The physical properties of ammonium paratungstate crystals are decided by nucleation rate and grain rate. APT nucleation rate depends on: 

(1) the velocity of APT periphery crystallized from a liquid phase, is proportional to the amount of oversaturation (difference between the solution concentration and the equilibrium concentration) of nuclei forming;

(2)the dissolution velocity of APT, that is a velocity that precipitated APT crystals goes into the solution again, it depends on the equilibrium solubility of solute. A major factor of nucleation rate is oversaturation. A new root of nucleation can only form when oversaturation up to a certain level. Growth mechanism of APT grain is still within reach. It is generally believed: After nucleation, the solute is deposited onto the lattice and gradually grow.

 

When the temperature rises, the diffusion coefficient and solubility will increase and also the crystal growth rate increases. If the oversaturation increases, the crystal nuclei within the solution was more then supersaturated nucleating amount will decrease, the growth rate decreases. So elevated temperature and reduce over-saturation of the solution in favor of coarse grain production. According to these principles, we chose a solution APT influence over saturation of various factors, by controlling the growth rate of nuclei formation rate and grain to the preparation of various size of APT.