Zn-Fe and Zn-Co-coatings

The use of the Zn alloy coatings with iron group elements such as Fe and Co is developing increasingly. Zn-Co alloy coatings have 0.4 - 2 wt% cobalt, but the Fe content of Zn-Fe alloy coatings would be up to 40 wt%. In this research, the reasons of high difference in amount of alloying element in the deposits in the same electrochemical conditions have been investigated. Zn-Co and Zn-Fe alloys deposited galvanostatically using acidic electrolytes in 25ºC for 10 minutes. The selected current densities were in the range of 4- 10 A/dm2. Composition of deposits was determined using EDAX analysis. Cathodic current efficiency and partial current density of Zn, Fe and Co were obtained using Faraday relations. Also, the thickness of coatings was determined for calculating of the deposition rate in Zn-Fe and Zn-Co alloys. The results indicate that Zn partial current density in Zn-Co deposition is more than in Zn-Fe. But Fe partial current density in Zn-Fe deposition is much more than Co in Zn-Co. Therefore, in the same current density, the presence of Fe in Zn-Fe alloy deposit would be much more than the presence of Co in Zn-Co deposit.