Mechanism of iron corrosion in water-polyethylene glycol (PEG 400) mixtures

The properties of water-polyethylene glycol (PEG 400) solutions vary with the PEG content. The highest acidity and conductivity values were observed in 20% PEG 400 solutions. Oxygen solubility in such solutions decreased as the PEG 400 content increased. Adsorption of PEG 400, estimated by EQCM, varied with the PEG 400 concentration, also reaching a maximum in 20% PEG 400 solutions, with the weight of the adsorbed layer reaching 3.5 μg cm⁻².Iron corrosion in water-PEG 400 solutions was studied by monitoring the corrosion potential and the polarization curves. Iron corrosion was highest in the 20% PEG 400 solution due to the compromise between the evolution of acidity, dissolved oxygen content and the adsorption and complexation properties of the PEG solutions. Through adaptation of the Bockris mechanism, PEG adsorption at the metal surface constituted the first stage in the iron corrosion mechanism. Iron (ions)/PEG complexes were then formed, which diffused in solution.