Intermediate Compound of Tungsten - Ammonium Paratungstate

Ammonium paratungstate (APT) is a primary product of tungsten, which is an important raw material for the manufacture of tungsten products and hard alloy. Also it’s the most common tungsten compound, and widely used in tungsten smelting. The quality of APT determines properties and quality of tungsten products in a large extent. WO3, blue tungsten oxide, tungsten acid, ammonium metatungstate can be generated through partly or completely heating. APT is a white transparent crystal with good loose and mobility. APT will begin to loose ammonia when heated in the air up to 60℃, begin to dehydration at 100℃, and begin to turn into yellow tungsten oxide at 450℃. APT is completely converted into blue tungsten oxide When heated to 300℃ in hydrogen, and turned into violet tungsten at 400℃, trioxide at 500 to 600℃, and turned into tungsten powder when the temperature reach to 600~900℃.

APT crystal powder can be prepared by evaporation of ammonium tungstate solution, the temperature supposed to be generally controlled at more than 50℃, and its particle size and composition changes with the temperature:
1. Evaporation and crystallization 80~100℃, APT present as flake crystal with 5 molecules of crystal water;
2. when the temperature is below 50℃, APT present as fine white needle crystal with 11 molecules of crystal water.

The number of water in APT crystal decided by the production conditions, and the solubility increased with temperature increasing. Heating the APT with high impurities content to get decomposition products, and then dissolve in ammonia solution, and heated at the same time, evaporate and crystallize, round cycle 1~2 times or more, then get high purity APT.