Abstract

SHAH, M.D.; PATEL, A.S.; MUDALIAR, G.V.  and  SHAH, N.K.. Schiff Bases of Triethylenetetramine as Corrosion Inhibitors of Zinc in Hydrochloric Acid. Port. Electrochim. Acta [online]. 2011, vol.29, n.2, pp.101-113. ISSN 0872-1904.

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 (ΔG_ads) and heat of adsorption (Q_ads) are negative, which suggests that there is spontaneous adsorption on metal surface, and from the values of (ΔG_ads) and (Q_ads), the values of entropy of adsorption (ΔS_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.

Keywords : corrosion; zinc; hydrochloric acid; inhibitor.

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