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

Abstract

Production of solar-grade silicon through metallurgical refining methods can be less expensive than current production methods both in terms of energy use and capital cost. Slag refining is a potential metallurgical refining method for removal of boron from silicon. The distribution of boron between silicon and binary CaO-SiO 2 and MgO-SiO 2 slags, and between silicon and ternary CaO-MgO-SiO 2 and CaO-Al 2 O 3-SiO 2 slags has been investigated in this work at 1873 K (1600°C). The distribution coefficient of boron has been found to be between 2 and 2.5 in the binary CaO-SiO 2 and MgO-SiO 2 systems. It has also been found to be in the same range across the entire CaO-MgO-SiO 2 system. In these systems the distribution coefficient is unaffected by slag composition. The distribution coefficient has been found to decrease with increasing Al 2 O 3 content in the slag in the ternary CaO-Al 2 O 3-SiO 2 system.

Mass Production Test of Solar Cells and Modules Made of 100% UMG Silicon. 20.76% Record Efficiency

“…Unfortunately, both impurities are difficult to remove by traditional purification routes such as directional solidification or acid leaching, due to their large segregation coefficients K B = 0.8 and K P = 0.35 [23]. Therefore, several alternative methods have been studied and developed to remove boron such as slag refining [24,25] plasma refining [26], and gas refining [27,28].…”

Thermodynamic Activities and Distributions of Calcium and Magnesium Between Silicon and CaO-MgO-SiO2 Slags at 1873 K (1600 °C)

“…More details about the experimental and analytical procedure are given in a previous paper. [1] The holding time required for boron to reach equilibrium in the previous paper was also chosen in the present work even if it may have reached equilibrium faster with respect to calcium and magnesium since they are major components in the slag. Some of the experiments with the shortest holding times in the binary CaO-SiO 2 and MgO-SiO 2 systems were, therefore, disregarded when evaluating the results.…”

“…Experiments CS1 and CS2 were excluded from the evaluation of the data because the system was not in equilibrium with respect to boron in the previous study, [1] and may therefore also not be in equilibrium with respect to calcium. The calcium concentration in silicon is seen to increase significantly with increasing concentration of CaO in the slag.…”

“…The concentrations found in the present work are also listed in Table II. Experiments MS1, MS2, and MS3 were excluded from the evaluation of the data because the system was not in equilibrium with respect to boron in the previous study, [1] and may therefore also not be in equilibrium with respect to magnesium. Most of the values found in the present work are seen to be somewhat lower than the two measurements by Morita et al The binary section of the surface fit of the magnesium concentration in silicon in the ternary CaO-MgO-SiO 2 system with 95 pct confidence bands is also shown together with the measured values.…”

Effect of solidification conditions on the silicon growth and refining using Si–Sn melt

“…The purification of MG-Si through metallurgical routes such as directional solidification [1,2], slag refining [3][4][5], oxidation with plasma melting [6][7][8][9], and vacuum melting [10,11] has been investigated. The individual process has its own limitations and does not allow removal of all impurities.…”