Effects of lanthanum oxide on the properties of barium-free alkaline-earth borosilicate sealant glass

We have explored the effects of lanthanum oxide (La2O3) on the properties of barium-free SrO-CaO-ZnO-B2O3-SiO2 glass system varying its content from 0 to 6 mol%. The coefficient of thermal expansion and glass transition temperature of the glasses are found to be in the ranges 10.6-10.8 × 10− 6/K (50-600 °C) and 650-690 °C respectively. Differential scanning calorimetric studies revealed an increase in crystallization peak temperature and thermal stability of the glasses up to 4 mol% and then decrease on further addition. A monotonic increase in characteristic shrinkage temperature of glass powder compact is observed on addition of La2O3 as revealed in the heating stage microscopic study. X-ray diffraction studies revealed reduced crystallization peak intensity in La2O3 added glasses. Fourier transformed infrared spectra disclosed that the addition of La2O3 stabilized the glass structure by reducing the number of non-bridging oxygens. Vickers micro hardness of the glasses varied in the range 2.6-5.6 GPa. Scanning electron microscopy revealed the formation of particulate nature of microstructures in parent glass which is not observed in the La2O3 added glasses. Activation energy of crystallization has increased from 331 to 361 kJ/mol determined by Kissinger and Augis-Bennett models. Above properties of these glasses clearly advocate their applicability as solid oxide fuel cell sealants.