The Preparation And Application of Tungsten Carbide Powder
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Update time : 2021-03-08 10:25:06
Tungsten carbide is a compound composed of tungsten and carbon, with a molecular formula of WC and a molecular weight of 195.85. Tungsten carbide is a black hexagonal crystal with metallic luster and hardness similar to diamond. It is a good conductor of electricity and heat. Tungsten carbide is insoluble in water, hydrochloric acid and sulfuric acid, but easily soluble in a mixed acid of nitric acid and hydrofluoric acid. Pure tungsten carbide is fragile, and if a small amount of titanium, cobalt and other metals are added, the brittleness can be reduced.
The Preparation of Tungsten Carbide
Using metal tungsten and carbon as raw materials, tungsten powder with an average particle size of 3 to 5 μm and carbon black of the same amount are dry mixed with a ball mill, fully mixed, press molded, and placed into a graphite plate, and then placed in a graphite resistance furnace Or it can be heated to 1400～1700℃ in an induction electric furnace, preferably 1550～1650℃. In the hydrogen stream, W2C is initially produced, and continues to react at high temperature to produce WC. Or firstly, tungsten hexacarbonyl is thermally decomposed in a CO atmosphere at 650-1000°C to obtain tungsten powder, and then reacted with carbon monoxide at 1150°C to obtain tungsten carbide. Temperatures higher than this temperature can generate W2C.
Tungsten trioxide WO3 is hydrogenated and reduced to prepare tungsten powder (average particle size 3～5μm). Then the mixture of tungsten powder and carbon black in an equimolar ratio (dry-blended with a ball mill for about 10 hours) is press-formed under a pressure of about 1t/cm2. Put the pressurized material block into a graphite pan or crucible, and heat it to 1400～1700℃ (preferably 1550～1650) in a hydrogen stream (using pure hydrogen with a dew point of -35℃) using a graphite resistance furnace or an induction electric furnace ℃), carburizing will produce tungsten carbide.
The reaction starts from around the tungsten particles, because W2C is generated at the beginning of the reaction, and because the reaction is incomplete (mainly because the reaction temperature is low), unreacted W and intermediate W2C remain besides WC (tungsten carbide). Therefore, it must be heated to the above-mentioned high temperature. The maximum temperature should be determined according to the particle size of raw tungsten. For coarse particles with an average particle size of about 150 μm, the reaction proceeds at a high temperature of 1550 to 1650°C.
The Application of Tungsten Carbide
Tungsten carbide is widely used as high-speed cutting tools, furnace structural materials, jet engine parts, cermet materials, resistance heating elements, etc.
Tungsten carbide is used to manufacture cutting tools, wear-resistant parts, melting crucibles for metals such as copper, cobalt, and bismuth, and wear-resistant semiconductor films.
Tungsten carbide is used as super-hard tool material and wear-resistant material. It can form a solid solution with many carbides. WC-TiC-Co cemented carbide tools have been widely used. It can also be used as a modified additive of NbC-C and TaC-C ternary system carbides, which can reduce the sintering temperature and maintain excellent performance. It can be used as aerospace materials.
Tungsten carbide (WC) powder is synthesized by using tungsten anhydride (WO3) and graphite in a reducing atmosphere at a high temperature of 1400～1600℃. Dense ceramic products can be obtained by hot pressing sintering or hot isostatic pressing sintering.
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