A model of Kirkendall hollowing of core-shell nanowires and nanoparticles controlled by short-circuit diffusion

We propose a model for the hollowing of the core-shell nanowires caused by the Kirkendall effect during chemical reaction (oxidation) on the nanowire surface. We consider the self-diffusion of the atoms of the core along the grain boundaries in the shell, on the exposed surface of the core, and along the core-shell interface as the main factors controlling the hollowing kinetics. The model relies on the variational method of calculating the chemical potential of the metal atoms diffusing along the core-shell interphase boundary. A comparison of model predictions with the results of hollowing studies of Ni-NiO core shell nanoparticles [J.G. Railsback et al., ACS Nano 4 (2010) 1913-1920] gave a value for the self-diffusion coefficient of Ni along the grain boundaries in NiO at 573 K of 3 x 10(-20) m(2) s(-1), in good agreement with the literature data. We demonstrate that high values of the contact angle of the core on the shell promote pore instability and formation of secondary side pores (pores multiplication). (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.