Study of glasses/glass-ceramics in the SrO–ZnO–SiO2 system as high temperature sealant for SOFC applications

Glasses having composition (in wt.%) 51SrO-9ZnO-(40−x)SiO2 (SZS), where x represents the additives like B2O3, Al2O3, V2O5, and Cr2O3, were prepared by melt-quench method and transformed into glass-ceramics by controlled crystallization based on differential thermal analysis (DTA) data. Glasses and glass-ceramics were characterized using dilatometry, X-ray diffraction (XRD), microhardness, and Raman spectroscopy. XRD revealed that glass-ceramics are composed of mainly Sr2ZnSi2O7 and SrSiO3 crystalline phases along with residual glassy phase. Raman spectroscopy showed that main constitutes of the glass network are the Q1 and Q2 silicate structural units. With the addition of B2O3 and other additives silicate glass network depolymerizes and concentration of Q1 structural units increases at the expense of Q2 units. Formation of phases during crystallization depends on the presence of different silicate structural units in the glass matrix. B2O3 goes into the glass network as triangular (BO3) borate structural units and at higher concentration of B2O3, only a part of the B2O3 forms tetragonal (BO4) structural units. Investigated glasses and glass-ceramics have thermal expansion coefficient (TEC) in the range of 105–120 × 10−7/°C which matches with TEC of other cell components. B2O3 containing SZS glasses show good adhesion/bonding with YSZ and Crofer 22 APU. Elemental line scans indicate that interdiffusion of Fe, Cr and Si across interface is responsible for good bonding with Crofer 22 APU and interdiffusion of Sr, Si, Y and Zr is responsible for good bonding with YSZ.