Nano Tungsten Carbide Perfect Carbonization

Nano-cemented carbide not only has high hardness, good wear resistance, but also has high strength and toughness, and has good comprehensive properties. Its application field is expanding constantly. It has been widely used in manufacturing micro-drills, precision tooling and difficult cutting fields. As the basic raw material of nano-cemented carbide production, nano tungsten carbide has been prepared and its properties for the production of nano-cemented carbide. It has a great influence and has almost become the bottleneck in the production of nano-cemented carbide. For this reason, many enterprises and research institutes in many countries have carried out a lot of research.

Recently, some scholars have published an academic scheme to prepare nano tungsten carbide by reducing nano-tungsten powder with purple tungsten oxide. The process is as follows:

In a continuous reduction furnace, the hydrogen flow rate was adjusted to 40m³/h and the temperature was 750 ℃. The purple tungsten oxide was placed in a boat with a loading capacity of 500g/boat. It was pushed into the reduction furnace every 15 minutes for reduction. The tungsten powder with average particle size of 46 nm obtained by reduction was milled with 100 nm carbon black, vanadium oxide and chromium oxide in a ball mill with water jacket. Among them, nano-carbon black accounted for 6.50%, vanadium oxide 0.35%, chromium oxide 0.55%, remaining tungsten powder and milling time was 10 hours. Nitrogen or argon or other inert gases are added to the ball mill, and water jackets are added to the ball mill to prevent the oxidation of the mixture caused by excessive temperature. The ball-milled mixture was carbonized in a carburizing furnace. The carbonization temperature was 1500 ℃, the carbonization time was 10 minutes, and then the uniform nano tungsten carbide with particle size of 120 nm was obtained by rapid cooling.

In the scheme, because violet tungsten is used as raw material and placed in 40-50 m³/h strong hydrogen flow at 600-800 ℃, violet tungsten is reduced in strong hydrogen flow and boat loading is reduced, water content in reduction atmosphere can be reduced and the effect of water vapor on reduction process can be eliminated rapidly, thus uniform nano tungsten powder with average particle size less than 50 nano can be obtained, while nano-tungsten powder is used. Carbon black can improve the activity of carbon in the process of carbonization, which is conducive to a large number of nucleation to obtain fine tungsten carbide.

Further more, appropriate proportion of carbon black and inhibitors vanadium oxide and chromium oxide can be used to obtain finer tungsten carbide. High temperature and short time carbonization can greatly improve the activity of reactants in the carbonization process, which is more conducive to large number of nucleation, thus obtaining nano tungsten carbide with very fine particle size. Rapid cooling can make the reactants rapidly detach from the reaction state to prevent the growth of the formed tungsten carbide particles, thus obtaining nano tungsten carbide powder with uniform particle size. This high temperature carbonization technology has the advantages of short carbonization time, complete carbonization, good stability and easy mass production.

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