287660 Indium and Zinc Alloys As Cadmium Brush Plating Replacement
Since cadmium and its corrosion product (cadmium oxide) are carcinogenic and toxic, efforts to eliminate cadmium from original equipment and repair processes have continued. Cadmium oxide remains semi-conductive, while most other pure metal oxides are electrical insulators, such as aluminum oxide, nickel oxide, and zinc oxide, and, therefore, fail in meeting the requirement for bonding and grounding. One potential replacement is indium because as it oxidizes it also exhibits semi-conductive properties. The semi-conductive properties of indium oxide alloys make it possible to use these for cadmium brush plating replacement in applications where contact resistance and impedance are critical parameters. Critical requirements of an alternative to cadmium brush plating in a corrosive industrial atmosphere are (1) be sacrificial to mild steel and (2) provide good electrical conductivity. Similar to cadmium oxide, indium oxide is semi-conductive, but indium exhibits other properties such as cold welding. Another coating system that offers potential maintaining electrical conductivity during environmental and extreme temperature exposure is brush-plated zinc-nickel systems.
This presentation is an update on alloy coating development activities, and discusses electroplating approaches to overcome the insulating limitation of pure metal plating and to replace cadmium brush plating for the system. Test methods for impedance versus frequency qualification will be described. Test results of various brush electroplated alloy coatings will be reported.
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