Accelerated devitrification of a strontiumlanthanumaluminoborosilicate based intermediate temperature solid oxide fuel cell glass sealant and its effect on thermophysical behaviour of the glass ceramics

A strontiumlanthanumaluminoborosilicate based intermediate temperature solid oxide fuel cell (IT-SOFC) glass sealant has been investigated for isothermal devitrification under accelerated conditions. Sintering of the glass up to 100 h at 1000 °C, results in the formation of two crystalline phases evidenced by X-ray diffraction (XRD) analysis. Hexacelsian phase evolves from the initial hours of sintering; however, lanthanum silicate phase appears at longer hours of sintering. Quantitative XRD of the glass ceramics reveals that hexacelsian occupies majority of the crystalline phases and lanthanum silicate is occupying minor quantity. Formation of crystalline phases has been reconfirmed by microstructure analysis of glass ceramics through Scanning Electron Microscopy (SEM) and elemental analysis of phases by energy dispersive spectroscopy (SEM-EDS). Crystalline phases in the glass ceramics have been quantified by analysis of SEM images through Imagepro plus software. At different stages of sintering, CTE of the glass ceramics has been measured by dilatometer. Correlation of CTE with crystalline phases in the glass ceramics indicates that with formation of hexacelsian phase CTE of the glass ceramics increases, however, formation of lanthanum silicate phase reduces the CTE of the glass ceramics. Phase property correlation indicates that after 100 h of accelerated devitrification at 1000 °C, the glass ceramics attains phase stability therefore the CTE stabilizes and the value remains well within the requirement limit of SOFC sealant.