Sintering silicon carbide

Reaction bonded silicon carbide (RBSiC) or self sintered silicon carbide (SSSiC)—see API Standard 682 for SiC application guidelines in mechanical seals... 

The properties of silicon carbide (4—6) depend on purity, polytype, and method of formation. The measurements made on commercial, polycrystalline products should not be interpreted as being representative of single-crystal silicon carbide. The pressureless-sintered silicon carbides, being essentially single-phase, fine-grained, and polycrystalline, have properties distinct from both single crystals and direct-bonded silicon carbide refractories. Table 1 lists the properties of the fully compacted, high purity material. 

Sintered silicon carbide retains its strength at elevated temperatures and shows excellent time-dependent properties such as creep and slow crack growth resistance. Reaction-bonded SiC, because of the presence of free silicon in its microstructure, exhibits slightly inferior elevated temperature properties as compared to sintered silicon carbide. Table 2 (11,43) and Table 3 (44) show selected mechanical properties of silicon carbide at room and elevated temperatures. 

V. Venkateswaran, J. M. Halstead, and B. Mehosky, "Synthesis of High-Purity Sinterable Silicon Carbide Powders," in Proceedings of the 23rd... 

The fracture toughness values of the silicon carbide deposits on steel thus calculated (cf. Table 6) are of the same order of magnitude as the toughness of a sintered silicon carbide (1 to 4 MPa.m On a tantalum substrate, these are lower. These differences are probably due to residual stresses which vary considerably depending on the nature of the underlying substrate. 

Sintered silicon carbides are formed by all the traditional methods as well as standard plastic forming techniques such as injection molding. These compacts are sintered with small amounts of additives at very high temperatures in inert atmospheres to form essentially a single phase silicon carbide structure. 

L.S.Sigl. Thermal conductivity of liquid phase sintered silicon carbide. J. Euro. Ceramic Soc., 2003,23, 1115-1122... 

MICROSTRUCTURE OF LIQUID PHASE SINTERED SILICON CARBIDE CERAMICS WITH HIGH FRACTURE TOUGHNESS ... 

Microstructure of Liquid Phase Sintered Silicon Carbide Ceramics... 

A. Sayano, F. Sutoh, S. Suyama, Y. Itoh, and S. Nakagawa, Development of a Reaction-sintered Silicon Carbide Matrix Composite, J. Nucl, Mater., 271-272, 467-71 (1999). 

The elastic modulus of sintered silicon carbide with 5 % porosity is 468.9 GPa. What is the porosity of a specimen with an elastic modulus of 350 GPa ... 

A rather different approach has been developed for reaction sintered silicon carbide (RSSC), first developed in the former Soviet Union. In this process a powder preform of mixed graphite and silicon carbide is immersed in a liquid bath of molten silicon. The silicon wets and infiltrates the preform, reacting with the finely-divided graphitic component (carbon black). In the best case, all graphite is reacted and the residual sihcon content is no more than a few percent. The product of the reaction, silicon carbide, firmly bonds the silicon carbide preform powder... 

Table 6. Microstructure and SiC-polytype phase composition in sintered silicon carbide (B/C, Al/C and B/Al/C doped SSiC materials). 

Tomizawa et al. [217] performed pin-on-disk experiments on friction of SSiC against itself in water at room temperature. The authors found a friction coeflBcient of 0.26 and noted that wear of sintered silicon carbide occurs by a combination of tribochemical dissolution and the formation of pits by fracture of SiC grains. The amount of material removal varied from one SiC grain to the other, due to a strong dependence of tribochemical wear on crystallographic orientation of SiC grains. 

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