Crystallization behavior and microstructure of ZnO–Al2O3–SiO2–B2O3-based glass-ceramics using MgO and CaO modifiers

The role of glass-structure modifiers was examined by analyzing the crystallization behavior and microstructure of a ZnO–Al₂O₃–SiO₂–B₂O₃ glass system with MgO and CaO substitutions. Differential thermal analysis indicated that the crystallization temperature (T_p) increased with MgO substitution but decreased with CaO substitution. X-ray diffraction analysis demonstrated that increasing the amounts of MgO and CaO led to the formation of a gahnite crystalline phase after treatment at 1200 °C. Nano-sized crystals were observed when the specimen was heat-treated at 1000 °C, and dendrite crystals were observed on the surface when treated at 1200 °C. Non-isothermal analysis revealed that the substitution with MgO and CaO resulted in surface crystallization behaviors with high activation energies (271.72 and 301.75 k·J·mol^-1) and low Avrami constants (2.05 and 1.67). Micro-Vickers hardness showed maximum values of 7.65 and 6.86 GPa when MgO and CaO were substituted, respectively.