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.