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Factors Influencing the Quality of Reaction Sintered Silicon Carbide
Silicon carbide ceramics have excellent properties such as high mechanical strength, high temperature resistance, strong oxidation resistance, good thermal stability, high thermal conductivity, good wear resistance, good chemical corrosion resistance, high hardness, and good thermal shock resistance. . Silicon carbide has the best oxidation resistance of all non-oxide ceramics.
The basic principle of reactive sintering is: the reactive liquid silicon or silicon alloy penetrates into the carbon-containing porous ceramic green body under the action of capillary force, and reacts with the carbon in it to form silicon carbide, and the newly generated silicon carbide is in-situ combined. The original silicon carbide particles in the china, and the impregnating agent fills the remaining pores in the china to complete the densification process.
The microstructure and mechanical properties of silicon carbide ceramics prepared by reaction sintering are affected by some factors, such as forming process, SiC wafer addition, green body preparation process parameters, oxidation, green body density and vacuum heat treatment system.
Compared with the green body prepared by the in-situ solidification forming method, the green body diameter is more uniform and unimodal, and the shape of the holes is regular. In addition, there are a lot of residual Si and C in the sintered body prepared by dry pressing and slip casting, while there is no large residual Si and C in the silicon carbide sintered body prepared by in-situ solidification forming process, and the bending strength is greatly increased. be improved.
2.Green body preparation process parameters
The process parameters for green body preparation include the carbon content of the green body, the forming pressure and the amount of petroleum coke added to the green body, the particle size of the original silicon carbide, the particle size of carbon powder, and the like.
1) The carbon content of the green body. With the increase of carbon content in the green body, the strength and density of the material show a trend of increasing first and then decreasing. When the carbon powder added is 20%, the strength and density of the ceramic are the highest.
2) Forming pressure. As the green forming pressure increases, the content of silicon carbide in the ceramic increases. However, when the green body forming pressure is too large, residual carbon will appear in the ceramics, and in severe cases, it will cause incomplete sintering of the green body. With the increase of green forming pressure, the strength and density of the material show a trend of first increase and then decrease, and both reach the maximum value when the pressure reaches 140MPa.
3) The amount of green petroleum coke added. With the increase of the amount of green petroleum coke added, the amount of Si phase decreases, the content of silicon carbide increases, the separated silicon carbide particles are gradually connected to form a network framework, and the residual carbon tends to increase. In addition, it was found that with the increase of the amount of petroleum coke, the strength and density of the reaction sintered SiC material increased first and then decreased, and reached the maximum when the amount of petroleum coke was 10%.
4) The original silicon carbide particle size. The original silicon carbide particle size also affects the structure and properties of the material. As the original particle size of silicon carbide increases, the strength of the material will decrease and the density will increase.
5) Toner particle size. As the particle size of carbon powder gradually increases, the strength and density of silicon carbide ceramics tend to decrease.
High temperature oxidation in air at 1300 °C will affect the fracture strength of reaction sintered silicon carbide ceramics. With the prolongation of the high temperature oxidation time, the room temperature fracture strength of the reaction sintered silicon carbide ceramics showed a trend of first increase and then decrease. When the oxidation time was 22.5h, the room temperature fracture strength of the silicon carbide material reached the highest.
With the increase of green density, the flexural modulus of reactive sintered silicon carbide ceramics all tend to increase first and then decrease. When the density of the green body is 0.96g/cm, the bending strength and modulus of the reaction sintered silicon carbide both reach the maximum value.
Vacuum heat treatment temperature
The vacuum heat treatment process at 1600℃ and 1800℃ can completely remove the free carbon in the reactive sintered silicon carbide. The strength of the material after heat treatment at 1800℃ is significantly higher than that after heat treatment at 1600℃. The recrystallization of silicon carbide and the change of the shape of pores in the material during the vacuum heat treatment at 1800℃ are the main reasons for the strengthening of the material.
Heat treatment equipment selection: The RVS-S vacuum sintering furnace provided by SIMUWU is an excellent product for handling the silicon carbide reaction sintering process. The product has the characteristics of good temperature uniformity, high temperature control accuracy, stable sintering, and fully automatic control. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process, reduce the cost of trial and error in production, and are committed to giving customers the most convenient and fast experience.
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