Corrosion inhibition process oxidative mechanisms

The EDS spectrums reveal that the presence of C, O, and S for NH as elements which take place in the inhibition mechanism The carbonyl, methoxy and hydroxyl group arranged around the aromatic ring are determined as functional group of VL in inhibition process. The C atoms in TS are recognized by the EDS analysis, where these atoms involve in the adsorption process in alloy surface. The formation of paecipatates of oxides/hydroxides of these inhibitors results in improved corrosion resistance. 

Study of the inhibition mechanism of molecules requires systematic investigation of the adsorption/desorption processes of inhibitor molecules on the metal/electrolyte interface. The adsorption phenomena of inhibitors on corroding metals are fairly complex and dependent on the surface feature, such as the composition and structure of the oxide-hydroxide layer, the local pH gradient near the interface, and interaction between the inhibitor molecules and components of the oxide layer. The study of adsorption/desorption processes of corrosion inhibitors on a noble metal surface is of great importance for fundamental aspects. Therefore knowledge of the adsorption properties of inhibitor molecules on a well-defined surface structure might be beneficial, and may contribute to a better understanding of the kinetics and mechanisms of inhibition processes on constructional materials of industrial importance. 

The overall mechanism for corrosion inhibition for this case is simplistically illustrated in Fig. 31.40. Wes-sling [20] and Lu et al. [26,29] clearly demonstrated that when doped polyaniline is placed in contact with mild steel, the steel surface undergoes a rapid oxidation process to provide a layer of y-Fe203 at the polyaniline/ iron interface. This process is shown schematically in Fig. 31.40 by the transformation of (a) to (b) and occurs according to the equation... 

The overall mechanism for corrosion inhibition on exposed bare steel surfaces adjacent to the polyaniline coating (overcoated with epoxy) is outlined in Fig. 31.41. It is quite evident that the process of corrosion inhibition and passive oxide layer formation occurs by mechanisms that are more complex that those shown here. However, this figure highlights several important steps that are consistent with the electrochemical, visual, and spectroscopic data. 

The mechanism of corrosion inhibition, with these heavy metal chromates, hinges on the fact that they can passivate aluminium [22-24], When such a corrosion-inhibited bonded joint is attacked, a mixture of hydrated aluminium oxide and chromic oxide (Cr203) is formed (cf. the Alocrom process) This not only seals the oxide film, repairing the damage caused by the ingress of the electrolyte, but the presence of the stable chromic oxide also reduces the rate of dissolution of the aluminium oxide. The longevity of such a protection is due to the low solubility ( 1.2 g/1 at 15°C) of the chromate in water [25], which means that the chromate remains active for a considerable period of time. 

Zinc and zinc-coated products corrode rapidly in moisture present in the atmosphere. The corrosion process and its mechanism were studied in different media, nitrate [283], perchlorate [259], chloride ions [284], and in simulated acid rain [285]. This process was also investigated in alkaline solutions with various iron oxides or iron hydroxides [286] and in sulfuric acid with oxygen and Fe(III) ions [287]. In the solution with benzothia-zole (BTAH) [287], the protective layer of BTAH that formed on the electrode surface inhibited the Zn corrosion. 

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