Corrosion inhibition of A36 mild steel in 0.5 M acid medium using waste citrus limonum peels

Research effort is being intensified on the establishment of organic substances that can actively perform the role of metal inhibition. Investigation on corrosion inhibition of A36 mild steel in 0.5 M H2SO4 medium using waste citrus limonum peels as inhibitor was carried out. Gravimetric tests (weight loss, corrosion rate and inhibition efficiency) involving the variation of citrus limonum peels inhibitor concentration (0-4 w/v%), corrosion time (0-12 h) and reaction temperature (28 degrees C and 45 degrees C) were conducted. Langmuir and Freundlich adsorption isotherms were considered in the establishment of the adsorption behavior of citrus limonum peels inhibitor on A36 mild steel surface. The thermodynamic parameters (adsorption equilibrium constant k(ads), change in Gibbs free energy delta G(ads), change in heat of adsorption delta H-ads and entropy change delta S-ads) of the adsorbed inhibitor on mild steel surface were determined. The results of the study showed that 0.4 w/v% citrus limonum concentration gave highest inhibition efficiency of 94% and 92% on A36 mild steel at 28 degrees C and 45 degrees C respectively. And the surface adsorption of citrus limonum inhibitor on A36 mild steel was described by both the Langmuir and Freundlich adsorption isotherms. The negative values of delta S, delta G(ads), delta H-ads indicated that the inhibitor adsorption is exothermic and spontaneous (physical adsorption). SEM/EDX analysis showed that inhibitor adsorption of citrus limonum was better at 28 degrees C compare to 45 degrees C, by giving a more evenly distributed particles at 0.4 w/v% inhibitor concentration.