Preparation, Characterization and Applications of Glass-Ceramic-to-Metal Seals

It is recognized that many factors need to be taken into consideration in the successful design and manufacture of high quality glass-ceramic-to-metal seals, particularly if an adequate component lifetime is to be achieved. During their preparation, undesirable reactions may occur between diffusing metal species and glass constituents, and these can lead to the formation of highly localized internal stresses, the presence of which can initiate failure of a seal either during manufacture or, more seriously, whilst in service due to the influence of static fatigue. In the case of high temperature systems, reactions under hostile operating conditions also need to be taken into consideration. A thorough understanding of the relevant glass-ceramic/metal interactions is therefore required in order that steps can be taken to avoid or at least minimize reactions within the interfacial region that may lead to localized modifications of the glass-ceramic microstructure. In this contribution, factors influencing the lifetime behaviour of glass-ceramic/metal systems are reviewed and discussed, with particular reference given to SOFC sealants and also to advanced electrical components developed at AWE including seals to stainless steels and Ni-based superalloys. Fundamental studies on bonding to pure Fe, Ni and Cr are also included.