Mica (KMg3AlSi3O10F2) based glass-ceramic composite sealant with thermal stability for SOFC application

Abstract

In this work, pre-synthesized fluorophlogopite mica (KMg3AlSi3O10F2) crystalline powder was added into potassium-magnesium boro-alumino-silicate (K2O–MgO–B2O3–Al2O3–SiO2) glass powder to synthesize glass-ceramic composite (GCC) sealant for solid oxide fuel cell (SOFC) application. The basic purpose was to report the influence of KMg3AlSi3O10F2 on microstructure, thermal expansion and volume shrinkage behavior of GCCs in terms of their SOFC sealing ability. The predominant crystalline phase was also identified as fluorophlogopite mica (KMg3AlSi3O10F2) by X-ray diffraction in the GCCs heat-treated at 900 °C (for 2 h) followed by 800 °C (for 10 h). Higher thermal expansion (10.65–10.81 × 10−6/K at 50–800 °C) compatible with SOFC components (metallic electrode/interconnect, ceramic electrolyte) was realized for 5–10 wt % mica containing GCC. However, it was found decreased linearly with adding further KMg3AlSi3O10F2 content (20–40 wt%) in the composites. GCC with 5 wt % of mica was stable under thermal cycling testing and no significant degradation was observed in thermal expansion till 10 cycles. Field emission scanning electron microscopy revealed the spherical shaped nanocrystallites morphology of those GCCs and that was ascribed for their compact bonding with SOFC components. Heating stage microscopy (HSM) ensured the lower softening temperature (752 ± 7 °C) for 5 wt % mica containing GCC which furthermore showed 11–13% volume shrinkage (to ensure the self-healing) in SOFC operating temperature. In a summary, the above factors confirmed the suitability of 5 wt % mica (KMg3AlSi3O10F2) containing K2O–MgO–B2O3–Al2O3–SiO2 system (GCC) for SOFC sealant application.