The preparation methods of silicon carbide include silicon dioxide carbon thermal reduction method, carbon-silicon direct synthesis method, polymer pyrolysis method and chemical vapor deposition method, etc. In recent years, a sol-gel method has appeared to prepare silicon carbide powder. Silica carbothermal reduction method was invented by Acheson, also known as Acheson method, is the most important industrial production method of silicon carbide raw materials.
The raw materials are fused silica, graphite and coke, sodium chloride and wood chips as additives, and silicon carbide is prepared by carbothermal reduction reaction at 2000 ～ 2400 ℃.
Then, the obtained silicon carbide can be used as a raw material for abrasives or refractory products after being treated by crushing, washing, decarburizing, removing metal impurities, classification and the like.
Silicon carbide is a material with strong covalent bonding, and the diffusion rate is very low during the sintering process; at the same time, due to its strong unidirectional bonding during the sintering process, only adjacent necks can be formed between the adjacent particles of silicon carbide, so no shrinkage can occur. Silicon carbide without the addition of special additives cannot be sintered and compacted, and it is necessary to make use of special sintering process to specialize additives or combine with the second to achieve the density of silicon carbide, such as pressure sintering, reaction sintering and microwave sintering. Due to the differences in raw materials, preparation process, material composition, and microstructure, the performance of silicon carbide ceramic materials is quite different. Overall, there are several differences:
(1) Hot pressing sintering and hot isostatic pressing sintering can obtain the most dense material;
(2) The mechanical properties of reaction sintered silicon carbide are moderate and the density is good, but the chemical stability and mechanical properties at high temperature are poor;
(3) Liquid phase sintered silicon carbide has good performance at room temperature or low temperature, and its strength and toughness are relatively high;
(4) Solid-phase sintered silicon carbide forms clean grain boundaries, has good chemical stability and excellent high-temperature mechanical properties;
(5) In-situ toughening forms long columnar grains, the fracture energy is improved, and the material has good fracture toughness;
(6) The electrical properties of silicon carbide ceramics can be adjusted through composition and grain boundary design.
Since silicon carbide ceramics have the advantages of high melting point, high strength, good chemical stability, wear resistance, thermal shock resistance, corrosion resistance, etc., they are widely used in petroleum, chemical, machinery, aviation, building materials and other fields. For example, silicon carbide is used as a refractory material, and many of the kilns, sticks, pads, pillars, etc. of ceramic kilns are silicon carbide materials; silicon carbide has high temperature strength, good friction performance, and high temperature corrosion resistance. The main candidate materials for high-temperature structural materials such as chambers and turbochargers; due to its high temperature resistance, ablation resistance, wear resistance, light weight, and wave absorption, silicon carbide has become more and more important in the field of defense military and aerospace Because of its high thermal conductivity and high insulation performance, some silicon carbide ceramics can also be used in electronic packaging materials, substrates and other components of the microelectronics industry; because carbon and silicon have low atomic numbers, silicon carbide can be used as Structural materials for atomic reactors, etc.