The brass (Cu-Zn alloy) is widely used for the water pipe of constructional plant and the joint of the device material. One of the corrosion problems of Cu-Zn alloy is the dezincing, which is the selective dissolution of Zn from Cu-Zn alloy. The fundamental studies of anodic dissolution of Cu-Zn alloy were reported by Pickering et al. (1-3). They indicated that a porous Cu-rich layer was formed on the surface of Cu-Zn alloy due to the preferential dissolution of Zn from Cu-Zn alloy. They proposed the two types of the dissolution mechanisms, which were simultaneous and selective. However, the stability of the Cu-rich layer formed on the Cu-Zn surface has not been clarified yet. In the present study, the dissolution of Cu-Zn alloy in the fresh water was investigated by an electrochemical impedance spectroscopy (EIS). The measurement of the electrochemical impedance was performed by three-electrode system. The working electrode (0.785 cm2) was Cu-Zn alloy (Cu-35at%Zn) and the counter electrode was the platinum wire. The KCl-saturated silver/silver chloride electrode (SSE) was used as the reference electrode. All the potentials in this study were referred to SSE. In order to investigate the stability of the Cu-rich layer formed on the surface of Cu-Zn alloy, the formation of the Cu-rich layer was conducted as follows. The Cu-Zn alloy (Cu-35at%Zn) was abraded by #1200 emery paper under running water. Then, the galvanostatic polarization of Cu-Zn alloy was measured at 1.0 mA/cm2 for 24 h. The electrolyte solution was 0.5M NaCl containing 5mM NaHCO3. The temperature of the electrolyte solution was keep at 60 oC by thermostatic bath. The impedance spectra of the Cu-Zn alloy before and after the formation of Cu-rich layer on the surface of the Cu-Zn alloy were measured to examine the stability of the Cu-rich layer. In addition, the results of the rest potential and the anodic polarization curve were also discussed in the present study. Reference 1. H. W. Pickering and C. Wagner, Journal of the Electrochemical Society, 114, 698 (1967). 2. H. W. Pickering, Journal of the Electrochemical Society, 115, 143 (1968). 3. H. W. Pickering and P. J. Byrne, Journal of the Electrochemical Society, 116, 1492 (1969).
Analyses of dissolution mechanisms of copper and copper-alloys are important to obtain the fundamental knowledge concerning corrosion and etching. Various electrochemical measurements were performed to investigate the electrochemical properties of copper and copper-alloys with a channel double flow electrode (CFDE). CFDE is one of hydrodynamic technique whose principle is similar to a rotating ring disk electrode. The mass transfer in the electrolyte solution can be controlled by the solution flow in the channel. Therefore, the measurement with CFDE allows direct information concerning dissolution rate and the species by monitoring the emitted ions from the working electrode at detecting electrode. For example, the in-situ detections of cuprous and cupric ions were carried out with measuring of polarization curves of copper, brass and bronze. The polarization curve of brass showed two potential regions for different dissolution mechanisms and the dezincing was serious in less noble potential region. An electrochemical impedance spectroscopy (EIS) was used in order to discuss the detailed dissolution mechanisms because the EIS enables us to discriminate the time constants of elementary steps in the dissolution process. In addition, the formation of porous structure of brass surface due to dezincing was investigated with the equivalent circuit involving transmission line model (TLM).
The dezincification corrosion of the brass has been investigated to obtain the fundamental knowledge concerning the selective dissolution mechanisms. Pickering et al. (1-3) reported that a porous Cu-rich layer was formed on the brass surface due to the selective dissolution of Zn from brass. They classified the dissolution of the binary alloy into two types, which is the selective dissolution and simultaneous dissolution. In the present work, we investigated the dissolution of brass by an electrochemical impedance spectroscopy (EIS). The EIS enables us to discriminate the time constants of elementary steps in the dissolution process. The Cu-enriched layer was formed on the brass surface by following method: The galvanostatic polarization of the brass was performed at 1.0 mA/cm2 for 24 h in the electrolyte solution of 0.5M NaCl containing 5mM NaHCO3. The temperature of the electrolyte solution was keep at 60 oC by thermostatic bath. In order to investigate the porous structure of the Cu-enriched layer formed on the brass surface due to dezincing, the impedance spectrum was measured to examine the current distributions within the pores. In addition, impedance and complex capacitance corresponding to the typical equivalent circuits involving a transmission line model (TLM) are discussed to propose the evaluation method for the dezincification of brass. Reference 1. H. W. Pickering and C. Wagner, Journal of the Electrochemical Society, 114, 698 (1967). 2. H. W. Pickering, Journal of the Electrochemical Society, 115, 143 (1968). 3. H. W. Pickering and P. J. Byrne, Journal of the Electrochemical Society, 116, 1492 (1969).
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