Thermodynamic Modeling and Experimental Study on Interaction of Fe to P in Silicon Solution
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TION
FOSSIL fuel as a non-renewable resource has been substantially consumed. It was predicted that the global oil and coal resources would be exhausted by around 2042 and 2112, respectively.[1,2] The large-scale consumption of fossil energy also brings severe environmental pollution problems. Renewable energy, including from the sun, wind, tides, and waves, supplies some alternatives and opportunities for environmental recovery. Solar energy is one of the most popular sources of renewable energy. Crystalline silicon is one fundamental material for the preparation of solar cells. The metallurgical process is considered one of the most economical approaches for the purification of solar-grade silicon (SoG-Si).[3,4] Several purification technologies such as secondary refining, vacuum refining, and directional solidification are applied during this process, which use metallurgical-grade silicon (MG-Si) as the raw material.[5–9] Phosphorus, as one of the crucial nonmetallic
FAN YANG is with the State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, P.R. China. JIJUN WU and WENHUI MA are with the State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology and also with the Faculty of Metallurgical and Energy Engineering, Kunming 650093, P.R. China. Contact e-mails: [email protected]; [email protected] Manuscript submitted March 21, 2020
METALLURGICAL AND MATERIALS TRANSACTIONS B
impurities, seriously affects the photoelectric conversion efficiency of solar cells. Vacuum refining is the main method for phosphorus removal.[10–12] It is meaningful for silicon purification to investigate the thermodynamic properties of phosphorus in silicon solution. Thermodynamic study of silicon solution has always been one of the focuses for MG-Si purification. Tao [13,14] proposed a molecular interaction volume model (MIVM) to predict the activity coefficients of iron (Fe), aluminum (Al), and boron (B) in Si solution at 1687 K and 1823 K. The activity interaction coefficient of Fe to Al at 1687 K was calculated as well. The Gibbs free energy of P in silicon solution at 1723 K to 1848 K was determined by melting a silicon-phosphorus alloy under controlled pressure.[15] The removal of phosphorus from MG-Si by vacuum refining has been further verified. Yan et al.[16] used the MIVM to calculate the thermodynamic parameters of P in Si-P and Si-Fe-P systems, and the relationship between the infinite dilute activity coefficient of P and the temperature was characterized. Zhou et al.[17] determined the activity interaction coefficient of Al to Fe in a Si-Fe-Al system where the temperature ranged from 1663 to 1723 K through the same activity method. The activities of components in binary Si-Ca and ternary Si-Ca-Fe systems were predicted by a metal coexistence theory in our previous work,[18] and the infinite dilute activity coefficient of Ca and the activity interaction coeffi
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