Abstract
This present study seeks to exploit the use of eco-friendly, Okro leaf extract as an inhibitor in mitigating corrosion on carbon steel metal in acidic environment Gravimetric method was used to study the corrosion process. It was revealed that the inhibition efficiency of the extract on carbon steel decreases as temperature increases. This trend confirmed the physical adsorption mechanism for the corrosion process that resulted in a high rate of corrosion of the carbon steel. Activation energy Ea, enthalpy (ΔHº), and entropy (ΔSº) calculated showed good interactions. The rise in activation energy with inhibitor concentration confirmed the physical (physisorption) adsorption mechanism for the corrosion of a carbon steel surface. The positive value of adsorption enthalpy (ΔHº) obtained confirmed the endothermic nature of the corrosion process. The activation entropy (ΔSº) values obtained were all negatives which show that the activated complex in the rate-determining step represents association rather than dissociation step. Corrosion inhibition occurred by an attribute of inhibitor molecules adsorption on the surface of carbon steel which is seen to be in conformity with Langmuir, Freundlich, and El-Awady adsorption isotherm models. To obtain the least weight loss of carbon steel, optimization of the process variables affecting the corrosion process was carried out using Response Surface Methodology (RSM). Three parameters were varied viz; inhibitor concentration, contact time and temperature, and their effects on weight loss of carbon steel were established. The obtained data fitted well to the quadratic model which was also validated. The model predicted the lowest weight loss of 0.045 g with the optimal condition of inhibitor concentration of 198.71 ppm, 2.04 hrs of contact time, and 40.29°C of temperature.
Highlights
The consequences of corrosion are numerous, diverse and effects of these on the efficient, safe and reliable operation of equipment or edifices are often more serious than simple loss of a mass of metal
Response Surface Methodology (RSM) has not been reported on corrosion inhibition of carbon steel using Okro leaf extract
The model equation in terms of coded factors complemented by a chemical interaction between the for the prediction of weight loss of carbon steel is metal surface and the inhibitor that showed expressed in Eq (15) Table 11: chemisorption adsorption process
Summary
The consequences of corrosion are numerous, diverse and effects of these on the efficient, safe and reliable operation of equipment or edifices are often more serious than simple loss of a mass of metal. The Okro leaf phytochemical is rich in tannins, steroids, flavonoids, phenols and terpenoids (Dheba et al, 2017) These phytochemical constituents especially tannins have an array of hydroxyl and carboxyl groups through which the molecules can adsorbed on corroding metallic surfaces inhibiting the corrosion process on the carbon steel (Oki et al, 2011). RSM has not been reported on corrosion inhibition of carbon steel using Okro leaf extract This present work studied the Okro leaf extract as an inhibitor, kinetics and mechanism of adsorption and optimized the process variables already reported in literature affecting corrosion process (Yawas, 2005). The work established the process condition in a view to achieving minimum weight loss on carbon steel which could be applied to local and industrial corrosion treatment
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