Thermodynamic assessment of Si-P and Si-Fe-P alloys for solar grade silicon refining via vacuum levitation

Thermodynamic properties of phosphorus in Si and Si-Fe alloys were studied using the Molecular Interaction Volume Model (MIVM), aiming to better understand the behavior of phosphorus at low concentration during its removal from these alloys. The model parameters were optimized based on published results for the sub-binary systems of Si-Fe-P, and were shown to reproduce the experimental activity results with good reliability. A relationship between the Henrian activity coefficient, namely infinite dilute activity coefficient, of phosphorus in liquid Si and temperature was established as lnγPinSio=−2117/T+0.197. Further, the separation coefficients, removal efficiencies and equilibrium compositions during vapor-liquid equilibria of Si-P and Si-Fe-P were calculated under vacuum levitation refining conditions.