Oxidation behavior of cobalt nanoparticles studied by in situ environmental transmission electron microscopy  

作　　者：Dejiong Zhang Chuanhong Jin Z.Y.Li Ze Zhang Jixue Li 

机构地区：[1]State Key Laboratory of Silicon Materials,School of Materials Science and Engineering,Zhejiang University [2]Nanoscale Physics Research Laboratory,School of Physics and Astronomy,University of Birmingham

出　　处：《Science Bulletin》2017年第11期775-778,共4页科学通报（英文版）

基　　金：supported by the National Natural Science Foundation of China(11227403,11327901,51472215,51222202);the National Basic Research Program of China(2014CB932500,2015CB921004);Cyrus Tang Center for Sensor Materials and Applications;the resources of the Center of Electron Microscopy of Zhejiang University(ZJU)

摘　　要：The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to polycrystalline tricobalt tetroxide,in the presence of oxygen with a low partial pressure.Numerous cavities(or voids) were formed during the oxidation,owing to the Kirkendall effect.Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law,which was consistent with diffusion-limited kinetics.In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered.The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation,and formed the hollow structure.Irradiation by the electron beam,which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate,played an important role in activating and promoting the oxidations.These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental trans- mission electron microscopy. Firstly, cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide, then to polycrystalline tricobalt tetroxide, in the presence of oxygen with a low partial pressure. Numerous cavities （or voids） were formed during the oxidation, owing to the Kirkendall effect. Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law, which was consistent with diffusion-limited kinetics. In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered. The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation, and formed the hollow structure. Irradiation by the elec- tron beam, which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate, played an important role in activating and promoting the oxidations. These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.

关 键 词：COBALT Nanoparticle Oxidation dynamics Parabolic rate Environmental transmission electron microscopy （ETEM） Electron irradiation 

分 类 号：O614.812[理学—无机化学] TB383.1[理学—化学]