Structure, sintering, and crystallization kinetics of alkaline-earth aluminosilicate glass-ceramic sealants for solid oxide fuel cells

The most common approach to seal an electrolyte or a ceramic anode with a metallic interconnect in solid oxide fuel cells of planar configuration (pSOFC), in order to achieve a hermetic and stable cell, is to use rigid glass or glass-ceramic (GC) seals. The properties of these sealants can be tailored specifically for use in SOFCs through variation of the glass composition. In the present manuscript, we aim to study the structure, sintering behavior, and crystallization kinetics of a new series of aluminosilicate GC sealants derived from substitution via scheme 0.1(Ca²⁺+Si⁴⁺)↔0. 1(La³⁺+Al³⁺) in a pure CaMgSi₂O₆ (diopside) system. The substitution of BaO for CaO and the addition of fixed amounts of B₂O₃, Cr₂O₃, and NiO were attempted in order to achieve desirable traits that qualify the investigated GCs for sealing application in pSOFCs. The investigated glasses showed a steady increase in density, coefficient of thermal expansion, and molar volume with addition of Cr₂O₃ and increasing BaO contents while no significant variation in glass transition temperature (T_g) was observed. Sintering and crystallization behavior of the glasses were investigated using hot-stage microscopy and differential thermal analysis, respectively. The microstructure and the properties of GCs were investigated under nonisothermal heat treatment conditions (800° and 850°C; 1 h). Finally, Rietveld-R.I.R. technique was used to quantify the amount of crystalline and amorphous content in the GCs. It was observed that while addition of Cr₂O₃ improved the sinterability of glass-powder compacts and decreased the amorphous content in the resultant GCs, substitution of BaO for CaO led to an increase in amorphous content in the GCs.