Electrochemical Formation and Characterization of Functional Ag-Re Coatings

TL;DR

Researchers developed a method to create durable silver-rhenium coatings for use in electronics and energy sectors.

Contribution

A new electrochemical method for synthesizing Ag-Re coatings with controlled composition and improved functional properties.

Findings

Ag-Re coatings with thicknesses of 2.0–13.7 μm and Re content of 0.15–13.5 wt.% were successfully produced.

Coatings deposited under specific current densities and temperatures showed nanocrystalline structures and improved mechanical properties.

The Hall–Petch relationship was confirmed, indicating grain boundaries significantly influence coating hardness.

Abstract

Silver-white, matte, smooth, and durable deposits of silver-rhenium, with thicknesses ranging from 2.0 to 13.7 μm and containing 0.15 to 13.5 wt.% Re, were obtained with a current efficiency of 66–98% from a developed dicyanoargentate–perrhenate bath based on a borate–phosphate–carbonate silver-plating electrolyte. This study was focused on the influence of bath composition, the [Ag(I)]:[ReO4−] ratio, surfactant additives, applied current density, temperature, and stirring, on the alloys’ composition, structure, morphology, microhardness, adhesion, and porosity. A voltammetric analysis was conducted, considering the influence of ethanolamines on electrode processes. In baths with triethanolamine (TEA), coatings similar to a silver matrix with rhenium doped in mass fractions are likely achievable. Monoethanolamine (MEA) is recommended due to its process-activating properties. All coatings were nanocrystalline (τ = 28.5–35 nm). For deposits containing less than 10 wt.% Re, characteristic silver XRD peaks were observed, while for other deposits, additional peaks attributed probably to Re(VII) and Re(VI) oxides. A linear relationship Hv − τ−1/2, typical for Hall–Petch plots, was obtained, confirming that grain boundaries play a crucial role in mechanical properties of coatings. The conditions for stable electrochemical synthesis of promising functional Ag-Re coatings of predetermined composition (0.7–1.5 wt.% Re) were proposed for practical use in power electronics and energy sectors for manufacturing electrical contacts operating across a wide temperature range. This was realized by deposition from an Ag-rich bath in the area of mixed electrochemical kinetics, at potential values corresponding to the region of half the limiting current: j = 2.5–6 mA cm−2, t = 19–33 °C.

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