Indium-Zinc and Zinc-Nickel Alloys as Cadmium Brush Plating Replacement

摘要

As cadmium and its corrosion product (cadmium oxide) are carcinogenic and toxic, efforts are ongoing to eliminate cadmium from original equipment and repair processes such as brush plating. The objective of this project requires that the brush plating cadmium replacement meet electrical impedance and corrosion resistance requirements, defined by the customer for specific applications. Cadmium oxide is semi-conductive, while most other pure metal oxides are electrical insulators, (i.e. aluminum oxide, nickel oxide, and zinc oxide) and, therefore, fail to meet electrical impedance requirements. One potential replacement for cadmium is indium because, as it oxidizes, indium also exhibits the desired semi-conductive properties and may allow alloys of indium to be a possible cadmium replacement in brush plating applications where impedance is a critical parameter. Another possible coating system that offers suitably low electrical impedance during environmental exposure is brush-plated zinc-nickel systems. Both coating systems have the potential to meet corrosion resistance requirements and have been investigated as alternatives to cadmium. This paper discusses alloy coating development activities to replace cadmium, and electroplating approaches to overcome the insulating limitation of pure metal plating. Test results of various brush electroplated alloy coatings will be discussed.