Combinations of nanoscale and microscale silver particles were used to construct heterogeneously conductive paths in graphite composites for improving through-thickness thermal conductivity. Composites with four different pitch-based graphite fibers were studied and compared to realize the improved thermal conductivity with adequate mechanical performance. The test panels of EWC300X graphite fibers and sliver fillers achieved a through-thickness thermal conductivity of ～10.0 W/m·K at 25 °C. The rheological behavior of Epon862/curing agent resin and silver flakes filled Epon862/curing agent resin was studied for the standardization and quality control of large panel fabrication. By adding 40wt% silver flakes in the resin system, the viscosity greatly increased. The lowest viscosity of 40% silver flakes filled Epon862/cu ring agent resin system occurred at 65 °C; therefore, the curing process was modified accordingly to ensure resin/fiber wetting and reduction of voids. The hybrid composites with IM7 and pitch-based carbon fiber were also made in order to optimize the composite performance with a balanced thermal conductivity and mechanical properties. The failure mechanisms of laminated composites with and without silver fillers were investigated. The IM7/EWC300X hybrid composite with a density of 2.31 g/cm~3 showed a thermal conductivity of 5.29 W/m·K and adequate mechanical properties for structural applications.
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