Coarse Grain Tungsten Powder Restored from Ammonium Paratungstate

Ultrafine and ultracoarse tungsten carbide (WC) grains are the two development directions of tungsten carbide in recent years. Coarse grain WC powder is the important raw material for coarse grain tungsten carbide. It has been widely used in oil drilling and petroleum perforating element material, anti ballistic missile system and heavy armor penetrator material, because of the less structural defects at high temperature, high hardness, low micro strain and a series of special properties.



Tungsten powder of coarse particles obtained by one-step reduction method from tungsten trioxide (WO₃),  in molybdenum wire furnace under the high temperature of 1200℃ at present industrial. However, tungsten particles obtained by this method usually in shape of nearly equiaxed, and the size is relatively small with poor formability, which make it to have to forming by adding organic matter as a binder. And that is not conducive to large products formed and properties controlled. Coarse grain powder was prepared by direct reduction process of ammonium paratungstate (APT) in this paper, and carbonization for preparing WC powder.

The preparation steps are as follows:
1. Use the tungstate solution of 37% concentration; place it in the reaction furnace to heating, evaporation and crystallization to obtain APT crystal;
2. Grinding and crushing the APT, pass through 60 mesh sieve for controlling crystal size;
3. Place APT in a single hydrogen furnace for reduction, set the reducing conditions as follows: hydrogen section flow for 50ml/cm².min, temperature at 850℃ to 1000℃, keep warm for 90~180min, then tungsten powder obtained;
4. Put tungsten powder into the deionized water, vibration with ultrasonic, cleaned until the solution cleared, drying, grinding, sieving;
5. Mixing tungsten powder and carbon black in a certain proportion and placed in a carbon tube furnace, carbonization under high temperature 1700~1800℃, then milling and sieving to obtain coarse grain WC powder.

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