Pattern transition in Cu–Zn binary electrochemical deposition

Electrochemical deposits from a mixed aqueous solution of copper and zinc in a thin-layered circular cell were examined. The variations in the patterns depending on the concentration of copper and zinc in the electrolyte were observed by an optical microscope and a scanning electron microscope (SEM). The chemical composition of the electrodeposits was analyzed by X-ray fluorescence, and by energy-dispersive analysis of X-rays using SEM equipment. Identification of the phase in the Cu–Zn binary system was also performed by X-ray diffraction. Five different patterns appeared when the concentration ratio of copper versus zinc was changed. Two of these were each unique and were observed for the first time; they were composed of fine hair-like branches or sharply bent branches. The chemical composition of the deposits changed depending on the concentration ratio of the corresponding electrolyte. Deposits were mixtures of alloys of copper and zinc, and the ratio of the alloy phases varied depending on the composition. The formation of each pattern was discussed based on the constitutent phase.