Tungsten carbide powder is dark gray, has metallic luster, and its hardness is similar to that of diamond. It is a good conductor of electricity and heat. Melting point 2870 ℃, relative density 15.63, mainly used in the production of cemented carbide. Tungsten carbide is insoluble in water, hydrochloric acid and sulfuric acid, and is easily soluble in nitric acid hydrofluoric acid mixed acid. Pure tungsten carbide is fragile. If a small amount of titanium, cobalt and other metals are added, the brittleness can be reduced. As a steel cutting tool, tungsten carbide is often added with titanium carbide, tantalum carbide or their mixture to improve its explosion resistance. Tungsten carbide is chemically stable. Tungsten carbide has insufficient high-temperature oxidation resistance. When the temperature reaches 500 ℃ - 800 ℃, it is easy to oxidize and decompose into W2C and carbon in air. To solve this problem, tungsten carbide particles can be pre protected by using heat-resistant and oxidation-resistant metal as coating or bonding phase. It can also form composite carbides with TAC, tic and other solid solutions to improve the heat resistance and oxidation resistance of tungsten carbide. Tungsten carbide is still stable when heated to 2850 degrees in Ar atmosphere, and is not affected in high temperature nitrogen.
Production method of tungsten carbide powder: 1. Tungsten powder (average particle size 3 ~ 5) is prepared by hydrogenation and reduction of tungsten trioxide WO3 μ m）。 Then, the average particle size is 3 ~ 5 with tungsten powder and carbon black as raw materials μ M of tungsten powder and carbon black in equal amount shall be dry mixed with a ball mill, fully mixed, pressurized and formed, put into a graphite disc, and then heated to 1400 ~ 1700 ℃ in a graphite resistance furnace or induction furnace, preferably 1550 ~ 1650 ℃. In the hydrogen gas stream, W2C is initially generated and continues to react at high temperature to generate tungsten carbide. Or firstly, hexacarbonyl tungsten [w (CO) 6] is thermally decomposed in 650 ~ 1000 ℃ and co atmosphere to obtain tungsten powder, and then reacts with carbon monoxide at 1150 ℃ to obtain tungsten carbide. If the temperature is higher than this temperature, W2C can be formed.
2. Gas phase decomposition method. Tungsten powder was prepared by thermal decomposition of hexacarbonyl tungsten w (CO) 6. A method for preparing tungsten carbide by carburizing with carbon monoxide gas. The characteristic of this method is that tungsten carbide can be easily prepared at low temperature (1150 ℃) with a relatively simple reaction device without the high temperature as method1.
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