Evaluation of Dezincification Corrosion of Brass By Electrochemical Impedance

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).