The oxidation of nickel particles was studied in situ in an environmental transmission electron microscope in 3.2 mbar of O2 between ambient temperature and 600°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.
Acta Materialia, 2014, Vol 67, p. 362-372
In situ transmission electron microscopy (TEM); Electron energy-loss spectroscopy; Oxidation; Kinetics; Diffusion