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.

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... e 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.