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Detailed Description of Pulse Isotopic Exchange Method for Analyzing Oxygen Surface Exchange Behavior on Oxide Ion Conductors
Chun-lin Song*,Jian-xin Yi,Yan Yan*
Author NameAffiliationE-mail
Chun-lin Song* School of Materials and Energy, Southwest University, Chongqing 400715, China chunlinsong@swu.edu.cn 
Jian-xin Yi State Key Laboratory of Fire Science, Department of Safety Science and Engineering, University of Science and Technology of China, Hefei 230026, China  
Yan Yan* School of Materials and Energy, Southwest University, Chongqing 400715, China yanyan2013@swu.edu.cn 
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 isotopologues 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 of 350?900 oC. 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-δ(BSCF) and La2NiO4+δ 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 oC 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, Ba0.5Sr0.5Co0.8Fe0.2O3-δ
FundProject:
用于分析氧离子导体的氧表面交换行为的脉冲同位素交换方法
宋春林*,易建新,严 岩*
摘要:
本文详细描述了一种用于测量氧化物离子导体的氧表面交换速率的新型脉冲18O-16O同位素交换(PIE)技术. 该技术采用装有氧化物粉末的连续流动填充床微反应器实现. 通过在线气相质谱法测量通过反应器的富含18O的脉冲的等温响应. 表观氧交换速率可以通过在给定的反应器停留时间和可用于交换的表面积下氧化物吸收18O的数量来计算. 相比于其他氧同位素交换的技术,PIE技术不需要快速加热/淬火步骤,具有快速、简单、非常适合筛选材料和系统研究反应机理的优点. 此外,利用氧同位素18O216O18O和16O2在流出脉冲中的相对分布可以深入研究氧的表面交换反应机理. 本文采用PIE技术分析YSZ、Ba0.5Sr0.5Co0.8Fe0.2O3-δ和La2NiO4+δ在350∽900 oC范围内表面氧交换性能. 根据同位素交换反应的两步式反应模型分析,对于混合导体BSCF和La2NiO4+δ,O2分子在氧化物表面的解离吸附速率为速率控制步骤. 对于YSZ,在800 oC 时,其表面氧交换的速率控制步骤由氧离子的晶格溶入变成O2分子在氧化物表面的解离吸附步骤.
关键词:  同位素交换,氧表面交换,离子导体,BSCF
DOI:10.1063/1674-0068/cjcp1811245
分类号: