Characterization of the Surface Film Growth During the Electrochemical Process; Part 1: Nickel - Sea Water System

摘要

In order to understand the resistance of passive 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 sea water solution at room temperature and at two different potentiostatically controlled potentials (-800 mV and +450 mV versus Ni/NiO). The chemical changes at the metal interface were studied over a period of 72 hours. The x-ray diffraction results indicated that the structure of both the inner and the outer passive layers, at -800mV (versus Ni/NiO), is comprised of both Ni(OH)2 and gamma- NiOOH. Similarly the structure of the the interfaces at +450 mV (versus Ni/NiO) contains both NiO and Ni2O3. XPS analysis of the surface structure (primarily of the outer passive layer) suggests that at -800 mV (versus Ni/NiO) the structure consists of nearly 100 % Ni(OH)2. The structure at +450 mV (versus Ni/NiO) consists of nearly 90 % Ni2O3 and 10 % Ni(OH)2. It is therefore possible that the structure of inner passive layer is gamma-NiOOH at - 800 mV and Ni(OH)2 at +450 mV.