reaction bonded Silicon Carbide vs. Recrystallized silicon carbide

reaction bonded Silicon Carbide, also known as self-reactive bonded SiC, is produced by mixing a-SiC powder and graphite in a certain ratio to form a billet blanks, and heated to about 1650 ℃, at the same time fusion infiltration of Si or through the gas phase Si infiltration into the blanks, so that the reaction with the graphite to form B-SiC, the original a-SiC. At the same time, fusion infiltration of Si or infiltration of Si through the gas phase into the blank, so that it reacts with the graphite to form B-SiC, which combines the existing a-SiC particles. If the infiltration of Si is complete, a completely dense reaction sintered body without size shrinkage can be obtained.

Although reaction sintering can produce dense reaction bonded Silicon Carbide with complex shapes and good thermal shock resistance, the reaction sintered bodies have a considerable amount of Si in them.The presence of a considerable amount of Si in the sintered body makes the reaction sintered SiC ceramics poor high-temperature performance. The strength of reaction-sintered SiC ceramics before 1400 ℃ is basically independent of the content of Si, more than 1400 ℃ due to the melting of Si, the strength of the sudden drop. The advantages of this method are lower sintering temperature (1400-1700℃), more forming methods (extrusion, injection, pressing and casting), and the ability of the reaction sintered SiC ceramics to be molded in the same way as the reaction sintered SiC ceramics. Pressure, injection, pressing and casting, etc.), small dimensional changes, while the toughness of the material is also better. Its shortcomings are There are 8% -15% of free silicon, can only be used at 1400 ℃ below.

SiC powder without additives, directly molded blanks sintered at temperatures above 2000 ℃,  the main sintering mechanism is evaporation-coalescence. No volume change during sintering, very small shrinkage, high porosity (20%), low strength (100MP).The strength is low (100MPa). Due to sintering above 2000°C, the B-SiC present in the powder will be transformed to a-SiC, the obtained material has a single phase. Thus, Recrystallized silicon carbide has good electrical conductivity, thermal conductivity, chemical resistance and thermal stability. However, because of its low strength, recrystallized silicon carbide is only used in high-temperature conductive and refractory materials.

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