Novel Refractory Alkaline Earth Silicate Sealing Glasses for Planar Solid Oxide Fuel Cells

Abstract

Refractory" Sr-Ca-Y-B-Si sealing glasses were developed for solid oxide fuel cells ͑SOFCs͒. 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 ͑Ͼ950°C͒ are higher than traditional sealing temperatures for intermediate-temperature SOFC stacks ͑Ͻ850°C͒. 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-1͒ was used to seal anode-supported electrolyte membranes to metallic interconnects at temperatures ranging from 900 to 1050°C in air. Microstructure analysis revealed the presence of SrCrO 4 near the glass-ceramic/metal interface. The effect of composition on thermal properties and a possible reaction mechanism for the chromate formation are discussed.

Tuning the thermal properties of borosilicate glass ceramic seals for solid oxide fuel cells

“…Borosilicate and aluminoborosilicate [4][5][6][7][8][9][10][11] seals, however concerns about boron volatility at elevated temperatures [12][13][14][15] restricts their wider applications as sealing materials. In general, the borate content in a glass-ceramic sealant is often limited to 20 mole% or less [4][5][6][7][8][9][10][11]16,17 to reach a balance between the desired sealing properties and tolerable volatility.…”

Synthesis and long-term test of borosilicate-based sealing glass for solid oxide fuel cells

“…In borosilicate glasses B 2 O 3 /SiO 2 ratio plays a crucial role in tailoring their thermal properties, namely, glass transition, glass softening, and CTE. [23][24][25][26][27][28][29] Generally, increasing the B 2 O 3 /SiO 2 ratio results in the reduction of T g , T s , and viscosity. 25,28 This phenomenon is due to "boron anomaly effect" which means the conversion of three-coordinated boron to four-coordinated boron.…”

Compliant alkali silicate sealing glass for solid oxide fuel cell applications: The effect of protective alumina coating on electrical stability in dual environment

“…The metals were tested either in the asreceived state or coated with Al 2 O 3 . For SOFC application, the ferritic stainless steel AISI441 requires a protective coating to block the Cr diffusion, which can cause cathode poisoning and seal degradation by forming chromates with very high CTEs if sealing glass contains alkaline earths (e.g., Ba and Sr) [9,19,32]. In this study we have adopted a novel reactive air aluminizing coating process involving ultrasonic spraying of AISI441 substrates with a mixture of Al powders in a binder solution, followed by drying and oxidizing at 1000 C for 1 h in air [33].…”