The Development of a Stable Citrate Electrolyte for the Electrodeposition of Copper‐Nickel Alloys

Abstract

The stability of citrate electrolytes for the electrodeposition of copper-nickel alloys and multilayers has been investigated. It was found that electrolytes operating at pH 4 are unstable due to the formation of an insoluble citrate complex. This complex had previously been thought to be copper citrate dihydrate, Cu2C6H4O7'2H,O, but elemental analysis of the precipitate revealed it to be a heteronuclear copper-nickel citrate complex. Calculations of the distribution of citrate species in a typical plating solution was undertaken to identify experimental conditions under which the insoluble citrate complex is not formed. These studies indicate that increasing the pH of the citrate solution from 4 to 6 should produce a stable electrolyte. Experimental studies show that the electrolytes at pH 6 are stable for periods of several weeks, in agreement with the predictions of the speciation calculations. The stable citrate electrolytes were used to deposit Cu-Ni alloys. It was found that alloys could be deposited from these electrolytes with almost 100% current efficiency and with a morphology and composition comparable to those.obtained from the unstable citrate electrolytes.

Metal Matrix Composite Coatings of Cupronickel Embedded with Nanoplatelets for Improved Corrosion Resistant Properties

“…Previous data has shown that Ni ions adsorb to the surface of the Mt platelet [42]. Nickel is in excess in the solution because of the deposition conditions and most of the copper is complexed with citrate [44]. At pH values greater than 5, the heterobinuclear deprotonated species, CuNiCit 2 H 2 4− , predominate in the solution over the binary deprotonated species, Cu 2 Cit 2 H 2 4− .…”

“…Figure 1 shows the TEM image of the Mt where the individual platelets can be seen after exfoliation. Citrate was used as the ligand in the electrochemical baths containing copper and nickel ions since citrate complexes with the metal ions [43][44][45]. The working, counter, and reference electrodes were a stainless steel substrate, coiled chromel wire, and a saturated calomel reference (SCE), respectively.…”

“…At pH values greater than 5, the heterobinuclear deprotonated species, CuNiCit 2 H 2 4− , predominate in the solution over the binary deprotonated species, Cu 2 Cit 2 H 2 4− . With Cu present in the plating solution, less citrate is available to complex with the nickel, resulting in a lower concentration of the certain species containing nickel and citrate (NiCit 2 H 3− and NiCit 2 4− ) and an increase in NiCit − species [44]. The slight change in the Cu-Ni ratio of the coatings can be attributed to the embedding of the Mt particles with a greater percentage of Ni over Cu adsorbed onto the surface of the platelets.…”

Nano-nickel–copper alloy deposit for improved corrosion resistance in marine environment

“…Bradley et al (1996) studied the nickel-copper alloy deposit from sulphamate electrolyte; Vu Quang et al (1985) and Abd El Rehim et al (1999) investigated the electrodeposition of nickel-copper alloy from citrate-based formulation and studied the effects of current, agitation, and temperature. Green et al (1998) also investigated the stability of citrate electrolyte and the effect of pH on alloy deposition. Dube et al (1995) made a detailed study on electroreduction of heterotetranuclear complexes during alloy deposition.…”

Voltammetric and in situ FTIRS study on CN− and Au(CN)−x complexes at the polycrystalline gold surface in citrate medium

“…The technological relevance of both citrate and citric acid in the field of electroplating processes is testified by their wide use as additives for the electrodeposition baths of several (mainly transition) metals and their alloys [3][4][5][6][7][8][9]. Electrochemical studies have, so far, focussed mainly on the reduction kinetics of the metal ions in the presence of citrate in the deposition bath [8].…”