Factor Interactions Governing Aluminium Corrosion Inhibition by <i>Sida acuta</i> Leaf Extract: Response Surface Methodology and Gravimetric Study

Abstract

The growing demand for environmentally benign corrosion inhibitors has intensified research into plant-based alternatives to toxic synthetic chemicals. This study evaluated the corrosion-inhibition performance of Sida acuta leaf extract on aluminum in 0.1 M H₂SO₄ using gravimetric techniques and optimizing via Response Surface Methodology (RSM). A Box–Behnken design investigated the combined effects of immersion time (24–168 h), temperature (20–60 °C), and inhibitor concentration (1–7 % v/v) on inhibition efficiency (IE). Experimental IE values ranged from 46.86% to 88.83%, indicating strong dependence on operational conditions. High efficiencies were observed at short exposure times and mild temperatures, including 82.17 % at 24 h, 20 °C, 4 % v/v, and 80.76 % at 24 h, 40 °C, 7 % v/v, with the highest experimental IE (88.83 %) at 96 h, 20 °C, 7 % v/v, reflecting rapid adsorption and protective film formation. The RSM model predicted a maximum IE of 88.81 % at 24 h, 20 °C, and 7 % v/v, indicating optimal protection under low-temperature, moderate-exposure conditions. Extended immersion and elevated temperatures reduced protection, with minimum IE values of 50.56 % and 46.86 % at 168 h, 60 °C, 1 % v/v. Fit summary statistics confirmed the linear model as most suitable (sequential p < 0.0001; adjusted R² = 0.7586; predicted R² = 0.5895), while sequential sum of squares highlighted significant linear effects (F = 17.76, p < 0.0001) and negligible contributions from interaction (F = 0.6638, p = 0.5930) and quadratic terms (F = 0.2166, p = 0.8819), with the cubic model being significant but aliased. ANOVA further identified immersion time (F = 33.96) and temperature (F = 15.15) as dominant factors, though the significant lack-of-fit suggests caution in over interpreting predictions. Overall, Sida acuta leaf extract demonstrates strong potential as a sustainable green inhibitor, particularly under short-term, low-temperature conditions.