The first stage
90~180℃, lose crystal water:
5(NH4)2O•12WO3•5H2O=5(NH4)2O•12WO3•H2O+4H2O↑
second stage
180~260℃, loss of ammonia:
5(NH4)2O•12WO3•H2O=3(NH4)2O•12WO3•3H2O+4NH3↑
Ammonium metatungstate (AMT)
The third phase
260~350℃, further dehydration and ammonia, and ammonium tungsten bronze (ATB) appears:
3(NH4)2O•12WO3•3H2O＝(NH4)2O•12WO3+4NH3↑+5H2O↑
The fourth stage:
At 350~450°C, ammonia begins to decompose to generate hydrogen and nitrogen:
2NH3 =N2 ↑ + 3H2 ↑
The chemical reaction at this stage may be
(NH4)2O•12WO3 + H2＝12(NH4)xWO3+H2O+(2-x)NH3↑
(NH4)xWO2.8~3.0.
Fifth stage:
450~550℃, ATB decomposes to produce WO3 and WO2.9,
Sixth stage:
At 550~650°C, high-valent tungsten oxide transforms into low-valent tungsten oxide. In addition to a small amount of ATB, there are tungsten oxides such as WO3, WO2.9 and WO2.72 in the decomposition products, and even WO2 appears.
More details of tungsten oxide product, please visit website: tungsten-oxide.com
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