The novelty of this paper is the analysis in a medium containing sulfide ion due to the generation of this ion in petroleum industries, in the refining stage (the sulfide ion is also present on the produced water). The performance of 1-hydroxyethylidene-1,1-diphosphonic acid inhibitor (HEDP) was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss measurements in a dissolution of AISI 304 stainless steel immersed in a solution containing chloride and sulfide ions. The protection of the stainless was increased with the addition of divalent cations (Ca 2+ , Zn 2+ , and Mg 2+ ). Potentiodynamic polarization studies have shown that the inhibitor alone has anodic protection, but the addition of Ca 2+ (10 mg•L −1 ) favors the cathodic protection, and the addition of Zn 2+ (20 mg•L −1 ) and Mg 2+ (10 mg•L −1 ) mixed-type is observed. Electrochemical impedance spectroscopy was performed at three distinct potentials: −0.3 [V vs. SCE], E corr [V vs. SCE], and 0.1 [V vs. SCE]. This revealed that calcium is responsible for favoring the formation of the film and the other elements (zinc and magnesium) favor the stabilization of the protective film. Scanning electron microscopy analysis revealed that the addition of cations provided the adsorption of HEDP on the metal surface. Weight loss results showed that the presence of zinc in a solution containing HEDP favored greater inhibitor efficiency (Zn 2+ η m = 85.2% and for Mg 2+ η m = 70.4%).
The study of the inhibiting effect of certain pyridine and aniline derivatives on the corrosion of copper in persulphate solutions enables the compounds to be arranged in the following series of decreasing inhibiting power; 2,6‐lutidine – 2‐picoline – pyridine – m‐anisidine – p‐phenetidine – aniline.
Inhibition may generally be attributed to the adsorption of organic molecules, nitrogen being an electron donor and becoming attached to the metal surface. Symmetric substitution by methyl groups in the pyridine molecule increases the inhibiting effect. In the case of aniline derivatives m‐anisidine is superior to the other compounds studied. On the base of electrochemical experiments it may be concluded that the reaction is under cathodic control, the cathode being extremely polarized at high current densities.
Three molecules containing morpholine, 1,4-naphthoquinone, 7-chloroquinoline and 1,3,5-triazine cores, scaffolds with recognized anti-corrosive activity, were synthesized and had their anticorrosive activity evaluated through potentiodynamic polarization and electrochemical impedance studies. Both studies were conducted in a simulated production water medium containing 150,000 mg•L −1 Cl − and 5 mg•L −1 S 2−. Corrosion inhibition efficiency ranged from 67%-86%, amongst which the naphthoquinone-containing derivative (compound 1) was the most effective. These compounds act through formation of a protective film on the surface of AISI 316 stainless steel. Investigation of the molecular properties of the prepared inhibitors by DFT calculations revealed that the LUMO energy and chemical hardness of the molecules can be directly correlated with their inhibition efficiency.
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