Ammonium paratungstate (APT) is an important intermediate product of the production of tungsten metal powder. To ensure the quality of tungsten powder, the average particle size, particle size distribution and crystal morphology should also meet certain requirements while the APT chemical purity does. With the rapid development of modern science and technology, there’re more and more demands for different grain size and shape of tungsten powder production, and thus the requirements of raw material APT are also getting higher and higher.

 

For APT crystallization conditions, the scholars have carried out extensive exploration and discussion, but the overall reports are rare, and the results are not entirely consistent. In order to investigate the basic conditions of APT production, for the preparation of APT crystallization problems, this article attempts to make some analysis and discussion on theory and the process practice based on a number of experimental studies made recently and some views are put forward by reference.

 

Test results are shown on Figure. With the increase of evaporation temperature, the crystal growth rate of APT is faster than the nucleation rate, which makes a particle size enlargement and increases the bulk specific gravity of APT (see figure). The reasons are increasing temperature , faster molecular motion, more opportunities of molecules colliding with each other, which are conducive to grain growth. 

 

Plane grain formation rate on the grain surface is affected a lot by temperature. When temperature increases to 10 ℃, speed needs to increase 2 to 4 times, so the increasing temperature is most significant for grain growth. It was also observed in the experiment that APT crystalline grains were much coarser than other parts on the crystallizer wall. This may be due to an indirect steam heating, the temperature on wall is higher than other parts , which is conducive to grain growth. It was also found in the experiment that the crystalline particles is more regular in a higher temperature than a lower one, and size distribution is more well-distributed.