Crystallization kinetics of binary La2O3-Al2O3 glass

Abstract

The ALaE glass with eutectic composition (76.2 mol% Al2O3, 23.8 mol% La2O3) and the ALaP glass with LaAlO3 (lanthanum-aluminium perovskite) composition (50 mol% Al2O3, 50 mol% La2O3) were prepared by combination of sol-gel Pechini method and flame synthesis in the form of glass microspheres (diameter ≈ 10 μm). The prepared glasses were characterized by OM, SEM, XRD and DSC. The prepared samples contained only completely re-melted spherical particles. However, more detailed study by SEM revealed small fraction of crystalline microspheres. Traces of crystalline LaAlO3 were detected in X-ray powder diffraction patterns of both glasses. DSC analysis in the temperature range 35–1200 °C with heating rates 2, 4, 6, 8 and 10 °C/min was performed in nitrogen atmosphere to study the thermal behaviour and crystallization kinetics of prepared glasses. In the DSC curve of the eutectic ALaE glass recorded at 10 °C/min two exothermic effects were observed at 920 and 936°. Only one exothermic effect at 868 °C was present in the DSC curve of the ALaP sample with perovskite composition. The high-temperature X-ray powder diffraction analysis was carried out in the temperature interval 25–1200 °C. For both compositions formation of LaAlO3 as the main crystalline phase was observed in the whole measured temperature range. In order to study the crystallization kinetics, the DSC curves were transformed into dependence of fractional extent of crystallization, α on temperature. The JMAK model was found suitable for description of crystallization kinetics of both studied systems. The kinetic parameters (A, Eapp and m) were calculated for this model and crystallization mechanisms have been proposed.