Studies were made on anodic behavior of each or together of zinc and iron in various kinds of alkaline zinc plating baths.
The results obtained were as follows:
1) The polarization of zinc anode was decreased with the decrease in concentration of OH or CN ions and was increased with the increase in concentration of Zn ions in plating baths.
2) In activated state, anodic current efficiency of zinc was 100%. A film corresponding to Zn(OH)₂ grew at the potential between critical passivity and Flade; and a film corresponding to ZnO grew at the potential for retaining passivity. The anodic current efficiency of zinc was decreased under these conditions. However, the current efficiency for zinc both contained in the films and dissolved was about 100%.
3) When both of zinc and iron were used together for anode, only anodic behavior of zinc was indicated at the initial stage; and then, the bath was led to potential for generating oxygen from iron when the current passed through the critical passivity of current density of zinc. At this stage, zinc anode was electrolyzed at the potential for retaining passivity.
The problems mentioned above are important in controlling of anode and plating bath in practice of alkaline zinc plating.