Studies On The Interfacial Behavior And Inhibition Mechanism Of Inhibitors By Electrochemical Methods And AFM

Recognition of small molecules on metal surfaces at nanometer scale by AFM imaging is based on the precondition of excellent tip quality and high flatness of the substrate. There are still many obstacles to achieve quantitative description of monomolecular layer on rough surface,such as the adsorption film of corrosion inhibitor on the metal/solution interface. The using of AFM in corrosion field is almost limited in real-time imaging. Some functions to examine surface's physical characters which have been applied widely in life and polymer science field have been rarely applied in corrosion studies. Therefore, to develop AFM physical character examination functions in inhibitor researches and to establish methods for quantificationally describing the adsorption of corrosion inhibitors on rough polycrystalline surface has important significance and application value for our understanding of inhibition mechanism on microcosmic viewpoint. Electrochemical methods, fractal analysis and AFM force curves were used to investigate the adsorption behavior of C12SH SAM on rough polycrystalline gold surface. The results showed that with increasing of C12SH concentration in solution for self-assembling the SAM tended to be more ordered and denser. The phase contrast value and fractal dimension of phase image increased initially with increasing C12SH concentration and then decreased at 0.005mol/L, reflecting the surface changed from metal phase to two coexist phases of metal and SAM, and finally to main SAM phase again at higher C12SH coverage. The distribution of adhesive force values measured by force curves at different C12SH concentrations measured is in good agreement with the results deduced from electrochemical methods and fractal analysis, testifying that fractal analysis of AFM phase images and AFM force curves can be used to describe the adsorption behavior of C₁₂SH SAM on polycrystalline gold surface. The adsorption behavior of sodium dodecyl sulfonate (SDS) on rough polycrystalline Al surface were also studied by electrochemical methods, fractal analysis and AFM force curves. The results showed that for Al in HCl solution the inhibition efficiency of SDS did not increased obviously above the CMC (critical micelle concentration). The phase contrast value and fractal dimension of phase image increased initially with increasing SDS concentration and then decreased while above CMC, reflecting the surface of metal changed from metal phase to two coexist phases of metal and SDS film, and finally to the main SDS phase. The distribution of adhesive force values measured by force curves at different SDS concentrations is in good agreement with the results deduced from electrochemical methods and fractal analysis, testifying that fractal analysis of AFM phase images and AFM force curves can be used also to describe the adsorption behavior of corrosion inhibitor films on rough and polycrystalline surfaces of active metals. The inhibition mechanism and adsorption behavior of dodecylamine on a copper-nickel alloy in NaCl solutions were studied by electrochemical methods and AFM. The results showed that dodecylamine formed monomolecular layer on alloy surface and was more pronounced on cathodic corrosion reaction. The adsorbed film tended to become more density and orderly with increasing dodecylamine concentration, and so the inhibition efficiency was increased. The adsorbed film changed the structure of the double-electric layer on the metal/solution interface and made the potential of zero charge (PZC) shift to the positive direction. The adsorption of the protonated dodecylamine molecules onto the negatively-charged alloy surface led to the decrease of electrostatic repulsive force between the AFM tip and the sample. The influence of sodium chromate and dodecylamine on enhanced dissolution of the Cu-Ni alloy initiated by AFM tip scratching in NaCl and HCl was investigated. The lateral force traces and force versus distance curves were measured by AFM to investigate their action mechanism. The results indicated that the enhanced dissolution caused by AFM tip scratching could be inhibited by adding sodium chromate or dodecylamine into the solutions, but their inhibition mechanisms were different. The tip scratching might destroy the surface mechanically, What's more the friction forces between the tip and the sample caused local heating of the substrates which provided enough energy to overcome the activation barrier for the chemical reaction of the chloride anions with the metal ions. As a total result the dissolution of the substrates were accelerated. The inhibition effect of sodium chromate is due to its oxidation ability to repair the destroyed protection film and the increase of rigidity of metal surface. On the other hand, the inhibition effect of dodecylamine is due to the organic adsorption film on metal surface to weaken the friction forces between the tip and the sample and to elevate the ionization energy of metal.