PNNL

Abstract

One of the challenges in manufacturing solid-state electrochemical devices, such as planar solid oxide fuel cells (pSOFC), is in joining the ceramic and metallic components such that the resulting joint is rugged and stable under continuous high temperature operation in an oxidizing atmosphere. A well proven method of joining dissimilar materials is by brazing. Unfortunately many of the commercially available ceramic-to-metal braze alloys exhibit oxidation behavior which is unacceptable for potential use in a pSOFC application. As a result, glass sealing is currently favored for stack assembly. However, the maximum operating temperature that a glass joint may be exposed to is limited by the softening point of the glass. In addition, high temperature glasses with appropriately matching coefficients of thermal expansion typically display signs of devitrification within the first few hours of exposure at operating temperature. As they crystallize, the carefully engineered expansion properties of these seal materials change significantly, ultimately limiting the number of thermal cycles and the rate of cycling at which the joints are capable of surviving. Recently, we have developed an alternative braze composition which designed specifically for use in air. The results of this study to date will be discussed.