Synthesis Of Silicon Carbide Powder

There are three main methods to synthesize silicon carbide powder: solid phase method, liquid phase method and gas phase method.

The solid phase method is to prepare silicon carbide fine powder by carbothermal reduction reaction of silicon dioxide and carbon or direct reaction of silicon powder and carbon black fine powder in inert atmosphere. Silicon carbide smelted by Aichison process or ESK process can be mechanically processed into SiC fine powder. At present, the fine powder prepared by this method has a surface area of 1~15m²/g, oxide content of about 1.0%, and metal impurity content of 1400~2800ppm (1ppm=10-6). Its fineness and composition depend on subsequent treatment processes and means such as crushing and pickling. Silicon carbide powder can also be continuously produced by shaft furnace or high-temperature rotary kiln to obtain high-quality b-SiC powder. The mixture of SiO2 fine powder and carbon powder undergoes thermal reduction reaction in the inert atmosphere of the shaft furnace at a temperature lower than 2000 ℃ to synthesize b-SiC powder. The particle size of SiC obtained is micron. However, it often contains non reactive SiO2 and C, which requires subsequent pickling and decarburization. High quality SiC fine powder can also be produced by using high-temperature rotary kiln. 

The liquid phase reaction method can be used to prepare high-purity, nanometer sized SiC powder, and the product has good uniformity, which is a method with good development prospects. The preparation of SiC powder by liquid phase reaction mainly includes sol-gel method and polymer thermal decomposition method. The core of preparing SiC micro powder by sol-gel method is to form a mixture or polymer solid with uniform distribution of Si and C at the molecular level through the sol-gel reaction process. During the heating process, first form a uniform mixture of SiO2 and C, and then generate SiC by carbothermal reduction reaction at 1400~1600 ℃.

Polymer thermal decomposition mainly refers to heating polysilane and other polymers to release small monomers and form Si-C skeleton. SiC prepared by pyrolysis is b-SiC. If the pyrolysis temperature is lower than 1100 ℃, it is amorphous SiC.

Gas phase method is to use silicon containing raw materials and carbon containing raw materials to generate SiC through gas phase reaction. [6] According to different heating methods, it can be divided into resistance furnace and flame heating, plasma and arc heating, laser heating, etc.