Effect of interaction between impurity elements on silicon purification during Al–Si solvent refining

Abstract

Al–Si solvent refining is a promising method to purify silicon. Boron and phosphorus are key impurity elements during the purifying process. The common raw materials for Al–Si solvent refining are metallurgical grade silicon and industrial aluminum. There are many impurity elements except boron and phosphorus in the metallurgical grade silicon and the industrial aluminum. The effect of these impurity elements on boron and phosphorus removal during Al–Si solvent refining is studied in this work. The hypereutectic Al–Si melts with these impurity elements were solidified, and the hypereutectic Al–Si melts without these impurity elements were solidified at the same cooling rate. Boron and phosphorus contents in purified silicon are determined by inductively coupled plasma optical emission spectrometer (ICP-OES). It is found that when silicon ratio increases from 20% to 70% in samples without other impurity elements, boron removal rates decrease from 0.4 to 0.3, and phosphorus removal rates decrease from 0.96 to 0.92. When silicon ratio increases from 20% to 40% in samples with other element impurities, boron removal rates decrease from 0.87 to 0.57, and phosphorus removal rates increase from 0.63 to 0.9. The different removal rates between samples with and without other impurity elements are attributed to the interaction between impurity elements. In addition, boron-containing intermediate compound forms and locates in the Al–Si matrix, while phosphorus-containing intermediate compound forms and locates in the primary silicon phase.