Application of Electrochemical Noise Analysis in High Subcritical and Supercritical Aqueous Systems

Abstract In this study, electrochemical noise analysis (ENA) is used to identify corrosion mechanisms and to analyze the effect of pressure on corrosion reactions in high subcritical and supercritical aqueous systems. Two corrosion mechanisms, “chemical oxidation” (CO) and “electrochemical oxidation” (EO), are used to describe the corrosion reactions in supercritical aqueous systems, depending upon the density and dielectric constant of the fluid. ENA is used to differentiate the two corrosion mechanisms by postulating that only the electrochemical mechanism gives rise to spontaneous fluctuations in current and potential. A rugged electrochemical noise sensor has been developed to monitor the fluctuations in the coupling current between two identical specimens. Experiments show that the electrochemical mechanism is the dominant corrosion process when the temperature is less than 350 °C and that it becomes of progressively lower importance as the temperature increases above the critical temperature (Tc = 374.15 °C). ENA is also used to explore the effect of pressure on the rate of corrosion of metals at supercritical temperatures. As predicted by the pressure-effect model, the experimental data demonstrate that the electrochemical corrosion rate increases with increasing pressure in low-density supercritical systems, corresponding to an increase in the density and the dielectric constant.