Electrochemical and Analytical Study of the Corrosion Inhibitory behavior of Expired Pharmaceutical Compounds for C- Steel Corrosion

Expired pharmaceutical compounds cause environmental pollution which can lead to public health problems. Also, they represent economical problems for pharmaceutical companies because of high disposal costs. On the other hand, the widely used corrosion inhibitors have toxicity problems. To solve the above problems, this work aimed to evaluate the effectiveness of selected expired pharmaceutical compounds as corrosion inhibitors. Hydrochlorothiazide (HCT), captopril (CAP) and guaifenesin (GFN) were chosen as representative examples. These drugs were evaluated as corrosion inhibitors for C-steel in 2 M hydrochloric acid solution at 30°C by various analytical techniques. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and electrical frequency modulation (EFM) methods were used in this study. Weight loss technique data was also discussed. The electrochemical results indicated that these compounds are efficient inhibitors for C-steel corrosion. Their efficiencies were up to 81.8 % at the tested temperature. The increase in drug concentration caused increase in the corresponding inhibition efficiency (%IE) values. The adsorption amount and the coverage of pharmaceutical molecules were also increased with increasing concentration. The adsorption of these compounds on C-steel surface obeyed the Temkin adsorption isotherm. Polarization curves indicated that, the investigated pharmaceutical compounds were mixed-type inhibitors. The corrosion kinetic parameters were discussed. The chemical data were in good agreement with those obtained from electrochemical methods.