Nano tungsten trioxide, which may be applied for producing nano-ceramic color master, may be synthesized by hydrothermal method using sodium tungstate and hydrochloric acid as raw materials. Then, the influence of different pH values on the structure, morphology and photochromic properties of tungsten trioxide are analyzed.
Influence of pH Value of Hydrothermal System on Synthesis of Tungsten Trioxide
The figure below shows the XRD pattern of WO3 powder prepared at different pH value at 120°C. In the figure, a: pH = 1.0; b: pH = 1.5; c: pH = 2.0; d: pH = 2.5. As can be seen from the figure, the pH value of the hydrothermal system has a great influence on the structure and the grain size of the synthesized WO3 powder. If the pH value of the reaction system is 1.0 and 1.5, the synthesis product is hexagonal tungsten trioxide. If the pH value is 2.0 and 2.5, the synthesis product is cubic tungsten trioxide. There is no impurity phase in the two products, and the diffraction peak has obvious broadening phenomenon, which indicates that the grain size of the hexagonal tungsten trioxide powder and cubic tungsten trioxide powder synthesized respectively under different pH conditions is in the nanoscale due to hydrothermal effect.
The synthesized product is hexagonal tungsten trioxide if the other reaction conditions are the same and pH value of the reaction system is less than 1.5. With the increase of the pH value of the system, the XRD diffraction peak broadens and the peak intensity of the diffraction peak increases, which indicates that the grain size of the product becomes smaller. The synthesized product is completely cubic tungsten trioxide if the pH value is greater than 2.0.
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