Mechanism of enhancing B removal from Si with V addition using AlSi as the refining solvent

The Si purification mechanism was investigated by using AlSi solvent with small amounts of V to enhance B removal. The results indicated that a small amount of V enhanced the removal of B from the AlSi melt, as it formed the VBX compound. The VBX was determined to be VB2 via EPMA. The solubility product of the VB2 in the Al-43at. %Si melt at 1273 K and the Al-35at. %Si melt at 1173 K were initially measured experimentally with equilibrium technology, and were determined to be 8.15×10-11 (1273 K) and 5.97×10-12 (1173 K). The relationship between the solubility product of VB2 and the liquidus temperature of AlSi melt was estimated, which indicated that an excessive V addition or a lower temperature is needed to enhance the efficiency of B removal from the AlSi melt. Based on the thermodynamic analysis, V was used as an additive in the Si purification process with the Al-35at. % Si solvent that had electromagnetic solidification. The results of the Si purification indicated that a small amount of V could enhance the B removal efficiently and VSi2 was found in eutectic AlSi phase along the Si crystals boundaries. The maximum removal rate of B was about 76%. The supplementary V was completely eliminated together with the B and did not contaminate the refined Si.