Preparation Of MgO-SiC-C Refractory Composite By Forsterite-c As Raw Material

Forsterite is a kind of silicate minerals with island structure, the chemical formula for the Mg2SiO4 or 2MgO?SiO2, and it is crystal structure stability, high lattice energy(17572.8KJ/mol), high melting point(1890℃) , high hardness(6.5-7.0), and high density. The characteristics of structure and performance of forsterite is the key to meet metallurgical and high temperature industry application, and suit for refractory, metallurgical furnace, foundry sand ceramic coating etc.In our present work, the MgO-SiC-C composite powders were prepared by using forsterite and carbon black powders as the starting materials in nitrogen, argon or reducing atmospheres. Fe2O3 transformed Fe, Si and C ternary carbide or FeSi alloy. The phase compositions of the sintered samples were investigated by X-ray diffractometry(XRD). The microstructures of the synthesized samples were examined by scanning electron microscope (SEM). The oxidation process of the synthesized samples was researched by the differential thermal analysis (DTA) and the thermal gravity analysis (TG).By analyzing the experimental results, we got some conclusions as follows.(1) The reaction happened among Fe2O3, SiO2 and C after high temperature sintered, so Fe2O3 was transformed FeSi .(2) M2S and carbon black were transformed MgO and SiC at the high temperature, and the MgO phase existed with lumps(in argon atmosphere) or the octahedral structures(in nitrogen atmosphere). The silicon carbon phase existed with striped defoliation, and a lot of SiC whisker existed in the sintered samples in nitrogen atmosphere.(3) With the increasing of sintered temperature(among 1550℃-1700℃) and the content of carbon black,the reaction between forsterite and carbon black were accelerated, and made for synthesized MgO and SiC phases.(4) The MgO and SiC phases appeared in the sample sintered at 1600℃in argon and nitrogen atmospheres, but the MgO phases appeared in the sample sintered at 1700℃in reducing atmosphere, so the reaction between forsterite and carbon black more effective in argon and nitrogen atmospheres(5) The weight increment of the MgO-SiC-C composite powders synthesized in nitrogen and argon atmosphere reach to 10% and 23%, respectively, so the MgO-SiC-C composite powders synthesized in nitrogen atmosphere had better the oxidation resistance.