No abstract

The performance of triethylenetetramine-tribenzylidene (TTTB) and triethylenetetramine-trisalicylidene (TTTS) as corrosion inhibitors for zinc in hydrochloric acid is investigated. At lower concentrations, both inhibitors accelerate the attack but inhibit corrosion at higher concentrations, e.g., 96-100% with 1.0% concentration in 0.5 M and 1.0 M HCl. The efficiency of TTTB decreases while that of TTTS remains almost constant (≥ 99.7%) up to 120 minutes and in the temperature range 35 -65 ºC. The activation energies are higher in inhibited than in plain acid with both inhibitors. The free energy of adsorption (∆G ads ) and heat of adsorption (Q ads ) are negative, which suggests that there is spontaneous adsorption on metal surface, and from the values of (∆G ads ) and (Q ads ), the values of entropy of adsorption (∆S ads ) were calculated. Galvanostatic polarization shows that corrosion is under mixed control with predominance of the cathodic part. In uninhibited 1.0 M HCl, complete cathodic protection is achieved at a current density of 4.2224 Adm -2 , but in presence of these inhibitors, much lower current densities are required. Plot of log (θ/1-θ) versus log C inh gives a straight line, suggesting that inhibitors cover both the anodic and cathodic regions through general adsorption following Langmuir isotherm. The mechanism of inhibition has been proposed.

PurposeThe purpose of this paper is to describe the behavior of salicylidene‐N‐N′‐dimorpholine as a corrosion inhibitor for zinc in hydrochloric acid and the mechanism of its action.Design/methodology/approachThe effects of various parameters on the behavior of this inhibitor have been studied using weight loss, galvanostatic polarization, and cathodic protection methods. Thermodynamic parameters and adsorption data also were utilized.FindingsThe inhibitor showed excellent corrosion inhibition (>99 percent) at effective concentration. It appeared from thermodynamic parameters that an efficient inhibitor is characterized by a relatively greater decrease (i.e. more negative) in free energy of adsorption (ΔGA°), positive values of entropy of adsorption (ΔSA°), and lower heat of adsorption (QA). Galvanostatic polarization data indicate that this is a “mixed” type inhibitor with predominant effect on the cathode. The inhibitor followed Langmuir adsorption isotherm behavior. The cathodic protection indicated that the conjoint action of the inhibitor and the cathodic current was either synergistic or additive.Originality/valueVery few inhibitors exhibit such excellent inhibitive effect on zinc in aggressive corrosive media as is shown in this paper.