Brown tungsten oxide is also called tungsten dioxide, which is named because it appearing in brown powder, the general process is calcinating ammonium paratungstate under 500°C in the air into tungsten trioxide, or reduced into blue tungsten oxide under 450°C hydrogen atmosphere.
The reduction of brown tungsten oxide process can be divided into two part: Firstly, brown tungsten oxide is reduced into tungsten dioxide under 630°C. And then reduced into tungsten powder under 820°C. The purpose of reduction is to make kalium control the particle size of tungsten powder in a certain degree. Then it is pressed in a special mould into rectangular bar. Put the bar in charge under hydrogen atmosphere and heat to 3000 degree celsius, then the density of tungsten bar can reach to 85% of the theory(19.3g/cm3). Then the tungsten bar can be processed in to tungsten rods of 3mm. Then it can be processed into tungsten filament of different dimensions.