Synergistic Effects Between Oil Tribopolymerisation and Abrasive Wear in Forming a Protective Third Body in a Conductive Polymer/noble Metal Electrical Contact

The study of a sliding contact between a carbon-particle filled polymer and a noble (AgPd) alloy, lubricated with a silicone oil/PTFE grease, has shown the formation of a third body in the interface. The electrical application of the system has required an in-depth study of this third body to make sure that electrical conductivity was not endangered. Thanks to different chemical and electrical analyses, the third body, recognised as a tribofilm, can be described as a heterogeneous layer, composed mostly by transformed grease components and conductive wear particles. Coupling these observations and results from the literature, the formation mechanism is identified as tribopolymerisation by cross-linking of the silicone oil molecules, analogous to the well-known 'gelation' of silicone oils. The conditions for this phenomenon to occur in this system are discussed. Inclusion of wear particles from the conducting first bodies into the third body ensures low resistance: the tribofilm formed by this combination of mechanisms is a protective layer, which prevents polymer tracks from severe wear, without degrading electrical performance.