Liquid Additives to Improve Conductivity in Electric Contacts

Electric contacts generally have high contact resistances because of the relatively small number of conducting contact spots and correspondingly small area through which to transfer current. Liquid metals have been used in the past to provide complete coverage in the contact region but generally require protective atmospheres to prevent corrosion of the liquid metal. Adding an atmospherically stable, non-consumable, conductive liquid additive to the electric contact could hypothetically increase the conductivity of the interface by increasing the contact area and, in the case of sliding contacts such as found in slip rings for example, may reduce wear. This paper presents the results of an initial investigation of several conducting aqueous solutions that could be used as conductivity enhancers for electric contacts. Cation solution pairs were formed using mixtures of the constituent single cation solutions. The technique is based on flowing electrolyte batteries; however energy is not stored in this application. Characteristics of the solutions containing cations of iron or copper in two different valance states, which serve as electron acceptors and electron donors, were evaluated without protective atmospheres. DC conductivity, pH, and half-cell voltage of each solution were measured. The solution with the cation pair had significantly higher conductivity than that of a solution with only one cation valance state. Because of the relatively high redox half-cell potentials of the solutions used in this initial investigation, noble metal electrodes including gold and palladium were required. In future experiments additives based on other types of ions, which may be compatible with lower cost electrodes such as silver, carbon or copper, will be evaluated.