The synergistic effect of corrosion natural corrosion inhibitor and iodide ions for corrosion control of steel in acidic

Chemistry Department at the College of Science – University of Diyala, discussed the thesis masters student (Nagham Arif Ahmed) entitled (The synergistic effect of corrosion natural corrosion inhibitor and iodide ions for corrosion control of steel in acidic) on (Thursday) (2018/1/25) in the Discussions Hall at the Deanship of the College of Science.

Corrosion of low carbon steel in 1M at different temperature (30 – 60 oC) in presence of plant extracts and absence by weight loss technique. Two plants extracts were used; Cardaria draba leaves (CDL) and Xanthium strumarium leaves (XSL) in the concentration range of (2 – 10 ml/L). Effect of potassium iodide (KI) addition was also studied. It was seen that corrosion rate increased with temperature and decrease with inhibitor concentrations. Maximum individual inhibitor efficiencies were 94.3%, 94.8%, and 94.15% for CDL, XSL, and KI respectively at higher level of temperature and concentration. Synergistic effect has a positive performance and improves the inhibitors efficiency with maximum values of 95.5% and 97.02% for KI+CDL and KI+XSL respectively at higher level of temperature and concentration. The synergism parameter values obtained was found to be less than one , which indicate that the inhibition efficiency is enhanced by the addition of iodide ions thus , the synergistic effect adsorption is competitive in nature. Two adsorption isotherms were used to explain the adsorption behavior of inhibitors. Langmuir Adsorption Isotherm and Freundlich Adsorption Isotherm. It was found that all inhibitors fellow Langmuir Adsorption Isotherm by formation a monolayer on metal surface. The values of equilibrium constants were used to evaluate Heat of Adsorption (ΔGads) to determine the type of adsorption (Physical, chemical or mixed mode). In the present study adsorption involves both chemisorption and physisorption (comprehensive adsorption), but chemisorption is the predominant mode of adsorption , the values of Heat of Adsorption were negative that indicate a spontaneous adsorption on metal surface. Arrhenius Equation and Transition State Equation were used to evaluate the activation parameters (activation energy, activation enthalpy, and activation entropy). Fourier transform infrared (FTIR) before and after immersion tests was used to find the active groups in the solution. The comparison among results and the shift in FTIR indicate the adsorption on metal surface. The phenolic , alkaloid and flavonoids compounds were the most active one. Scanning electron microscopy (SEM) was also used to study the surface morphology before corrosion test and after corrosion in presence and absence of inhibitors. The images in presence of inhibitor were better and presence of them has a positive performance and the dissolution rate of the steel has decreased significantly and the smooth surface has been shown by forming a good protective layer of adsorption of the inhibitor molecules on the metal surface, which is responsible for the inhibition of corrosion.