To Study the Influence of Hydrated Multi-Fluxes on Boron Contene in Metallurgical Grade Silicon.

• Main Authors: Wu, Bo-Kai, 吳柏凱
• Other Authors: Liao, Fang-Chun
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/10406668269959862642

碩士 === 大葉大學 === 機械與自動化工程學系 === 102 === Studies on refining of polycrystalline silicon are always performed on the basis of cost down, reducing air pollution and energy consumption. As a result, the process of low cost and low pollution oxide fluxes is applied in the experiment to eliminate the boron impurities in silicon. The study plan implemented various formulas of hydrated multi-fluxes constituent with a selection of Induction Heating Method to start the smelting process. ICP-OES is then used to analyze the residual of boron impurity in silicon ingots. By doing so, we investigate the parameters of types, quantity, proportion and frequency of adding hydrated multi-fluxes in comparison to the effect of using ordinary mixing method to eliminate boron residuals. From experimental results showed that SiO2 and CaO should be the main ingredients of preparing hydrated multi-fluxes constituent and scum viscosity is found more suitable when the ratio of CaO/SiO2 falls between 4/5~5/4 range. That, therefore, is supposed to have better effects on later-on smelting slag-off and the reduction of boron residuals. Increase the quantity of flux is definitely beneficial in the elimination of boron impurity. However, it has capped limitation. As for the effect of eliminating boron content by using sequential addition of hydrated multi-fluxes, it is found no distinct difference to that by adding the whole lot in at once. It was also found in smelting results by comparing hydrated and non-hydrated multi-fluxes constituent, that using hydrated method to mix silica powder with flux constituent represents evenly blended mixture. Therefore, flux can react more efficiently with silica powder when smelting. If flux constituent is added in at once when smelting, the hydrated multi-fluxes should be utilized to have better effect on eliminating boron. Yet, if non-hydrated multi-fluxes constituent is chosen, sequential addition of it has better boron impurity removal rate than the use of hydrated multi-fluxes. According to the comprehensive experimental results, it suggests that 4SiO2-5CaO-1Na2CO3 should be the best hydrated multi-fluxes constituent proportion. Along with the quantity of 150 wt.% addition and 10 minutes of smelting holding time, it should have the most significant effect on eliminating boron impurity from metallurgical grade silicon. The boron content in original polycrystalline silicon reduced from 8.5 ppm. to 2.6 ppm., which showed the removal rate up to 69%.