With many excellent properties, superfine crystal tungsten carbide has a wide application prospect in the fields of PCB bit and cutting tool. At present, the preparation methods of superfine crystalline tungsten carbide include direct reduction carburization, mechanical alloying and so on.

 

 

Direct reduction carburization method is actually similar to the conventional hard alloy raw material production process. It is carried out in two processes that are made of tungsten or tungsten compounds as raw materials for carbon black or hydrocarbon gases as reductants and carbonization materials for reduction and carbonization. This is a widely used method for the preparation of WC-Co composite powder.

 

The chemical vapor migration caused by the hydrogen reduction of tungsten oxide leads to the growth of grain, and the ultrafine tungsten powder cannot be prepared effectively. In order to avoid the effect of chemical vapor phase migration, carbon reduction method is used in the production of ultrafine tungsten powder in various countries.

 

First, the mixed ultrafine WO₃ and carbon black are mixed, and the WO₃ is reduced to a variety of tungsten powder in the high temperature nitrogen with carbon black. Then the tungsten powder is carbonized to get ultrafine tungsten carbide powder by using the residual carbon black in the mixed powder in high temperature hydrogen. The production process control requirements are extremely demanding, and the products are easily mixed with multiple phases, especially the high W2C phase.

 

Direct reduction processing is carried out in two rotary furnaces. In the first furnace, the superfine WO₃ changes from WO₃ to WO₂ at high temperature. In the process of transformation, the volume contraction and density increase. And the WO₂ (OH) ₂ hydrate will not appear in the presence of carbon black. In the second furnace, the ultrafine tungsten powder reduced in the first furnace was carbonized into ultrafine WC powder directly under the atmosphere of high temperature and hydrogen.