The Effect of Natural Corrosion Inhibitors on Mild Steel Used in Electrical Equipment Casings and Conductors in Hydrochloric Acid (HCl) Environments: A Study Using Hexalobus Crispiforus Stem Bark Extract

Corrosion of mild steel components remains a significant challenge in electrical and industrial applications, particularly under acidic conditions, where material degradation can compromise structural integrity, operational reliability, and service life. This study investigated the corrosion inhibition performance of Hexalobus crispiflorus stem bark extract on electroplated mild steel exposed to hydrochloric acid (HCl) environments. The study adopted an explanatory research strategy supported by an experimental methodology. Mild steel coupons were electroplated and subsequently subjected to yellow passivation treatments, while fresh Hexalobus crispiflorus stem bark was processed into a fine powder and applied at concentrations of 2, 4, and 6 g. HCl solutions of 0.02, 0.04 and 0.06 M were prepared as the corrodent media. Gravimetric weight-loss measurements were conducted at ambient temperature over exposure periods ranging from 2 to 8 days using passivated specimens. Corrosion rate, inhibition efficiency, and surface coverage were determined, while the adsorption characteristics of the inhibitor were evaluated using the Langmuir, Temkin, Freundlich, and El-Awady adsorption isotherm models. The results showed that the weight loss of the mild steel decreased with increasing inhibitor concentration from 2 to 6 g compared with the uninhibited control. The Hexalobus crispiflorus extract achieved a maximum inhibition efficiency of 40.59% at 6 g concentration using the yellow-passivated mild steel specimen. The inhibition efficiency was influenced by both inhibitor concentration and the concentration of the corrosive medium. The adsorption behaviour of the biomass on the plated mild steel surface was found to conform more closely to the El-Awady, Temkin, and Freundlich adsorption isotherms than to the Langmuir model, based on their comparatively higher coefficients of determination. The findings demonstrate the potential of Hexalobus crispiflorus stem bark extract as an environmentally friendly corrosion inhibitor for mild steel and provide a basis for further investigation under varying temperature conditions.