engleski

Inhibiting action of imidazole derivatives on metal corrosion

Corrosion inhibitors are widely used for corrosion protection during the storage and transport as well as in the systems like pipelines. A certain number of commercially used, very efficient corrosion inhibitors, are found to be toxic and must be replaced with new ones in near future. For this reason, research on new and non-toxic compounds that could give an efficient corrosion protection is very important. Different imidazole derivatives are efficient metal corrosion inhibitors. In the previous investigations performed with a group of 4-methyl imidazoles it was found that phenyl substituted imidazoles are efficient copper corrosion inhibitors. Two of them were found as the most effective: 4-methyl-1-phenyl imidazole and 4-methyl-1-(p-tolyl) imidazole. This thesis aims to carry out the more detailed investigation of the mechanism by which these two compounds protect copper from corrosion. Investigations are therefore performed in chloride and sulphate solutions whose pH value was ranging from 0 to 6. In this way it is possible to study the influence of the solution pH and anion on their inhibiting action. Investigations are performed by use of electrochemical (polarization measurements, electrochemical impedance spectroscopy, and electrochemical quartz crystal microbalance) and spectroscopic techniques (SEM, EDX and AFM). It is found that in chloride solutions inhibiting efficiency of both studied imidazoles increases with the increase of the solution pH value, from about 20% in 0.5 M HCl to 92% in 0.5 M NaCl. In sulphate solutions almost the same inhibiting efficiency (about 60%) for both inhibitors at all pH values is observed. In acid solution high inhibitor concentrations are necessary to obtain this efficiency while in near neutral solutions decrease of the corrosion rate is observed only for small inhibitor concentrations. Indeed both compounds act as activators if present in too high concentration. This behavior is explained with formation of the soluble copper(II) imidazole complexes in neutral sulphate solutions. EIS measurements show that the inhibitors examined do not improve the barrier properties of the surface film but rather hinder corrosion kinetics assessed by the increase of the charge transfer resistance. Investigations performed in this work show that the copper corrosion and its inhibition by studied imidazole derivatives are significantly influenced by the type of anion and pH value of the solution.

AFM; copper; corrosion inhibitors; EIS; EQCM; imidazole; pH; SEM

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