Evaluation of the suitability of various glass sealant-alloy combinations under SOFC stack conditions

The suitability of combinations of sealing material and alloy under simulated SOFC stack conditions has been evaluated by a novel test method. This method is based on test items of two metallic sheets, joined together with a glass or glass-ceramic sealant. The outer side of the sample is exposed to ambient atmosphere, whereas the inner side can be exposed to different gas compositions. The whole set-up is placed in a furnace. Optionally, an external voltage can be applied across the sheets. Experiments revealed that the chemical and electrical behaviour of the sandwich samples strongly depends on the experimental conditions. Under oxidative conditions (air) no undesirable interactions take place, which detrimentally affect the electrical properties, indicating satisfactory suitability of the tested sealant-alloy combinations. However, different results were obtained when SOFC conditions were simulated by the use of a dual environment including air on the outer part and hydrogen on the inner part of the sample. Under these test conditions, and depending on the chemical composition of the alloy, a strong decrease of the resistance, measured between the two metallic sheets, was observed, due to excessive chemical reactions between the sealant, the alloy, and the surrounding gas atmosphere. Well-chosen test conditions can more closely simulate real stack conditions, and as a result, the electrical, physical, and chemical behaviour of investigated samples is closer to that of materials applied in real SOFC stacks. Therefore, before performing model experiments simulating complete SOFC devices, it is recommended that a critical analysis should be made of the experimental conditions as present in SOFC devices. (C) 2005 Springer Science + Business Media, Inc.