Zinc oxide nanoparticles produced from pumpkin pods and zinc acetate as corrosion inhibitor on aluminium metal in acidic medium: kinetics and thermodynamics study

Abstract

This study investigates the kinetic and thermodynamic potential of using zinc oxide nanoparticles produced from pumpkin pods and zinc acetate as corrosion inhibitors on Aluminium metal immersed in an acidic medium. Kinetics and thermodynamic studies of the corrosion process are crucial for analysing and controlling corrosion processes. The corrosion study was conducted using an electrochemical spectroscopy method at temperatures of 35°C, 45°C, and 55°C.  The kinetic study was analysed using Open Circuit Potential (OCP) and Linear Polarisation Resistance (LPR) for a 1.0MHCl Solution. The electrochemical measurement shows that the inhibitor concentration exhibits better corrosion resistance than the control, indicating that the coated sample provides an inhibitive effect against the entrance of the hydrochloric acid solution into the active site of the metal. This zinc oxide nanoparticle acts predominantly as an anodic, cathodic, and mixed-type inhibitor. The results show that using varying inhibitor dosages of 30 ppm, 110 ppm, and 190 ppm reduces the corrosion of aluminium metal in a hydrochloric acid environment. The polarisation resistance and corrosion rate results from the LPR and OCP measurements confirmed the effectiveness of this inhibitor. The corrosion rate from the electrochemical test indicated a gradual decrease as the dosage of the inhibitor increased, resulting in increased polarisation resistance. The results show a higher activation energy for the inhibited process at 110 ppm in comparison with the control, indicating that the inhibitor hinders the corrosion of aluminium metals. Conversely, this is not the case for 30 ppm and 190 ppm.  This trend suggests that the inhibited process at a 110 ppm dosage is due to physisorption, while chemisorption occurs at 30 ppm and 190 ppm, respectively. The enthalpy change (∆H) for 30 ppm, 110 ppm, and 190 ppm solutions are 242,881.4 J/mol, 147,632 J/mol, and 95,266.6 J/mol, respectively, which is higher than that of the control (65,487.1 J/mol). Both enthalpy change and entropy change (∆S) values are positive, indicating that the adsorption on the aluminium metal is endothermic and increases the rate of disorderliness of the process.