Portugaliae
Electrochimica Acta

Abstract Pinus oocarpa seed extract corrosion inhibition effect on galvanized steel has been studied in 2 M hydrochloric acid, at 303 K and 333 K, by gravimetric methods. The inhibitor efficiency decreased with higher temperatures, which suggests physisorption. Potassium iodide (KI) synergistic action produced an increase in the extract inhibition efficiency, but its parameter decreased with higher inhibitor concentrations. The galvanized steel optical microscopy shows that the metal surface was coated with P. oocarpa seed extract, and that the cracks observed in the inhibitor absence were filled. This observation suggests that the extract can be used as a coating to prevent galvanized steel corrosion. Keywords: corrosion inhibitor, optical microscopy, gravimetric methods, P. oocarpa and synergistic effect.

Abstract The formation of thick anodic oxide films on antimony in diluted solutions of oxalic acid (CO(OH)2) was studied under galvanostatic and isothermal conditions. The film formation was always accompanied by a dissolution process which strongly depended on the growth conditions. The formation efficiency, as determined by the dissolved metal amount, was affected by the CO(OH)2 concentration, the current density and the anodization time. The dissolved antimony amount increased with higher CO(OH)2 concentrations and anodization time, and with lower current densities. The analysis of the total current density suggests the occurrence of a formed film and a dissolving component. According to the calculations, the anodic oxides composition is close to Sb2O3. The growth of anodic Sb2O3 took place at high electric fields within the oxide film. The thicknesses of the formed films were calculated by taking into account their dissolution. The film formation efficiency was determined at various current densities. Keywords: antimony anodic dissolution, film formation efficiency, galvanostatic anodization and electric field intensity.

Abstract Green corrosion inhibitors find various applications in the field of corrosion engineering and technology. In the present work, powder forms of Pimenta Dioica leaves were added into corrosion media to study their effect. Mild steel coupons corrosion studies showed an increase in the inhibitor efficiency, at higher concentrations, in corrosive media. The coupons electrochemical behavior was studied by OCP measurements. P. Dioica inhibition efficiency, adsorbed layers mechanism and mild steel corrosion rate were analyzed using weight loss measurements. Keywords: Pimenta Dioica, green inhibitor, mild steel, potable water and corrosion study.

Abstract Aniline corrosion inhibitor effect on zinc in a H2SO4 solution has been evaluated by weight loss (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Scanning Electron Microscope (SEM) techniques. The corrosion rate increased with higher acid concentrations. At constant inhibitor content, with higher acid concentrations, the corrosion rate increased. With higher inhibitor concentrations the corrosion rate decreased, while inhibition efficiency (IE) percentage increased. The maximum IE of 90.18% was obtained at 60 mM of aniline in a 0.5 M H2SO4 solution. Polarization studies revealed that aniline acts as a mixed type inhibitor. EIS spectra are semicircular, which indicates that zinc corrosion was mainly controlled by a charge transfer process. SEM reveals the appearance of a smooth surface on zinc in aniline presence, probably due to the formation of an adsorptive film of electrostatic character. It was found that there is a good agreement between the different tested techniques. Keywords: Zinc, H2SO4, aniline effect, polarization and EIS.

Abstract The adsorption capability of the series of some Macrocyclic Polyether compounds containing 1, 3, 4-thiadiazole entity n-MCTH (n = 1-5), especially 3- MCTH, 4-MCTH and 5 MCTH, and their protonated forms, was studied in the light of DFT quantum modeling and Monte Carlo dynamics calculations. Sensitivity to corrosion has been quantified using the degree of planarity, global and local electronic proprieties, as well as the inhibitor strength of interaction, in neutral and protonated forms, with the (111) iron surface in the metallic complex. The results of both approaches showed the supremacy of the interactions of neutral and proton variants of the 5-MCTH-Fe complexes, compared to their homologues of 3-MCTH-Fe and 4-MCTH-Fe, due to the significant involvement of aryl rings, in addition to the thiadiazole ring, in the process of electron donation and acceptance. Keywords: DFT calculations; Monte Carlo dynamics calculations; global electronic proprieties; local electronic proprieties; and complexation strength.