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

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 1 300 degrees 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 1 300 degrees 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 Ca(2)Al(2)SiO7 increased and new phase of Na(AlSi3O8) and K(AlSi3O8) precipitated.