Development of a novel alkaline zinc–iron plating bath containing sorbitol and the chemical, physical and morphological characterization of the Zn–Fe films

Abstract

An alkaline bath for the electrodeposition of Fe–Zn was developed, with sorbitol as the complexing agent for Fe(III) and Zn(II). The voltammetric studies showed that the sorbitol complexing agent had a beneficial effect, displacing the reduction potential of Fe(III) species to near that of the Zn(II) species (zincate), so that codeposition of iron and zinc occurred. The potentiometric study of the plating bath showed the presence of [Fe(sorb) 2] and [Fe(sorb) 2] − species and spectrophotometric analysis of the plating solution showed that Fe(III) is complexed by sorbitol. Light grey, grey and dark grey Zn–Fe electrodeposits were successfully obtained at deposition potentials of − 1.36, − 1.4 and − 1.6 V, respectively. SEM micrographs demonstrated that the sorbitol leads to high quality deposits, since cracks and dendrites were not observed. EDS analysis showed that the content of iron in the Fe–Zn films ranged from 74% (− 1.36 V) and 70% (− 1.4 V) to 40% (− 1.6 V). X-ray analysis of the Zn–Fe films obtained at − 1.36, − 1.4 and − 1.6 V suggested the occurrence of a mixture of Fe 4Zn 9, Fe 3Zn 10 alloys, Fe and Zn in the deposit. In sum, this system showed potential for industrial applications since it offers economic and environmental advantages.