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 (Tg) and softening temperatures (Ts), while the coefficient of thermal expansion (CTE) decreased. Glasses with TiO2 content exceeding 24 wt% exhibited crystallization at temperatures over 800 degrees 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 degrees C.