Preparation of SiC/Al₂O₃ composite materials from coal fly ash

By using coal fly ash as a raw material and graphite as a reducer in the protective atmosphere of argon,SiC/Al₂O₃ composite materials were synthesized by carbothermal reduction.The reaction process of reduction of the coal fly ash was studied,and its influencing factors were investigated.The composition of products obtained at different temperatures was analyzed by X-ray diffraction,and the microstructure was observed by scanning electron microscopy and energy dispersive spectroscopy.The results show that the phases of quartz and mullite in the coal fly ash are almost completely reactive at 1673 and 1773 K,respectively.With increasing temperature,the contents of SiC and Al₂O₃ increase,and the suitable temperature condition is 1773 to 1873 K.The extension of holding time is good for the formation of SiC and Al₂O₃,and the appropriate holding time is 3 to 4 h.Increasing the carbon content has positive effect on the formation of SiC and Al₂O₃,and the optimum molar ratio of C/Si is 4 to 5.In the prepared SiC/Al₂O₃ composite materials,SiC is homogeneously dispersed in the products,and its granularity is less than 20 μm.