PNNL

Abstract

Sealing technology is currently considered a top priority task for planar solid oxide fuel cell stack development. Compressive mica seals are among the major candidates for sealing materials due to their thermal, chemical, and electrical properties. In this paper, a comprehensive study of mica seals will be presented. Two natural micas, Muscovite and Phlogopite, were investigated in either a monolithic single crystal sheet form or a paper form composed of discrete mica flakes. A “hybrid” mica seal, developed after identification of the major leak paths in compressive mica seals, demonstrated leak rates which were hundreds to thousands times lower than leak rates for conventional mica seals. The hybrid mica seals were further modified by infiltration with wetting materials; these “infiltrated” micas showed excellent thermal cycle stability with very low leak rates (10-3 sccm/cm). The micas were also subjected to studies to evaluate thermal stability in a reducing environment as well as the effect of compressive stresses on leak rates. In addition, long-term open circuit voltage measurements versus thermal cycling showed constant voltages over 1000 cycles. The comprehensive study clearly demonstrated the potential of compressive mica seals as sealing candidates for solid oxide fuel cells.