Dependence of temperature on the corrosion protection properties of vanillin and its derivative, HMATD, towards copper in nitric acid: theoretical and electroanalytical studies

The interaction and corrosion protection properties of vanillin and one of its derivatives, HMATD, on copper in nitric acid (0.5, 1, and 1.5 M) at different temperatures have been studied by polarization, electrochemical impedance spectroscopy, adsorption, surface studies, and computational calculations. Polarization studies showed that these molecules act as mixed type inhibitors. Both vanillin and its derivative HMATD act as effective inhibitors for copper in HNO3 (0.5, 1, and 1.5 M) at different temperatures (30, 35, and 40 A degrees C). At room temperature, HMATD was found to be a more effective inhibitor than vanillin, whereas at higher temperatures, vanillin was found to be more effective. From spectroscopic and pH measurements, it is evident that vanillin has undergone a chemical change at higher temperatures in the presence of HNO3. The mechanism involves adsorption of inhibitor molecules on the metal surface and this process obeys the Langmuir isotherm.