Sintering kinetics and prediction of viscosity of BaO–CaO–Al2O3–SiO2 glass using a heating stage microscope

A systematic study was conducted to investigate the sintering kinetics of BaO–CaO–Al2O3–SiO2 (BCAS) glass using a heating stage microscope. The analysis focused on densification behaviour, densification rate as a function of temperature and evaluation of the activation energy. Experimental results reveal that significant densification occurs within the temperature range of 800–900°C, indicating that pore elimination and shrinkage are most effective in this regime due to viscous flow mechanisms. The densification rate increases sharply up to 860–885°C, depending on the heating rate (5–40°C/min), followed by a gradual decline at higher temperatures. Activation energy for densification, estimated using Chen's equation based on fixed levels of shrinkage, ranges between approximately 620 and 670 kJ/mol. It is observed that the activation energy increases with the extent of shrinkage, attributed to the increasingly dense glass structure and the transition of porosity from open to closed and isolated state. Conventional sintering experiments further corroborate the densification trends. The viscosity–temperature relationship was predicted by fitting data obtained from the heating stage microscope and mechanical dilatometer to the Vogel–Fulcher–Tammann (VFT) equation.