Behaviour of ferritic stainless steels subjected to dry biogas atmospheres at high temperatures

International audienceThe 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) + 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(-23) to 10(-20) bar for temperature between 700 and 900 degrees C 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 degrees C, serving as an efficient barrier to carbon penetration. However, when the temperature reaches 900 degrees C, cracks and pores appear in the oxide scale, carbon can precipitate and diffuse easier than at 800 degrees C and may lead to internal carbide formation. In such biogas atmospheres, 800 degrees C seems the maximum operating temperature of devices containing this ferritic stainless steel

Effect of Humidity on the Corrosion Kinetics of Ferritic Stainless Steels Subjected to Synthetic Biogas.

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Oxidation Kinetics of AISI 441 Ferritic Stainless Steel at High Temperatures in CO2 Atmosphere

International audienceFerritic stainless steels used as interconnectors in SOFC stacks are subjected to air and fuel atmospheres at 800 A degrees C. The use of hydrogen as fuel gas may be substituted by fermentative biogas consisting of mainly CO2 and CH4. In this gas mixture, carbon dioxide leads to steel oxidation whereas methane induces carburization. The objective of this study was to investigate the oxidation kinetics of the AISI 441 ferritic stainless steel under pure CO2 in order to understand oxidation mechanisms. The results show that the kinetic behaviour is linear at low temperatures (800-900 A degrees C) and initially linear then parabolic at higher temperatures (925-1,000 A degrees C). Oxide scale consisted of major Cr2O3-rich oxide, topped with MnCr2O4 and a dispersion of TiO2. The chromium-rich oxide was analysed by using the photoelectrochemical method. It exhibits N-type semi-conductor. Oxidation kinetics is modelled by the mixed surface and oxide-diffusion limited step

Comments on the Quantification of Mechanical Adhesion Energy of Thermal Oxide Scale on Metallic Substrate Using Tensile Test

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