Study On Properties Of Reaction Sintered Silicon Carbide Formed By Gel-casting Process

The preparation of high-strength reaction sintered silicon carbide has been one of the problems in the study of silicon carbide ceramic, the key factor is to obtain ceramic green body with a homogeneous structure and density. The green body formed by Gel casting process has a uniform density and high bending strength. In this paper, the modification of sub-micron silicon carbide powder and the dispersion of carbon black have been studied to enhance the dispersion of raw materials; a stable dispersion of low viscosity silicon carbide/carbon black ceramic slurry has been prepared. By adjusting the parameters during the gel casting process, we had obtained the RBSC green body with a uniform structure. The effects of Pressure forming and Gel-casting molding on the microstructure and bending strength of RBSC have been investigated. The relationship between the structure and properties of sintered body has also been studied. A fine grain RBSC with a uniform structure has been prepared by using the low-temperature sintering process. The main results are as follows:(1)The dispersion of carbon black in water and the surface modification of silicon carbide powder were studied, as a result, the dispersion of raw materials particles had been improved greatly. The silicon carbide/carbon black slurry with a solid volume fraction of 54vol% and the viscosity of 750mPa·s was successfully prepared by using a single sub-micron particle size (0.8μm) of silicon carbide powder and carbon black (0.38μm).(2)The influencing factors of gel casting process had been investigated. The suspension was solidified uniformly by controlling the temperature and humidity as well as the proportion of monomer and cross linking of the polymerization process; The RBSC ceramic green body with strength of 14MPa was prepared by stirring foaming in a vacuum environment, and Complicated shapes of SiC/C green bodies were successfully prepared by gel casting process.(3)The density and components of RBSC obtained under different molding methods could be precisely controlled by calculating the total carbon density of green compact. This result is instructive for guiding RBSC ingredients and practical application.(4)The fine grain RBSC with a uniform structure was prepared by using sub-micron silicon carbide powder and carbon black. The strength of RBSC came up to 693MPa and the hardness reached 27.2GPa, which have surpassed the average value of hot pressing sintered silicon carbide.(5)We have compared the effects of pressing forming process and gel casting process on the uniformity of green body structure and discussed the relationship between structure and properties of RBSC.For a fine grain RBSC, the size and distribution pattern of free silicon significantly affect the strength of material.