Effect of BaO/Al2O3 ratio and Li2O content on viscosity and crystallization of BaO–Al2O3–TiO2-based mold slags

Abstract

In the current study, the influence of different BaO/Al2O3 ratios and Li2O contents on the viscosity, melting temperature, crystallization behavior and structure of BaO–Al2O3–TiO2-based mold slags was investigated through the measurement of the viscosity-temperature relationship, hemisphere point method, crystallization process and crystallization temperature, and the calculation of NBO/T and optical basicity. With the increase of the BaO/Al2O3 ratio from 0.60 to 1.67, the viscosity at 1573 K and the melting temperature of mold slags decreased from 0.3 to 0.05 Pa s, and 1261 K–1217 K, respectively, while those also slightly decreased from 0.15 Pa s to 0.11 Pa s, and 1244 K–1213 K with the Li2O content from 4 % to 6 %, respectively, which was related to the increase of fluxing reagent or oxygen ions released by basic oxide in slags. In current slags, precipitated phases mainly existed as LiTiO2 and BaTiO3, and the difference of the BaO/Al2O3 ratio and Li2O content resulted in the competitive precipitation of these phases. With the increase of BaO/Al2O3 ratio from 0.60 to 1.67, precipitated phases gradually changed from LiTiO2 to BaTiO3, and the initial crystallization temperature had the tendency to decrease and increase. On the contrary, the precipitated phase gradually changed from BaTiO3 to LiTiO2, and the initial crystallization temperature as well as the break temperature decreased with the Li2O from 4 % to 8 %. The parameter NBO/T and optical basicity of molten slags increased with the increase of BaO/Al2O3 and Li2O content, and the polymerization degree of the melt decreased, resulting in the decrease of the activation energy of viscous flow and the viscosity. Hence, the increase of the BaO/Al2O3 ratio and Li2O content within limits could lower the viscosity, melting temperature, break temperature and crystallization ability of mold slags, and then improve the lubrication of the slag on solidified shell.