engleski

Electrochemical and FM study of corrosion inhibition with respect to application method

One of the most important methods for the corrosion protection of metals is the use of organic inhibitors. It is common to apply corrosion inhibitor either by adding it directly to the corrosive media or form protective inhibitor film prior to exposing the metal to the corrosive environment. The choice between these two methods usually depends on the properties of the inhibitor and on the type of the corrosion media. Imidazole derivatives were found to be efficient copper corrosion inhibitors in various corrosive environments [1-3]. Previous research has shown that their inhibiting action depends on the anion and the pH value of the solution [4]. The aim of this work was to study if it is possible to obtain higher efficiency of the inhibitor by varying the method of its application. Two imidazole compounds were studied 4-methyl-1-phenyl imidazole and 4-methyl-1-(p-tolyl) imidazole. Their efficiency as copper corrosion inhibitors was examined in chloride and sulphate media. Inhibitors were either added to corrosive solution or the inhibitor film was formed prior to immersion in the corrosive solution. Investigations were performed by the means of electrochemical methods (polarization measurements and EIS) and atomic force microscopy. Figure 1 shows polarization curves of copper in 0.5 M NaCl solution with and without the addition of 4-methyl-1-phenyl imidazole and the polarization curve of copper electrode covered by 4-methyl-1-phenyl imidazole film formed in organic solvent. It can be readily seen that for both manners of inhibitor application decrease of corrosion rate was observed. In the case when inhibitor had adsorbed on metal surface in organic solvent, polarization curve obtained was in shape very similar to that for unprotected electrode and the corrosion potential was almost the same. On the contrary polarization curve measured in 0.5 M NaCl containing inhibitor differs in the shape and the corrosion potential is shifted towards nobler values. From these observations it can be concluded that there are differences in inhibiting mechanism of two differently formed inhibitor layers. These differences were also observed with AFM study of metal surface. The differences in morphology of samples prepared by two techniques (i.e. in the first case the inhibitor was dissolved in the NaCl solution, in the second one the experiment was carried out by copper with previously developed inhibitor layer) is demonstrated in Figure 2a and b. Formation of polymer-like structures was observed in the case when inhibitor was directly added to chloride solution but not when the inhibitor film was separately preformed. Investigations performed in sulfate media with the other inhibitor (4-methyl-1-(p-tolyl) imidazole) have also shown that protection mechanism and inhibitor efficiency significantly depend on the application method of inhibitor.

corrosion inhibitors; electrochemical impedance spectroscopy; AFM

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