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

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 K_SP 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 Ca^{2 +}. For example, when 10 mol% of MgO is substituted for CaO, K_SP 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.