What Are the Main Physical Properties of Tungsten Carbide Powder?
Tungsten carbide powder is a variety of tungsten carbide powder with different carbon content, crystal form and particle size prepared by the reaction of tungsten metal and carbon black at 1400 – 2000 ° C. In addition, there is also a process of directly using blue WO reaction to produce tungsten carbide powder. The compounds of W and C include W5C2, W3C2 (formed in the process of heating up and quickly converted into high-carbon compounds), and close-packed hexagonal α- W2C (product at 1400~1900 ℃), face-centered cubic β- W2C (carbonization product above 2000 ℃) and simple hexagonal WC. The heating and carbonization of tungsten metal powder in a certain protective atmosphere is a reaction diffusion process, that is, the diffusion of carbon is based on the particles of tungsten metal powder (W). A thin layer of polycrystalline WC is formed at the periphery of the particles and gradually advances to the core. The growth of polycrystalline WC is carried out by extending to the W core and moving to the WC grain boundary.
Tungsten carbide has a high melting point at 2870 ° C (5200 ° F). At a pressure equivalent to 1 standard atmospheric pressure (100 kPa), its boiling point is 6000 ° C (10830 ° F), its thermal conductivity is 110 • W • m-1 • K-1 and its thermal expansion coefficient is 5.5 μ M • m - 1 • K-1. The low resistivity of tungsten carbide is about 0.2 µ Ω • m, which is equivalent to some metals (such as vanadium 0.2 µ Ω • m).
Tungsten carbide powder is very hard after processing, with a Mohs hardness of about 9 to 9.5 and a Vickers number of about 2600. Its Young's modulus is about 530-700 GPa, a bulk modulus of 630-655 Kpascals and a shear modulus of 274 Kpascals. Its ultimate tensile strength is 344MPa, its ultimate compressive strength is about 2.7GPa, and its Poisson's ratio is 0.31.
Tungsten carbide is a black hexagonal crystal with metallic luster and hardness similar to diamond. It is a good conductor of electricity and heat.
The chemical properties of tungsten carbide are stable. Tungsten is insoluble in water, hydrochloric acid and sulfuric acid, but easily soluble in the mixed acid of nitric acid and hydrofluoric acid. Active oxidation begins when the temperature is above 500 ℃ in the air, and the antioxidant capacity is weak. Strong acid resistance. Chemical reaction formula: W+C=WC Note: reaction at 1150 ℃. Does not react with chlorine below 400 ℃; It can react violently with fluorine at room temperature; It is oxidized to tungsten oxide when heated in air.
Tungsten carbide is fragile. If a small amount of titanium, cobalt and other metals are added, its mechanical properties can be improved and its brittleness can be reduced. Tungsten carbide powder is often added with titanium carbide, tantalum carbide or their mixture to make cemented carbide for cutting tools such as steel.
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