Oxidation of nickel particles in an environmental TEM

Q. Jeangros, Thomas Willum Hansen, Jakob Birkedal Wagner, Rafal E. Dunin-Borkowski, C. Hébert, J. Van herle, A. Hessler-Wyser

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    Abstract

    The mechanisms controlling the growth of an oxide film during oxidation are subject to controversies at intermediate length scales (20-1000 nm) [1]. Relating rate-controlling mechanisms and resulting structural changes, which is essential to the understanding of oxidation processes, has proved challenging under these conditions.

    Here, nickel particles are oxidized under 3.2 mbar of O2 inside an environmental TEM (ETEM) equipped with a post-column filter [2]. Images, diffraction patterns and core-loss electron energy-loss spectra are acquired to monitor the structural and chemical evolution of Ni during oxidation, whilst increasing the temperature up to 600 °C.

    Nucleation of NiO on Ni is observed to occur rapidly at room temperature before the introduction of O2 in the environmental cell (in the vacuum of the microscope). It involves the formation of randomly orientated oxide domains of a few nanometres in size. These domains impinge and cover the particles surface. As the temperature increases under O2, the NiO film grows and creates irregular structures composed of many crystallites. The reaction kinetics are inferred by EELS using different techniques analyzing changes in shapes of the Ni L2,3 white lines [3]. The results indicate that the oxidation process is diffusion-controlled, similarly to results from the literature that were obtained at larger oxide thicknesses [1]. Pores are observed to form at the Ni/NiO interfaces, resulting in the loss of metal/oxide contact (Fig. 1). These observations illustrate that the outward diffusion of Ni2+ ions through NiO is the dominant mass transport mechanism under these conditions (in opposition to O2/O2- transport). Images
    also indicate that the NiO film might rupture in some regions, a process that should enable some inward diffusion of O2 and therefore inward growth of NiO. An activation energy for Ni oxidation comparable to the ones found in the literature is determined from our EELS data.

    By using ETEM, we are able to relate the structural and chemical changes occurring at the nanoscale during the oxidation of Ni particles with O2 at high temperature, providing new insights into oxidation/corrosion processes.
    Original languageEnglish
    Publication date2013
    Number of pages2
    Publication statusPublished - 2013
    EventMicroscopy and Microanalysis 2013 - Indiana Convention Center, Indianapolis, United States
    Duration: 4 Aug 20138 Aug 2013
    http://microscopy.org/mandm/2013/

    Conference

    ConferenceMicroscopy and Microanalysis 2013
    LocationIndiana Convention Center
    CountryUnited States
    CityIndianapolis
    Period04/08/201308/08/2013
    Internet address

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