Activation of metal oxidation over the zone of electrodiffusion

Abstract

It is shown that an oxide layer saturated by chromium oxides is formed on the surface of chromium steel at a higher rate under electrocontact (10⁴–10⁵ A/cm²) vacuum dc annealing (10^–2 Torr, 300°C) than under furnace heating. Such activation of oxidation is due to the formation of an electrodiffusion zone in the surface steel layer. At further stages, grain boundaries emerge to the metal surface that act as oxidant transportation channels from the surrounding medium into the conductor bulk, which results in accelerated oxide formation in the bulk of the surface metal layer. Apart from the uniform oxide layer, individual hematite nanoflakes and nanoleaves with the thickness of 50–40 nm and average diameter of 450 nm are formed on the positive electrode and grow vertically on the steel surface. The average surface density of nanoparticles is 10⁸ 1/cm². Such activation of metal oxidation over the zone of electrodiffusion can provide pronounced properties for accelerated formation of protective surface layers, in addition to its intrinsic functional (sensor, catalytic, semiconductor, adsorption) properties.