M.D. Shah, A.S. Patel, G.V. Mudaliar and N.K. Shah*

Chemistry Department, School of Sciences, Gujarat University, Ahmedabad, Gujarat – 380009, India

DOI: 10.4152/pea.201102101

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 (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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Acknowledgement

M.D. Shah, A.S. Patel and G.V. Mudaliar are grateful to Chemistry Department, School of Sciences, Gujarat University, Gujarat, for laboratory facility. One of the authors, Aesha Patel is also thankful to UGC-BSR for research fellowship.

* Corresponding author. E-mail address: nishchem2004@yahoo.co.in

Received 24 September 2010; accepted 29 March 2011