CHARACTERIZATION OF THE SURFACE FILM GROWTH DURING THE ELECTROCHEMICAL PROCESS

摘要

In order to better understand the behavior of films formed during corrosion processes, an analytical technique using x-ray diffraction was developed to examine the structure of metal in closest proximity to the metal / liquid interface. The in-situ structure at the metal liquid interface was examined for pure nickel in KOH solution at room temperature at potentiostatically controlled potentials of-800 mV and +450 mV (versus Ni/NiO). The chemical changes at the metal interface were studied over a period of 48 hours. It was found that after a continued application of the potential over 72 hours, the nickel foil was perforated and the testing has to be stopped. The x-ray diffraction results for pure nickel in KOH indicated that the structure of both the inner and the outer oxide layers, at -800 mV (versus Ni/NiO), comprises both Ni(OH)_2 and NiOOH. Similarly, the structure of the interfaces at +450 mV (versus Ni/NiO) contains both NiO and Ni_2O_3 and Ni(OH)_2. XPS analysis of the surface structure (primarily of the outer layer) suggests that at -800 mV (versus Ni/NiO) the structure consists of Ni(OH)_2. The structure at +450 mV (versus Ni/NiO) consists of NiO and Ni(OH)_2. It is therefore, possible that the structure of inner layer may be NiOOH at -800 mV and Ni_2O_3 at +450 mV.