Study On Graphite/epoxy Resin/BaTiO₃ Based PTC Composite

In order to reduce the room temperature resistivity of BaTiO₃-based PTC ceramics, BaTiO₃-based PTC ceramic particles were mixed with graphite particles and the composite materials were molded with epoxy resin. The electroless nickel plating method was used to prepare nickel electrode on the surface of the composite,to avoid the influence of traditional electrode preparing technology on epoxy resin.The effects of molding pressure, solidification time of resin, electroless nickel plating and the heat treatment after plating process on PTC characteristics of the composite were discussed through lots of experiments. The optimal values for each technical parameter were obtained via the analysis of experimental datas. The optimal gradation value of graphite-ceramic particle was also obtained through comparison experiments.The influencing rule of the content of graphite and resin on the PTC characteristics was discussed on the basis of the work above. The results showed that the room temperature resistivity of the composite declined slowly along with the augment of the graphite content at the initial stage, and declined abruptly when the mass ratio between graphite and graphite-resin was 1.6, and then the resistivity declined slowly until the samples became conductors. The room temperature resistivity of the composite declined along with the augment of the resin content at the initial stage and increased after that. The resistivity jump magnitude of composite changed according to the conversing"V"-shape curve with the augment of the graphite content and it was low when the content of graphite was too high or too low. The resistivity jump magnitude increased along with the augment of the resin content in the beginning and decreased after that.According to various influencing factors, the new composite system which had distinct lower room temperature resistivity and a little lower resistivity jump magnitude than BaTiO₃ based PTC ceramic was prepared.The correlated PTC theory, the seepage theory in conducting high polymer and the effective medium theory were applied to explain these phenomena.