Influence of CaO/MgO ratio on the crystallization kinetics and interfacial compatibility with crofer 22APU and YSZ of strontium based alumino-borosilicate glasses for SOFC applications

Abstract

High temperature hermetic sealants are required for the stability and good efficiency of the solid oxide fuel cells (SOFCs). Glass and glass ceramics are promising sealant materials due to their desirable properties and flexible compositions. In the present study, the novel glass series (10 + x) CaO-(10 − x) MgO-10SrO-10B2O3-20Al2O3-40SiO2 (x = 0, 2.5, 5, 7.5) has been synthesized via melt quenching route. These glass/glass ceramics are characterized by X-ray diffraction to evaluate the amorphous nature and phase formation, respectively. The activation energy has been analyzed by using three different theoretical models – Kissinger Model, Moynihan Model and Augis and Benett Model. In addition to this, the characteristic glass temperatures and coefficient of thermal expansion (CTE) have been obtained from DTA, differential DTA (DDTA) and Dilatometry. Various stability parameters like Hruby parameter, Saad Parameter, fluctuation free volume (fg) and bulk thermal expansion coefficient (αf) are also calculated with varying CaO/MgO ratio (R). Furthermore, to analyze the stability of the glasses with varying CaO/MgO ratio over a broader range of temperature, k parameters i.e. kb (T) and kf (T) are also evaluated for different heating rates. The diffusion couples of glasses with pre oxidized Crofer 22APU and YSZ fabricated at 850 °C for 500 h have been characterized using scanning electron microscopy (SEM) and X-ray dot mapping to investigate the sealing characteristics with varying CaO/MgO ratio. The glass series 15 CaMg is very stable and promises to be a good sealant for solid oxide fuel cells.