Glass-Ceramic Sealant Reinforcementfor High-Temperature Applications

摘要

In the development of solid oxide fuel cells, the components most in need ofimprovement are still the sealants. Over the last decade, several types of sealants havebeen investigated for use under high temperatures, such as compressive, compliant,and rigidly bonded seals. Of these three types, rigidly bonded glass-ceramic seals arethe most promising. Their properties can be tailored to match the requirements of SOFCsealants. These include the coefficient of thermal expansion, joining temperature,crystallization behavior, electrical insulation, and gas-tightness. Nevertheless, in thepast, the developed sealant compositions failed to demonstrate sufficient mechanicalstrength. This property is extremely important to avoid catastrophic failure of the rigidseals during SOFC operation. Additionally, there is a lack of standardized methods tocharacterize the mechanical strength of joined components in the research community.This makes it difficult to rely on the results of the state of art measurements, toreproduce them, and indeed to compare them.In order to improve the mechanical strength of glass-ceramic sealants, this workproposes reinforcing the glass-ceramic sealant with different metallic and ceramicparticles. A new concept of laminate sealant, known as a multilayer design, wasdeveloped in an attempt to combine the properties of two types of composites in onejoint. In addition, three possible methods for mechanical strength characterization weredeveloped.The reinforcement concept is mainly based on adding fillers to the glass matrixnamed “87”, which is a composition from the system BaO-CaO-SiO2. The chosen fillerswere metallic particles including nickel (Ni), nickel-chromium (NiCr) (80-20), copper(Cu), and silver (Ag), as well as ceramic fillers such as gadolinium-doped ceria (CGO)particles and yttrium-stabilized zirconia (YSZ) particles or fibers. These materials weretested in different weight concentrations in the glass matrix to form the composites. Thisapproach showed that adding filler materials (metallic or ceramic) improved themechanical strength values. The multilayer design was also proven to be effective incombining the properties of two different composite layers in one joint. Electricallyinsulating samples with sufficient mechanical strength were produced with single layersof reinforced sealant as well as with the multilayer approach