Improved protection performance of modified sol-gel coatings with pyridinium-based ionic liquid for cast iron corrosion in 0.5 M HCl solution

Unmodified and ionic liquid-modified sol-gel materials, based on tetraethylorthosilicate and 3-mercaptopropyl-trimethoxysilane, were synthesized and applied as protective coatings for cast iron corrosion in 0.5 mol L-1 HCl solution. The modification is done by adding 4-methyl-1-(prop-2-nyl) pyridinium ionic liquid at the early stage of the sol-gel synthesis, as an internal modifier, or by adding the ionic liquid in the corrosive medium while applying unmodified sol-gel coating on the metal surface, as an external modifier. Scanning electron microscope (SEM) is used to investigate the surface features of different coatings. Electrochemical measurements such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) were performed to prove the synergism in the protection ability caused by the combination of the sol-gel coating and the ionic liquid inhibitor. The charge-transfer resistance of the sol-gel coating is increased by six times in the presence of the ionic liquid. The effect of the ionic liquid concentration on the protection efficiency in both types of modification was examined. Internal modification is more efficient at relatively higher ionic liquid concentration. Tafel polarization, conducted at different exposure time, showed the high operation stability of ionic liquid-modified sol-gel coatings.