Effects of B₂O₃ and CaO/Al₂O₃ on Structure of CaO–Al₂O₃–B₂O₃ System

Abstract

CaO–Al₂O₃-based mould fluxes are the most significant slag systems for the continuous casting of high-Al steel. In this study, to investigate the structure of the CaO–Al₂O₃–B₂O₃ system, molecular dynamics simulation and infrared spectroscopy experiments with different amounts of B₂O₃ and CaO/Al₂O₃ ratio were carried out. The results showed that the structural unit of B–O and Al–O are of great stable while B atom is easier to bond with O atom than Al, and [BO₃]³⁻ trihedron is more stable than [AlO₄]⁵⁻ tetrahedron. With the content of B₂O₃ increases, the increased [BO₃]³⁻ trihedral structure units can balance the excessive negative charges in [AlO₄]⁵⁻ tetrahedron structure, and Al₂O₃, acts more acid in a highly alkaline surrounding, can absorb O²⁻ and results in forming [AlO₅]⁷⁻ structure at high CaO/Al₂O₃ ratio, which promotes the transformation of O_nb into O_b, while CaO results in an increase in the content of O_nb with the increase of CaO/Al₂O₃ ratio. The results of infrared spectrum are consistent with simulation results that B₂O₃ addition promotes the complexity of the network structure, and the depolymerization of the large complex network structure with increased CaO/Al₂O₃ ratio.