Kinetics and Thermodynamic Study of Inhibition Potentials by Ethoxyethane Extracts of Cochlospermum tinctorium for the Oxoacid Corrosion of Mild Steel

摘要

The corrosion inhibition efficiency of a Cochlospermum tinctorium (CTE) on mild steel in 0.5M H₂SO₄ solution has been investigated using weight loss measurements, thermometric measurement and scanning electron microscopy studies. The weight loss measurement indicates increase corrosion inhibition efficiencies that reach 97%. The weight loss and thermometric data established that the inhibition efficiency on mild steel increases with increase in the concentration of inhibitor, CTE. The adsorption of CTE obeys Langmuir adsorption isotherm. Thermodynamic parameters were calculated using the adsorption isotherm. Activation parameters of the corrosion process were also calculated from the corrosion rates obtained from temperature studies. The adsorption isotherm indicates that the adsorption of CTE inhibitor on the surface of mild steel is physisorption and the thermodynamic values obtained indicates spontaneous and exothermic corrosion processes.Furthermore, this thesis includes the thermometric study for the mild steel corrosion in 0.5M H₂SO₄ acid solution in absence and presence of different CTE concentrations as inhibitor. Thermometric measurements data show that adding CTE to 0.5M H₂SO₄ and acid solution leads to decrease in the reaction number RN and the percentage reduction in RN in the presence of CTE increases with increasing CTE concentrations, therefore the Inhibition efficiency increases with increasing CTE concentration and it reaches to the highest value 90% by using 500 mgL^-1 of CTE.Surface morphology of the mild steel specimens in the presence and absence of the inhibitor was evaluated by SEM analysis. SEM analysis revealed that the addition of inhibitor retarded the corrosion processes, where the grain boundary attacks were completely hindered by the adsorbed inhibitor molecules. The micrograph in the presence of CTE showed a near smoother surface with pit morphology lower than in the absence of plant extract.