Tungsten carbide is main material for producing cemented carbide products, its chemical formula is WC. Tungsten carbide is black crystal with six square. It is a good conductor of electricity and heat with metallic luster. Tungsten carbide is insoluble in water, hydrochloric acid and sulfuric acid. But it is easy to soluble in the mixed acid of nitric acid and hydrofluoric acid. Pure tungsten carbide is easy to be broken. If incorporation of small amount titanium, cobalt metal, it will reduce the brittleness. Tungsten which used as steel cutting tools always put in titanium carbide, tantalum carbide or their mixture to improve the anti explosion capacity. Certainly, chemical properties of tungsten carbide is stable. Coarse tungsten carbide have different special properties and applications in different conditions. Especially it has many advantages under high temperature, such as less structural defects, high hardness, low micro strain. So it is widely used in mining, oil drilling, lathe processing. And its hardness is only second to the diamond with high value.
At present, there are many production methods of coarse tungsten carbide. Details are as follows:
1.High temperature carbonization with tungsten powder.
Carbonization for a long time with high temperature can make the lattice defects to a minimum, the micro strain to minimum and the plasticity of tungsten carbide is improved. It is currently the main production mode. Some studies indicate that reduced particle size of the tungsten, improve the temperature of carbonization and reduce the carbonization time can improve the quality of the tungsten carbide.
2.Tungsten oxide doped with lithium salt reduction and high temperature carbonization temperature.
This method is mainly used for preparing mine and cold micro-mold alloy.
3.Adding cobalt, nickel high temperature carbonization.
Adding a small amount of cobalt, nickel or their oxides can change mechanism of carbonation and improve the speed of carbonation. Coarse grain Tungsten Carbide produced by this method has great affected with the distribution of cobalt content. More bigger amount of the distribution of cobalt content will get more coarse tungsten carbide.
4.Adding sodium salt method.
Adding sodium salt to the APT and then reduction under high temperature, you can get coarse tungsten powder which grain size is larger than 10μm. Finally carbonization with high temperature. This method is under study, so some technology is still not mature.
5.Boiling layer of hydrogen halide reduction.
Firstly put H2 and the original tungsten powder into the bottom of the reactor and make boiling layer. But halide vapor enter to the reactor, reduced to tungsten powder at an optimum temperature which is given. And deposited on the original tungsten powder that will make the original tungsten coarsening gradually and unloading the tungsten powder from the reactor regularly. This method is used for preparation of tungsten powder which particle size is greater than 40μm.
6.Coarse-grained thermite process.
This method can produce carbide powder grains with high purity, coarse particles, large pieces and single-phase.
7.Gas injection method.
This method is in low cost but with high impurity content. So it needs a long time of chemical treatment.