Research Of Silicon Nitride Bonded Silicon Carbide Materials Preparation From Crystalline Silicon Cutting Waste

In recent years, under the pressure of energy shortage and environmental protection, the solar industry has a good development trend.However, how to deal with crystalline silicon cutting waste is a difficult problem. The cutting waste contains about30%～35%of SiC powder and more than9%crystalline silicon. All of these provide a necessary condition from directly preparing silicon nitride bonded silicon carbide products using the cutting waste.At the same time, silicon nitride bonded silicon carbide composite material has a broad market prospect. Therefore, we propose the preparation of the refractory using solar crystalline silicon cutting waste as the raw material. The purpose of this study is to find a routine to prepare of silicon nitride bonded silicon carbide composites from the crystalline silicon cutting waste.In this thesis, the silicon nitride bonded silicon carbide refractories have been investigated by the method of the high-temperature nitride sintered with crystalline silicon cutting waste (from Jinzhou Yangguang Energy Co., Ltd) as the raw material. We determine the physical properties of the crystalline silicon cutting waste, study the influence of the technology parameters of the green body preparation and nitriding process on the properties of the refractory, optimize the technology parameters of the green body preparation and the nitriding process, and get the sample performance under optimal conditions. The main results are as follows:(1) The physical properties of the cutting waste material were investigated using X-diffraction (XRD), XRF, chemical quantitative analysis, and granularity. It has been found that the cutting waste consist of11.85wt%silicon,77.43wt%silicon carbide. Cutting waste exits in the form of fine particles, and the particles have the size distributing in the range of1.0～23.8μm. Among them, the particles having size between1.0～4.8μm occupy50%of the total volume, and the particles with size between1.0～23.8μm occupy90%of the total volume.(2) We have studied the effect of the binder type and content, pressure and dwell time on the green density. The optimized technology parameters for preparing green body are as follows:HTMC is used as the experimental binder, the content of HTMC is1wt%, the pressure of making billet is25MPa, and dwell time is3min. The density of the sample prepared under such conditions is1.868g cm-3.(3) We have studied the influence of the final nitriding temperature, the holding time at the final nitriding temperature, the density and thickness of the the green body, the Si content on the density, porosity, flexural strength and compressive strength of the samples. When nitriding temperature ranging from1260℃to1380℃, the compressive strength, rupture strength, density increases and the porosity decreases with temperature rising. When nitriding the temperature is higher than1380℃, the density and porosity curve gently change, but the compressive and rupture strength decreases with temperature rising. The product have best performance at the nitriding temperature o1380℃. With the increase of the nitriding time, compressive and rupture strength first increase and then decrease, the nitride reach maximum when the nitriding time is3h. When the nitriding time is less than3hours, with the nitriding time increasing, the density increases and porosity decreases. When the nitriding time is more than3hours, the density and porosity curves bend gently. With increasing the density of the green body, the density, compressive strength, and the rupture strength of the products after nitriding gradually increase, and the porosity gradually decreases. Effect of thickness on the rupture strength and compressive strength is small, but when the thickness exceeds a certain value, the density of products decreases and porosity increases. When the thickness is in the range of8-12mm, the properties of the samples after nitriding is better. When the products are made from the raw material containing15%Si, the properties of the samples after nitriding is better. Too high silicon content will cause nitrogen channel blockage, hinder the internal diffusion of N2, affect nitriding rate, and cause the degradation of the performance. The obtained optimal nitriding conditions are as follows:the final nitriding temperature is1380℃, the holding time at the final nitriding temperature is3h, the pressure of making body is25MPa, the green body thickness is8～12mm, and the Si content is15%. The samples prepared under such conditions have the density of2.413g· cm-3, the porosity of15.7%, the flexural strength of25MPa, and the compressive strength of175.3MPa. These results show it is feasible to preparpe refractory using the crystalline silicon cutting waste. In the subsequent experiments, we can consider ZrSiO4, Al2O3and other additives on the properties of silicon carbide products; the performance of the sample could be improved by improving the pressure of making green body, and making the nitridation under vacuum so on.