冷却速率对Al-30wt%Si合金初晶硅形貌和杂质的影响研究

Effect of Cooling Rate on the Microstructure and Impurity of Primary Silicon in Al-30wt%Si Alloy

合金法提纯是制备太阳能级多晶硅的工艺之一,在Al-Si合金提纯多晶硅工艺中,冷却速率对初晶硅的形貌和纯度都有重要的影响。本文对成分为Al-30wt%Si合金采用不同冷却速率进行处理,分析初晶硅的形貌以及杂质含量的变化。结果表明,随冷却速率的降低,初晶硅的长度和宽度逐渐增加,初晶硅收率逐渐增加,并且在较低冷却速率下,初晶硅晶粒的<111>择优生长更加明显。同时,冷却速率对初晶硅中的杂质含量产生了显著影响,在较低冷却速率下,杂质的去除率较高,并且有利于Ti和B杂质的去除。为了获得较高的收率和较好的杂质去除率,Al-30wt%Si合金杂凝固过程中的冷却速率应低于3℃/min。

Solvent refining is one of the processing methods for production of solar-grade silicon.During Al-Si solvent refining process,the cooling rate has a significant effect on microstructure and purity of primary silicon.In this paper,the Al-30wt%Si melt was solidified at different cooling rates,then the microstructures and impurity contents were analyzed.The results show that the length and width of primary silicon increase with the cooling rate decrease,which results in the increase of recovery rate of primary silicon.The<111>-orientation was preferred in the lower cooling rate range during growth of primary silicon grains.Meanwhile,it is obvious that the impurity content is related to the cooling rate.In the lower cooling rate range,the removal rate of impurities is higher,especially for the B and Ti impurities.Accordingly,to improve the recovery rate and purity of primary Si in the refining process of Al-30wt%Si alloy,the cooling rate of molten solvent should be lower than 3℃/min.