Comprehensive Effects of Alkali Oxides and CaO/Al₂O₃ on the Structure and Properties of Aluminate Slag

Abstract

To obtain aluminate-based mold fluxes with appropriate performances for continuous casting of high-aluminum steel, the effects of Na₂O and K₂O contents on the structure and properties of aluminate slag with various CaO/Al₂O₃ (C/A) were investigated using Fourier transform infrared and Raman spectroscopy, hemispheric melting point instrument, rotational viscometer and X-ray diffraction. It is concluded that with Na₂O and K₂O addition, the polymerization degree, viscosity at 1300°C and break temperature of aluminate slag first declined and then grew at C/A ratio of 1.1 since Al₂O₃ changed from a basic oxide to an acidic oxide, and the transition points corresponding to Na₂O and K₂O contents were 6 wt% and 2 wt%, respectively, while they reduced continuously at C/A=1.3 due to Na⁺ and K⁺ augment evolved the complex anionic group into a simple structure with Al₂O₃ acting as an acidic oxide. Combing the melting temperature and structural evolution, it demonstrated that the structure polymerization plays a predominant role in effecting the viscosity at 1300°C. The crystallization ratio increased with Na₂O and K₂O enhancement, especially when their contents exceed 6 wt% at C/A=1.1 and 4 wt% at C/A=1.3, because of peak intensities of crystals CaF₂ and Ca₂Al₂SiO₇ increased and new phase of Na(AlSi₃O₈) and K(AlSi₃O₈) precipitated.