Assessment of Natural Plant Extracts as Green Corrosion Inhibitors for Steel in Acidic Media

Thesis Abstract

The pervasive issue of steel corrosion in acidic environments poses significant economic and safety challenges in various industrial sectors, necessitating the development of environmentally sustainable and cost-effective corrosion inhibition methods. This study aims to evaluate the efficacy of selected natural plant extracts as green corrosion inhibitors for mild steel in hydrochloric acid solutions, addressing the urgent need for eco-friendly alternatives to conventional chemical inhibitors. Specifically, the research objectives include identifying potent plant extracts through preliminary phytochemical screening, quantifying their corrosion inhibition efficiencies, elucidating their mechanisms of action, and comparing their performance with standard inhibitors such as zinc sulfate. Employing a mixed-methods approach, the research integrates quantitative laboratory experiments with qualitative analyses to provide comprehensive insights into the inhibition performance and chemical interactions involved. The study adopts a descriptive experimental design involving 150 mild steel coupons prepared according to ASTM standards, with samples randomly assigned to various treatment groups. Data collection centers on weight-loss measurements obtained through gravimetric analysis, electrochemical measurements using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), and surface characterization techniques including scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The plant extracts—specifically, neem, moringa, and hibiscus—were obtained via standardized solvent extraction methods, and their phytochemical constituents identified using gas chromatography-mass spectrometry (GC-MS). Data analysis employs statistical techniques such as analysis of variance (ANOVA) to determine significant differences among treatment groups at a 95% confidence level, with further application of regression analysis to model the relationship between extract concentration and corrosion inhibition efficiency. The surface morphology and chemical interactions are interpreted through SEM and FTIR spectra, enabling an understanding of the adsorption mechanisms. The research incorporates the theoretical framework of the Langmuir and Temkin adsorption isotherm models to interpret inhibitor adsorption behavior, supported by quantum chemical calculations to elucidate the relationship between molecular structure and inhibition performance. Expected findings demonstrate that the selected plant extracts exhibit substantial corrosion inhibition efficiencies, reaching up to 85% at optimal concentrations, with neem extract showing the highest performance due to its phenolic and flavonoid contents. Surface analyses reveal that the extracts form protective bio-films on steel surfaces, reducing metal dissolution by blocking active sites. The corrosion inhibition mechanism is anticipated to be predominantly through physical adsorption (physisorption), corroborated by adsorption isotherm fitting. The study also highlights the influence of extraction solvent polarity and phytochemical composition on the inhibitory effectiveness. This research contributes to the expanding body of knowledge on eco-friendly corrosion control, providing empirical evidence and detailed mechanistic insights into plant-based inhibitors in aggressive acidic media. It demonstrates that natural plant extracts are viable, sustainable alternatives to conventional inhibitors, with potential applications in cleaning, pipeline, and marine industries. The findings advocate for the integration of phytochemically derived inhibitors into industrial corrosion management practices, promoting environmental safety and cost reduction. The study concludes that plant extracts such as neem, moringa, and hibiscus can serve as effective green corrosion inhibitors, with efficiency influenced by extract concentration and chemical composition. Based on these insights, recommendations include further exploration of synergistic effects among plant extracts, scale-up studies for industrial implementation, and detailed evaluation of long-term stability and environmental impact. Future research should also focus on bioengineering approaches to enhance the inhibition properties of phytochemicals and investigate their applicability across diverse corrosive environments.