Impact of Impurities in Metallurgical Grade Silicon on Removal Efficiency of Vacuum Evaporation

Abstract

Vacuum evaporation is usually utilized to remove volatile impurities in metallurgical grade silicon to prepare solar grade silicon by metallurgical routes. Especially phosphorus needs to be removed by vacuum evaporation. And the removal efficiency of impurities strongly influenced the quality and performance of products. In this paper, the removal efficiency of impurities is studied by using different raw material. The results indicated that the content of impurities in raw material had deep effect on the removal efficiency of vacuum evaporation. The high quality product can be obtained by vacuum evaporation only once from raw materials with the lower content of impurities whereas it is not for high content of impurities in raw material. This is due to the vapor-liquid equilibrium in the vacuum furnace. The impurities can be removed effectively by vacuum evaporation many times.

A mathematical model for distribution of calcium in silicon by vacuum directional solidification

“…6, k E increases with the temperature. It is well known that, for a reaction about evaporation in the gas-liquid interface, Ca (l, in Si) = Ca (g), and the saturated vapor pressure of calcium can be express as follows [24] (1112~1756K) (17) According to Eq. (11) and Eq.…”