APT is the abbreviation for ammonium paratungstate. It may be reduced to tungsten powder (W powder) by hydrogen reducing agent. There are two processes - direct reduction and secondary reduction.
1. Direct Reduction
Adopt H2 to directly reduce APT to W powder. Calcination and reduction are generally completed in a furnace tube where is controlled by multiple temperature zones, and the obtained W powder has the characteristics of fine grain size and dark gray color. However, this producing method isn’t applied to industrial production because of the low productivity of W powder and the difficulty in subsequent processing of tungsten rods produced from this W powder. In addition, it is also a major challenge to timely remove the process products - NH3 and H2O.
2. Secondary Reduction
The secondary reduction process replaced tungsten trioxide hydrogen reduction process and has been widely applied in industrial production. APT is reduced to blue tungsten oxide (BTO) at first stage, and BTO is reduced to W powder at second stage. That is, the reduction is carried out in two stages:
(1) In the low temperature stage, the reduction temperature is 923K. The main reaction is:
WO3-x=WO2+β-W+α-W
(2) In the high temperature stage, the reduction temperature is 1073~1173K. The main reaction is:
WO2+β-W+α-W=α-W
More details, please visit:
http://www.ammonium-paratungstate.com/english/index.html
