Study On Preparation Of Si₃N₄ -SiC Composite Materials And Its Application In Iron Runner Castable

Iron runner is used as refractory material in blast furnace, whose application performance, usage age and iron passing through will influence the production cost, labor intensity and working environment. In this work, aiming at meeting the requirement for high-performance of blast furnace iron runner, Al₂O₃-SiC-C castable with different amounts of calcium aluminate cement were prepared by palm corundum, silicon carbide, ultra-fine alumina, fine silicon powder, spherical asphalt and calcium aluminate cement (CAC) as raw materials, and the effect of calcium aluminate cement amuont on physical properties of Al₂O₃-SiC-C castable was studied. The Si₃N₄ was prepared by natural quartz and coke as raw materials through carbothermal reduction and nitriding reaction.The phase and micro morphologies of the products were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The influence of Si₃N₄ amount on the physical properties at room temperature, as well as oxidation resistance and resistance to slag erosion at high temperature of Al₂O₃-SiC-C iron runner castable were investigated.The samples were prepared using quartze and carbon as raw materials by carbothermal reduction and nitriding reaction.after 1600℃×3h sintering the main phase of the samples wereβ-Si₃N₄ andβ-SiC.As been observed by SEM, there were large mountβ-SiC whiskers at the surface of samples and some Si2N2O irregular shape in the powder.Al₂O₃-SiC-C castable with different amounts of calcium aluminate cement were prepared by using palm corundum, silicon carbide, ultra-fine alumina, fine silicon powder, spherical asphalt and calcium aluminate cement (CAC) as raw materials. The effect of calcium aluminate cement amounts on physical properties of Al₂O₃-SiC-C castable were researched. The results showed that the rupture strength, crushing strength,apparent porosity, bulk density, permanent linear change and oxidation resistance well reached the performance requirements when CAC amount was up to 3%.When heat-treated at 1450℃for 3h, a new phase of Moissanite in the sample formed, which was the reaction product of silicon powder in the sample with carbon. The influence of Si₃N₄ amounts (0, 3%, 6%, 9% and 12%) on physical properties at room temperature, oxidation resistance and resistance to slag erosion of Al₂O₃-SiC-C iron runner castable were investigated. The results showed that, the rupture strength and the crushing strength of the optimized specimen (with 6% Si₃N₄) were 11.63 MPa and 34.50 MPa, respectively. The permanent linear change of specimen treated under 1450℃was only 0.07%. More specifically, the specimen with 6% Si₃N₄ had the best oxidation resistance. The thickness of oxide layer was 2.98 mm when treated at 1450℃, while that of the one without adding Si₃N₄ was 3.88 mm. Si₃N₄ could prevent the slag from eroding and penetrating to the iron runner castable. The optimal Si₃N₄ amount was 6%, and under this condition, the comprehensive performance of Al₂O₃-SiC-C castable was the best.This work provides scientific basis and new technical route for researching and developing high-performance iron runner castable. Applying low-cost minerals to substitute high-consumption corundum and silicon carbide materials can lower the iron runner cost, improve energy saving and mineral resources utilization effectively.