A Novel Electrodeposition Process for Plating Zn-Ni-Cd Alloys

Abstract

Zn-Ni-Cd alloy was electrodeposited from an alkaline electrolytic bath under potentiostatic conditions. Bath analyses using a pH concentration diagram reveal that addition of a complexing agent is essential to maintain the bath stability. Introduction of a low concentration of CdSO 4 reduces the anomalous nature of the Zn-Ni deposit. Deposits obtained from the electrolytic bath which contains 60 g/L of ZnSO 4 •7H 2 O, 40 g/L of NiSO 4 •6H 2 O, 1 g/L of CdSO 4 , and 80 g/L of (NH 4 ) 2 SO 4 in the presence of additives and ammonium hydroxide at pH 9.3 has a composition of 50 wt % of Zn, 28 wt % of Ni, and 22 wt % of Cd. By optimizing the Cd concentration in the bath, it is possible to control the amount of Ni in the deposit. At large overpotentials, the surface of the electrode is covered with hydrogen which lowers the deposition current density. Rotating disk electrode studies indicated that the deposition of Cd is under mass control, while Ni deposition is under kinetic control.

Development of Novel Process for the Deposition of Nanostructured Ternary Alloys and Composites for Replacement of Cadmium Coatings

“…The Zn-Ni ratio [24] was as low as 1.7:1. Also the corrosion resistance of the coating was improved by an order of magnitude when compared to that of commercial Zn-Ni and cadmium coatings.…”

“…Also the barrier properties of the coating increases with increased nickel content in the deposit. Several attempts have been made earlier to decrease the anomaly and increase the nickel content by either introducing an inert species in the bath or by developing a ternary alloy [17][18][19][20][21][22][23][24]. Nonyl phenyl polyethylene oxide (NPPO) has been used to reduce the Zn-Ni ratio and produce more corrosion resistant deposits.…”

“…The nickel ratio increased from 6 to 8 % with the addition of small amounts of tin. Earlier, we have developed a novel plating process for the electrodeposition of Zn-Ni-Cd coatings [22][23][24]. It was found that use of small of ternary alloying elements like cadmium can effectively control the Zn-Ni ratio.…”

Optimization of electroless Ni–Zn–P deposition process: experimental study and mathematical modeling

“…Due to the high zinc content in the deposit, these alloys are more electronegative than cadmium and hence dissolve rapidly in any corrosive environments. Typical nickel composition in the Zn-Ni alloy is 10-15%, and any further increase in nickel composition is based on using a higher-than-predicted Ni/Zn ratio in the bath [9][10][11][12]. Attempts were made to decrease the anomaly in case of Zn-Ni alloys by either introducing inert species in the bath or by developing a ternary alloy [10,11].…”

“…Typical nickel composition in the Zn-Ni alloy is 10-15%, and any further increase in nickel composition is based on using a higher-than-predicted Ni/Zn ratio in the bath [9][10][11][12]. Attempts were made to decrease the anomaly in case of Zn-Ni alloys by either introducing inert species in the bath or by developing a ternary alloy [10,11]. Zhou and Keefe [12] have studied the effect of tin additions on the anomalous deposition of Zn-Ni alloy.…”