Silicon  carbide ceramic materials have excellent properties such as high  temperature strength, high temperature oxidation resistance, good wear  resistance, good thermal stability, small thermal expansion coefficient,  high thermal conductivity, high hardness, thermal shock resistance and chemical resistance. Automobiles,  mechanical chemicals, environmental protection, space technology,  information electronics, energy and other fields have been widely used,  and have become an irreplaceable structural ceramics with excellent  properties in many industrial fields.
Modern  defense, nuclear energy and space technology, as well as the rapid  development of the automotive industry and marine engineering, are  increasingly demanding materials such as rocket combustor liners,  aircraft turbine engine blades, nuclear reactor structural components,  high-speed pneumatic bearings and mechanical seal parts. There is a need to develop a variety of new high performance structural materials. SiC  ceramics have been widely used in the petrochemical industry as a  variety of corrosion resistant containers and pipes. The machine  industry has been successfully used as a variety of bearings, cutting  tools and mechanical seal components in the aerospace and automotive  industries. It is the most promising candidate for future gas turbine, rocket nozzles and engine components.
 1. Basic characteristics of silicon carbide
 Chemical property
 Resistance  to compounding: When the reaction temperature of silicon carbide  material reaches 1300 ° C in oxygen, a silicon dioxide protective layer  has been formed on the surface layer of the silicon carbide crystal. As  the protective layer is thickened, the silicon carbide inside is  resisted from being combined, which gives the silicon carbide a better  resistance to compounding. When  the temperature reaches 1900K (1627 ° C) or more, the silica protective  film has been destroyed, and the silicon carbide compounding effect is  aggravated, so that 1900 K is the maximum working temperature of silicon  carbide in an oxidizing atmosphere.
 Acid  and alkali resistance: In terms of the acid resistance, alkali and  compound effects, because of the effectiveness of the silica protective  film, silicon carbide has a very strong acid resistance and a slightly  poor alkali resistance.
 Physical properties
 Density:  The particle density of each silicon carbide crystal form is very  similar. Generally, it should be 3.20g/mm?, and the stacking density of  silicon carbide abrasive is between 1.2-1.6g/mm?, its height depends on  its particle size. Number, particle size synthesis and size of the particle shape.
Hardness: The hardness of silicon carbide is: Mohs 9.5. The hardness of single crystal silicon is: Mohs 7 grade. The hardness of polycrystalline silicon is: Mohs 7 grade. They are all relatively high hardness materials. Knoop  hardness is 2670-2815 kg / mm, higher than corundum in abrasives and  second only to diamond, cubic boron nitride and boron carbide.
  Thermal  conductivity: Silicon carbide products have very high thermal  conductivity, low thermal expansion parameters, and very high thermal  shock resistance. They are high-quality refractories.
  Electrical properties
 Industrial silicon carbide is a semiconductor under constant temperature and is an impurity conductive. High-purity silicon carbide with internal temperature increase
The  silicon carbide containing impurities is different according to its  impurity, and the electrical conductivity is also different. Other attributes
  Good hydrophilicity.
  It is well known that SiC is a compound having a strong covalent bond. According to Pauling's calculation of electronegativity, the ionicity of Si-C bond in SiC is only about 12%. Therefore, SiC has high hardness, large modulus of elasticity, and excellent wear resistance. It  is worth noting that when SiC is oxidized, the silicon dioxide layer  formed on the surface suppresses further diffusion of oxygen, and  therefore, the oxidation rate is not high. In  terms of electrical properties, SiC has semiconductor properties, and  the introduction of a small amount of impurities causes it to exhibit  good electrical conductivity: in addition, SiC also has excellent  thermal conductivity.
  2. Sintering process of silicon carbide ceramics
 At  present, methods for preparing high-density SiC ceramics include  pressureless sintering, hot pressing sintering, hot isostatic pressing  sintering, and reaction sintering. The  SiC component of complex shape and large size can be prepared by a  pressureless sintering process, and is therefore considered to be the  most promising sintering method of SiC ceramic. Only  a simple shape of SiC parts can be prepared by a hot press sintering  process, and the number of products prepared by one hot sintering  process is small, which is disadvantageous for commercial production. Although  the hot isostatic pressing process can obtain SiC products of  complicated shapes, it is necessary to encapsulate the green bodies, so  that industrial production is also difficult to achieve. The  SiC component with complex shape can be prepared by the reaction  sintering process, and the sintering temperature is low, but the high  temperature performance of the reaction-sintered SiC ceramic is poor. The  table below gives some of the properties of SiC ceramics in  pressureless sintering, hot press sintering, hot isostatic pressing and  reaction sintering. Obviously, the properties of SiC ceramics vary from sintering to sintering. In  general, the overall performance of pressureless sintered SiC ceramics  is superior to that of reaction-sintered SiC, but inferior to  hot-pressed sintering and hot isostatically sintered SiC. At present, the company has mastered two sintering processes of pressureless sintering and reaction sintering.