Yellow tungsten oxide is a finely divided, yellow crystalline powder. It is produced by roasting ammonium paratungstate at closely controlled temperatures to drive off water and ammonia. Exact time and temperature control determine, to a large extent, the physical characteristics of yellow tungsten oxide.
Yellow tungsten oxide has two colors for different grain size. When the grain size of yellow tungsten oxide is around 1.5um, it shows the color of yellow, and when the grain size of yellow tungsten oxide is around 15um, it shows green. The property is similar.
Yellow tungsten oxide can be produced by APT calcination method, hydrothermal method, tungstic acid calcination method, precipitation method, sol-gel method, micro emulsion method, spray pyrolysis method, vapor phase method and ion exchange method.