Electrochemical and theoretical investigation of oxadiazole derivatives as corrosion inhibitors for brass (Cu58Zn40Pb2) in simulated cooling water

The effect of temperature and immersion time on the anticorrosion character of two oxadiazoles derivatives, namely 2,5-bis(3-methylphenyl)-1,3,4-oxadiazole (3-MPOX) and 2,5-bis(4-methylphenyl)-1,3,4-oxadiazole (4-MPOX) for a brass Cu58Zn40Pb2 substrate in a simulated cooling water system (SCWS) solution was investigated using a potentiodynamic polarization curve (PDP) and electrochemical impedance spectroscopy (EIS). In order to explain the action mode and confirm the anticorrosion performance order, DFT calculations and MD simulation were conducted. The PDP results showed that 3-MPOX and 4-MPOX act as a mixed type inhibitor and their anticorrosion efficiency losses slightly with temperature electrolyte from 91 % and 90 % at 305 K to 81 % and 78 % at 335 K for 3-MPOX and 4-MPOX, respectively. Thermodynamic and kinetic parameters for the adsorption process indicated that these compounds adsorbed via physical adsorption. Additionally, the EIS results demonstrated that the performance of these compounds enhances remarkably with immersion time, reaching its extreme of 98 % and 95 % after 24 hours of immersion for 10⁻³ M 3-MPOX and 10⁻³ M 4-MPOX, respectively. Therefore, for two effect temperature and immersion times, it is found that the inhibition efficiency depends on the –CH₃ position in the ring and follows the classmen: 3-MPOX ≥ 4-MPOX. Finally, the DFT calculations indicated that 3-MPOX is more reactive than 4-MPOX confirming the obtained experimental performance. MD simulation indicated that the 3-MPOX and 4-MPOX molecules are oriented parallel to the Cu/Zn atoms surface, succeeding adsorption by a great portion of the C-O / C-N groups and CC bonds of aromatic benzene. These findings explained and confirmed the action mode and the obtained performance order.