Kinetic evolution of ZrO2-modified silicate-based glass sealants during sintering and crystallization in planar solid oxide fuel cells

Abstract

Glass-composite sealants are critical for reliable high-temperature sealing in planar solid oxide fuel cells (SOFCs). This work investigates the influence of ZrO₂ on the sintering and crystallization kinetics of silicate-based glass-composite sealants. Dilatometry analysis reveals ZrO₂ promotes earlier densification and extends the sintering stage, with 200 nm particles exhibiting the strongest effect. Viscosity–temperature relationships, derived from differential scanning calorimetry (DSC) and the Vogel–Fulcher–Tammann model, indicate ZrO₂ increases viscosity by filling free volume, while excessive 50 nm ZrO₂ (>30 wt%) reduces viscosity due to nanoparticle agglomeration. Scanning electron microscopy (SEM) observations confirm that 200 nm ZrO₂ forms a rigid percolation framework, improving local sintering and promotes pore closure. X-ray diffraction analysis (XRD) indicates the incorporation of ZrO₂ does not alter the crystalline phases composition. Crystallization kinetics analysis shows ZrO₂ acts as heterogeneous nucleation centers, promoting diopside formation. For 2 µm and 50 nm ZrO₂, the crystallization activation energy increases with doping up to 30 wt% but decreases thereafter due to agglomeration-induced energy localization, whereas 200 nm ZrO₂ yields a continuous reduction, reflecting a balance between surface activity and dispersion stability. These findings provide insights for designing glass-composite sealants with optimized microstructures and improved performance in SOFC applications.