<i>Talinum triangulare</i> (Waterleaf) Methanol Leaf Extract as Corrosion Inhibitor on Mild Steel Surface in H<sub>2</sub>SO<sub>4</sub>

Abstract

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 H2SO4 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 H2SO4 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 H2SO4 at 303K, 54.86% for 0.6g/L in 0.5M H2SO4 at 303K and 61.66% for 0.6g/L in 0.6M at 303K. In 2.5M H2SO4, 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 (Ea) 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 (R2≈1) with the first order rate law, and the half-life (t1/2) 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 Ea and ∆Goads values are less than 80kJ/mol and -20kJ/mol respectively.