Inhibition of mild steel corrosion in H2SO4 solution by coconut coir dust extract obtained from different solvent systems and synergistic effect of iodide ions: Ethanol and acetone extracts

• Ethanol and acetone extracts of coconut coir dust inhibited mild steel corrosion in H2SO4.
• The adsorption of ethanol and acetone follows Freundlich isotherm model.
• The extracts behave as a mixed-type inhibitor but under cathodic control.
• Ethanol extract is a better inhibitor than acetone extract of coconut coir dust.
• Addition of I− ions enhanced inhibition efficiency significantly.

Weight loss and electrochemical (open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy) techniques were used to assess the effectiveness of ethanol and acetone extracts of coconut coir dust as corrosion inhibitor for mild steel in 0.5 M H2SO4 solution at 30–60 °C. It was found that both ethanol and acetone extracts of coconut coir dust retard the dissolution of mild steel in 0.5 M H2SO4 solution, but a pronounced effect was noted with ethanol extract. The inhibition efficiency increased with increase in extract concentration but decreased with rise in temperature, which is suggestive of physical adsorption mechanism. Addition of KI was found to synergistically enhance the protective ability of coconut coir dust extracts obtained from both solvent systems investigated. The synergistic effect was confirmed from the synergism parameter (S0) which was found to be greater than unity. Potentiodynamic polarization result suggests that coconut coir extracts functioned as mixed-type inhibitor. The adsorption of coconut coir dust extracts onto the mild steel surface followed Freundlich adsorption isotherm model. The mechanism of physisorption of the extracts onto the steel surface is proposed from the trend of inhibition efficiency with temperature which is corroborated by the values of activation parameters obtained from the experimental data.

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