Dapsone: A Novel Corrosion Inhibitor for Mild Steel in Acid Media

Abstract: Corrosion inhibition of mild steel in 1 M HCl and 0.5 M H 2 SO 4 by dapsone were studied by polarization resis-tance, Tafel polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurement. Results obtained revealed that inhibition occurs through adsorption of the drug on metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization suggested that it acts as a mixed type predominantly cathodic in HCl and predominantly anodic in H 2 SO 4 . Electrochemical impedance spectroscopy was used to investigate the mechanism of corrosion inhibition. Thermodynamic parameters such as E a , °
Ha , °
Sa , °
Hads were calculated to investigate mechanism of inhibition. The adsorption of dapsone followed Langmuir adsorption isotherm. Keywords: Mild steel, Acid solution, weight loss, EIS, Drug. 1. INTRODUCTION Inhibition of corrosion of mild steel is a matter of theo-retical as well as practical importance [1]. Acids are widely used in industries such as pickling, cleaning, descaling etc. Because of their aggressiveness, inhibitors are used to reduce the rate of dissolution of metals. Compounds containing ni-trogen, sulphur and oxygen have been reported as excellent inhibitors [2-7]. The efficiency of an organic compound as an inhibitor is mainly dependent on its ability to get adsorbed on metal surface which consists of a replacement of water molecule at a corroding interface. The adsorption of these compounds is influenced by the electronic structure of inhib-iting molecules, steric factor, aromatic, and electron density at donor site, presence of functional group such as –CHO, –N=N, R–OH etc., molecular area and molecular weight of the inhibitor molecule [8-11]. A large number of organic compounds are known to be applicable as corrosion inhibitors for mild steel [12, 13]. However, only a few non-toxic and eco-friendly compounds have been investigated as corrosion inhibitors. Tryptamine, Succinic acid, L-ascorbic acid, Sulfamethoxazole and Ce-fatrexyl, were found to be effective inhibitors for acid envi-ronments. Dithiobiurets exhibited the best performance to-wards the corrosion of mild steel in HCl solutions showed very less toxicity [14-19]. The inhibitive effect of four anti-bacterial drugs, namely Ampicillin, Cloxacillin, Flucloxacil-lin and Amoxicillin towards the corrosion of aluminum was investigated [20]. The inhibition action of these drugs was attributed to blocking the surface