Real-Time Cross-Sectional Surface Observation of Brass to Investigate Dezincification Corrosion

Abstract

The dezincification corrosion of brass (Cu-Zn alloy) is a serious problem in the plumbing system because it may cause the leakage accident. When the dezincification corrosion occurs on the brass surface, a porous copper rich layer is formed on the brass surface due to the selective dissolution of zinc1,2. In order to understand the dissolution mechanisms, it is important to explore the relationship between the dissolution behavior of zinc and the growth of the copper rich layer. Our group3-5 developed the real-time surface observation system with channel flow double electrode to investigate localized corrosion of copper and magnesium. In the present study, a real-time cross-sectional surface observation system combined with electrochemical measurement was developed for the investigation of the dezincification corrosion of brass. A video of the cross-sectional surface morphology of brass was taken by an optical microscope combined with a charge-coupled device (CCD) camera during the anodic polarization. The electrochemical cell was constructed using transparent acrylic plates. The electrochemical measurement was carried out by a three-electrode cell. The working electrode and the counter electrode were a brass plate and a platinum wire, respectively. A KCl-saturated silver/silver chloride electrode (SSE) was used as a reference electrode. The electrolyte solution was 0.5 M NaCl containing 5 mM NaHCO3 and kept at 60 oC. The surface of brass plate was covered with the transparent resin except the active surface area (0.393 cm2). The brass plate was fixed at wall surface to record the video of the active surface area. The galvanostatic polarization was performed for 24 h to observe the dissolution behavior of brass. After 3 hours, the copper rich layer was formed on the brass surface due to the selective dissolution of zinc. The localized dissolution was observed after 6 hours, and the dissolution was then observed on the whole surface. The selective dissolution of zinc and simultaneous dissolution of zinc and copper from brass surface were discussed based on the video images and the potential changes of brass during the measurement.