Glass-forming ability, sinterability and thermal properties in the systems RO–BaO–SiO2 (R = Mg, Zn)

Glass-ceramics in the systems RO–BaO–SiO2 (R = Mg, Zn) have good thermal properties for sealing materials on planar-type solid oxide fuel cells (SOFC) at high and intermediate temperatures. In this work, the glass forming regions in the two systems have been determined. Composition lines with different BaO/RO ratios have been defined varying the silica content. The dilatometric properties of the melted glasses (coefficient of thermal expansion, glass transition temperature and softening temperature) have been measured to identify the glasses that best fulfill the cell requirements, such as a thermal expansion coefficient in the range (8.5–12) × 10−6 K−1. Since the sealing process is carried out employing paste technology during the heating and working schedule of the cell, it is important to study the interaction between sintering and crystallization to make dense materials with an adequate microstructure. The sintering and crystallization kinetics have been characterized for some selected glass compositions by using hot-stage microscopy (HSM) and differential thermal analysis (DTA). A new parameter SC = TX − TMS which takes into account the onset crystallization temperature (TX), temperature of maximum shrinkage (TMS) is proposed as an empirical method to evaluate the ability of glass sintering of the studied compositions and indicate good materials for glass-ceramic SOFC products.