Yellow tungsten oxide, i.e., tungsten trioxide (WO3), may be applied for the preparation of thermal insulation dispersion liquid. Studying the growth mechanism of yellow tungsten oxide nanorods helps to understand the characteristics of the dispersion liquid.
WO3 nanorod may be synthesized using sodium salt as a directing agent. While the product does not show a rod-like morphology using sulfate as a directing agent. Therefore, it is supposed that Na+ plays a decisive role in the formation of WO3 nanorods. The picture below shows the XRD image of WO3 derived from different hydrothermal times when the molar ratio of sodium sulfate to sodium tungstate is 4:1.
As can be seen from the picture, the product is pure hexagonal WO3 when the hydrothermal time is longer than 24h. The (200) crystal plane of hexagonal WO3 appeared when the hydrothermal time was 6h, and the (001) crystal plane did not appear until 12h. It shows that (200) of WO3 hexagonal crystal is the dominant crystal plane in the initial growth, which has more chance to adsorb Na+ in the solution and reduces the chance of WO3 crystal growing to the (200) crystal plane, making WO3 grows toward another dominant crystal plane (001). With the increase of hydrothermal time, the (001) crystal surface grows significantly. After 48h hydrothermal reaction, WO3 nanorods formed.
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