Surface analysis of mixed-conducting ferrite membranes by the conversion-electron Mossbauer spectroscopy


Conversion-electron Mossbauer spectroscopy analysis of iron surface states in the dense ceramic membranes made of (57)Fe-enriched SrFe(0.7)Al(0.3)O(3-delta) perovskite, shows no traces of reductive decomposition or carbide formation in the interfacial layers after operation under air/CH(4) gradient at 1173 K, within the limits of experimental uncertainty. The predominant trivalent state of iron cations at the membrane permeate-side surface exposed to flowing dry methane provides evidence of the kinetic stabilization mechanism, which is only possible due to slow oxygen-exchange kinetics and enables long-term operation of the ferrite-based ceramic reactors for natural gas conversion. At the membrane feed-side surface exposed to air, the fractions of Fe(4+) and Fe(3+) are close to those in the powder equilibrated at atmospheric oxygen pressure, suggesting that the exchange limitations to oxygen transport are essentially localized at the partially reduced surface. (C) 2011 Elsevier Inc. All rights reserved.



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Waerenborgh, JC; Tsipis, EV; Yaremchenko, AA; Kharton, VV

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This work was supported by the FCT, Portugal (projects PTDC/CTM/64357/2006, PTDC/CTM-CER/114561/2009 and SFRH/BPD/28629/2006).

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