Correlation Between Electrochemical Noise Resistance and Noise Impedance for Mild and Stainless Steel as a Function of pH

Studies of electrochemical noise resistance in the time domain (R_n) and impedance noise in the frequency domain (R_sn) have been carried out on 1018 (UNS G10180) carbon steel and Type 304 (UNS S30400) stainless steel in distilled water in the whole pH range. As a result, a good correlation between R_n and R_sn was found in solutions with different pH values (0 to 14), using the electrochemical noise (EN) technique. Additionally, linear polarization resistance technique (LPR) was used to obtain the polarization resistance (R_p) for comparison for the R_n and R_sn. Results showed a good correspondence between R_n and R_p values in the whole pH range. R_sn was calculated using the fast Fourier transformation (FFT) algorithm, using voltage and current signals. These were obtained using the method established by Bertocci and Mansfeld and by an alternative method. Both methods generated similar results and present a similar pattern for R_p, R_n, and R_sn values. This was true for alkaline, basic, and acidic environments as evidenced by the results in this work.