Material Degradation during Isothermal Aging and Thermal Cycling of Hybrid Mica Seal with Ag Interlayer under SOFC Exposure Conditions

Abstract

Hybrid phlogopite mica seals with silver interlayers were evaluated in terms of material degradation in a combined isothermal aging and thermal cycling test. The hybrid mica was composed of a phlogopite mica paper sandwiched between two foils. The hybrid micas were first aged at for in a low hydrogen fuel , followed by short-term thermal cycling between and . The combined test was repeated three times for a total of aging at and 119 thermal cycles. The results of high-temperature leak rates showed very good thermal stability and thermal cycle stability with leak rates of . The hybrid mica was also tested in a high-water-content fuel and demonstrated similar leakage during the isothermal aging and the subsequent thermal cycles. Postmortem analyses showed no extensive reaction of Ag with phlogopite mica as well as the mica degradations. The issues of volatility of Ag and mica in the solid oxide fuel cell (SOFC) environments were discussed. Simple models were simulated to estimate the effect of leakage on the open-circuit voltage and the total fuel loss at various SOFC stack sizes. The results showed very minute fuel loss for the current hybrid micas and demonstrated it to be a good candidate for SOFC sealing.