Because the grain uniformity of hard alloy mainly depends on the particle size distribution of WC powder, the particle size distribution of WC powder is hereditary in tungsten powder. Therefore, the preparation technology of tungsten powder and tungsten carbide powder by submicron size and narrow size is very important. The key technical indexes of fine grain, submicron, ultrafine or nanocrystalline cemented carbide for WC powder are the purity, particle size and particle size distribution, and it is clearly stipulated that there is no type of type III coarse in WC powder.
Some scholars have adopted the following technical schemes to prepare submicron tungsten powder or tungsten carbide powder, including the following steps:
(1) Ammonium paratungstate (APT) is pyrolyzed to ammonium metatungstate (AMT) and dissolved in ammonia solution or deionized water and filtered to obtain ammonium tungstate solution, or using ammonium paratungstate (APT) production line after ion exchange or crystallization liquid as raw material.
(2) In the ammonium tungstate solution, the dispersant solution and the dispersing agent are added simultaneously and stirred evenly.
(3) Spray drying equipment was used for rapid crystallization drying to obtain fine particle hollow thin-walled spherical ammonium tungstate crystals.
(4) In the presence of hydrogen, nitrogen, nitrogen hydrogen mixture or air, the precursor of tungsten oxide, yellow tungsten, blue tungsten or violet tungsten was pyrolyzed at 500~700°C.
(5) Reduction of submicron and narrow particle size distribution of tungsten powder by hydrogen gas.
(6) In situ forming submicron and narrow particle size tungsten carbide powders by carbon mixing, ball milling and carbonization.
The results show that the average particle size of tungsten powder and tungsten carbide powder prepared by these methods is submicron grade, and has a narrow size distribution range, and it is convenient to prepare the tungsten powder and tungsten carbide powder with the purity of 4N or 5N in submicron size distribution.