Viscosity and Liquidus Temperature of Ternary Glasses Close to the Eutectic Composition in the CaO–Al₂O₃–SiO₂ System

Abstract

Thermal properties of ternary glass-forming systems within the known CaO-Al 2 O 3 -SiO 2 system were evaluated. Different glass compositions near the lowest eutectic composition (around a liquidus temperature of 1170°C) within the CaOAl 2 O 3 -SiO 2 system were melted from pure raw materials. The investigated target range of compositions in wt% was between 60.5 and 63.5 SiO 2 , 13.1 and 16.1 Al 2 O 3 , and 21.4 and 25.4 CaO. The chemical compositions, the glass transition temperatures, and the temperatures attributed to viscosities of 10³ dPa*s were determined experimentally. It was of special interest to obtain information of all these properties of the glasses and the effect of small composition changes hereon. The liquidus temperature changed less than expected for a composition close to the eutectic composition. Temperatures at a viscosity of 10³ dPa*s varied between 1263 and 1363°C AE 6°C. A liquidus temperature of 1157°C AE 7°C (with a confidence interval of 95%) of the eutectic composition was found. The results reported here may be useful for understanding and improvement of the modeling within the CaO-Al 2 O 3 -SiO 2 glass system.

Electronic polarizability in silicate glasses by comparison of experimental and theoretical optical basicities

“…The structure and properties of CAS glasses, in particular the coordination state of Al 3+ ions, has been studied extensively, and it is well known that Al 3+ ions have different oxygen coordination states depending on the [Al 2 O 3 ]/[CaO] molar ratio and SiO 2 content 70–78 . The following structure model has been widely accepted: In the glasses with [Al 2 O 3 ]/[CaO] = 1 (tectosilicate) such as 20CaO–20Al 2 O 3 –60SiO 2 , the fully polymerized network structure consisting of SiO 4 and AlO 4 tetrahedral units is created without forming any NBOs, and CaO locates to compensate the negative charge of (AlO 4 ) − units.…”