β Scribed by P. Promdirek; G. Lothongkhum; S. Chandra-ambhorn; Y. Wouters; A. Galerie
No coin nor oath required. For personal study only.
The objective of this study is to understand the high temperature corrosion behaviour of the ferritic stainless steel type AISI 441 (18CrTiNb), a candidate for SOFC interconnectors, under dry synthetic fermentation biogas (CH 4 ΓΎ CO 2 mixtures), possibly used at the anode side of the cell. Thermodynamic analysis showed that, in such mixtures, the partial pressure of oxygen lies in the range of 10 Γ23 to 10 Γ20 bar for temperature between 700 and 900 8C and that the formation of solid carbon may take place in several conditions. XRD results confirmed the formation of Cr 2 O 3 and Mn-Cr spinel, with a mixture of internal carbides. In this temperature range, kinetic experiments showed linear mass change. Comparing with the linear rate constants of 441 oxidised in pure CO 2 , corrosion in biogas was larger and increased with increasing the methane content in the biogas. The surface morphology of the corroded specimens showed a dense oxide scale at temperatures less than 800 8C, serving as an efficient barrier to carbon penetration. However, when the temperature reaches 900 8C, cracks and pores appear in the oxide scale, carbon can precipitate and diffuse easier than at 800 8C and may lead to internal carbide formation. In such biogas atmospheres, 800 8C seems the maximum operating temperature of devices containing this ferritic stainless steel.
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