Thermodynamics, adsorption, and response surface methodology investigation of the corrosion inhibition of aluminum by Terminalia chebula Ritz. extract in H3PO4

Abstract

This study focuses on investigating the effect of Terminalia chebula Ritz. extract (TCE) for corrosion inhibition of Al in phosphoric acid (H3PO4) using potentiodynamic polarization (PDP) technique. In this study, the effect of concentration of TCE extract, the concentration of H3PO4 acid medium, and temperature (T) was investigated on the corrosion current density (icorr) and inhibition efficiency (IE). The TCE was characterized by FTIR analysis, and the adsorption of TCE was justified with the help of kinetic, thermodynamic, adsorption isotherm parameters. The surface morphology study was done using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS), and atomic force microscopy (AFM). The study also focuses on identifying the optimum process parameters for obtaining the maximum IE by applying the response surface methodology (RSM) and desirability function approach. The maximum IE of 83.24% was achieved at a temperature of 30 ℃, the concentration of TCE extract of 500 ppm, and H3PO4 acid concentration of 0.5 M. Regression analysis, Pareto chart, normal chart, main effect, and interaction effect plots are employed to acquire an in-depth understanding of process variables on IE. The IE obtained from the experiments and the predicted model is in a close match and a high value of the coefficient of determination (R2 = 99.98%) displays that the generated model was able to estimate the IE accurately from the selected process variables.

Chemical, electrochemical, thermodynamic and adsorption study of EN8 dual-phase steel with ferrite-martensite structure in 0.5 M H2SO4 using pectin as inhibitor

“…The CR's were calculated at different temperatures (40-70 °C) by the weight loss method was applied for the determination of E a (activation energy), ΔH # (activation enthalpy), and ΔS # (activation entropy) (Prabhu et al 2021). The determination of each activation parameter is done as per the literature (Prabhu and Rao 2019).…”

“…The correlation coefficient (R 2 ) and best fits are the deciding criteria for selecting the suitable adsorption isotherm. The calculation of standard free energy of adsorption (∆G°a ds ) was obtained from the adsorption equilibrium constant (K) (Prabhu and Rao 2013;Prabhu et al 2021). The standard enthalpy of adsorption (ΔH°a ds ) and standard entropy of adsorption (ΔS°a ds ) were obtained from a plot of ∆G°a ds vs T.…”

“…For PDP and EIS studies the procedures were as per the literature (Prabhu et al 2021). The specimen with a surface area of 0.5 cm 2 was taken for the study.…”

“…Measurements of the EIS were also performed according to the literature (Prabhu et al 2021). Impedance charts are given in the Nyquist representation and the Bode phase and magnitude graphs.…”

“…The activation parameters for the deterioration of EN8 steel in 0.5 M H 2 SO 4 comprising pectin are presented in Table 2. As inhibitor concentrations increase, activation energy (E a ) has increased, indicating that the energy barrier increases as pectin concentration increases (Prabhu et al 2021). Activation enthalpy (∆H # ) values vary depending on E a , indicating the recommended mechanism.…”