Glass–ceramic sealant with different alkali contents made from natural and waste materials for SOFC

Abstract

In this study, three different mixtures including natural volcanic rock basalt, waste window glass, and Na2CO3 were developed as sealants for using solid oxide fuel cell (SOFC). The mixtures were melted at 1500 °C and cast into the water and graphite mold. The bulk glass parts were used in dilatometer analysis to determine the coefficient of thermal expansion. Glass cast into the water were milled and sized − 53 μm and, after certain pretreatments, coated on Crofer, AISI 409 and 439 stainless steel by dip-coating method. After the coating, heat treatment was performed at 850, 900, and 950 °C in order to ensure permanent bonding and sealing between glass–ceramic sealing and steel substrate. As a result of the heat treatment, the transformation from a glassy structure to a glass–ceramic structure occurred. The interface between glass–ceramic sealing and steel substrate, bonding, and sealing properties were examined by scanning electron microscopy and X-ray diffraction analysis to determine its suitability for SOFC. Furthermore, the activation energies for the precipitation of crystalline phases have been evaluated, and the crystallization mechanisms have been studied by DTA results. The crystallization kinetics was described in terms of the nucleation growth Johnson–Mehl–Avrami model. The results showed that surface crystallization became more effective instead of volume crystallization with increasing Na content.