Oxidation mechanism of nickel particles studied in an environmental transmission electron microscope

The oxidation of nickel particles was studied in situ in an environmental transmission electron microscope in 3.2 mbar of O-2 between ambient temperature and 600 degrees C. Several different transmission electron microscopy imaging techniques, electron diffraction and electron energy-loss spectroscopy were used to study the evolution of the microstructure and the local chemical composition of the particles during oxidation. Our results suggest that built-in field effects control the initial stages of oxidation, with randomly oriented NiO crystallites and internal voids then forming as a result of outward diffusion of Ni2+ along NiO grain boundaries, self-diffusion of Ni2+ ions and vacancies, growth of NiO grains and nucleation of voids at Ni/NiO interfaces. We also observed the formation of transverse cracks in a growing NiO film in situ in the electron microscope. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.