Corrosion Inhibition of Mild Steel in Sulphuric Acid by Methanol Leaf Extracts of Milicia Excelsa
[1]
Vincent Ishmael Egbulefu Ajiwe, Department of Pure and Industrial Chemistry, Nnamdi Azikiwe University, Awka, Nigeria..
[2]
Chinedu Emmanuel Ejike, Department of Pure and Industrial Chemistry, Nnamdi Azikiwe University, Awka, Nigeria..
Methanol leaf extract of Milicia excelsa was tested as a corrosion inhibitor for mild steel in sulphuric acid solutions using gravimetric and gasometric techniques. This was done with a view to determine the inhibitive potentials of the methanol leaf extract with regard to the corrosivity of acid solutions used in oil pipelines and descaling of equipment. The weight loss method of corrosion tests were carried out at 2,4,6,8 and 10 hours of exposure time using various concentration of extracts (0.2, 0.4 and 0.6) g/L at different temperatures (303K, 313K and 323K) in varying acid concentration (0.4M, 0.5M and 0.6M). The gasometric measurements were carried out at 5,10,15,20,25 and 30 minutes exposure time using various concentrations of extracts (0.2, 0.4 and 0.6) g/L in 2.5M H2SO4 solution. Gravimetric measurements were also carried out concurrently with the gasometric measurements to compare methodological variation in data between them. The phytochemical screening results revealed the presence of tannins, saponins, flavonoids, terpenes, steroids and alkaloids. From the results, the corrosion rates decreased with increase in inhibitor concentration. The maximum inhibition efficiency of the methanol leaf extract of Milicia excelsa was 62.07% for 0.6g/L inhibitor concentration, in 0.4M H2SO4 at 303K. In 2.5M H2SO4, the maximum inhibition efficiency for gasometric method was observed to be 49.82% in 0.6g/L inhibitor concentration at 298K while that of the gravimetric method was 28.97% in 0.6g/L inhibitor concentration at 298K. From the results of the kinetic and thermodynamic studies, a physical adsorption mechanism was proposed for the methanol leaf extract as the values obtained for E a and ∆Goads are less than 80KJ/mol and -20KJ/mol respectively.
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