tungsten is Swedish for "heavy stone".
Colloquially among workers in various industries (such as machining), tungsten carbide is often simply called carbide.
Tungsten carbide is prepared by reaction of tungsten metal and carbon at 1,400–2,000 °C. Other methods include a lower temperature fluid bed process that reacts either tungsten metal or blue tungsten(VI) oxideWO3 with CO/ mixture and H2 between 900 and 1,200 °C.
WC can also be produced by heating WO3 with graphite: directly at 900 °C or in hydrogen at 670 °C following by carburization in argon at 1,000 °C. Chemical vapor deposition methods that have been investigated include:
reacting tungsten hexachloride with hydrogen (as a reducing agent) and methane (as the source of carbon) at
WCl6 + H2 + CH4 → WC + 6HCl
reacting tungsten hexafluoride with hydrogen (as reducing agent) and methanol (as source of carbon) at
WF6 + 2H2 + CH3OH → WC + 6HF + H2O
There are two well-characterized compounds of tungsten and carbon, WC and tungsten semicarbide, W2C. Both compounds may be present in coatings and the proportions can depend on the coating method.
Official source
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