Effect of divalent cations and SiO2 on the crystallization behavior of calcium aluminate glasses

• Calcium aluminate glasses are of interest but suffer from poor glass stability (GS).
• We study the role of composition on isothermal and dynamic crystallization behaviors.
• Partial substitution of Ca2 + for R2 + with large size difference improves GS.
• Addition of SiO2 improves GS, but only up to a certain concentration (~ 10 mol%).

Calcium aluminate glasses are of technological interest due to their excellent optical and mechanical properties. However, the glass-forming ability (GFA) and glass stability (GS) of these systems are poor, with the best binary CaO–Al2O3 glass-forming composition occurring at the eutectic point (64CaO–36Al2O3, in mol%). In this work, we have investigated the crystallization processes of CaO–Al2O3 based glasses with different additives (SiO2, MgO, SrO, BaO, and ZnO) during dynamic and isothermal heating. It is found from X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses that both the dynamic and isothermal glass stabilities increase with the initial addition of SiO2. The glass stability parameter KSP increases from 3.4 to 11.0 K upon the addition of 10 mol% to the eutectic CaO–Al2O3 composition, but then decreases upon further addition of SiO2. Partial substitution of CaO for different divalent cation oxides also increases the GS, with the largest impact found for the cations with the greatest difference in ionic radius compared to Ca2 +. For example, when 10 mol% of MgO is substituted for CaO, KSP increases from 3.4 to 6.9 K. These results are useful for designing new CaO–Al2O3 based glasses that can be produced on an industrial scale.