Blue tungsten oxide nano powder for transparent thermal insulation window film can be used to prepare tungsten powder, wherein there are two reduction methods --- static reduction method and dynamic reduction method. In static reduction, the powder has a certain layer thickness. The gradient of H2O/H2 concentration from the surface of the powder layer to the inside thereof is gradually increased, and the particle size of the tungsten powder gradually increases from the surface layer to the lower layer. When the material layer is thick and the reduction temperature is high, the H2O emission rate generated by the reaction of the lower layer material is slow, the local WO2(OH)2 concentration is increased, and the chemical vapor phase migration is strong, and the crystallized coarse tungsten powder can be formed.
During dynamic reduction, as the material is flipped and moved forward by the scraper, the water vapor discharge speed is increased, and the water vapor concentration distribution inside the powder is fairly uniform, and the particles are uniformly grown. Compared with the static reduction for producing tungsten powder with the same grade, the H2/WO3-x ratio of dynamic reduction is much smaller. But, due to the rapid discharge of water vapor, it is difficult to reach the theoretical equilibrium state, and the generated tungsten powder crystal is incomplete so that this method is not suitable for the production of tungsten powder of coarse crystal.
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