ИСТИНА

The theory of low temperature oxidation or oxidation in thin films was for the first time formulated by Caberra and Mott (C–M theory) [5]. It involves the appearance of an electric potential (Mott potential) between oxide–adsorbed oxygen and oxide–metal boundaries at the initial time moment. The corresponding electric field can pull out metal atoms and move them toward the outside oxide surface, where an oxide film grows. The theory qualitatively correctly describes the formation of planar thin oxide films, but ignores potential gradients in films and assumes that the diffusion coefficients of metal ions, oxygen ions, electrons, and vacancies are constant. As it is known, the oxidation of Co nanoparticles is accompanied by the Kirkendall effect, forming void spherical structures consisting of CoO and Со3О4 [6]. The formation of void structures is explained by preferable diffusion of metal ions to the oxide–oxygen interface and accumulation of vacancies, followed by their association under the oxide layer. The reduction of these structures with hydrogen can generally lead to different results. One scenario is a collapse of the void spherical particle, forming a reduced Co particle of the initial size; another mechanism is the decomposition of the oxide shell, forming a system of finer Co particles during the reduction. Here, we tried to answer the question: does magnetic field effect the results of oxidation–reduction treatment? The formation of cavities at the metal–oxide boundary should likely cause a more substantial decrease in the rate of oxidation than is predicted by the C–M theory due to accumulation and condensation of vacancies and corresponding decrease of the real metal-oxide separation surface the metail ions diffuse through. One should note that corresponding information concerning the kinetics of oxidation of metal nanoparticles is exceedingly scarce. We used an experimental setup for "in situ" control of magnetic properties of ferromagnetic metals to investigate the kinetics of oxidation process.