Performance evaluation for Ag and Au nanoparticle containing K2O-MgO-B2O3-Al2O3-SiO2-F glass sealants for SOFC application

The present work illustrates the effect of Ag and Au nanoparticle addition on the density, microstructure, phase formation and thermal performance of K₂O-MgO-B₂O₃-Al₂O₃-SiO₂-F glass-ceramics considered as a potential sealant material for solid oxide fuel cell (SOFC) applications. Addition of 0.2 wt.% Ag and Au nanoparticles caused a steep increase in the density of the base glasses in comparison to the glass containing an equivalent amount (0.2 wt%) of Cu nanoparticle. The glass-ceramics were prepared from the base glasses by controlled heat treatment at 900°C, a temperature relevant for SOFC operation. They were multicrystalline having fluorophlogopite (KMg₃AlSi₃O₁₀F₂) as the predominant crystal phase and norbergite (Mg₂SiO₄.MgF₂) and enstatite (MgSiO₃) as additional phases. Fluorophlogopite crystals form in both plate-like and rod-like morphologies within the glass matrix in the microstructure of the glass-ceramics. The size of the plate-shaped fluorophlogopite crystals increases for Ag nanoparticles containing glass-ceramics in comparison to either Cu or Au nanoparticles containing glass-ceramics. The density of the Ag and Au nanoparticle glass-ceramics are also considerably higher due to the formation of a compact interlocked crystalline microstructures. The Au nanoparticle containing glass-ceramics is characterized by a large thermal expansion (coefficient of thermal expansion, CTE= 11.29 × 10⁻⁶/K in 50–800°C range) which is comparable to other SOFC components. This glass/glass-ceramics sealant also possess maximum volume shrinkage in the range of 30–900°C as well as nearly constant CTE without any considerable decrease up to 10 cycles of SOFC operations making it suitable for SOFC sealant applications.