Effect of electric load and dual atmosphere on the properties of an alkali containing diopside-based glass sealant for solid oxide cells

A new alkali-containing diopside based glass-ceramic sealant for solid oxide cells was synthesized, characterized and tested. The composition was designed to match the coefficient of thermal expansion (CTE) of Crofer22APU interconnect. The sealant has a glass transition temperature of 600 °C, a crystallization peak temperature of 850 °C and a maximum shrinkage temperature of 700 °C, thus suggesting effective densification prior to crystallization. The CTE of the glass-ceramic is 11.5 10−6 K−1, a value which is compatible with the CTE for Crofer22APU stainless steel. Crofer22APU/glass-ceramic/Crofer22APU joined samples were tested in simulated real-life operating conditions at 800 °C in dual atmosphere under an applied voltage, monitoring the electrical resistivity. The effect of two different applied voltages (0.7 V and 1.3 V) was evaluated. A voltage of 1.3 V led to a rapid decrease in the electrical resistivity during the test; such a drop was due to the formation of Cr2O3 “bridges” that connected the two Crofer22APU plates separated by the sealant. There was no decrease in the resistivity when a voltage of 0.7 V was applied. Instead, resistivity value remained stable at around 105 Ω cm for the 100 h test duration. The degradation mechanisms, due to both the alkali content and the applied voltage, are investigated and discussed.