Abstract
Response surface methodology was applied to predict the optimum control of mild steel corrosion in acid medium with bitter kola leaf extract as inhibitor. The experiment was carried out to investigate the mutual interactions between the considered independent variables and the expected responses. Thermometric, gravimetric, potentiodynamics polarization and electrochemical impedance spectroscopy were used in the corrosion inhibition study. As a supplementary technique, infrared spectroscopy was used to analyze the pure extract and corrosion products and it was observed that some peaks shifted while some disappeared. Inhibition efficiencies of 88.24 %, 86.81 %, 90 %, 89.5 % and 85.3 % were obtained from optimization, thermometric, gravimetric, potentiodynamics polarization and electrochemical impedance spectroscopic techniques, respectively. The bitter kola leaf extract behaved as a mixed-mode inhibitor. Application of response surface methodology in this study was found to be good in predicting the optimum range for controlling of metal corrosion thereby reducing the number of experimental runs. Keywords: Acid, bitter kola leaf, Fourier transform infrared, mild steel, electrochemical impedance spectroscopy, potentio dynamics polarization
Highlights
Mild steel is a useful metal in engineering
Bitter kola leaf extract with the corrosion product formed after immersion in 1.2 M HCl solution were investigated using FTIR technique
The peak numbers indicate the functional groups of the extract as expressed by other research work,[21] the stretched O-H at 3601.14 cm–1 peak of the pure extract shifted to 3547.1 cm–1 in the corrosion product
Summary
Mild steel is a useful metal in engineering. While many of other metals (for example, silver, gold and platinum) have strong stability in very aggressive environments such as strong acids. Maintenance operations like pickling and cleaning are employed. Aggressive hydrochloric acid used for pickling and cleaning operations often corrodes the metallic structures. Among the various techniques of controlling corrosion, application of an inhibitor is one of the best known techniques.[1,2] The quest for corrosion control by the application of an inhibitor is widely acceptable to maintain the stability of metallic structures.[3] Organic compounds containing oxygen, nitrogen and phosphorus atoms are presumed to have strong ability to inhibit corrosion of metals in acid environments.[4]
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