Chemical interaction between Crofer 22 APU and mica-based gaskets under simulated SOFC conditions

Mica gaskets and also composite gaskets containing compressive mica interlayers are under consideration as sealing materials in solid oxide fuel cells (SOFC). To study potential interactions between the interconnect steel Crofer22APU and the mineral phases vermiculite (exfoliated) (K,Mg,Fe)₃(Si,Al)₄O₁₀(OH)₂) and talc (Mg₃Si₄O₁₀(OH)₂), corrosion experiments were conducted in simulated SOFC conditions. The opposite walls of the gaskets were simultaneously exposed to air and wet H₂. A substantial increase in the thickness of the oxide layers formed by the interconnect steel is observed with specimen containing talc. The Cr₂O₃/(Cr,Mn)₃O₄ duplex layer normally formed on the Crofer is replaced by a thicker (factor of 5–10) layer of a complex microstructure that is assumed to contain Cr₂O₃, (Cr,Mn,Mg,Fe)₃O₄ and Fe₂O₃ phases. The modified microstructure is found in the entire air manifold, with an increased thickness up to a distance of 300 μm from the mica. It is proposed that magnesium is the critical component responsible for the accelerated oxide formation. A decomposition of talc is observed, which is discussed as the mechanism for the release of magnesium.