Liquidus temperatures of calcium magnesium alumosilicate glass-forming compositions determined via gradient furnace and from the melting peak by differential thermal analysis

• Liquidus temperatures of glasses were determined using a gradient furnace.
• Endpoint of melting peaks was also evaluated via differential thermal analysis.
• The values are comparable to each other and differ in most cases by less than 10 K.

The liquidus temperatures (TL) of good glass forming systems within the CaO–SiO2–MgO–Al2O3 system (CMAS) were evaluated. The determination of TL via differential thermal analysis (DTA) was studied in terms of reproducibility and was compared with results from the gradient furnace method. Seventeen different glass compositions within the CaO–SiO2–MgO–Al2O3 system were melted from technical raw materials. Since those glasses are reluctant to crystallize, a prior heat treatment was necessary to induce crystallization. The onset and the endpoint of the melting peaks of pre-crystallized materials were measured with a heating rate of 2 K/min and compared with the liquidus temperatures obtained by the gradient furnace method (following the ASTM standard procedure C 829-81 [1]). The endpoint temperatures of the melting peaks were closest to the results determined via the ASTM procedure. Most endpoint results via DTA differ by not more than 10 K compared to the liquidus temperatures. Because of the simultaneous crystallization pretreatment of many different compositions, the small amount of glass needed, and the speed of the DTA, this technique may be a valuable option to estimate the liquidus temperature of complex multicomponent glasses.