2006 Volume 55 Issue 7 Pages 306-311
The charge transfer resistance Rct and the electrode reaction impedance Z0 of a carbon-steel electrode were measured in ethanol with 0.0064 to 0.13 mass% HCl and 2 mass% H2O, in order to obtain basic data for applying on line corrosion-monitoring using electrochemical-impedance method in ethanol plants. The value of Rct was estimated from the mass-loss of the carbon steel and the value of Z0 was measured from the real-axis intersects of best-fitting curves to Nyquist plots. The ratio of Z0 to Rct was about 8 over the HCl contents examined in this study. The value of Z0 could be approximated 0.5 · (R0.1Hz-R1kHz), under the conditions employed in this study ; the value of R1kHz and R0.1Hz are the impedance measured by two-electrode method at 1 kHz and around 0.1 Hz, respectively. Thus, the corrosion rate icorr of carbon steel under similar conditions examined in this study would be given from the R1kHz and the R0.1Hz measured in the field as follows.
icorr=2 · 160 mV/(R0.1Hz-R1kHz),
where 160 mV is an apparent Stern-Geary constant under the examined conditions.