Potassium salt based alkaline bath for deposition of Zn-Fe alloys

摘要

A new alkaline bath was proposed based on highly concentrated potassium hydroxide for electrodeposition of Zn-Fe alloys. Triethanolamine was used as the complexing agent to eliminate precipitation of ferrous hydroxide and to enable the co-deposition of Zn and Fe. The conductivity value of the proposed baths is 161-188% higher than that of a known formula. From cathodic linear sweep voltammograms the co-deposition of Zn and Fe in the proposed bath is applicable. Zn-Fe alloys with different compositions were achievable by tuning the deposition variables such as the ion ratio Zn/Fe and the deposition current density. The co-deposition of Zn and Fe is an anomalous type under a small current density and switches to the regular one under a larger current density. The transition current density was found to be 0.075 and 0.05 A cm(-2) for Baths 1 (ion ratio Zn/Fe = 13) and 2 (Zn/Fe = 25), respectively. A mechanism based on adsorbed Fe-TEA barrier-layer was proposed to explain this transition. There is a more than 40% enhancement in cathodic current efficiency by using the proposed Bath 2 versus the known formula. Comparing with Zn coating, the deposited Zn-Fe layer reveals 10% nobler corrosion potential, -0.987 vs. -0.897 V-SCE, and two times smaller corrosion current density, 42.0 vs. 19.7 mu A cm(-2). The proposed baths are much easier for bath control during deposition. (c) 2006 Elsevier B.V. All rights reserved.