Investigation of the inhibition behavior of an octacalcium phosphate as a green corrosion inhibitor against carbon steel in 3 % NaCl medium

Abstract

The development of new corrosion inhibitors constitutes a significant endeavor for researchers. In this study, the efficacy of octacalcium phosphate (OCPa), an inorganic green corrosion inhibitor for carbon steel in a 3% NaCl solution, was evaluated. This investigation marks the first application of this compound in a saline environment. The phosphate inhibitor was synthesized through a double aqueous decomposition process in an equimolar solution of water and ethanol, and subsequently characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), chemical analysis, and SEM/EDX to ascertain its properties and morphology. Meanwhile, the electrochemical behavior was investigated using techniques such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) to assess the anticorrosive performance of the studied phosphates. Analysis of the carbon steel surface morphology of the resultant layer was conducted using SEM/EDX and FTIR. According to the electrochemical results, OCPa demonstrated an impressive inhibitory effect, with an efficiency reaching 93.1% at an optimal concentration of 50 ppm, exhibiting a cathodic type of inhibition. Moreover, the charge transfer resistance was found to be 2450 Ω.cm2 in the presence of 50 ppm of the inhibitor, as compared to 161.0 Ω.cm2 in the uninhibited solution. The thermodynamic parameters indicated an endothermic nature for the adsorption process in the presence of OCPa. Examination of the carbon steel surface morphology by SEM revealed the formation of a protective layer, serving to shield the metal from corrosion. The experimental findings underscore the potential of octacalcium phosphate as a promising inorganic green corrosion inhibitor for carbon steel in saline environments, opening new avenues for the exploration and development of environmentally benign anti-corrosive substances.