Tungstic Acid Producing Tungsten Powder
Tungstic acid is the main raw material of producing tungsten powder, which is slightly dissolve in hot water, but can not dissolve in the cold water; dissolve in alkali, hydrofluoric acid and ammonia water, and hardly dissolve in inorganic acid but for HF. Tungstic acid will begin to dehydrate at 100℃, and turn to tungsten trioxide after calcination under a high temperature, with the boiling point of 1473℃. By treatment of ortho-tungstic acid or paratungstate solution with dilute acid can get colloidal tungstate with different amount of water, with the larger solubility and activity in water than yellow tungstic acid. The powdery white tungstic acid is more active than yellow tungstic acid, and can be get by adding tungstate into dilute nitric acid solution.
Yellow tungstic acid can be used for manufacturing tungsten powder, while the powdery white tungstic acid can be used for producing metatungstic acid and tungsten heteropoly acid salt. The tungstic acid producing tungsten powder can firstly get tungstic acid colloidal particles from the raw materials of sodium tungstate and hydrochloric acid with the additive of acetic acid under the condition of ultrasonic vibration, then generate tungsten powder by hydrogen reduction of tungstic acid.