Silver-Alloys Electrodeposition for Electrical Conductivities

Abstract

The needs of the ecological transition are based on a larger use of electricity in several processes and access to new resources in large quantities such as hydrogen. The production of the latest by electrolysis as well as the electrification of the means of land transport and the anticipation of the needs of the aeronautics relies on higher capacities in current transmission. The specifications of the connectors and power transmission devices are increasingly stringent, requiring high-quality coatings when intended for contact current transmission. Silver and silver alloys appears to be an excellent choice for such application [1].The standard electrochemical potential of silver being among the highest, the stability range of its oxides, in aqueous solution, is all the more reduced. In order to maintain these oxidized forms in solution and thus be able to reduce them to the cathode, formulations mixing complex, pH buffer system and other additives have been developed. The electroplating of hard silver in cyanide environments remains the most widely used industrial process, but the specifications can only be obtained by the use of chemical species whose mechanism of action is often poorly known. Moreover, nature and concentrations of additives used in the bath have a direct impact on the coatings properties. An alternative exists in the complexation of other metals with silver, to form an alloy with properties which depends strongly on the electrolysis parameters. To work properly, the working potential must be shifted from the thermodynamic equilibrium [2]. The present study is part of the SILAHPERF project, led by IRT-M2P and UTINAM Institute, which try to investigate the codeposition mechanism of various silver-based alloys of interest with a particular focus on silver-tungsten while seeking for environmental-friendly solution, focused on electrolysis parameters. Indeed, an alternative to cyanides as complexing agent is expected, face to the raising number of regulations. Therefore, a large number of complexing agent are evaluated, with their electrochemical behavior in i=f(E) curves, and with the deposition yield as well as the alloying element content as a function of the deposition potential. As an example for silver-tungsten alloys, complexing agents may be a combination of a carboxylic acid and an amino compound. The most popular couple is the citrate-thiourea system, however tartrate, oxalate, ammonia and urea are also good candidates. Finally, coating properties are evaluated by several technics (SEM – XRD, GDOES ...)[1] M. Myers, ‘Overview of the Use of Silver in Connector Applications (503-1016), p. 14.[2] A. Kola, X. Geng, and E. J. Podlaha, ‘Ag–W electrodeposits with high W content from thiourea–citrate electrolytes’, Journal of Electroanalytical Chemistry, vol. 761, pp. 125–130, Jan. 2016, doi: 10.1016/j.jelechem.2015.12.002.