Liquidus Temperature of SrO-Al2O3-SiO2 Glass-Forming Compositions

Despite the important role of strontium aluminosilicate glasses in various technologies, there is no available phase diagram for this ternary system in the ACerS-NIST Phase Equilibria Diagrams Database. Establishing the liquidus surface (liquidus temperature T_liq and primary devitrification phase) is crucial for glass composition design, because the liquidus temperature is intimately connected with the glass-forming ability of the melt. In this work, we have determined the liquidus surface by X-ray diffraction phase analyses of isothermally reacted samples from powder mixtures of 24 compositions. In the composition range of interest for industrial glasses, T_liq tends to decrease with increasing strontium-to-alumina ratio. We find that cristobalite, mullite, and slawsonite are the dominant devitrification phases for the compositions with high SiO₂, SiO₂+Al₂O₃, and SrO contents, respectively. By comparison with the phase diagrams for CaO-Al₂O₃-SiO₂ and MgO-Al₂O₃-SiO₂ systems, we have found that for the highest [RO]/[Al₂O₃] ratios, T_liq exhibits a minimum value for R = Ca. Based on the phase diagram established here, the composition of glass materials, for example, for liquid crystal display substrates, belonging to the SrO-Al₂O₃-SiO₂ family may be designed with a more exact control of the glass-forming ability by avoiding the regions of high liquidus temperature.