Sintering, crystallization and foaming of La2O3·SrO·5B2O3 glass powders - effect of the holding temperature and the heating rate

The specific aim of this study was to highlight the influence of sintering temperature and heating rate on the densification process and the final structure of glass-ceramic samples. It was shown that zero water adsorption and minimum closed porosity of ~ 3% were obtained at heating rate of 2 °C/min and at about 1 h holding at 690 °C. The temperature increase accelerated intense foaming process that resulted in formation of total porosity of 35-45%. It was also demonstrated that the foaming depended on the heating rate: the higher the heating rate - the more intensive was the bloating. The observed foaming process was related to intensive crystallization and re-crystallization of La2O3·SrO·5B2O3 crystal phase. The phase formation processes entirely completed after 30-60 min at 730-740 °C with the formation of intriguing and unusual crystal structures.