Tungsten trioxide nanopowder applying for thermal insulation film may be synthesized by hydrothermal method. And the XRD diffraction peak gradually sharpens with the increase of the hydrothermal temperature under the same reaction conditions. According to Scherrer formula, it shows that the grain size of tungsten trioxide gradually becomes larger. And the peak intensity of each diffraction peak gradually increases as the reaction temperature increases, indicating that the degree of crystallinity of the synthesized product gradually becomes stronger.
The reason may be: Crystal growth is a process of nucleation and growth. In this process, the higher the temperature, the more energy the reaction system obtains and the more crystals grow. If the temperature is higher than 160°C, the gradual increase of energy causes the W/O in the reaction system to re-bond. The distortion of tungsten-oxygen octahedron and the displacement of tungsten atoms from octahedral center to octahedral edge, which makes tungsten oxide transforming from hexagonal phase to cubic phase. But, the conversion is not complete at 180°C, and hexagonal tungsten trioxide remains.
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