High-purity violet tungsten oxide nanopowder may be prepared by using tungsten oxide WOx (2≤x≤3) as raw material.
Adopt WOx, or WOx generated during preparation as raw material; NH3 and/or H2 are introduced through the air inlet, and water vapor is introduced depending on WOx. If NH3 is introduced, NH3 will react under the catalytic effect of WOx in formula (1) at high temperature:
2NH3=N2+3H2 (1)
1. WOx contains WO3. When the reaction temperature rises above 500°C, WO3 reacts with the introduced H2 in the reduction reaction of formula (2):
WO3+0.1H2=WO2.9+0.1H2O (2)
When the reaction temperature continues to rise above 600°C, the reaction product WO2.9 in formula (2) will undergo the reduction reaction in formula (3) with the introduced H2.
2. WOx contains WO2.9. When the reaction temperature continues to rise above 600°C, WO2.9 reacts with the introduced H2 to form the reduction reaction in formula (2):
WO2.9+0.18H2=WO2.72+0.18H2O (3)
Water vapor is generated in formula (2) and formula (3). If the amount of water vapor generated by the reaction of formula (2) and/or formula (3) is insufficient, water vapor is introduced through the air inlet. The water vapor generated in formula (2) and/or formula (3), and/or the introduced water vapor can reversibly react with WOx at high temperature:
WOx+(4-x)H2O⇌WO2(OH)2+(3-x)H2 (4)
The needle-shaped violet tungsten oxide with a diameter of less than 100nm is generated by vapor phase migration of hydrated tungsten oxide WO2(OH)2 if the partial pressure and temperature of WO2(OH)2 gas is suitable.
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