What are the preparation methods of  silicon carbide powder?

Silicon carbide (SiC) ceramic powder has the advantages of high temperature strength, good oxidation resistance, high wear resistance and thermal stability, small thermal expansion coefficient, high thermal conductivity, good chemical stability, etc. Therefore, it is often used in the manufacture of combustion chambers, high temperature exhaust devices, temperature resistant patches, aircraft engine components, chemical reaction vessels, heat exchanger tubes and other mechanical components under harsh conditions, and is a widely used advanced engineering material. It not only plays an important role in the high-tech fields under development (such as ceramic engines, spacecraft, etc.), but also has a broad market and application fields to be developed in the current energy, metallurgy, machinery, building materials, chemical industry and other fields.

The preparation methods of silicon carbide powder can be mainly divided into three categories: solid phase method, liquid phase method and gas phase method.

1. Solid phase method

The solid phase method mainly includes carbothermal reduction method and silicon carbon direct reaction method. Carbothermal reduction methods also include Acheson method, vertical furnace method and high temperature converter method. Silicon carbide powder preparation was initially prepared by Acheson method, using coke to reduce silicon dioxide at high temperature (about 2400 ℃), but the powder obtained by this method has a large particle size (>1mm), consumes a lot of energy, and the process is complicated. In the 1980s, new equipment for synthesizing β-SiC powder, such as vertical furnace and high temperature converter, appeared. As the effective and special polymerization between microwave and chemical substances in solid has been gradually clarified, the technology of synthesizing sic powder by microwave heating has become increasingly mature. The silicon carbon direct reaction method also includes self-propagating high temperature synthesis (SHS) and mechanical alloying method. SHS reduction synthesis method uses the exothermic reaction between SiO2 and Mg to make up for the lack of heat. The silicon carbide powder obtained by this method has high purity and small particle size, but the Mg in the product needs to be removed by subsequent processes such as pickling.

2 liquid phase method

The liquid phase method mainly includes sol-gel method and polymer thermal decomposition method. Sol-gel method is a method of preparing gel containing Si and C by proper sol-gel process, and then pyrolysis and high temperature carbothermal reduction to obtain silicon carbide. High temperature decomposition of organic polymer is an effective technology for the preparation of silicon carbide: one is to heat gel polysiloxane, decomposition reaction to release small monomers, and finally form SiO2 and C, and then by carbon reduction reaction to produce SiC powder; The other is to heat polysilane or polycarbosilane to release small monomers to form a skeleton, and finally form silicon carbide powder.

3 Gas phase method

At present, the gas phase synthesis of silicon carbide ceramic ultrafine powder mainly uses gas phase deposition (CVD), Plasma Induced CVD, Laser Induced CVD and other technologies to decompose organic matter at high temperature. The obtained powder has the advantages of high purity, small particle size, less particle agglomeration and easy control of components. It is a relatively advanced method at present, but with high cost and low yield, it is not easy to achieve mass production, and is more suitable for making laboratory materials and products with special requirements.

At present, the silicon carbide powder used is mainly submicron or even nano level powder, because the powder particle size is small, high surface activity, so the main problem is that the powder is easy to produce agglomeration, it is necessary to modify the surface of the powder to prevent or inhibit the secondary agglomeration of the powder. At present, the methods of dispersion of SiC powder mainly include the following categories: high-energy surface modification, washing, dispersant treatment of powder, inorganic coating modification, organic coating modification.

Post time: Aug-08-2023