Preparation Of Si₃N₄ And Its Composites By Microwave Heating Industrial Waste Silicon Powder

In recent years,with the rapid development of the photovoltaic industry and the semiconductor industry,the global demand for solar-grade silicon has grown rapidly.When solar-grade silicon rods are cut into silicon wafers,a large amount of cutting waste will be generated.The waste components are mainly silicon,silicon carbide,cutting fluid and metal scrap.It has a very high economic benefit for recycling fine silicon powder after separation and purification of cutting waste.At the same time,how to realize its high value utilization is also an urgent problem to be solved.Silicon nitride and its composite materials have a series of excellent properties such as hi gh strength,high temperature resistance,wear resistance,corrosion resistance,and low specific gravity.They are widely used in aerospace,electronics,metallurgy and other fields.It is considered to be the most application potential materials in high temperature structural ceramics,such as aerospace for aero engines,and electronic packaging substrate materials.Therefore,the use of solar-grade waste silicon powder to prepare silicon nitride materials is an effective way to achieve its high value uti lization.In this paper,based on the characteristics of high purity and fine particle size of solar-grade fine silicon powder,as well as the high-efficiency heating characteristic of microwave on silicon materials,it is proposed to use microwave heating fine silicon powder to prepare silicon nitride powder by direct gas-solid nitriding reaction.The silicon powder is heated to 1250°C under nitrogen pressure of 121 k Pa for 20 min and has a good nitriding effect.The conversion rate of the nitriding reaction can reach97.96%.The product is mainly?-Si₃N₄,which is uniform and columnar.And the nitriding reaction time is shortened by more than 77.7%,the energy consumption is reduced by 88.6%,and the preparation efficiency of Si₃N₄ powder is improved.The research on microwave activated sintering Si₃N₄ ceramic materials was carried out.The results show that as the forming pressure increases,the sintering temperature increases and the sintering time increases,the relative density and hardness of Si ₃N₄ceramics gradually increase,the porosity decreases gradually,and the thermal diffusion coefficient increases first and then decreases trend.When the sintering time is 20 min,the sintering temperature is 1500°C,and the forming pressure is 40 MPa,the prepared Si₃N₄ ceramic has good performance,its porosity is 14.44%,the relative density reaches 85.56%,the hardness reaches 128.10 MPa,and the thermal diffusion coefficient 3.727 mm_·²s^-1.Compared with conventional sintering,the relative density is increased by 3.35%,the hardness is increased by 1.45 times,and the thermal diffusion coefficient is increased by 86.34%.The Si C/Si₃N₄ composite material activated by microwave was sintered.The results show that the relative density and hardness of the Si C/Si₃N₄ composite increase with the increase of the content of Si C,and the thermal diffusion coefficient of the composite gradually decreases with the increase of the content of Si C.When the content of Si C is 20%,the relative density of the composite material is 73.53%,the hardness reaches 380.80 MPa,and the thermal diffusion coefficient is 8.179 mm_·²s^-1.Compared with conventional sintering,the relative density of the composite material increased by 4.77%,the hardness increased by 84.76%,and the thermal diffusion coefficient increased by 99.20%.