High-Current Brush Material Development, Part I: Sintered Metal-Coated Graphite

The technique for coating powders with copper or silver by chemical plating and the preparation of the sintered metal-coated graphite composites are described. A process has been developed for coating graphite powders of sizes down to 38 mum. Metal contents ranging from 20 to 97 percent, by weight of the final product, have been achieved by simple and multiple platings. Metallographs of the sintered products reveal the ideal structure of a continuous three-dimensional metal lattice throughout the composite. The electrical resistivities of the sintered products were measured and are compared with metal-graphite brush materials fabricated by conventional powder metallurgy and metal infiltration techniques. As expected, at the same metal contents, the sintered metal-coated graphite composite always exhibits much lower electrical resistivities than the conventional materials. The difference in electrical resistivity is attributed to the metal structure of the metal-graphite systems.