Investigation On Inhibition Mechanism Based On AFM And Electrochemical Methods

Since their special physical and chemical effects on the interface between metal and solution, inhibitors can prevent materials from corrosion. The effects of inhibitors can be investigated through atomic force microscopy (AFM) and electrochemical methods, and the inhibition mechanism can be further comprehensive studied.Dodecylamine can adsorb on carbon steel spontaneously in hydrochloric acid solution through its polar group(-NH2), and its non-polar group(-C12H13) is in hydrochloric solution and its direction is perpendicular to the metal surface. Each adsorption dodecylamine molecule replaces 1.1 water molecule on the metal surface, and dodecylamine molecules forms a monolayer film on carbon steel surface. The inhibition mechanism of dodecylamine for carbon steel is geometric blocking effect. Since dodecylamine forms a hydrophobic membrane on carbon steel surface, the wettability of the surface is reduced. The adsorption of dodecylamine on carbon steel surface is accord with Arrhenius equation, the adsorption increases apparent activated energy and reduces pre-exponential factor, thus decreases the corrosion rate. The adsorbed dodecylamine film also changed the structure of the double-electric layer and made the potential of zero charge shift to the positive direction. AFM force curves indicate that at the area without adsorbed dodecylamine, there is no obvious adhere force, however at the area with adsorbed dodecylamine, there is average 1.3nN adhere force.The anodic process of carbon steel in sodium chloride solution is inhibited significantly by molybdate and chromate, they can form nonconducting film on carbon steel surface. At the same concentration, the passive film formed by chromate is more compact and harder than that by molybdate. Chromate has better inhibition effect on carbon steel general and pitting corrosion. The noise corresponding to pitting corrosion can be picked up from the recorded signal based on wavelet transform. Through analysis of the picked up noise, it is learned that the pit nucleation rate, average current amplitude and lifetime of current transient, integrated current decreased with the addition of molybdate and chromate. The inhibition efficiency of chromate is higher than molybdate on carbon steel pitting corrosion. The cathodic process of copper in sodium chloride solution is controlled by oxygen diffusion, when there are self-assembled monolayers (SAMs) of dodecanethiol on copper surface, cathodic reaction is inhibited, oxygen diffusion is no longer control process. The absolute value of peak current in cyclic voltammetry curves and surface friction force decrease with the increase of self-assembling dodecanethiol time, the inhibition efficiency increases with the increase of self-assembling time, when the self-assembiling time reaches 40min, the surface is entirely covered by dodecanethiol, the inhibition efficiency changes little with the increase of self-assembiling time. Since the roughness of copper surface is very high, no important information can be got form AFM topography, but there's big difference among the AFM phase images of copper surface by self-assembling dodecanethiol different time. The multifractal spectrum f(α)-αprovides important information for the adsorption of dodecanethiol, as for bare copper surface,ΔαandΔf value are small, which means the surface is very uniform, butΔαandΔf value increase greatly after self-assembiling dodecanethiol of a short time, which indicates the surface inhomogeneity increase, the surface is partly covered by dodecanethiol, a further self-assembly with dodecanethiol monolayer makesΔαandΔf decrease again, which indicates the surface is covered by dodecanethiol entirely and become uniform again.