Medium yellow tungsten oxide or medium tungsten trioxide may be prepared by tungstic acid calcination method, in which tungstic acid is dried and calcined. The tungstic acid calcination method is commonly applied in the industry for producing tungsten trioxide.
Tungstic Acid Calcination Method to Produce Yellow Tungsten Oxide
It is recorded that tungstic acid is dried under 100℃, mainly by removing moisture absorbed in the product. Ammonia and combined water need to be calcinated under high temperature. Tungstic acid is dehydrated under 180℃, completely dehydrated under 500℃ and generate yellow tungsten oxide. 
Tungstic acid is the combination of tungsten trioxide, mix with water under different ratio and forms. It can be divided into yellow tungstic acid, white tungstic acid and metatungstic acid, among which yellow tungstic acid is common seen. Tungstic acid is mainly applied to produce tungsten powder and tungsten products, also used as mordants, pigments, dyes, inks, and so on.
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