Application Of Kinetics – Thermodynamics Model And Adsorption Mechanisms For Inhibition Of Acid Corrosion On Mild Steel By Red Onion Peel Extract
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Date
2021-06-01
Authors
Mansor, Nuramirah
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
The study of kinetics–thermodynamics parameters and adsorption isotherms of
the inhibition of corrosion mild steel in acid medium using red onion peel extract (ROPE)
as green corrosion inhibitor was carried out. The inhibition efficiency was found to
increase with increasing inhibitor concentration but decrease with increasing temperature
of acid medium because at higher temperature the mild steel is oxidized at higher rate and
causing the inhibitor to desorb back from mild steel surface. The value for heat of
adsorption, Qads ranged from -39.89 to -41.71 KJ.mol-1
indicates that the reaction is
exothermic. The adsorption data fitted well to Langmuir adsorption isotherm model.
Thermodynamic equations were used to determine the activation energy (Ea), enthalpy
change (∆H) and entropy change (∆S). The adsorption isotherms such as Langmuir,
Freundlich, Flory–Huggins, Temkin, and Frumkin were used to evaluate the change of
Gibb’s free energy from the adsorption equilibrium constant, Kads, value. The adsorption
of the inhibitor on surface of mild steel was found to be spontaneous and consistent with
the physical adsorption mechanism as ∆Gads is negative value and less than -20 KJ.mol-1.