Green corrosion inhibition: Tobacco stem extract and KI on steel in H₃PO₄ – experimental, modeling, and theoretical insights

Background

Tobacco stem extract (TSE) has shown promise as a corrosion inhibitor, but its time-dependent behavior and synergistic effects with potassium iodide (KI) in phosphoric acid remain underexplored. Given the tobacco stem waste in China, further research on the corrosion inhibition performance of TSE is crucial. This is particularly important for phosphoric acid systems, where the complex dissociation behavior and film instability pose distinct challenges for corrosion control.

Methods

The corrosion inhibition of TSE in combination with KI on cold rolled steel (CRS) in 5.0 M H₃PO₄ was evaluated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Surface morphology was analyzed using SEM and AFM, while TOF-SIMS and XPS were used to examine the chemical composition. LC-MS identified the active components in TSE, and quantum calculations, along with molecular dynamics simulations, provided insight into the adsorption mechanisms.

Significant Findings

Weight loss analysis demonstrated 92.9 % inhibition efficiency for TSE/KI at 20 °C. Electrochemical tests indicated that TSE/KI suppresses both anodic and cathodic reactions, forming a stable protective film. Surface characterization confirmed the inhibition effects. Key adsorption sites on TSE include nitrogen atoms and conjugated double bonds. These findings offer a deeper understanding of the synergistic mechanism between TSE and KI, providing valuable guidance for the development of eco-friendly, plant-based corrosion inhibitors. A novel mathematical model based on capacitance evolution was constructed using MATLAB to assess time-dependent electrochemical behavior. These findings provide mechanistic and predictive insights into the use of TSE/KI as a sustainable corrosion inhibitor in phosphoric acid environments.