| During the process of solar cell manufacture, carbon components, including graphite and C-C composites, are widely used as heat-resistant parts in the polycrystalline silicon ingot production furnace. The carbon components would produce carbon atoms diffuse into the silicon melt and bring about polycrystalline silicon contaminating at high temperature, which can seriously influence pc-Si solar cell conversion efficiency. However, carbon components are irreplaceable. SiC coating on components is regard as one of the most important resolution schemes.This thesis mainly research silicon liquid immersion and thermal spraying for preparation of SiC coating on carbon components. Silicon liquid immersion method using high purity silicon material embedding graphite matrix, and chemical reactions with different heat preservation time0.25h,0.5h,1h,2h at different temperature1430℃,1450℃are studied to find out the reaction influence factors. Silicon liquid immersion method is simple, but the residual silicon on graphite surface is vast and cause loss of silicon material. Spraying method is to form a certain thickness silicon powder layer on graphite surface, and to be annealed at1500℃to prepare SiC coating. Spraying process can reasonably control silicon powder consumption, effectively avoid the waste of silicon material, and it is a very potential preparation of SiC coating.2D weave C/C composite material is of a porous system with high porosity, and the penetration speed of liquid silicon is very big. Therefore controlling of silicon powder unit area of quality on surface is one of the key factors during the preparation process of coating.In the present work, it is found that reaction temperature and holding time play positive role in the preparation of SiC coating during silicon liquid immersion. The higher reaction temperature and more heat preservation time, the surface coating thicker and silicon carbide grain bigger are. SiC coating on graphite matrix has good mechanical compatibility and thermal shock performance. During the spraying process, slurry ratio is a key point. It can be obtained by adjusting its density and PH value and make suitable slurry with appropriate floating stability and rheology. In this paper, the slurry ratio is lOg silicon powder,67ml PEG200,33ml H2O, temperature of graphite matrix90℃, spraying pressure for30psi (1psi=6.895KPa) with distance30cm is a good spray way. The results show that the forming process of coating on graphite matrix accompanied by liquid silicon penetrates to substrate. Coating is made up of part A and part B, which A is dense SiC coating on matrix surface and B is intermediate SiC-C mesh structure. It is the competition results between reaction on matrix surface and silicon liquid penetration. During the paste coating for C/C composite, it forms gradient condition of constituent and density in coatings, which contains dense SiC coating on surface and SiC particles in pores. Because of high porosity, the penetration speed of liquid silicon is very big, and to ensure the reaction time between C/C surface and silicon liquid,600μm silicon powder layer is appropriate. The formation of coating can effectively improve the density of C/C composite matrix, reduce carburizing channel, with good mechanical compatibility, stripping off has not occurred after thermal shock. |
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