Composition & Microstructure Design And Property Analysis Of Si₃N₄ Bonded SiC

Silicon nitride bonded silicon carbide is one kind of new structural ceramics. It doesn't react with nonferrous metal and has a high thermal conductivity rate. Its properties of thermal shock resistance, scour resistance and corrosion resistance are very excellent. So silicon nitride bonded silicon carbide is a eximious refractory of Al, Cu, Zn, Mg melting field. Compared with carbon, silicon nitride bonded silicon carbide has better oxidation resistance and bigger resistance ratio, which make it be a perfect line material of Al electrolysis cell. Si3N4/SiC, Si2N2O/SiC and Sialon/SiC are the three embranchments of silicon nitride bonded silicon carbide. This paper is concentrated on preparing Si3N4/SiC, Si2N2O/SiC and O'-Sialon/SiC by reactive sintering techniques. The components of raw materials and microstructure of these three ceramics were studied. At the same time, molten Al, Cu, Zn, Mg and cryolite corrosion resistance of silicon nitride bonded silicon carbide were tested too. The main conclusions are as follows:(1) O'-Sialon/SiC has been prepared by reactive sintering techniques. The content of O'-Sialon is 85wt%. The flexural strength is 43.17MPa. After thermal shock experiment, the flexural strength is 48.76 percent of the primal strength.(2) The thermal shock resistance of Si3N4/SiC is mainly dominated by its strength. Increasing its strength by adjusting granularity of SiC is an effective way to optimize its thermal shock resistance. The best result is: 50wt% 46-mesh SiC, 16.67% 90-mesh SiC, 33.33% 180-mesh SiC.(3) In air atmosphere, weight gain of Si3N4/SiC, Si2N2O/SiC and O'-Sialon/SiC by oxidation follows logarithm rule at 1000 癈 . The oxidation resistance of O'-Sialon/SiC is the best among these three ceramics. Si3N4/SiC is the worst. The weight gains of Si2N2O/SiC, O'-Sialon/SiC and S13N4/S1C are 0.03mg cm-3, 0.13 mg-cm-3 and 0.36 mg cm-3 respectively.(4) In air atmosphere, the molten Al, Zn corrosion resistance of Si3N4/SiC,Si2N2O/SiC and O'-Sialon/SiC is excellent. Mg corrosion resistance of Si3N4/SiC is excellent too. These three ceramics were slightly corroded by molten Al at 1000℃. While at 800℃, Si component of molten Al increases by 0.08% after 60-hour corrosion experiment.(5) Atmosphere affects Cu corrosion resistance of Si3N4/SiC greatly. In air atmosphere, Cu2O in molten Cu corrodes Si3N4/SiC quickly. In nitrogen atmosphere or some slipcover existing, Cu corrosion resistance of Si3N4/SiC is very excellent. No obvious corrosion was observed after the 400-hour using.(6) Cryolite corrosion resistance of Si3N4/SiC is very excellent in air atmosphere. The property of Si3N4/SiC is the best among Si3N4/SiC Si2N2O/SiC and O'-Sialon/SiC. O'-Sialon/SiC is the worst. After the 25-hour corrosion experiment, cryolite only penetrated into Si3N4/SiC slightly. No corrosion phenomenon was observed.