Synthesis and characterization of green corrosion inhibitors from plant extracts for mild steel in acidic media: a comparative electrochemical and surface analysis study.

Project Abstract

In this study, plant-derived extracts are explored as sustainable green corrosion inhibitors for mild steel in acidic environments, with a focus on comparative electrochemical performance and surface characterization to elucidate inhibitory mechanisms. A diverse set of botanical sources, selected for rich heteroatom content (N, O, S) and conjugated pi systems, were prepared as crude extracts and subjected to rigorous chemical profiling using FTIR, GC-MS, and HPLC to identify principal active constituents responsible for corrosion inhibition. Electrochemical techniques, including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR), were employed in 0.5 M H2SO4 and 1.0 M HCl solutions at varying temperatures (25–65°C) to determine corrosion current densities, corrosion potentials, charge-transfer resistances, and double-layer capacitances, establishing inhibition efficiency as a function of extract concentration. The study reveals that certain plant extracts form a protective adsorbed layer on the mild steel surface, leading to decreased anodic and cathodic reaction rates, with adsorption behavior best described by Langmuir isotherms at ambient conditions and by Temkin isotherms at elevated temperatures, indicating physisorption-dominated and chemisorption contributions, respectively. Surface analysis using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM) corroborates electrochemical findings, showing reduced surface roughness, decreased pit density, and the presence of a uniform organic coat on inhibited specimens. X-ray photoelectron spectroscopy (XPS) further confirms the involvement of heteroatoms (N, O) and sulfur-containing species in the adsorbed film, suggesting coordination with Fe2+/Fe3+ and the formation of Fe–N, Fe–O, and Fe–S bonds. A comparative assessment of multiple extracts identifies structure–activity relationships, with extracts rich in heterocyclic rings and conjugated systems achieving higher inhibition efficiencies, surpassing 80% at optimal concentrations and moderate temperatures. Thermodynamic parameters derived from temperature-dependent studies indicate spontaneous adsorption (negative ?Gads), with a transition from physical to chemical adsorption mechanisms as temperature rises. Kinetic analyses indicate a diffusion-limited corrosion process in the absence of inhibitors, transitioning toward surface-controlled processes in the presence of inhibitors. The study also evaluates extract stability, leaching, and potential environmental impacts, demonstrating favorable biodegradability and low ecotoxicity relative to conventional inorganic inhibitors. The research integrates multidisciplinary approaches to provide a robust mechanistic framework for green corrosion inhibition, highlighting practical implications for industry by offering cost-effective, renewable, and scalable inhibitors derived from readily available plant resources. Recommendations for optimizing extraction methods, formulation of synergistic blends, and field-scale testing are discussed, along with considerations for compatibility with paint systems and industrial cleaning protocols. Overall, the work advances the understanding of natural product-based corrosion inhibitors and establishes a template for systematic screening and application of plant-derived compounds in acidic corrosion scenarios.

Project Overview

What This Project Is About

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This project looks at natural substances from plants to protect metal (mild steel) from rusting in acidic cleaners. It compares how well these plant-based compounds work as shields, using simple tests to see how they stop corrosion and what happens on the metal surface.

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The Problem It Addresses

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Industrial steels often corrode in acidic environments, leading to higher maintenance costs and safety concerns. Synthetic inhibitors can be costly and less eco-friendly. This project investigates affordable, green alternatives from plants that could reduce corrosion without harming the environment.

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Objectives of the Project

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1. Identify plant extracts with potential corrosion?inhibiting properties.
2. Characterize the chemical features of the plant compounds involved.
3. Test and compare corrosion protection performance in acidic conditions.
4. Analyze the metal surface before and after exposure to understand protection mechanisms.
5. Assess environmental and economic feasibility of using plant inhibitors.

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What You Will Do Step by Step

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1) Collect plant samples and prepare extracts. 2) Expose mild steel coupons to acidic solutions with/without inhibitors. 3) Measure corrosion rates using simple electrochemical tests (like potential and current changes). 4) Study the metal surface with basic surface analysis observations. 5) Compare results to identify best-performing extracts. 6) Interpret findings to explain how plant compounds protect steel.

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Expected Outcome

We expect to identify one or more plant extracts that significantly reduce corrosion in acid, with an understanding of how they work. The study should offer practical, eco-friendly options for industries and outline next steps for real-world testing.