Electrodeposition of zinc–iron alloy from an alkaline bath in the presence of sorbitol

Abstract

The chronopotentiometric technique was used to analyze the electrodeposition of Fe–Zn film on a Pt electrode. Three different Fe³⁺/Zn²⁺ molar ratios, Fe26.8 wt.%–Zn73.2 wt.%, Fe46 wt.%–Zn54 wt.% and Fe66.6 wt.%–Zn33.4 wt.%, were used in a solution containing sorbitol as the Fe³⁺-complexing agent, with a total concentration of the two cations of 0.20 M. Coloration of Fe–Zn films were light gray, dull dark gray and bright graphite, depending on the Fe³⁺/Zn²⁺ ratios in the deposition bath. The highest stripping to deposition charge density ratio was 47.5%, at 15 mA cm⁻² in the Fe26.8 wt.%–Zn73.2 wt.% bath. Energy dispersive spectroscopy indicated that the codeposition type of Fe and Zn in the Fe26.8 wt.%–Zn73.2 wt.% and Fe46 wt.%–Zn54 wt.% baths was normal at all j_d tested, while in the Fe66.6 wt.%–Zn33.4 wt.% bath there was a transitional current density from normal to equilibrium codeposition at 50 mA cm⁻². Scanning electron microscopy showed that Fe–Zn films of high quality were obtained from the Fe66.6 wt.%–Zn33.4 wt.% and Fe26.8 wt.%–Zn73.2 wt.% baths, since the films were smooth. X-ray analysis of the Zn–Fe films obtained at 15, 25 and 50 mA cm⁻², in the Fe26.8 wt.%–Zn73.2 wt.%, Fe46 wt.%–Zn54 wt.% and Fe66.6 wt.%–Zn33.4 wt.% plating baths, suggested the occurrence, in general, of a mixture of Fe₁₁Zn₄₀, Fe₄Zn₉, βFe, αFe, Fe₂O₃, Zn and PtZn alloys in the deposit.