Novel refractory alkaline earth silicate sealing glasses for planar solid oxide fuel cells

Refractory Sr-Ca-Y-B-Si sealing glasses were developed for solid oxide fuel cells (SOFCs). The objective was to develop sealing glasses with appropriate thermal properties and minimal interfacial reactions with SOFC stack components, particularly ceramic electrolytes and metallic interconnects. The new glasses are described as refractory because their sealing temperatures (>950 degrees C) are higher than traditional sealing temperatures for intermediate-temperature SOFC stacks (< 850 degrees C). Six glasses were formulated and made by a conventional glass-making process. The glasses exhibited rapid crystallization kinetics during intermediate temperature heat-treatments. Their thermal properties were characterized in both the initial glassy state and the final crystallized state. Candidate glasses were also aged for 1000-2000 h at elevated temperatures. Thermal expansion measurements showed minimal change after aging. One candidate glass (YSO-1) was used to seal anode-supported electrolyte membranes to metallic interconnects at temperatures ranging from 900 to 1050 degrees C in air. Microstructure analysis revealed the presence of SrCrO4 near the glass-ceramic/metal interface. The effect of composition on thermal properties and a possible reaction mechanism for the chromate formation are discussed. (C) 2007 The Electrochemical Society.