# 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.

## Key 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.