Nano Tungsten Carbide Preparation by Direct Reduction Carbonization Process

Tungsten carbide cemented carbide has a series of excellent properties, such as high hardness, wear resistance, good strength and toughness, heat resistance and corrosion resistance, especially its high hardness and wear resistance, which remain basically unchanged even at 500 ℃ and still have high hardness at 1000 ℃.

It is generally believed that the performance of tungsten carbide depends on the particle size and purity of its powder raw materials. The finer the grain, the smaller the defect, the stronger the performance of the carbide cutting tool can be prepared. Some scholars used direct reduction carbonization process to prepare nano tungsten carbide composite powder. The process is as follows:

1. Raw materials
The compositions of WC-Co composite powders are as follows: tungsten 55-92wt%, cobalt 3-40wt%, carbon 3-6wt% and raw materials 0-2wt% with crystal inhibitor. Among them, tungsten compounds are: ammonium metatungstate; cobalt compounds are cobalt nitrate hydrate; crystal inhibitor raw material is molybdenum oxide; soluble carbon source is ethylenediamine; and carbon-containing gas is methane CH4.

2. Ball milling process:
Water, ethanol, acetone and hexane are used as wet grinding media. Material: ball: liquid = 1:20:1, or dry grinding, material: ball = 1:20, milling time 1-120 hours, ambient atmosphere is air, inert gas or vacuum.

3. Spray pyrolysis:
The mixed concentration of W-Co raw material and crystal inhibitor or W-Co raw material, crystal inhibitor and soluble carbon source is 30-70 wt%. The pyrolysis temperature is controlled at 400-700 ℃. The ambient atmosphere is air or inert gas.

4. Spray drying:
The mixing concentration of tungsten cobalt raw material, inhibitor and soluble carbon source is 30-70wt%, the spray drying temperature is controlled at 110-400 ℃, and the ambient atmosphere is air or inert gas.

5. Burning:
The reaction is carried out in ordinary heating furnace or rotary furnace or fluidized bed furnace. The ambient atmosphere is hydrogen or carbon-containing gas. The temperature is controlled at 200-1200 ℃ and the reaction time is 0.5-12 hours.

6. Direct reduction carbonization and carbon washing processes:
The reaction is in tubular furnace or rotary furnace. The ambient atmosphere is hydrogen or carbon-containing gas. The temperature of direct reduction carbonization is controlled at 500-1200 ℃, the reaction time is 1-10 hours, the temperature of carbon washing is controlled at 300-800 ℃ and the reaction time is 0.5-10 hours. WC-Co composite powders were prepared by cooling them to room temperature in N₂ atmosphere.

The direct reduction carbonization process has wide practicability. During the process of ball milling, spray pyrolysis, spray drying, burning, reduction and carbonization, a variety of preparation equipment can be selected, and by controlling the type and content of the environmental atmosphere, reaction temperature and time, the reduction and carbonization temperature is much lower than the traditional preparation method, and the process control is simple and safe, and has a good scale. 

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