Preparation Of Sialon/Si₃N₄-SIC Composite Refractories Mateirlas From Kyanite Tailings

According to the urgent requirement of high performance carbon-containing oxide/non-oxide refractories in the new technical of metallurgy and to solve the bottleneck problems in low comprehensive utilization of kyanite tailings and the high cost of silicon aluminum composite refractories, kyanite tailings were used as raw material to synthesize Si C-Al2O3 and Sialon/Si3N4-Si C composite refractory materials by carbothermal reduction and carbothermal reduction nitridation, respectively. And the further high performance Sialon/Si3N4-Si C composite refractory materials were prepared, using the synthesized Si C-Al2O3 and Sialon/Si3N4-Si C composite powder as raw materials. The results are presented as follows:The optimized preparative variable of carbothermal reduction for Si C-Al2O3 composite powder was found to be synthesized at 1600 °C for4 h, with a carbon content in excess of 50 wt% than theoretical stoichiometry. Under this optimal condition, high purity Si C-Al2O3 composites were obtained and the final conversion of this reaction was calculated to be 96.8%.The optimized synthesis parameters of carbothermal reduction nitridation reaction for Sialon-Si C composite was indicated to be 1550 °C for 4 h, with a carbon content in excess of 20 wt% than theoretical stoichiometry.Under this condition, high purity Sialon-Si C compositepowder was also prepared and the corresponding conversion rate was calculated to be 95.2%.The Si C-Al2O3 composite materials were prepared at different sintering temperatures, using the synthesized Si C-Al2O3 powder as raw material. With the increase of the temperature, the flexural strength and fracture toughness of Si C-Al2O3 materials increased firstly, presented a maximum value at 1550 °C, and then decreased with the further increasing temperature. The maximal flexural strength and fracture toughness of Si C-Al2O3 composite material, prepared at 1550 °C, were investigated to be 85.38 MPa and 3.26 MPa, respectively.The Sialon/Si3N4-Si C composite materials were prepared by high temperature pressureless sintering at 1550°C for 4h, using the prepared Sialon-Si C powder and the industrial Si3N4 powder as raw materials. The flexural strength of Sialon/Si3N4-Si C materials decreased firstly with the addition of Sialon-Si C powder, then increased to the maximum with a addition of 25 wt%, and finally decreased. The Sialon/Si3N4-Si C composite, with 25 wt% Sialon-Si C added, obtained the best flexural strength and compressive strength with the value of 41.83 MPa and 61.64 MPa, respectively.