Eletroless Plating of Copper on Graphite Powders for Homogeneous Copper-Carbon Composite

Abstract

DC motor brush facilitates current connection between moving parts and stationary wires in motor. Copper wire brushes are traditionally used in the past, but carbon brushes are more widely used in recent days. Although carbon brush offers high resistance and better commutation between commuter segments, it wears more rapidly than copper brushes due to its softness. New copper and carbon composite brushes have been developed to overcome this drawback of copper wire, however, the density difference between the carbon and copper results in inhomogeneity during mixing which causes poor sinterability and less than expected performance of the final product. A simple way to bypass this problem is the coating of copper on carbon powder which easily reduces inhomogeneity caused by the density difference. In this work, copper is electrolessly plated on graphite powders and the effect of plating variables on the sintering behavior of the coated graphite powders. Prior to the electroless plating of copper, standard activation and sensitization procedures are applied to graphite powders using SnCl2-PdCl2 solution and PdCl2, respectively. For electroless plating of copper, formaldehyde is used as reducing agent of copper sulfate. Various ratios of amount of copper sulfate and graphite powder, pH, and plating times are tested to find the optimum condition for sintering of the coated powder. The results show that the copper coated graphite successively produces homogeneous sintered compacts, which shows improved sinterability as well.