Microstructural effects of the reduction step in reactive consolidation of manganese cobaltite coatings on Crofer 22 APU

Abstract

The microstructural effects of the reduction step in the reactive consolidation of slurry processed Mn_1·5Co_1·5O₄ coated Crofer 22 APU were studied using cross-sectional scanning and transmission electron microscopies. Alloy samples were coated with a Mn_1·5Co_1·5O₄ slurry and then reduced in moist H₂ based forming gas at 850°C for 4 h. The reduced coating contained particles of MnO with the NaCl structure and Co with the face centred cubic (FCC) structure. The interface exhibited a thin dense chromia layer with a thicker porous MnCr₂O₄ overlayer with needle-like protrusions into the reduced coating. Evidence for inter-reactions during the concurrent coating reduction and substrate oxidation include Co rich metallic inclusions in the spinel layer and an enrichment of the spinel in Mn with distance from the chromia layer. The consequences of these observations for the complex microstructural variation during subsequent reoxidation and long term thermal exposure are discussed.

Keywords:

• Solid oxide fuel cell interconnects
• Manganese cobaltite coatings
• Microstructure
• Electron microscopy

Acknowledgement

This paper is based in part upon work supported by the US National Science Foundation under Grant No. 1100427.