The corrosion inhibition efficiency of methanol leaf extracts of Irvingia gabonensis for mild steel in 0.4, 0.5, 0.6 and 2.5M H 2 SO 4 was investigated using weight loss and gasometric techniques in other to determine the phytochemical components of the crude leaf extract, the corrosion inhibition potential of the leaf extract, the thermodynamic parameters that aided the corrosion inhibition, the adsorption isotherm of the corrosion inhibition of the extracts using the Langmuir and Freundlich models and investigate the kinetics of the corrosion inhibition process. Preliminary phytochemical screening revealed the presence of tannins, saponnins, flavonoids, terpenes and alkaloids. From the results, the corrosion rates decreased with increase in inhibitor concentration. The maximum inhibition efficiency of 58.71% was obtained at extract concentration of 0.6g/L in 0.4M H 2 SO 4 at 303K, 41.83% at extract concentration of 0.6g/L at 303K in 0.5M H 2 SO 4 and 57.33% at extract concentration of 0.6g/L in 0.6M H 2 SO 4 at 303K, for the gravimetric technique. In 2.5M H 2 SO 4 , maximum inhibition efficiency for the gasometric technique was 53.53% in 0.6g/L inhibitor concentration at 303K and for the gravimetric technique, the maximum inhibition efficiency was 29.42% in 0.6g/L inhibitor concentration at 303K. The kinetic and thermodynamic studies showed that activation energy (E a) in the presence of inhibitor is greater than in the absence of inhibitor. From the E a and ∆G o ads values obtained, a physical adsorption mechanism was proposed. The Langmuir isotherm was found to show better correlation (R 2) at lower temperature while the Freundlich isotherm had better correlation at higher temperature.
The inhibition effects of methanol leaf extract of Talinum triangulare on the corrosion of mild steel in 0.4, 0.5, 0.6 and 2.5M H 2 SO 4 solution were determined in this study. The inhibition efficiency was evaluated and the mechanism of inhibition determined, with a view to determining the inhibitive potentials of the inhibitor with regard to corrosivity of acid solutions used in oil pipelines, water treatment systems and descaling of equipment. Weight loss and gasometric techniques were used for the corrosion study of the metal. The weight loss method of corrosion tests was carried out at 2, 4, 6, 8 and 10 hours of exposure using various concentrations of extract (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 extract (0.2, 0.4 and 0.6) g/L in 2.5M H 2 SO 4 solution. Weight loss measurements were also carried out concurrently with gasometric measurements to compare methodological variation in data between them. The phytochemical screening results revealed the presence of tannins, saponnins, flavonoids, terpenes, steroids and alkaloids. From the results, the corrosion rates decreased with increase in inhibitor concentration. The maximum inhibition efficiency of the extract for the weight loss measurements are 70.77% for 0.6g/L in 0.4M H 2 SO 4 at 303K, 54.86% for 0.6g/L in 0.5M H 2 SO 4 at 303K and 61.66% for 0.6g/L in 0.6M at 303K. In 2.5M H 2 SO 4 , the maximum inhibition efficiency was observed to be 59.31% for 0.6g/L inhibitor concentration at 308K for the gasometric method and 53.38% for 0.6g/L at 308K for the weight loss method. The kinetic and thermodynamic studies showed that the activation energy (E a ) in the presence of inhibitor is greater than in the absence of inhibitor at all the temperatures studied. The reaction was proposed to be first order having shown good correlation (R 2 ≈1) with the first order rate law, and the half-life (t 1/2 ) values were obtained from the graphs of the rate law. The mechanism of physical adsorption was proposed for the extract, as within the temperature range investigated the E a and ∆G o ads values are less than 80kJ/mol and -20kJ/mol respectively.
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