Thermal Preparation Of Silicon Carbide In Crystalline Silicon Cutting Waste

Faced with the double pressure of serious environmental pollution and resource shortage,people are paying more and more attention to the development and utilization of renewable energy.In recent decades,with the development of the photovoltaic industry,the demand for crystalline silicon wafers for preparing solar cells has been increasing.In the production process of crystalline silicon wafers,a large amount of silicon is ground into powder to form cutting waste,which not only causes waste of solar grade crystalline silicon,but also causes environmental pollution.Therefore,the comprehensive utilization of cutting waste has become a research hotspot.This thesis aims to use silicon crystal cutting waste as raw material to prepare silicon carbide by internal heat method,which not only solves the problem of cumbersome recycling of silicon resources in cutting waste,but also produces high value-added silicon carbide by internal heat method.It is of great significance for the ecological utilization of cutting waste resources,the development of high-performance materials and environmental protection.In this paper,the smelting process of SiC(including α-SiC and β-SiC)prepared by thermal internal method was studied by using crystalline silicon diamond wire cutting waste as raw material.The main research contents are as follows:(1)Research on the physicochemical properties of cutting waste.X-ray diffraction analysis(XRD),Scanning electron microscope(SEM),chemical analysis,particle size analysis and other analytical methods were used to study the phase composition,microstructure,chemical composition and particle size distribution of the raw materials.The results of XRD analysis show that the crystalline silicon cutting waste is mainly composed of Si,SiO2 Fe and Fe2O3;The results of particle size analysis show that the particle size of the cutting waste is mainly concentrated in 0.5～10 μm and the average particle size is 1 μm.Chemical analysis showed that the mass fraction of Si in the cutting waste was 65.69%,the mass fraction of SiO2 was 23.24%,the mass fraction of Fe was 8.56%and the mass fraction of Fe2O3 was 2.51%.(2)Research on pickling and removing iron from cutting waste.The effects of leaching temperature,leaching time,liquid-solid ratio and sulfuric acid concentration on the iron removal rate were studied,and the optimum process conditions were obtained:leaching temperature was 90℃,leaching time was 3.5 h,sulfuric acid concentration was 4 vol%,the liquid to solid ratio was 3:1.The iron content in the raw material after pickling and iron removal was reduced to 0.12%,and the iron removal rate reached 98.92%.(3)The process of preparing β-SiC powder by internal heat method using cutting waste as raw material was studied.The effects of synthesis temperature,holding time,silicon-carbon ratio and carbon source on the purity,particle size and morphology of the synthesized β-SiC powder were studied.The process conditions for preparing β-SiC powder were determined:the reaction temperature was 1650℃,the holding time was 5 h,the silicon to carbon ratio was 5:3,and the carbon source was activated carbon.The β-SiC synthesized under this condition has a complete structure and good crystallinity.The particle size was about 235 μm,the purity was 97.63%,the ball milling toughness was 53.71%,the microhardness was 2750 MPa,and the magnetic content was 0.054%..(4)The process of preparing α-SiC powder by internal heat method using cutting waste as raw material was studied.The effects of synthesis temperature,holding time and silicon-carbon ratio on the purity,particle size and morphology of the synthesized α-SiC powder were studied.The process conditions for preparing α-SiC powder are determined:the reaction temperature was 1950℃,the holding time was 8 h,the silicon to carbon ratio was 5:4,and the carbon source was activated carbon.The α-SiC synthesized under this condition has a particle size of 495.461 μm,a purity of 98.86%,a ball milling toughness of 75.27%,a microhardness of 3125 MPa,and a magnetic content of 0.025%,which meets the requirements of industrial abrasive silicon carbide.