PNNL

Abstract

In most planar SOFC stacks operating at an intermediate temperature (700-800 degrees C), the interconnect is typically made from a ferritic stainless steel and has to be hermitically sealed to its adjacent components, such as the ceramic PEN (Positive electrode-Electrolyte-Negative electrode) by a sealing glass. To large extent the seal performance relies on the chemical compatibility of the sealing glass with the metallic interconnect. In this study, a barium-calcium-aluminosilicate (BCAS) based glass-ceramic, specifically developed as a sealant in SOFC stacks, and a ferritic stainless steel (446) were chosen as examples to investigate the chemical interactions or corrosions at the sealing glass interface with the ferritic stainless steels. Evaluation of the interfaces of coupon joints indicated that interactions between the BCAS glass-ceramic and the ferritic stainless steel depended on the exposure conditions. At the edges of joints, where oxygen or air was accessible, the interaction often led to the formation of BaCrO4, while in the interior of the joints, chromium or chromia dissolved into the glass to form a thin layer of chromium rich solid solution. It was also found that, in the interior of the joints, the interaction often resulted in the formation of pores aligning along the interface. The pore formation along the interface of sealing glass and ferritic stainless steel however could be avoided through a pre-heat treatment of the ferriitc stainless steel.