Distribution of Boron Between Silicon and CaO-MgO-Al 2 O 3 -SiO 2 Slags
- PDF / 623,393 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 55 Downloads / 232 Views
TION
SOLAR cells are considered to be one of the most promising energy sources in the future. The Earth receives energy from the sun that is orders of magnitude higher than both current and projected future energy demand. Solar cells are, however, too expensive at present to compete with fossil fuels in most countries. Crystalline silicon solar cells dominate the solar cell market and have proven to maintain high efficiency for decades. More advanced solar cell technologies may become more competitive in the future but crystalline silicon solar cells are predicted to have significant share of the market for many years to come since it is a wellestablished technology and based on abundant raw materials. Solar-grade silicon contributes significantly to the cost of the final solar module and this silicon is at present mainly produced through the Siemens process which is an expensive process both in terms of energy use and capital cost. Production of solar-grade silicon directly by use of metallurgical refining methods can reduce the cost and hence make energy from solar cells more attractive. It has, however, proven to be very challenging to bring the boron content in silicon to a sufficiently low level by these methods. Slag refining has been proposed as a potential metallurgical refining method for removal of boron from silicon. A limited number of studies have been conducted on slag refining of silicon for boron removal and the literature data is widely scattered. The ability of a slag for boron removal is given by the distribution coefficient of boron:
LARS KLEMET JAKOBSSON, Postdoctoral Research Fellow, and MERETE TANGSTAD, Professor, are with the Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim, Norway. Contact e-mail: [email protected] Manuscript submitted February 12, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
LB ¼
wðBÞ ; w½B
½1
where w(B) is the mass fraction of boron in the slag and w[B] is the mass fraction of boron in silicon. The value of the distribution coefficient has in the binary CaO-SiO2 system been found to be in the range from 0.5 to more than 5 in different works.[1–7] The literature values in the ternary CaO-MgO-SiO2 and CaO-Al2O3-SiO2 systems are also widely scattered.[3,8–11] The aim of this work has been to determine the distribution coefficient of boron for binary and ternary slags in the CaO-MgO-Al2O3SiO2 system at 1873 K (1600 C). All compositions are given on mass basis in the text and tables while mole fractions are used in the figures.
II.
EXPERIMENTAL
Master slags were made from oxides with a purity of at least 99 pct bought from commercial suppliers. The base oxides were: 99.9 pct SiO2 (Aldrich), 99.9 pct CaO (Aldrich), ‡99 pct MgO (Sigma-Aldrich), and 99.5 pct Al2O3 (Alfa Aesar). Each master slag had a weight of approximately 300 g and was made by melting a mixture of the oxides in a graphite crucible by induction heating under argon atmosphere. They were quenched in a water-cooled copper mold remelted at least two more ti
Data Loading...
