The initial stages of electrodeposition of Re-Ni alloys

The early stages of Re-Ni alloy deposition from citrate electrolytes were studied in terms of the apparent faradaic efficiency (FE) of the deposition process, the composition of the deposits and their morphology. The deposition time was varied in the range of 0.05 to 60 seconds. The apparent FE of the deposition process was calculated as the ratio between the charge consumed in electrochemical stripping of the deposit and the charge consumed during electrodeposition. The apparent FE and Re-content in the deposits (measured by energy dispersive X-ray spectroscopy)were shown to decreasewith deposition time. Anomalous values of the FE, well above 100%, were observed at short deposition times. Under these conditions, the deposition ofmaterial consisting of nanoparticles with diameters of 50-80 nm was observed by scanning electron microscopy studies, supporting the anomalous high deposition rates. This behavior is indicative of chemical reactions taking place at short times in parallel with electrodeposition. The effects of deposition time on the apparent FE and Re-content in the deposits are explained by the changes in catalytic activity of the cathode surface during deposition.