Abstract
Anodic polarization of nickel was studied by potentiostatic technique in neutral media in presence of two macrocyclic ligands. Pit initiation was detected by measuring pitting potential, Ep and the charge transfer, Q during the anodic polarization. Initiation of pitting and Q were found to be dependent on the structure and concentrations of inhibitors. Under steady state conditions, the inhibition efficiency was in the order 1, 4, 8, 11 tetraazacyclotetradecane (cyclam) > N, N’-bis (2-aminoethyl) 1, 3-propandiamine (2,3,2-tet) due to macrocyclic effect. These findings were confirmed by fitting the data to different adsorption isotherms. Adsorption on nickel surface was obeyed kinetic-thermodynamic model for the two inhibitors. Influence of [Cl–] on corrosion behavior of nickel in sulphate solution containing inhibitors was investigated. A mechanism involving three competitive equilibria of dissolution of nickel in presence and absence of the inhibitors was proposed. Empirical and theoretical kinetic equations were compared and discussed. There is a good agreement between the calculated and observed rate constants.
Highlights
The importance of nickel as basic material for corrosion resistant alloys and its catalytic properties with respect to many organic reactions is well recognized [1]
Nickel is known as corrosion resistant metal in many aggressive media, it corrodes at a significant rate in the presence of mineral acids or in neutral medium
It can be observed that the presence of 2,3,2-tet in the medium leads to improve the inhibition of pitting corrosion by shifting the critical pitting potential of initiation (Ep) towards more positive values
Summary
The importance of nickel as basic material for corrosion resistant alloys and its catalytic properties with respect to many organic reactions is well recognized [1]. Jha et al studied the effect of dicyandiamide, biguanide, and guanylurea on corrosion of nickel in neutral medium [3,4,5] They found that the presence of the inhibitors promote considerable inhibition at higher concentration as well as with increasing the temperature. The effect of the concentration and chemical nature of anions-activators, the pH and solution temperature on the inhibition process of pitting of nickel has been studied [8]. The purpose of the present study is to investigate the corrosion inhibition characteristics of the qundridenate macrocyclic ligand 1, 4, 8, 11, tetraaza-cyclotetradecane (cyclam) and its open chain analogous N, N’-bis (2amino ethyl) 1, 3-propandiamine (2,3,2-tet) on nickel dissolution in neutral media. To study the kinetics and mechanism of pitting corrosion of nickel in presence of inhibitors
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