Application of three-electrode electrolytic cell to evaluate thin films of vegetable and mineral oils

Films (∼5 μm) of rapeseed and mineral oils with or without antioxidants were coated on steel disc electrodes. Initial stages of corrosion and oxidation were monitored by potentiodynamic polarization and impedance spectroscopy in ammonium borate electrolyte at pH 9.0. Fresh films lead to spatial separation of electrochemical reactions without major changes in corrosion mechanism. However, heating in air (4 h, 70 °C) reduced current densities by 2 orders and produced dramatic changes in impedance and phase angle patterns. Data fitting was proposed and reasons discussed why mild heating changed the course of corrosion so strongly.