Effect of TiO₂ on crystallization and sealing behavior of Na₂O-K₂O-TiO₂-SiO₂-Al₂O₃-ZnO glass sealant for PCFCs

TiO₂-containing silicate glasses, composed of Na₂O-K₂O-TiO₂-SiO₂-Al₂O₃-ZnO, were developed as sealants for protonic ceramic fuel cells. The TiO₂ content was varied to investigate its effect on the thermal properties, structure, crystallization, and wettability of the glasses. An increase in TiO₂ content resulted in higher glass transition (T_g) and softening temperatures (T_s), while the coefficient of thermal expansion (CTE) decreased. Glasses with TiO₂ content exceeding 24 wt% exhibited crystallization at temperatures over 800 °C as confirmed by X-ray diffraction and Raman spectroscopy. X-ray photoelectron spectroscopy analysis revealed that higher TiO₂ content increases the concentration of [TiO₆] units and non-bridging oxygen atoms in the glass, which likely contributes to the observed structural modifications. Based on thermal properties and wettability, the optimal TiO₂ content range for these glasses was determined to be 20–24 wt%, while the sealing temperature should be below 800 °C.