Electrochemical Study of the Corrosion Behavior of Zinc Surface Treated with a New Organic Chelating Inhibitor

The effect of a new organic compound (N-[(1E)-(4 methoxy phenyl)methylene]hydrazinecarbothioamide), called ATSC, with chelating groups, on the corrosion behavior of zinc was investigated. Electrochemical study of the zinc specimens was carried out in aqueous electrolyte containing 0.2？M Na2SO4 and 0.2？M NaCl maintained at pH 5 using galvanostatic polarization curves. The surface treatment of zinc was achieved by immersion in solutions of different concentrations of ATSC and for different immersion time and bath temperatures. The zinc metal treated with ATSC at 5% has showed good corrosion resistance and maximum protection efficiency of about 84% at 300？K. Moreover, the treatment induced a basic modification of the cathodic nature of zinc and controls the corrosion by decreasing the electron transfer rate. The corrosion protection could be explained by the formation of a protective organometallic layer on the zinc surface due to the chelation reaction between zinc and inhibitor molecules. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) were applied to study the protective layer. 1. Introduction Zinc is one of the most important non-ferrous metals, which finds extensive use in metallic coatings. Zinc, like aluminium, is amphoteric in its behavior towards acids and alkalies. Zinc and zinc-coated products corrode rapidly in moist atmospheres forming white corrosion product—white rust. Thus it is necessary to protect it from corrosion in acid as well as in alkaline medium. This can be achieved by using special organic compounds. Various organic reagents have been used for inhibiting the corrosion process of zinc and galvanized steel in neutral, weak acid, and alkaline solutions. The dissolution behavior of zinc in acid and nearly neutral media is efficiently inhibited by compounds containing nitrogen and sulfur. Such organic compounds generally increase the hydrogen over voltage on corroding metal [1]. The studies pertaining to the effect of organic additives on corrosion rate of zinc in acid solutions have been the subject of interest for many investigators [2]. Several researchers have studied the effect of aldehydes and amines on corrosion of many metals in different corrosive environments [3–5]. Several pyrazole derivatives, substituted N-aryl pyrroles, quinolines, bisaminotriazole and triazole derivatives, ethanolamine derivatives, aromatic hydroxyl compounds have been acted in the literature as corrosion inhibitors for zinc in different media. [6–11]. It was established that these compounds form protective layer