摘要
为研究金属铈(Ce)水蒸气氧化微观过程及机理,本研究采用原位XRD技术研究了Ce水蒸气氧化的物相结构衍变过程,利用XRD、Raman和TEM技术分析了氧化产物的结构、种态和形貌,并采用第一性原理探讨了Ce水蒸气氧化机理。结果表明,CeH_(x)是Ce水蒸气氧化中间过程产物,H_(2)O在其表面更易吸附解离;CeH_(x)的生成降低了水蒸气氧化活化能,对水蒸气氧化动力学起到了关键作用。Ce水蒸气氧化产物主要是CeO_(2),且在其晶体中观察到了刃型位错缺陷;该线性缺陷改变了OH-和O^(2-)阴离子在CeO_(2)内的扩散路径,能加快水蒸气氧化速率。本研究揭示了Ce水蒸气氧化机理,认为在氧化物和金属的界面会发生CeHx的连续氧化及生成;只有CeH_(x)脱氢过程需吸热,认为是Ce水蒸气氧化的速控步骤。
Cerium(Ce)is a highly significant rare earth element with diverse applications in magnets phosphors,alloys,catalysis,and batteries.Currently,investigations into the oxidation of metallic cerium predominantly concentrate on environments involving oxygen,air,and humid air.In contrast,there is a scarcity of research pertaining to steam atmospheres,and even fewer studies have examined the microscopic mechanisms underlying steam oxidation.The investigation of the microscopic processes and mechanisms involved in the steam oxidation of Ce is essential for gaining a deeper understanding of its physical and chemical properties,which is crucial for enhancing its commercial applications Furthermore,Ce serves as an exemplary metal simulation material within the domain of nuclear engineering,and the exploration of its steam oxidation holds considerable importance for examining the conversion behaviors of significant actinide metals,including uranium and plutonium.To investigate the microscopic processes underlying the oxidation of Ce in water vapor,this study developed an experimental apparatus utilizing in situ X-ray diffraction(XRD)technology,which enables real-time monitoring of the phase structure evolution during the oxidation process.To ascertain the structure composition,and morphology of the oxidation products of Ce in water vapor,a combination of XRD Raman spectroscopy,and transmission electron microscopy(TEM)techniques was employed for analysis and characterization.Furthermore,to investigate the mechanism of Ce steam oxidation,the Vienna Ab initio Simulation Package(VASP)was employed to optimize the crystal structure.The Perdew-Burke-Ernzerhof(PBE)functional was utilized for the calculations,and the continuous image nudged elastic band(CINEB)method was applied to identify the transition state associated with the oxidation process of Ce in water vapor.The findings indicate that CeH_(x)serves as an intermediate product in the water vapor oxidation of Ce,with H_(2)O exhibiting a greater propensity for adsorption and dissociation on its surface.The generation of CeHx contributes to a reduction in the activation energy required for water vapor oxidation,thereby significantly influencing the kinetics of this process.The primary product resulting from steam oxidation is cerium dioxide(CeO_(2)),within which edge dislocation defects is identified.These linear defects alter the diffusion pathways of hydroxide(OH^(-))and oxide(O^(2-))anions in CeO_(2),potentially enhancing the rate of steam oxidation.It is concluded that the generation and release of stress within the oxide film are critical factors in the fracture and spallation of the CeO_(2)film,as well as in the development of linear crystal defects.This study elucidates the mechanism underlying the oxidation of cerium in water vapor,highlighting the continuous oxidation and formation of CeH_(x)at the oxide-metal interface.The theoretical analysis suggests that the dehydrogenation process of CeH_(x)is the only step requiring heat absorption,which is identified as the rate-controlling step in the steam oxidation of cerium.
作者
陈锦
姚曜晖
黄昆
杨建勋
刚发源
周晋
丁有钱
张生栋
CHEN Jin;YAO Yaohui;HUANG Kun;YANG Jianxun;GANG Fayuan;ZHOU Jin;DING Youqian;ZHANG Shengdong(China Institute of Atomic Energy,Beijing 102413,China;Shandong University of Technology,Zibo 255000,China)
出处
《原子能科学技术》
北大核心
2025年第4期783-792,共10页
Atomic Energy Science and Technology
