Production of Electrolytic Rhenium-cobalt Alloys

D. Kopyto, K. Leszczyńska-Sejda, G. Benke, A. Chmielarz, M. Ciszewski

Rhenium is a refractory metal, which finds its applications mainly in the production of superalloys. This paper shows the results of electrowinning tests of rhenium-cobalt alloys from aqueous solutions. For the preparation of these alloys a cobalt sulphate electrolyte was used, modified with ReO4- ions, delivered in the form of ammonium perrhenate and/or cobalt perrhenate. The following parameters of the process were checked: electrolyte composition (concentration of Co = 15 – 60 g/L, Re = 1-30 g/L, H3BO3 = 5 – 40 g/L), current density (0.5 – 15 A/dm2), temperature (25 – 65 °C), pH (1.2 – 6.0) and material of electrodes on the composition and quality of the alloys obtained. As results process parameters to obtain rhenium-cobalt alloys with a current efficiency above 90 %, using aqueous solutions under low temperatures of 50 – 55 °C were defined. Re-Co alloys obtained at cathodic current density jk ≤ 2.0 A/dm2 are dense metallic deposits containing 30 – 32 wt.-% Re and 68 – 70 wt.-% Co. A current density increase to values higher than 3.0 A/dm2 resulted in metallic alloy powder deposition with a composition of 78 – 82 wt.-% Re and 18 – 22 wt.-% Co. The advantages of using this technology are low energy consumption and a significant reduction of the melting point of the alloy in comparison to rhenium itself.