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Detailed description of pulse isotopic exchange method for analyzing oxygen surface exchange behavior on oxide ion conductors
宋春林
作者单位E-mail
宋春林 中国重庆、西南大学材料与能源学部 400715 chunlinsong@swu.edu.cn 
摘要:
A novel pulse 18O-16O isotopic exchange (PIE) technique for measurement of the rate of oxygen surface exchange of oxide ion conductors was presented. The technique employs a continuous flow packed-bed micro-reactor loaded with the oxide powder. The isothermal response to an 18O-enriched pulse passing through the reactor, thereby maintaining chemical equilibrium, is measured by on-line mass spectrometry. Evaluation of the apparent exchange rate follows from the uptake of 18O by the oxide at given reactor residence time and surface area available for exchange. The developed PIE technique is rapid, simple and highly suitable for screening and systematic studies. No rapid heating/quenching steps are required to facilitate 18O tracer anneal or analysis, as in other commonly used techniques based upon oxygen isotopic exchange. Moreover, the relative distribution of the oxygen isotopomers 18O2, 16O18O, and 16O2 in the effluent pulse provides insight into the mechanism of the oxygen exchange reaction. The PIE technique has been demonstrated by measuring the exchange rate of selected oxides with enhanced oxide ionic conductivity in the range 350 and 900 ?C. Analysis of the experimental data in terms of a model with two consecutive, lumped steps for the isotopic exchange reaction shows that for mixed conductors Ba0.5Sr0.5Co0.8Fe0.2O3-? (BSCF) and La2NiO4+? the reaction is limited by the apparent rate of dissociative adsorption of O2 molecules at the oxide surface. For yttria-stabilized zirconia (YSZ) a change-over takes place, from rate-limitations by oxygen incorporation below ~800 ?C to rate-limitations by O2 dissociative adsorption above this temperature. Good agreement is obtained with exchange rates reported for these materials in literature.
关键词:  isotopic exchange  oxygen surface exchange  ion conductor  BSCF
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Detailed description of pulse isotopic exchange method for analyzing oxygen surface exchange behavior on oxide ion conductors
Chunlin Song
Abstract:
A novel pulse 18O-16O isotopic exchange (PIE) technique for measurement of the rate of oxygen surface exchange of oxide ion conductors was presented. The technique employs a continuous flow packed-bed micro-reactor loaded with the oxide powder. The isothermal response to an 18O-enriched pulse passing through the reactor, thereby maintaining chemical equilibrium, is measured by on-line mass spectrometry. Evaluation of the apparent exchange rate follows from the uptake of 18O by the oxide at given reactor residence time and surface area available for exchange. The developed PIE technique is rapid, simple and highly suitable for screening and systematic studies. No rapid heating/quenching steps are required to facilitate 18O tracer anneal or analysis, as in other commonly used techniques based upon oxygen isotopic exchange. Moreover, the relative distribution of the oxygen isotopomers 18O2, 16O18O, and 16O2 in the effluent pulse provides insight into the mechanism of the oxygen exchange reaction. The PIE technique has been demonstrated by measuring the exchange rate of selected oxides with enhanced oxide ionic conductivity in the range 350 and 900 ?C. Analysis of the experimental data in terms of a model with two consecutive, lumped steps for the isotopic exchange reaction shows that for mixed conductors Ba0.5Sr0.5Co0.8Fe0.2O3-? (BSCF) and La2NiO4+? the reaction is limited by the apparent rate of dissociative adsorption of O2 molecules at the oxide surface. For yttria-stabilized zirconia (YSZ) a change-over takes place, from rate-limitations by oxygen incorporation below ~800 ?C to rate-limitations by O2 dissociative adsorption above this temperature. Good agreement is obtained with exchange rates reported for these materials in literature.
Key words:  isotopic exchange  oxygen surface exchange  ion conductor  BSCF