Study of expired drug Phenazopyridine hydrochloride as a novel corrosion inhibitor for carbon steel in 1 M Hcl solution

This study is designed to evaluate the effectiveness of expired drug such as phenazopyridine hydrochloride (PPH) as a novel corrosion inhibitor for carbon steel (CS-metal) in HCl solution (1 M). The recycling of expired drugs is considered an environmentally friendly and sustainable way to save on economic cost. The drug PPH was examined using FTIR spectroscopy to identify active groups likely to be associated with the metallic surface in order to form a protective coating to inhibit the corrosion. A number of weight loss and electrochemical studies were performed at different inhibitor concentrations for different periods of immersion of 1, 3, 6, 9, and 24 hours at 298 K. The results show that inhibition efficacy was concentration dependent, with inhibited efficiencies of 53 %, 58 %, 75 %, and 75 % achieved for inhibitions at 50, 100, 200, 300, and 400 ppm concentrations, respectively, according to standard immersion time. It was noted at optimum concentration of 300 ppm, the efficiency of inhibition was 75% after 9 hours of exposure. The study revealed that there is an agreement between measurements of weight lost and dynamic voltage polarization. The study also involves the application of scanning election microscopy (SEM) in assessing the alterations on the metal surface upon immersion in an acidic environment. The adsorption of PPH drug on the metallic surface follows Langmuir Isotherm whereby the process of inhibition shows a clear connection between physical and chemical adsorption mechanism. The experimental results were supported by a theoretical study through calculating a set of quantum mechanical parameters which provided a deep understanding of the inhibition mechanism.