Kinetic modeling and mechanism of low temperature corrosion of copper nanoparticles

International audienceNowadays the low temperature corrosion of copper is no longer only seen as a degradation phenomenon which is to be avoided; it can also be regarded as an innovative reaction to be exploited. The low temperature oxidation of copper nanoparticles as a new route for the synthesis of hollow nanoparticles, such as copper nanotubes, belongs to one of a new generation of reactions that are increasingly studied. However, most studies deal with the characterization of the morphological evolution of the particles during the processing as well as with the nature of the oxide phase being formed. In contrast, to the best of our knowledge, no kinetic modeling or mechanism study has been published up to now. In this study, we propose a mechanism and a kinetic model for the low temperature corrosion of copper nanopowder: Cu(s) + ¼ O2(g) = ½ Cu2O (s). The kinetic data corresponding to copper nanoparticles oxidation at low temperature were investigated using thermogravimetry (TGA), differential scanning calorimetry (DSC). The samples during reaction were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Isothermal and isobaric studies of the oxidation reaction were carried out at various temperatures and oxygen partial pressures. It was found that working under an oxygen partial pressure less than 8 kPa in the temperature range 125–145°C leads to reaction where nucleation of the oxide phase is in competition with its growth. Characterization of the powder after oxidation by transmission electron microscopy revealed the formation of hollow grains of cuprite (Cu2O). This result shows that oxidation occurs due to an outward diffusion of single ionized copper defects in the cuprite structure. On the other hand, from the study of the dependency of the growth rate on the oxygen partial pressure it could be concluded that the dissociative adsorption of oxygen on the surface of the oxide is the rate limiting step. Based on these results, a mechanism using the Kröger formalism and a kinetic model have been established to interpret the experimental curves. The rate law has been thus calculated as a function of the thermodynamic variables leading to the knowledge of the areic reactivity of growth. The expression of the extent of conversion was successfully confronted to the kinetic data up to α corresponding to a slowdown of the reaction which was attributed to the diffusion of gaseous molecules through the porosity of the nanoparticles agglomerates