Synthesis method of high-purity Silicon Carbide (SiC) powder

At present, the synthesis methods of high-purity SiC powder for growing single crystals mainly include: CVD method and improved self-propagating synthesis method (also known as high-temperature synthesis method or combustion method). Among them, the Si source of CVD method for synthesizing SiC powder generally includes silane and silicon tetrachloride, etc., and the C source generally uses carbon tetrachloride, methane, ethylene, acetylene and propane, etc., while dimethyldichlorosilane and tetramethylsilane can provide Si source and C source at the same time.

The previous self-propagating synthesis method is a method of synthesizing materials by igniting the reactant blank with an external heat source, and then using the chemical reaction heat of the substance itself to make the subsequent chemical reaction process continue spontaneously. Most of this method uses silicon powder and carbon black as raw materials, and adds other activators to directly react at a significant speed at 1000-1150℃ to generate SiC powder. The introduction of activators will inevitably affect the purity and quality of the synthesized products. Therefore, many researchers have proposed an improved self-propagating synthesis method on this basis. The improvement is mainly to avoid the introduction of activators, and to ensure that the synthesis reaction is carried out continuously and effectively by increasing the synthesis temperature and continuously supplying heating.

As the temperature of the silicon carbide synthesis reaction increases, the color of the synthesized powder will gradually darken. The possible reason is that too high temperature will cause SiC to decompose, and the darkening of the color may be caused by the volatilization of too much Si in the powder.

In addition, when the synthesis temperature is 1920℃, the synthesized β-SiC crystal form is relatively good. However, when the synthesis temperature is greater than 2000℃, the proportion of C in the synthesized product increases significantly, indicating that the physical phase of the synthesized product is affected by the synthesis temperature.

The experiment also found that when the synthesis temperature increases within a certain temperature range, the particle size of the synthesized SiC powder also increases. However, when the synthesis temperature continues to rise and exceeds a certain temperature range, the particle size of the synthesized SiC powder will gradually decrease. When the synthesis temperature is higher than 2000℃, the particle size of the synthesized SiC powder will tend to a constant value.

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