Combining experimental analyses and molecular dynamics simulations in impurity removal at the Si/slag interface

Abstract

Slag refining is a crucial step for Si purification by the metallurgical processes. In this study, the impurity removal at Si/SiO2–CaO–MgO slag interface was investigated experimentally and theoretically. The diffusion couple experiments show that the slag underwent the processes of sintering, solid particle dissolution, and composition homogenization. When the melted slag contacted the Si, the interfacial reaction occurred, and the impurity oxides formed and transferred into the slag phase. The thermodynamic analyses confirmed the existence of the oxidation reaction between impurities and slag. First-principles molecular dynamics simulations of the Si–X–O system (X = Al, B, Ca) clarified the binding behaviors of Al, B, Ca with Si. The calculated binding energy shows that the affinity ability of these impurities with Si are B > Al > Ca at the molecular level, and B impurity is the most difficult one to be removed from Si during the slag refining process.