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How much do you know about silicon carbide ceramic sintering technology?

Silicon carbide (SiC) ceramic materials have broad application prospects in traditional industrial fields such as high-temperature kiln tools, combustion nozzles, heat exchangers, sealing rings, sliding bearings, and high-tech fields such as semiconductors and space technology due to their excellent high-temperature mechanical strength, high hardness, high elastic modulus, high wear resistance, high thermal conductivity, and corrosion resistance. However, since silicon carbide is a strong covalent bond compound with a low diffusion coefficient, one of the main problems in its preparation process is the difficulty of sintering densification. Therefore, a large number of research works have been carried out to promote the densification process of silicon carbide, reduce the sintering temperature, refine the grains, and improve the various properties of silicon carbide ceramic materials through the study of sintering technology and the selection and optimization of sintering aids.

Silicon carbide ceramic sintering technology

1.Reaction sintering

Reaction sintered silicon carbide (RBSiC) was first proposed by P. Popper in the 1950s. The process is to mix the carbon source and silicon carbide powder, prepare the green body by slip injection molding, dry pressing or cold isostatic pressing, and then perform siliconization reaction, that is, heat the green body to above 1500℃ under vacuum or inert atmosphere, and the solid silicon melts into liquid silicon, which infiltrates into the porous green body through capillary action. Liquid silicon or silicon vapor reacts chemically with C in the green body, and the in-situ generated β-SiC combines with the original SiC particles in the green body to form reaction-sintered silicon carbide ceramic material. The advantages of reaction-sintered silicon carbide are low sintering temperature, low production cost, and high degree of material densification. In particular, there is almost no volume shrinkage during the reaction sintering process, which is particularly suitable for the preparation of large-sized and complex-shaped structural parts. High-temperature kiln furniture materials, radiation tubes, heat exchangers, desulfurization nozzles, etc. are all typical applications of reaction-sintered silicon carbide ceramics.

2.Hot-pressing sintering

The mechanical pressure provided during the hot-pressing (HP) process increases the driving force for densification by enhancing the rearrangement of particles in the early stage of sintering. After reaching a relatively high density, the mechanical pressure can reduce the porosity and inhibit grain coarsening. Compared with normal pressure sintering, hot-pressing sintering can achieve densification sintering at a relatively low temperature, thereby forming a good microstructure and improving its mechanical properties. When sintering aids and hot pressing are used at the same time, the sintering time and sintering temperature of silicon carbide can be significantly shortened. Hot-pressing sintering can obtain silicon carbide ceramic materials with better performance at a lower temperature, but due to the limitations of its equipment and molds, the products produced have simple shapes, low production efficiency, and high production costs, so its products are less used and are mainly used in some special occasions.

There are many sintering technologies for silicon carbide ceramic materials, and each technology has its unique advantages and application scenarios. Reaction sintering is suitable for the preparation of large-sized and complex-shaped structural parts, and hot-pressing sintering is suitable for special occasions. With the continuous advancement of technology, the sintering technology of silicon carbide ceramic materials will become more mature and its application fields will become more extensive.