A Ba‐free sealing glass with a high coefficient of thermal expansion and excellent interface stability optimized for SOFC/SOEC stack applications

Abstract

A new glass-ceramic composition containing Si, Mg, Ca, Na, Al, Zr, and B is presented here as sealant for planar SOFCs/SOECs, with the aim of joining the metallic interconnect (Crofer22APU) to the solid oxide cell (YSZ electrolyte or CGO barrier layer). Characteristic temperature, thermo-mechanical properties, and compositional variations are reviewed and discussed by thermal analyses and in situ XRD, in order to design and optimize the sealing profile and reduce the residual porosity. The glass after heat treatment partially devitrifies into augite and nepheline with residual glass phase of around 64.3%; after crystallization the glass-ceramic sealant has a coefficient of thermal expansion of 12.8 9 10 À6 K À1 and it is compliant with the other materials typically used for stack components.This work shows that the developed glass-ceramic can successfully join the ceramic cell with the Crofer22APU (preoxidized and alumina coating), proven by tests on small and large-scale samples. No signs of unwanted reactions at the glass-metal and the glass-cell interface are observed and sufficient gas tightness is achieved. K E Y W O R D Sglass-ceramics, solid oxide fuel cell, synthesis, thermal analysis

Enhancing the Robustness of Brittle Solid Oxide Cell Stack Components

“…The sealing material applied was an alumina-silicate-based glass (17). The powder used was prepared in-house at DTU Energy, (please see Ref.…”

“…The powder used was prepared in-house at DTU Energy, (please see Ref. (17) for further details on the preparation). The powders were screen printed on the coated interconnect "bars" (shorter ones) subsequently sandwiched with the full length pieces (60 mm long) , using the same procedure as for the contact layer.…”

“…During heat treatment the glass densifies, crystalizes and bonds with the adjacent surfaces (14). The samples are heat treated with an optimized heating profile (17), which corresponds to the one used for the heat treatment of the contact layers.…”

“…Here we show how the combination of an alumina based coating and a recently developed glass ceramic (15) can increase the fracture energy of the glass ceramic joint by more than a factor of 5, as compared to the adherence between the sealing and a preoxidized or Mn,Co-oxide (MCO) coated steel interconnect.…”

Improving the interface adherence at sealings in solid oxide cell stacks

“…From these perspectives, a promising new sealant was recently developed and used for this work: the V11 glass-ceramic 32 . The V11 glass-ceramic fulfils several of the requirements listed above.…”