Violet tungsten oxide nano powder may be produced by adopting tungstic acid mWO3?nH2O (m≥1, n≥1) as raw material.
1. Tungstic acid heated above 100°C:
mWO3?nH2O=mWO3+nH2O (1)
Introduce NH3, the introduced NH3 reacts in the formula (2) under the catalytic action of tungsten oxide WOx (2≤x≤3):
2NH3=N2+3H2 (2)
2. When the reaction temperature rises above 500°C, the reaction product WO3 in formula (1) and the reaction product H2 in formula (2) undergo the reduction reaction in formula (3):
WO3+0.1H2=WO2.9+0.1H2O (3)
If no NH3 is introduced or the amount of NH3 introduced is insufficient, H2 can be introduced through the air inlet. When the reaction temperature rises above 500°C, the reaction product WO3 in formula (1) will undergo the reduction reaction in formula (3) with the reaction product H2 in formula (2) and/or the introduced H2.
3. When the reaction temperature continues to rise above 600°C, the reaction product WO2.9 in formula (3) will undergo the reduction reaction in formula (4) with the reaction product H2 in formula (2):
WO2.9+0.18H2=WO2.72+0.18H2O (4)
If no NH3 is introduced, or if the amount of NH3 introduced is insufficient, H2 can be introduced through the air inlet. When the reaction temperature continues to rise above 600°C, the reaction product WO2.9 in formula (3) will undergo the reduction reaction in formula (4) with the reaction product H2 in formula (2) and/or the introduced H2.
4. In the formulae (1), (3), and (4), there is water vapor H2O generated, at high temperatures:
WOx+(4-x)H2O ?WO2(OH)2+(3-x)H2 (5)
The crystal nucleus of violet tungsten oxide formed in the formula (4) can be grown into needle-shaped violet tungsten oxide crystals by gas phase migration of WO2(OH)2.
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