Electrically-Enhanced Boron and Phosphorus Removal from Silicon by CaO–SiO2–Al2O3/–MgO Slag Treatment

It has been recognised that reactions between liquid metalMetals and liquid slagSlag are electrochemical in nature. Hence, manipulation of the reactions (enhancement or retardation) may be expected when an external electromotive force is applied. In this work, the removal of both, boronBoron and phosphorusPhosphorus, from silicon by CaO–SiO2–Al2O3/–MgOMgO slagsSlag, enhanced by applying electromotive force (EMF), was investigated. An improved cell configuration was developed and utilized. New data were generated by carrying out experiments in an argon atmosphere at 1773 K for 120 min with different currents (0.5 or 1.0 A) passed through the molten slagSlag and silicon. The change of the element concentrations as well as the current and potential difference across the slagSlag and silicon were tracked and measured. The current and potential readings of the experiments show that the molten CaO–SiO2–Al2O3 slagSlag was more electrically conductive than the CaO–SiO2–MgOMgO slagSlag at 1773 K. The electrical field that was applied to the system reduced the concentration of boronBoron in the silicon by 45.0% for the CaO–SiO2–Al2O3 slagSlag (with both electrical currents, 0.5 and 1 A), and 8.3% for CaO–SiO2–MgOMgO slagSlag (with 0.5 A imposed). The phosphorusPhosphorus concentration in the silicon was not influenced by the electric slagSlag treatment.