Article | REF: M1625 V2

Electrolytic deposition of gold and silver

Author: Lionel CHALUMEAU

Publication date: September 10, 2010

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ABSTRACT

The electrolytic deposition of gold and silver allows for obtaining a metal layer on a conductive substrate by the cathodic reduction of oxidized forms in solution of these two metals. The aim of this article is to provide assistance in choosing the type of coating according to the desired properties. A distinction is made between applications for decorative purposes and technical applications. Families of formulation, available at the industrial scale, are presented for each of these two metals treated separately, as well as the conditions for obtaining this coating and its main features.

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AUTHOR

  • Lionel CHALUMEAU: Doctor of Chemistry-Physics - Former manager of the R & D department, Enclosures, EGIDE SA - This edition is an updated and expanded version of Jean PICAUT's article entitled Dépôts électrolytiques des métaux nobles, published in 2002.

 INTRODUCTION

Gold and silver belong to the family of noble metals (gold, silver, palladium, platinum, rhodium, ruthenium, osmium and iridium). They have sought-after physical and chemical properties for both technical and decorative applications. These properties are often only required on the surface of manufactured parts. Made from a material that is generally non-noble for technical (mechanical, thermomechanical, thermal, mass) or economic reasons, these parts are surface-treated and a layer of the chosen noble metal is then developed using a carefully selected process.

When the substrate is conductive (or rendered conductive), it is easy to obtain this surface metal layer electrolytically.

As the standard potential of noble metals is among the highest, the stability range of their oxides in aqueous solution is all the more reduced. In order to maintain the oxidized forms of these metals in solution, and thus be able to reduce them at the cathode, formulations combining complexing agents, pH buffering systems and other additives, stabilizers or deposition gas pedals have been developed. These formulations make it possible to obtain coatings whose properties are correlated to the electrolysis parameters. Indeed, while it is often possible to obtain coatings with properties close to those of annealed raw metal, it is also possible to modify certain mechanical or electrical properties, by acting on temperature, agitation, current density or the concentration of certain constituents, for example. The choice of metal, as well as the coating process, will therefore depend on the desired functionalization of the substrate to be coated.

Electrolytic coatings produced in aqueous media use electrolytes (or baths) composed of mixtures of chemicals, often harmful and sometimes toxic. This is all the more true for the electrolytic coating of gold and silver, as the conditions for solubilizing their oxidized forms often involve cyanide, or highly concentrated acids and bases. Although a few less dangerous solutions have been proposed, their industrialization is still in its infancy. Every precaution must therefore be taken to protect the operator and his environment.

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Gold and silver electroplating
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