Corrosion Monitoring Of Cu And Cu-Ni Alloy By Electrochemical Noise

Electrochemical noise (ECN) is the spontaneous and stochastic fluctuations of current or potential in corrosion system. Electrochemical noise technique is simple and convenient. It doesn't bring extra disturbance to the corrosion system, the unique features of ECN measurement make it a leading role in the field of corrosion electrochemical study. It has been used in the industrial field recently, too.Electrochemical noise technique was used to measure the corrosion behavior of copper and copper alloys in artificial sea water and Postgate C medium containing sulfate reducing bacteria (SRB) in the laboratory. At the same time, a combination of electrochemical impedance spectroscopy (EIS), linear polarization method and scanning electron microscopy (SEM) were used to investigate the electrochemical behavior of copper and copper alloys. The main conclusions are as follows:(1) The metastable pitting and stable pitting was occurred when Cu immersing in simulated sea water. It was monitored by electrochemical noise and verified by SEM. It was found that the noise transients disappeared after adding the BTA inhibitor into the simulated seawater, meanwhile, the noise resistance (Rn), the spectral noise resistance(R0sn), the impedance |Z| and linear polarized resistance (Rp) increased remarkably.(2) From the ECN data of B10 and B30 copper alloys in sea water. The corrosion of B30 was found to be more serious than B10 until the passive film become more integral. Most transients in ECN curves disappeared after the dense passive film formed. The number of pits on the surface of B30 was found to be more than that on B10 by SEM after the corrosion products removed. The size of the pits on B10 and B30 were smaller than that on Cu. In addition, the values of Rn, R0sn, Rp and |Z| increased fast in the beginning, and slow in the end with time. (3) The corrosion of B10 and B30 in Postgate C medium containing SRB was also monitored by ECN, EIS and LPR. It was found that the corrosion potential of B10 and B30 moved negatively. Rn, R0sn, Rp and |Z| decreased quickly after 3 days because of the fast growth of SRB, and then kept stable for the left test period.(4) The comparison of the noise impedance spectra obtained from the power spectral density (PSD) plots with the traditional impedance spectra have been made, showing a good agreement between them in the frequency of 1Hz to 10 MHz.ECN can be applied to monitor the corrosion of Cu and Cu-Ni alloys. The result of ECN has a good agreement of other normal electrochemical measurements, such as electrochemical impedance spectroscopy (EIS) and linear polarization method.