Effect of the substitution of MgO with CaO on the structural and thermal properties of CaO-SrO-B2O3-SiO2 glass and glass-ceramics containing excess TiO2

Borosilicate glass-ceramics are promising materials for sealing applications in solid oxide fuel cells (SOFC). This work synthesized glass and glass-ceramics of the 18CaO-27SrO-10B2O3-45SiO2 composition containing 0, 2, and 4% TiO2 (mol) by conventional melting/quenching and characterized by structural and thermal techniques. The 11B-NMR and 29Si-NMR spectra indicate no significant change in the relative concentration of the tetrahedral (B-IV) and trigonal (B-III) boron populations of all glasses, with the presence of Q2, Q3, and Q4 species. The crystalline phases of CaSiO3, SrB2Si2O8, and Sr2SiO4 precipitated in all the compositions. The thermal expansion coefficients of the glasses and corresponding glass-ceramics are compatible with those of the other stack components, and their glass transition temperatures are below the operating temperature of SOFCs (R-.1 800-950 degrees C), thus can provide a hermetic seal. The sintering temperature of the T2 and T4 glasses is lower than 1000 degrees C, an essential characteristic for their application. However, the T4 glass exhibited even better sintering characteristics, making it a potential candidate for sealing.