Structured Thin Films Based on Synergistic Effects of MnTa2O6 Oxide and bis-Carboxy-phenyl-substituted Porphyrins, Capable to Inhibit Steel Corrosion

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.

Experimental and theoretical study on corrosion inhibition of mild steel by meso-tetraphenyl-porphyrin derivatives in acid solution

“…In contrast, cathodic Tafel slopes were less affected. This infers that compounds in the present study were inhibitors of mixed type, having dominant anodic reaction [21].…”

One A3B Porphyrin Structure—Three Successful Applications

“…The corrosion-inhibitory effect of porphyrins can be explained by their strong chemisorption on the surface of metals [ 34 ] due to both the planarity of the molecule and the extended conjugation of the π-electron system. Metalloporphyrins containing oxygen atoms in the peripheral meso-substituents, per se, or in different combinations with pseudo-binary oxides [ 35 , 36 ], resins [ 37 ] or nylon fibres [ 38 ], are capable of uniformly coating steel and protecting it from corrosion, in acidic mediums [ 34 , 35 , 36 , 37 , 38 , 39 ], salty environments [ 11 ] and in sweet corrosive mediums [ 40 ].…”

Efficient Decrease in Corrosion of Steel in 0.1 M HCl Medium Realized by a Coating with Thin Layers of MnTa2O6 and Porphyrins Using Suitable Laser-Type Approaches

“…As in the case of deposits realized by the drop-casting technique [ 26 ], with the protective layers formed by alternative MAPLE and PLD laser methods, the polarization resistance (R p ) of the modified OL steel electrodes increased. The highest polarization resistance (R p ) was obtained for the composite layers 5-(4-carboxy-phenyl)-10,15,20-tris (4-methyl-phenyl)-porphyrin/MnTa 2 O 6 (h), meaning that the porphyrin/oxide inhibitors adsorbed and blocked access to the active sites of the steel electrodes [ 38 , 39 ].…”

“…In the last decade, our group has conducted successful research regarding the synergism between pseudo-binary oxides and porphyrins or metalloporphyrins deposited in alternating sandwich layers on steel with the purpose of inhibiting its corrosion even in extremely aggressive acidic environments. The corrosion inhibition mechanism was achieved by covering the steel surfaces with extremely adherent mixed layers of pseudo-binary oxides and porphyrins, thus creating a protective mechanical barrier [ 25 , 26 , 27 , 28 ].…”