Gravimetric Evaluation of Calotropis procera Leaf Extract as a Green Corrosion Inhibitor for Mild Steel in Acidic and Alkaline Media

Abstract

Corrosion of mild steel remains a major industrial challenge, causing significant economic losses and equipment failure. Plant-derived corrosion inhibitors provide an environmentally friendly alternative to conventional synthetic chemicals. This study evaluated the corrosion inhibition performance of Calotropis procera (Sodom apple) leaf extract on mild steel in 0.5 and 1.0 M NaOH and 0.5 and 1.0 M H₂SO₄ using the gravimetric weight-loss method. Mild steel coupons were immersed in the corrosive media containing 0, 2, 4, 6, 8, and 10 g of the extract for 168, 336, 504, and 672 h. Weight loss, corrosion rate, inhibition efficiency (IE%), and surface coverage (θ) were determined to assess inhibitor performance. Results showed that the corrosion rate decreased progressively with increasing extract concentration, whereas inhibition efficiency and surface coverage increased, indicating concentration-dependent adsorption of phytochemical constituents onto the steel surface. The extract provided effective protection in both alkaline and acidic environments, with the highest inhibition efficiency of 94.3% and surface coverage of 0.943 achieved at 10 g after 672 h in 1.0 M H₂SO₄. Although corrosion was more severe in acidic than alkaline media, the extract markedly suppressed metal dissolution by forming a stable protective film on the mild steel surface. These findings demonstrate that Calotropis procera leaf extract is an efficient, eco-friendly, and cost-effective green corrosion inhibitor with strong potential for protecting mild steel in aggressive industrial environments and that it offers a sustainable alternative to conventional corrosion-control chemicals. The observed performance highlights its promise for environmentally sustainable corrosion management. Future industrial application is recommended.