SOME MECHANISMS OF THE ACTION OF ADDITIVES IN ELECTRODEPOSITION PROCESSES

This review is of mechanisms by which additives have been postulated t o affect the rate of deposition of metals and their alloys. Emphasis i s on recent work in our laboratories, where mechanisms have been teste d by choosing systems expected to exhibit the appropriate chemical beh avior. Mechanisms chosen for study include: (a) ion bridging, (b) ion pairing, (c) changes in interfacial tension, (d) hydrogen evolution ef fects, (e) hydrogen adsorption, and (f) electrode filming. The possibl e role of electrode filming in electrodeposition of difficult-to-plate metals is discussed, as well as anomalous and induced codeposition of alloys, and deposition of stoichiometric alloys, such as the nickel-t in system.