| A large quantity of cutting waste slurry is generated in the processing of crystalline silicon wafer needed by solar photovoltaic power generation.Excepting small amount of polyethylene glycol,the main components of the sold cutting waste were SiC and Si after dried,so it was called SiC-Si waste.In this work,the composition and the heating oxidation process of the SiC-Si waste from a factory were investigated.Silica refractory was prepared directly by sintering.Porous and mullite refractories with excellent performance were prepared via adjusting the amounts of Al2O3 added into the waste.The utilization of this solid waste to prepare refractory materials can reduce the pressure of environmental protection of the enterprise and the production cost of refractory materials.XRF,XRD,TG,SEM etc.were used to analyze the raw,oxidized and the prepared refractory materials.The influences of sintering temperature,heating rate and particle size on the oxidation process of the waste and the influences of preparation conditions on the formation,structure and performance of the products have been discussed.Based on a lot of experiments,the recipes and processing parameters have been optimized to make silica,porous and mullite refractories with the waste,respectively.Composition analysis shows that the waste contains 62.63 % SiC,27.49 % Si and other ingredients.The waste can be used as a silicon source for refractory materials.Combining the non-constant and constant temperature thermogravimetric analysis in the range of 20-1500 ? with X-ray diffraction analysis results,one can see that the oxidation process of the waste contains three stages: oxidation of Si,oxidation of Fe and oxidation of SiC.The complete oxidation products were cristobalite and Fe2O3.Ball milling pretreatment and a lower ramping rate benefits the oxidation of the cutting waste.Silica refractory with cristobalite as main crystalline phase is successfully prepared by the sintering the ball milled waste powder.The optimum preparation conditions are as follows: a shaping pressure of 50 MPa,heating to 1550 ? at a rate of 3 ?/min and sintering for 6 h.The content of SiO2 in the sample is 94.86 %,the volume density is 1.75 g/cm3,the flexural strength is 23.32 MPa,and the refractoriness is 1680 ?.The oxidation of SiC in the waste at high temperature would produce SiO2 and carbon oxide gas.Fe can be oxidized to Fe2O3.By adjusting the content of Al2O3 in the batch,liquid phase can be formed during sintering at high temperature,while the carbon oxide gas is difficult to release from the liquid-phase coating,leading to the formation of a porous refractory.The results show that when the content of Al2O3 is 20 %,a porous refractory can be prepared from the waste at 1515 ? for 2 h.The sample has a volume density of 0.78 g/cm3,a room temperature thermal conductivity of 0.354 W/(m?K),and a refractoriness of 1560 ?.It can be used as a high temperature thermal insulation material.The oxided waste mainly consisted of SiO2,67~80 % Al2O3 was added to the waste to obtain a higher content of mullite refractories.The effects of the alumina content,sintering temperature and time on the formation of mullite were studied.The results show that when the content of alumina is 75 %,the sintering temperature is 1550 ? and the sintering time is 2 h,the mullite phase content of the sample after heat treatment is the highest,reaching 92.99 %.The sample has a density of 1.63 g/cm3 and a refractoriness more than 1800 ?. |
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