ABSTRACT
The effects of organic resins (Methylene blue and Neutral red) and plant extracts (piliostigma thonningii and Gmelina arborea) on corrosion rate of medium carbon steel in 0.2M H2SO4 acid pickling solution were studied with a view to comparing them with a known standard inhibitor (Sodium Benzoate). Gravimetric and Gasometric measurements were carried out at different inhibitor concentration and Temperature ranges of 0.05 - 0.5% and 30 - 600C respectively. Results obtained revealed that all the four compounds tested acted as mixed-type inhibitors, reducing the dissolution of iron and retarding H2 evolution, comparing favourably with the standard inhibitor at all inhibitor concentrations and temperatures studied. The maximum inhibition efficiencies of the compounds tested were obtained at 300C and increased progressively in order of: Neutral red (83.29%), Methylene blue (90.96%), Sodium Benzoate (91.50%), Gmelina arborea (96.98%) and Piliostigma thonningii (97.94%). The mechanism of inhibition was elucidated by Kinetic and thermodynamic models. It was concluded that the adsorption of the compounds onto the steel surface, which obeyed the Langmuir and Temkin adsorption isotherms, is the main mechanism of inhibition by these compounds.