Boron partitioning between SiO₂–CaO–MgO slags and liquid silicon at controlled nitrogen potential

Abstract

During refining of silicon using slag treatment, boron dissolved in the silicon is extracted to a liquid oxide (slag) phase. In this investigation the partitioning of boron between SiO2–CaO–MgO slags and liquid silicon was examined at 1873 K over a range of slag compositions and CO–N2 gas mixtures. It was found that the distribution of boron is strongly dependent on the nitrogen partial pressure as well as the slag composition. The greatest partition ratios were achieved at 0.6 atm CO/0.4 atm N2 with low silica content in the slag. The concentration of MgO in the slag seems to have little or no impact on the boron partition ratio.

Distribution of Boron Between Silicon and CaO-MgO-Al2O3-SiO2 Slags

“…White et al [8] equilibrated CaO-MgO-SiO 2 slags with silicon under CO gas at atmospheric pressure. They used a holding time of 48 hours at 1873 K (1600°C) and their results are seen to be in relatively close agreement with the present work.…”

“…It is seen that White et al White et al also investigated the influence of nitrogen atmosphere on the distribution coefficient of boron. [9] They used mixtures of nitrogen and CO gas under atmospheric pressure where the nitrogen content was varied between 0.1 and 0.4 atm. The distribution coefficient was found to increase under nitrogen atmosphere where the mean value of the distribution coefficient under 0.4 atm nitrogen gas was 3.1.…”

“…[1][2][3][4][5][6][7] The literature values in the ternary CaO-MgO-SiO 2 and CaO-Al 2 O 3 -SiO 2 systems are also widely scattered. [3,[8][9][10][11] The aim of this work has been to determine the distribution coefficient of boron for binary and ternary slags in the CaO-MgO-Al 2 O 3 -SiO 2 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.…”