Study of thermal behavior and crystallization kinetics of glass microspheres in the Y3Al5O12-Al2O3 system

Five types of glass microspheres with alumina and 40–80 mol.% Y₃Al₅O₁₂ were prepared using solgel Pechini and flame synthesis techniques. Glass thermal behavior was analyzed using DSC/TG, XRD and SEM, and the JMAK model was applied to study crystallization kinetics and determine prevailing mechanisms. All samples, except the one with 80 mol.% YAG, had two exothermic effects in their DSC curves. The first appeared between 937 and 950 °C, while the second was observed between 958 and 1102 °C. XRD analysis of crystallized microspheres confirmed the presence of YAG and various forms of alumina phases in the samples with lower YAG/higher Al₂O₃ content (40 and 50 mol.%). The sample with the highest YAG content showed the strongest tendency to crystallize in the kinetics study. The value of apparent activation energy (E_app) of this sample was 987.3 ± 13.0 kJ mol⁻¹. For the remaining samples, the values of E_app were higher and ranged from 1215.1 ± 10.6 to 1847.5 ± 9.3 kJ mol⁻¹, indicating the lowest ability of these compositions to crystallization. The growth of three-dimensional (3-D) YAG crystals was predominant in glasses with the highest (80 mol.%) YAG content. One-dimensional (1-D) growth of γ-Al₂O₃ crystals and 3-D growth of YAG crystals was predominant in glasses with the lowest (40 mol.%) YAG content.