Experimental and theoretical study for corrosion inhibition of mild steel in hydrochloric acid solution by some new hydrazine carbodithioic acid derivatives K.F. Khaled * Chemistry Department, Faculty of Education, Ain Shams University, Roxy, Cairo 11711, Egypt Received 6 June 2005; received in revised form 10 June 2005; accepted 11 June 2005 Available online 15 July 2005 Abstract The corrosion inhibition of mild steel in 0.5 M hydrochloric acid solutions by some new hydrazine carbodithioic acid derivatives namely N 0 -furan-2-yl-methylene-hydrazine carbodithioic acid (A), N 0 -(4-dimethylamino-benzylidene)-hydrazine carbodithioic acid (B) and N 0 -(3-nitro-benzylidene)-hydrazine carbodithioic (C) was studied using chemical (weight loss) and electrochemical (potentiodynamic and electrochemical impedance spectroscopy, EIS) measurements. These measurements show that the inhibition efficiency obtained by these compounds increased by increasing their concentration. The inhibition efficiency follow the order C > B > A. Polarization studies show that these compounds act as mixed type inhibitors in 0.5 M HCl solutions. These inhibitors function through adsorption following Langmuir isotherm. The electronic properties of these inhibitors, obtained using PM3 semi-empirical self-consistence field method, have been correlated with their experimental efficiencies using non-linear regression method. # 2005 Published by Elsevier B.V. Keywords: Mild steel; Acid corrosion inhibitors; PM3 quantum method; EIS; Acid corrosion inhibition 1. Introduction In view of the fact that aggressive acid solutions are widely used for industrial purposes, inhibitors are commonly used to decrease the corrosion attack on metallic materials. The inhibition of corrosion of mild steel by acids was previously studied by some sulphur and/or nitrogen containing compounds [1–4]. Dithiocarbazate, NH 2 NHCS 2 , and its substituted derivatives have been synthesized and investigated over the past few decades [5–8]. Interest remains high in these compounds and the Schiff bases derived from them through condensation with various aldehydes and ketones because of the intriguing observation that they sometimes show different biological properties, although they may differ only slightly in their molecular structures [9]. Transition metal complexes of these ligands are widely studied because of their potential for therapeutic use [10]. They also find www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 4120–4128 * Tel.: +20 105 747059; fax: +20 225 81243. E-mail address: khaled.f@mailcity.com. 0169-4332/$ – see front matter # 2005 Published by Elsevier B.V. doi:10.1016/j.apsusc.2005.06.016