An Inhibitive Effect of Aeration on the Pitting Corrosion of Steels in Ethanolic Environments

Abstract

This work aims to illuminate localized carbon steel corrosion in ethanolic solutions. The effect of chloride, ethanol dehydration, and oxygen level are investigated, which all play a role in the carbon steel pitting behavior in ethanolic environments in the presence of a supporting electrolyte. Open-circuit potential measurement, cyclic potentiodynamic polarization, and potentiostatic testing are conducted on specimens exposed to ethanolic environments prepared from pure dehydrated ethanol to study the pitting behavior of carbon steel. Corrosion and passivation potentials are found to be significantly reduced due to the change in the cathodic reaction and the decrease in passivation kinetics under deaerated conditions. Energy-dispersive x-ray spectroscopy examination and scanning electron microscopy imaging indicate that no pitting corrosion is observed without chlorides, and chloride significantly destabilizes the surface film, resulting in the reduction of both pitting potential and passivation potential. Increasing the amount of dissolved oxygen in the solution reduces pitting susceptibility and, in low chloride concentrations, can eliminate the pitting nucleation. Iron oxide is identified as the significant corrosion product at different water and oxygen concentrations. Therefore, ethanol aeration can be an effective method to increase resistance to pitting corrosion in ethanolic solutions. Aeration can be used with caution due to the effect of oxygen on steel stress corrosion cracking in ethanol.