In-situ spectroelectrochemical study of the growth process of a lead decanoate coating as corrosion inhibitor for lead surfaces

摘要

We have monitored the growth of lead decanoate coatings in real time using electrochemical impedance spectroscopy (EIS) and synchrotron X-ray diffraction in a unique environmental cell. The measurements involved the immersion of lead substrates in a 0.05 m sodium decanoate solution and the simultaneous collection of spectroscopic and electrochemical data as the coating deposits. In separate experiments, the surface morphology was investigated with SEM. The stratigraphy and thickness of layers after 6 h of treatment (congruent to 1.5 mu m) was determined using RBS and ultra low energy SIMS combined with surface profilometry. Weight-gain measurements were also carried out. Overall, the results are consistent with an initially parabolic process, due simply to diffusionally limited two-dimensional growth across the surface from nucleation sites. This becomes linear over time as one-dimensional vertical growth sets in at full coverage (layer closure). The X-ray data and the microscopy show that the coating consists of fine, interlocking, randomly oriented flake-shaped crystals, with no obvious epitaxial relationship to the lead substrate. The growth rate of the coating and its corrosion resistance are extremely sensitive to preparation method of the NaC10 solution in ways which are still under investigation.