Influence of nucleating agents on the chemical interaction of MgO-Al2O3-SiO2-B2O3 glass sealants with components of SOFCs

The chemical interactions between different MgO-SiO2-Al2O3-B2O3 base glass sealants and components of solid oxide fuel cells (SOFCs) were investigated. The SOFC materials considered are ZrO2 stabilized with 8 mol % Y2O3 (as electrolyte and part of the anode), Ni (as part of the anode), and the oxide-dispersion-strengthened (ODS) alloy Cr5Fe1Y(2)O(3) (as interconnect). Glass compositions with no nucleating agent and with ZrO2, Cr2O3, or Ni as the nucleating agents were prepared. Powder mixtures of these sealants with the mentioned SOFC materials, as well as the sealant/material interfaces, were characterized by X-ray diffraction and scanning electron microscopy and energy dispersive spectroscopy in order to determine possible reaction phases and the diffusion behavior of different cations. Formation of cordierite and cristobalite as detrimental phases was detected in many of the mixtures. The formation of these phases can be suppressed if Cr2O3 or Ni is added to the glass as the nucleating agent. The most interesting feature of these results is the absence of the cordierite phase for all reaction powder mixtures if Cr2O3 is used as the nucleating agent. The sealants with Cr2O3 and Ni as nucleating agents formed a reaction zone at the interface with ODS, rich in Cr and Mg. A parabolic reaction rate equation describing the growth of the reaction zone thickness, the diffusion coefficient of chromium, and rate constants was evaluated. (C) 2004 The Electrochemical Society.