engleski

BIOMOLECULES AS CORROSION INHIBITORS FOR STEEL IN ALKALINE MEDIA CONTAINING CHLORIDE IONS

Investigation of nature-designed molecules and blends of naturally synthesized chemical compounds as possible inhibitor candidates is of raising interest due to the health and environmental hazards involved in the use of most synthetic corrosion inhibitors. In neutral and alkaline media, the oxide film is frequently present on the surface of the metal and in more aggressive environments this passive film can be destabilized thus leading to higher rate of metal dissolution through the appearance of localized forms of corrosion. The mechanistic action of inhibitors in such systems is rather complicated. Besides adsorption, corrosion inhibition on oxidized metal surfaces, may involve enhancement of passivation, competitive surface adsorption of inhibitor and aggressive ions, buffering of the pH in the local pit environment and competitive migration of inhibitor and aggressive ions into the pit. Despite of these complications, semi-empirical molecular modelling methods are applicable in study of the inhibitor influence on pitting corrosion. The molecular properties of inhibitors: the frontier molecular orbital (FMO) energies, the differences between lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energies, electronic charges on reactive centres, dipole moments and conformation of molecules may be correlated to the inhibitor action. In the present study, pitting inhibition by ascorbic acid (AA) has been performed by comparing the polarization curves and EIS data in the presence and the absence of the inhibitor. Inhibition action was evaluated from its ability to suppress the cathodic reaction of oxygen reduction as well as from its ability to suppress the onset of pitting. The mechanism of action was deduced by comparative interpretation of inhibitor’ s molecular properties and the data obtained from electrochemical experiments.

reinforcing steel; corrosion; inhibition; alkaline media; ascorbic acid

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