Electrochemical Corrosion Behavior of Low Carbon Steel (LCS) Exposed to Simulated Repository Environment: EIS and XPS Characterization

Venugopal Arjunan¹, Joshua Lamb¹, Dhanesh Chandra¹, Jaak Damen1, Denny Jones¹,

M. Engelhard ² and S. Lea²

1University of Nevada, Reno, Mackay School of Mines, MS 388, Reno, NV-89557 USA

2Pacific Northwest National Laboratory, Richland, WA-99352, USA

The corrosion rates of LCS were calculated through potentiodynamic polarization experiments at different temperatures (25, 45, 65 and 85^oC) and electrolyte concentrations (1x,10x and 100x) under aerated and de-aerated conditions. These results were compared with the Electrochemical Impedance Spectroscopy (EIS) to obtain additional information. Polarization results indicate that carbon steel exhibit high corrosion rates in oxygenated conditions and less in nitrogenated conditions at all temperature and electrolyte concentration levels. In the nitrogenated conditions, carbon steel exhibit passivity promoted by the added ions in the electrolyte. Absence of passivity was noted in oxygenated conditions due to the depolarizing effect of oxygen shifting the corrosion potential to pitting potential of carbon steel. Increase in temperature increased the corrosion rates up to 45^oC and thereafter the corrosion rate decreased in the case of oxygenated solutions. However, the measured corrosion rates did not vary significantly in the case of nitrogenated solutions at all electrolyte concentrations. This could be due to the decrease in the solubility of oxygen at higher temperatures and/or increased electrolyte concentrations at higher concentration levels. The nature of corrosion products formed at 45 and 85^oC in the case of oxygenated and nitrogenated electrolyte was analyzed through X-ray Photo electron Spectroscopy (XPS). The combined results of polarization, impedance spectroscopy and surface analyzes will be presented and discussed.