Research On Preparation Of Al-Si Alloys With Diamond-Wire Cutting Waste Of Crystalline Silicon

With the rapid development of photovoltaic(PV)industry in the world,the demand for cry stalline silicon wafers as the key material of solar cells is increasing year by year.At present,the mortar silicon carbide cutting process is gradually replaced by diamond-wire cutting process which is becoming the mainstream silicon wafer production method.In slicing process,about 35%?40%of the crystalline silicon is lost into cutting waste slurry,which is due to the diameter of the cutting wire is appromixately equal to the thickness of the silicon wafer.The production of cutting waste not only causes the waste of crystal silicon,but also brings great burden to the environment.Based on this situation,the purpose of this paper is to explore a technological route for preparation of Al-Si alloy with diamond-wire cutting waste of crystal silicon,thus providing a new method for the recycling of silicon diamond-wire cutting waste,which aims to solve the problem of dealing with the silicon cutting waste.This paper studies the smelting process of Al-Si alloy with the diamond-wire cutting waste of crystal silicon as raw material,which was provided by Jiangsu haobo new material company.The main research contents are as follows:(1)The properties of cutting waste were studied.Particle size analysis revealed that the particle size of cutting waste was micron grade and D50 was 1.386?m.The result of XRD confirmed that Si was the main phase of cutting waste,and the XRF analysis result indicated that the contents of impurity elements,such as Al,Ca and Fe in cutting waste were very low.SEM/EDS and infrared analysis results showed the presence of silicon oxides in the cutting waste.The contents of each component determined by Chemical analysis were Si 75wt.%,moisture 6wt.%,metallic impurities and their oxides 2.5wt.%,silicon oxide 14.5wt.%and diamond 2wt.%.(2)Al-Si alloy was prepared in cryolite molten salt with the cutting waste as raw material.In order to reduce the oxidation,the cutting waste was added in the pellets form,and the optimum parameters of pelletizing process were as follows:the binder addition 5wt.%,the water addition 15wt.%,the pelletizing pressure 12.5 MPa,the holding time 60 s.Under these conditions,the porosity of the pellet was 58.02%.The effects of molecular ratio of cryolite,smelting temperature and smelting time on the smelting results were investigated and optimized,the optimum melting conditions were as follows:the molecular ratio of cryolite 1.6,the smelting temperature 1150?,the smelting time 30 min,the mass ratio of the raw material 6.3:1:4.3(cryolite:cutting waste:aluminum).Under these conditions,the silicon content,utilization ratio of the cutting waste,loss ratio of aluminum of the Al-Si alloy were 12.02wt.%,64.25%and 5.60%,respectively.(3)The mechanism in the process of preparing Al-Si alloys with the cutting waste was studied.The process of preparing Al-Si alloy in cryolite molten salt was divided into three stages:Firstly,the cutting waste dissolved in molten salt of cryolite.The SiO2 on the surface of silicon particle dissolved in the molten salt,and the internal silicon particle dispersed directly in molten salt.Secondly,aluminothermic reduction reaction taked place when aluminium was added to the fusant,and the reaction proceeded in the molten salt and the interface between molten salt and metal phase.Thirdly,the Si originated from the cutting waste and produced by aluminothermic reduction reaction diffused into the metal phase and formed a silicon enrichment zone near the interface,while other products dissolved in the molten salt.