Nanosized structural features of electrodeposited Au–Co and Au–Ni alloy coatings

Abstract

The structure of Au–Co and Au–Ni alloy coatings deposited at low current density (2–20 mA cm⁻²) from weakly acidic additive-free electrolyte with higher (16–20 g L⁻¹ Co or Ni) than usually employed (0.1–1.0 g L⁻¹) concentration of the alloying element was investigated. Under these conditions, structural effects in the coatings were observed representing nanoscale, porous (in the case of Au–Co coatings) or hollow (in Au–Ni alloy coatings) formations, passing through the coating and ending at the surface as craters. They could be associated with the influence of the accompanying hydrogen evolution. On one hand, hydrogen bubbles are firmly adsorbed on the surface, and on the other hand, the electrolyte has very good penetrating and covering ability. As a result, depending on the dynamics of the deposition process, porous structures with different configurations are formed. The formation of the structures begins in the early stages of the electrocrystallisation and the substrate affects the number, size and distribution of the features.

Keywords:

• Electrodeposition
• Au–Co alloy coating
• Au–Ni alloy coating
• Hydrogen evolution
• SEM

Acknowledgements

The present studies were performed with the kind support of Deutsche Forschungsgemeinschaft (Research Project 436 BUL 113/97). This study on the deposition and of properties of Au/Co and Au/Ni alloys were carried out in the framework of co-operation between fem, Schwäbisch Gmünd and IPC, Sofia over an 8-year time period. The work reported in this paper represents the final unpublished results from this study.