A simple and versatile rotating disk electrode design for use in studies of electroless plating

Abstract

An important property of electroless plating baths is their plating rate. This rate is normally determined by suspending a planar substrate in the bath and determining its weight gain after an appropriate period of time [1, 2]. In recent years there has been a growing interest in applying electrochemical methods to the study of electroless plating bath characteristics. For example, measurements have been made of the plating potential [3, 4], Tafel regimes [3], polarization resistance [5-7] and polarization curves over a wider potential range [3, 8], in efforts to find useful correlations with the gravimetric plating rates. The advantages of the rotating disk electrode (RDE) in electrochemistry are well known, yet its use in electroless plating studies has been very limited. One obvious reason for this is the problem of making numerous quick and accurate gravimetric plating rate measurements on such electrodes, which tend to be either too small in area or too massive for accurate measurements of weight gain to be made in a reasonably short time. We have now developed a simple and effective design, described below, which is suitable for both gravimetric and simultaneous electrochemical measurements. In order to test the utility of this RDE, we have carried out studies on the low temperature alkaline nickel bath described by Feldstein [2]. Solutions were prepared using 'chemically pure' or better grade reagents and deionized water. The plating bath contained NiSO 4 9 6HzO (25gl l), Na4P207.10H20 (50gl 1), 25% aqueous NH3 (25.2mll -1) and N a H 2 P O z H 2 0 (25g1-~), and operated at pH 10.95. A one-compartment, water-jacketed Pyrex cell of volume 200 ml was used for all measurements. The RDE was driven through a shaft powered by a d.c. electric motor with a speed controller unit [11]. A saturated calomel electrode (SCE) was used as a reference electrode, and a sheet of nickel of area 15 cm 2 as the counter electrode when required. The polarization resistance measurements were obtained in linear potential sweeps at 0.2 mV s -~ , using a home made potentiostat. Plating on the iron disks was initiated by brief polarization to 9 5 0 mV vs SCE. All measurements were carried out without purging oxygen from the solutions. Temperature control was + 0.1 ~ C, using a circulator-regulator.