Corrosion inhibition effect of sodium iodide for mild steel in 1 M hydrochloric acid: mathematical, surface morphological, and kinetics studies

The corrosion of mild steel alloy in 1 M HCl in the absence and presence of sodium iodide as a corrosion inhibitor is investigated. The mathematical and statistical studies for the mild steel mass loss as a function of inhibitor concentration, temperature, and time are performed using the least-squares regression method. Furthermore, morphological studies via atomic force microscopy (AFM) and X-ray diffraction (XRD) are achieved for the polished, corroded, and inhibited mild steel samples. In addition, kinetic studies are employed to determine the reaction order and other kinetic parameters. Three mathematical models were proposed: the exponential model, exponential growth, and the polynomial model. Nonlinear estimation based on Levenberg-Marquardt as the estimation method showed that the best fit was obtained using exponential growth with a 0.988 correlation coefficient. AFM and XRD outcomes showed an improvement in the surface properties in the presence of NaI. The average roughness (Ra) for the polished, corroded, and inhibited steel samples is 131.35, 1343.4, and 219.65 nm. Kinetic experiments showed a zeroth order response with a significant correlation coefficient.