Corrosion Behavior of Aluminum in Carbon Dioxide Aqueous Solution at 50 oC

In this work, the corrosion behavior of aluminum in carbon dioxide solutions with different concentrations at high temperature (50 oC) was studied. The corrosion of aluminum in the carbon dioxide solutions was inhibited to a certain extent compared to the corrosion in deionized water. It was found that an aluminum electrode in 0.84 pmol L''1 carbon dioxide solution with pH 4.35 had the lowest corrosion rate as observed from its lowest corrosion current, the most positive corrosion potential, and the maximum charge transfer impedance. The mechanism for aluminum corrosion inhibition was that HCO3- generated by carbon dioxide ionization developed an ordered charge field on the aluminum surface, shielding the diffusion of aluminum ions and inhibiting the dissolution of the oxide film on the aluminum surface. SEM, EDS and XRD confirmed that the corrosion products covering the surface of the aluminum electrode were Al(OH)3 and/or Al2O3. Based on the above, it was elucidated that the Pt grading electrodes of the high voltage direct current (HVDC) valve cooling system lower the scaling rate in solutions with a certain concentration of carbon dioxide, and it was shown that the concentration of aluminum ions in the inner cooling water is a crucial factor affecting the scaling of grading electrodes. Therefore, reducing the concentration of aluminum ions in the inner cooling water, in other words, inhibiting the corrosion of aluminum, is the fundamental means for solving the scaling problem of the grading electrode. This paper will contribute to the research on production improvement techniques used for HVDC valve cooling systems.