Adsorption Isotherm Analysis of Black Seed (Nigella Sativa L.) Oil as an Eco-friendly Corrosion Inhibitor for Mild Steel in Acidic Environment

Abstract

The objective of this paper is to evaluate the adsorption isotherm analysis of black seed (Nigella Sativa L.) oil as an eco-friendly corrosion inhibitor for mild steel in acidic environment using appropriate standard techniques. Weight loss analyses showed that mild steel coupons immersed in the acidic solution without the inhibitor experienced much higher corrosion rates compared to those treated with the extract. Over time, corrosion rates increased initially but began to decline after 72 hours due to protective oxide film formation, consistent with observations from previous studies. Adsorption isotherm models were employed to understand the interaction between the inhibitor and the steel surface. The Langmuir isotherm was determined to be the best fit for the adsorption process, suggesting a monolayer coverage of the inhibitor on the mild steel surface. This model yielded a maximum adsorption capacity (Q_max) of 1.03 mg/g and a favorable Langmuir constant (K_L) of 0.24 dm³/g. Scanning Electron Microscopy (SEM) analysis revealed changes in surface morphology, indicating the formation of a protective layer that mitigated corrosion. The mechanism of inhibition is attributed to a donor-acceptor interaction between the inhibitor molecules and iron, leading to a reduction in anodic and cathodic reactions. In conclusion, black seed oil extract demonstrates significant potential as an eco-friendly corrosion inhibitor for mild steel in acidic conditions, providing a sustainable alternative to conventional synthetic inhibitors.