Sintering behavior of lanthanide-containing glass-ceramic sealants for solid oxide fuel cells

Abstract

This article reports on the influence of different lanthanides (La, Nd, Gd and Yb) on sintering behavior of alkaline-earth aluminosilicate glass-ceramic sealants for their application in solid oxide fuel cells (SOFCs). All the glasses have been prepared by the melt–quench technique. The in situ follow up of sintering behavior of glass powders has been done by a high temperature-environmental scanning electron microscope (HT-ESEM) and a hot-stage microscope (HSM) while the crystalline phase evolution and assemblage have been analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the glass compositions exhibit a glass-in-glass phase separation followed by two stage sintering resulting in well sintered glass powder compacts after heat treatment at 850 °C for 1 h. Diopside (CaMgSi₂O₆) based phases constituted the major crystalline part in glass-ceramics followed by some minor phases. The increase in lanthanide content in glasses suppressed their tendency towards devitrification, thus resulting in glass-ceramics with a high amount of residual glassy phase (50–96 wt%) which is expected to facilitate their self-healing behavior during SOFC operation. The electrical conductivity of the investigated glass-ceramics varied between (1.19 and 7.33) × 10⁻⁷ S cm⁻¹ (750–800 °C) while the coefficient of thermal expansion (CTE) varied between (9.4 and 11.2) × 10⁻⁶ K⁻¹ (200–700 °C). Further experimentation with respect to the long term thermal and chemical stability of residual glassy phase under SOFC operation conditions along with high temperature viscosity measurements will be required in order to elucidate the potential of these glass-ceramics as self-healing sealants.