The relationship between silicate structure and mass transfer of boron in slag refining of silicon
Slag refining of silicon is one of few feasible methods currently in use industrially for removal of boron in the production of silicon for photovoltaic applications. In order to optimize this process, there is a need to enhance the understanding of the relationship between slag composition and the kinetics of boron transfer from metal to slag. In this preliminary work, the kinetics of slag refining using SiO2-CaO-MgO based slags was studied. Small-scale experiments were performed aiming at comparing the boron mass transfer rate resulting from addition of CaO compared to addition of MgO to SiO2. A slag composed of 35％ CaO and 65％ SiO2 was brought to the molten state together with boron-containing high purity electronic grade silicon in a graphite crucible using a resistance heated tube furnace. The same procedure was carried out using a slag containing 35％ MgO and 65％ SiO2. The experiments were performed for a range of durations, after which the content of boron in the silicon could be obtained as a function of time by GDMS analysis. Mass transfer coefficients of boron were determined based on a mass balance consideration of the slag-metal system. The results indicate that the mass transfer rate of boron is higher when CaO is used as the basic constituent for the slag compositions studied. Using Raman spectroscopy, the molecular properties of the oxide structures have been investigated. The obtained mass transfer rates are discussed in light of these findings, assessing the relationship between oxide structure and boron transport through the bulk slag.
Slag refining Kinetics Mass transfer rate Boron Solar grade silicon Raman spectroscopy
Egil Krystad Jeffery Kline Merete Tangstad Gabriella Tranell
Dept. of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim, Norway
国际会议
Ninth International Conference on Molten Slags,Fluxes and Salts(第九届国际熔渣、溶剂与熔盐学术会议 MOLTEN12)
北京
英文
1-10
2012-05-27（万方平台首次上网日期，不代表论文的发表时间）