Publications

Microstructure and phase evolution of atmospheric plasma sprayed Mn-Co-Fe oxide protection layers for solid oxide fuel cells

Grünwald, N. and Sohn, Y.J. and Yin, X. and Menzler, N.H. and Guillon, O. and Vaßen, R.

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
Volume: 39 Pages: 449-460
DOI: 10.1016/j.jeurceramsoc.2018.08.027
Published: 2019

Abstract
Dense protective layers are needed to reduce chromium-related degradation in SOFC stacks. In particular, atmospheric plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) coatings demonstrated low degradation rates in stack tests. We show that short-term annealing in air induces crack healing within these coatings. Parallel to this effect, a phase transformation is observed originating from oxidation that proceeds by solid state-diffusion. The present contribution reveals the basic mechanisms of the microstructural and phase changes of coatings in long-term annealing tests of up to 10,000 h at 700 °C. The layer develops differently at the air-facing surface and in the bulk. Due to cation deficiency, oxidation is dominated by cation outward diffusion, leading to a Co-enriched surface layer. The bulk displays a fine distribution of the initial (rock salt) and the final (spinel) phases. Understanding the mechanisms leading to these irreversible changes enables predictions to be made concerning durable protectivecoatings in SOFCs. © 2018 Elsevier Ltd

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