Electrochemical and theoretical evaluation of dihydro-benzoimidazoquinazolines as corrosion inhibitors for API X-120 steel in acid medium

Abstract

In this paper, the corrosion inhibition of three dihydro-benzoimidazoquinazolines, namely 2´,6´diFDHBIQz 1, 2Br2´,6´diFDHBIQz 2 and 2,4diBr2´,6´diFDHBIQz 3 was determined for an API 5 L X120 steel in 0.5 M HCl. Electrochemical techniques such as Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization curves were used obtaining inhibition efficiencies greater than 90 %. In addition to this, Quantum chemical calculations using the DFT technique was used to correlate the inhibitors efficiency and their electronic properties. Results have shown that the three organic compounds are good, mixed type of corrosion inhibitors, with an efficiency that increased with their concentration but decreased with the temperature. The inhibitor efficiency decreased in the order 2´,6´diFDHBIQz 1 > 2Br2´,6´diFDHBIQz 2 > 2,4diBr2´,6´diFDHBIQz 3. All of them were adsorbed on to the steel surface following a Langmuir type of adsorption isotherm, however 2´,6´diFDHBIQz 1and 2Br2´,6´diFDHBIQz were adsorbed in a mixed chemical and physical way dominated by a physical type of adsorption, whereas 2,4diBr2´,6´diFDHBIQz 3 was physically adsorbed. Quantum chemical results revealed that 2´,6´diFDHBIQz 1 was the most efficient because it had the highest HOMO energy.