The Relationship Between the Phase of Tungsten Blue Oxides and the Processing Parameters

The phases of tungsten blue oxides produced by the light reduction of ammonium paratungstatc (APT) with hydrogen vary with the reduction temperature. The product reduced at 275℃ is noncrystalline ammonium tungsten bronze (ATB) and at 325℃ is crystalline ATB. The content of ATB in the reduced product gradually decreases with increasing the reduction temperature. There is no ATB in the product reduced at 575℃. The phase W₂₀O₅₈ appears above 325℃. Its content increases with the reduction temperature and reaches its maximum at 525℃, and then it decreases sharply above 525℃. The phases WO₂ and β-W appear at 525℃. The phase α-W appears between 525℃and 575℃.The phases of the products reduced at 525-575℃change remarkably from ATB andW₂₀O₅₈ to WO₂, β-W and α-W. The quantitative relationship between the phases of tungsten blue oxide and the reduction temperature of APT has been studied in this paper.
When WO₃ is lightly reduced by hydrogen, W₂₀O₅₈ appears at certain temperature between 425℃ and 525℃; W₁₈O₄₉ appears between 475℃ and 525℃; A little β-W appears at 625℃. When the reduction temperature is higher than 625℃, the content of α-W in the reduction product rapidly increases with the reduction temperature.
When APT is lightly reduced by hydrogen, β-W can be obtained at a very wide temperature range, compared with WO₃also reduced by hydrogen. The content of β-W obtained from APT is more than that obtained from WO₃.
When APT is reduced by hydrogen at 450℃ for five minutes, the product is crystalline ATB.If the reduction time is longer than five minutes, W₂₀O₅₈ phase will appear. The content of W₂₀O₅₈ increases gradually with the reduction time and at the same time the content of ATB decreases gradually. When the reduction of APT with hydrogen is carried out at 450℃, the relationship between the phases of tungsten blue oxide and the reduction time has been experimentally investigated in this article.