Fluconazole and fragments as corrosion inhibitors of API 5L X52 steel immersed in 1M HCl

© 2020 Elsevier LtdThe corrosion inhibition of API 5 L X52 in 1 M HCl due to fluconazole as active substance 1 or drug (Afungil), and its fragments: 1,2,4-triazole 2 and 1-bromo-2,4-difluorobenzene 3 was evaluated through electrochemical techniques and DFT calculations. At 20 °C, 1 exhibited c.a. 90 % corrosion inhibition efficiency, IE, from 5¿200 ppm. The fragment 2 displayed an IE of 83 % at 30 ppm, while the fragment 3 reached 80 % at all concentrations. However, the inhibition kinetics study of 1 demonstrated that it retained its IE properties up to 168 h of immersion with 84 % IE. 1 followed a Langmuir-type physisorption-chemisorption process while 2 and 3 a physisorption process. From SEM and AFM images it was directly verified the steel-protective capacity of 1 and from XPS analysis its presence onto the steel surfaces. Theoretical calculations, carried out at the dispersion corrected density functional theory BPW91-D2/6-311++G(2d,2p) level, are in full agreement with experimental observations, explaining that the physisorption-chemisorption process was provoked by the electrostatic interaction and electron pairs donation of fluconazole on the iron atoms. Similarly, the adsorption process of protonated fluconazole is due to electrostatic interactions and electrons shared from the metal cluster to the protonates species. Reactivity indices indicate that the steel surface is effectively covered and passivated.