Dark blue nano tungsten oxide for thermal insulation coating can be obtained by using ultra-pure ammonium paratungstate as a raw material and calcining it in argon. Thereafter, the obtained blue tungsten oxide is reduced in hydrogen. The tungsten powder obtained by the first reduction is oxidized to tungsten trioxide in air and then reduced to tungsten powder by the second reduction in hydrogen. The specific surface area of the tungsten powder after the second reduction was measured to be 0.180m2/g, which was 1.51 times of the specific surface area of the tungsten powder reduced from blue tungsten oxide in the first time in hydrogen.
So, it indicates the particle size of the tungsten powder after the second reduction is smaller than the particle size of the tungsten powder after the first reduction as a whole. The particle size distribution is 83.86% between 3μm and 10μm, and 7.39% between 1μm and 3μm, and 8.75% between 10μm and 15μm. It can be seen that after the second reduction, the particle size of the obtained tungsten powder is significantly reduced, and the coarse particle size tungsten powder is greatly reduced, and the largest particle size tungsten powder is only 15μm. Also, the particle size distribution tends to concentrate further, which is consistent to the SEM detection results.
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