Electrodeposition of Metastable Au-Ni Alloys

Published

May 13, 2010

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

Pub Type

Journals

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DOI Link

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 October 31, 2024)