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Electrodeposition of Metastable Au-Ni Alloys

Published

Author(s)

Gery R. Stafford, E. Rouya, Ugo Bertocci, J. J. Mallett, R. Schad, M. R. Begley, R. G. Kelly, M. Reed, G. Zangari

Abstract

The electrodeposition of Au-Ni alloys from near neutral, sulfite-based electrolytes derived from a commercial bath for soft gold plating is investigated. Alloy compositions ranging from 0 to 90 at% Ni were obtained by varying the deposition potential, with Ni content increasing with overpotential. Cathodic efficiency was lower than 50% due to concurrent parasitic reactions, including the reduction of products from the decomposition of sulfites and the hydrogen evolution reaction. As-deposited films from a continuous series of metastable solid solutions and exhibit a nanocrystalline morphology, with grain size decreasing with increasing Ni content. Thermal annealing at 200 degrees C was sufficient to start relaxation of the metastable solid solution towards the thermodynamically stable bi-phasic configuration of pure Au and Ni phases; however, a temperature of 400 degrees C was necessary to complete the phase separation process within about one hour. The formation of a metastable structure is interpreted in terms of kinetic processed at the growing interface. Finally, the excess free energy of the as-deposited alloys with respect to the stable, phase separated configuration is estimated between 6 and 18 kJ/mil, consistent with what can be expected in electrochemical processing.
Citation
Journal of the Electrochemical Society

Citation

Stafford, G. , Rouya, E. , Bertocci, U. , Mallett, J. , Schad, R. , Begley, M. , Kelly, R. , Reed, M. and Zangari, G. (2010), Electrodeposition of Metastable Au-Ni Alloys, Journal of the Electrochemical Society, [online], https://doi.org/10.1149/1.3421749 (Accessed April 21, 2024)
Created May 13, 2010, Updated April 28, 2020