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Abstract
Covering steel surfaces with suitable materials with the capacity to protect against corrosion represents a challenge for both research and industry, as steel, due to its paramount utility, is the most recycled material. This study presents the realization of new sandwich type materials based on 5,10-(4-carboxy-phenyl)-15,20-(4-phenoxy-phenyl)-porphyrin or 5,15-(4-carboxy-phenyl)-10,20-diphenylporphyrin and MnTa2O6 designed to improve corrosion inhibition of steel in aggressive media. The thin films, designed as single- or sandwich-type structures were obtained on carbon steel through the drop-casting technique. Morphological investigations of thin films were carried out by field emission-scanning electron microscopy (SEM) and atomic force microscopy (AFM). The inhibition of a steel corrosion process was evaluated in an aggressive environment of 0.1 M HCl by performing electrochemical investigations such as open circuit potential (OCP) and the potentiodynamic polarization technique. The influence of variations in the cathodic Tafel slopes βc and anodic Tafel slopes βa over the corrosion rates was discussed. The best corrosion inhibition efficiency of 91.76% was realized by the steel electrode covered with sandwich-type layers of 5,15-(4-carboxy-phenyl)-10,20-diphenylporphyrin on the bottom layer and MnTa2O6 on the top. The effect of location of the COOH groups in the cis or trans position on the tetrapyrrolic ring was also discussed to understand the corrosion inhibition mechanism.
Highlights
Carbon steel and its alloy derivatives play a vital role in many domains of engineering, such as constructions, all kinds of machinery, petroleum refineries equipment, and pipes due to their excellent resistance, and both physical and mechanical properties [1,2]
The drop-casting deposition of single and sandwich coatings consisting of MnTa2 O6 pseudo-binary oxide nanomaterials in association with 5,10-(4-carboxy-phenyl)-15,20-(4phenoxy-phenyl)-porphyrin or 5,15-(4-carboxy-phenyl)-10,20-bis-phenylporphyrin on carbon steel electrodes were realized
Correlating the results obtained from corrosion tests with the features revealed by atomic force microscopy (AFM) analysis, it can be concluded that the corrosion inhibition degree increases with the decreasing difference obtained for Sa, Sq and Sy roughness, before and after performing the corrosion tests
Summary
Carbon steel and its alloy derivatives play a vital role in many domains of engineering, such as constructions, all kinds of machinery, petroleum refineries equipment, and pipes due to their excellent resistance, and both physical and mechanical properties [1,2]. One of the main drawbacks of using equipment made of carbon steel is its chemical resistance in an acid environment [3,4,5,6,7,8,9,10]. Steel corrosion inhibitors bring significant benefits when used in descaling or in oil-well-acidizing treatments and in cleaning procedures using acids [11,12,13,14,15,16,17,18]. The application of the corrosion inhibitors [8,9,10,11,12] leads to a significant reduction in the corrosion of steel in an aggressive acid medium, increasing the feasibility and lifetime of the equipment and installations. The adsorption of inhibitors on metallic surfaces to uniformly create covering and adherent layers depends on certain physical–chemical properties of the inhibitor, as follows: electronic structure of the whole molecule, nature of grafted functional groups and the capacity to self-aggregate and generate supramolecular architectures [22,23]
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