Electrodeposition of Au-Sn alloys from acid Au(III) baths

Abstract

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed and investigated. The system was an acidic Au(III)–Sn(IV) bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations were based on cyclic voltammetry, linear-sweep voltammetry, galvanostatic electrodeposition experiments and in situ Raman spectroscopy. The electrode kinetics of alloy formation were elucidated by stripping voltammetry. The effects of cathodically adsorbed CN− were studied by in situ Raman spectroscopy. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Codeposition of Au and Sn gives rise to a single phase of approximately equiatomic composition over a current density interval of 10 to 40 mA cm−2. This orthorhombic phase is structurally the same as the ζ′ phase of the equilibrium Au–Sn system, but its stoichiometry and lattice parameters are different. The equilibrium two-phase δ, ζ′ structure can be obtained by heat-treatment.