Electropolishing behaviour of 73 brass in a 70 vol % h₃po₄ solution by using a rotating cylinder electrode (RCE)

The electropolishing behaviour of 73 brass was studied by means of a rotating cylinder electrode (RCE) in a 70 vol % H₃PO₄ solution at 27 ◦C. Owing to the formation of a blue Cu²⁺-rich layer on the brass-RCE, an obvious transition peak was detected from kinetic- to diffusion-controlled dissolution in the anodic polarisation curve. Electropolishing was conducted at the potentials located at the transition peak, the start, the middle, and the end positions in the limiting-current plateau corresponding to the anodic polarisation curve of the brass-RCE. A well-polished surface can be obtained after potentiostatic electropolishing at the middle position in the limiting-current plateau. During potentiostatic etching in the limiting-current plateau, a blue Cu²⁺-rich layer was formed on the brass-RCE, reducing its anodic dissolution rate and obtaining a levelled and brightened brass-RCE. Moreover, a rod climbing phenomenon of the blue Cu²⁺-rich layer was observed on the rotating brass-RCE. This enhances the coverage of the Cu²⁺-rich layer on the brass-RCE and improves its electropolishing effect obviously.