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Manufacturing and microstructure of porous metal supports for a Solid Oxide Fuel Cell

  • : Harald Gschiel1, Herbert Danninger1, Christian Gierl-Mayer1
  • : 1Vienna University of Technology
  • : PDF Download
  • : 2014

Abstract

The operating temperature of Solid Oxide Fuel Cells (SOFC) is typically between 800 and 1000°C, and fuel (or pure H2) and air (or pure O2) are fed as gases. The oxygen molecules in the air take up electrons and move as negatively charged ions through the electrolyte, where they react with hydrogen to form water (vapor). The SOFC is characterized by a very high electrical efficiency and the highest efficiency in combined heat and power units, but there are still problems concerning the longtime stability of the SOFC. In order to have mechanical stability in a fuel cell, the cell can be supported by a so-called porous metal support. On top of this porous metal support thin layers of anode, electrolyte and cathode are then deposited. For providing the electrodes with gases, the structure of the metal support needs to be highly porous but on the other hand mechanically stable. This paper is focused on processing these porous metal supports by different powder metallurgical techniques such as the press- and sinter route or gravity sintering; also metal injection molding and powder extrusion molding have been tried. If for example “co-sintering” – i.e. a combined sintering of the metal support and the ceramic layers- is desired, then a very critical parameter for the support is the shrinkage of the sample during sintering. For some samples the desired shrinkage of 15 – 20 % could be obtained as defined by the shrinkage of the ceramic functional layers. Also special metallographic techniques have been tried in order to compare the porosity (as well as the distribution of the pores) of these materials. Due to their high porosity, careful impregnation had to be applied before metallographic preparation and investigation by optical microscopy. The most promising manufacturing routes were found to be gravity sintering (about 50% porosity) and MIM (20 – 28% porosity): in both cases the pores are homogeneously distributed, and only slight agglomeration of pores can be seen.
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