Controllable thermal conductivity in composites by constructing thermal conduction networks

Thermal conduction networks formed by thermally conductive fillers are crucial to the thermal conductivity coefficients (l) of composites. In this paper, paraffin wax (PW) spheres with different sizes are prepared by instantaneous cooling granulation technology. With graphite coated on their surface by the micro-cladding method, the graphite/PW thermally conductive composites are then fabricated by hot pressing. The formation process of graphite thermal conduction networks at interfaces between the PW phases, and the influences of the density, distribution, and integrity of the networks on the l of the graphite/PW composites are analyzed in-depth. Besides, an innovative concept of Density of Thermal Conduction Networks (DTCN) is proposed to explain the l difference among different graphite/PW composites. The DTCN of the graphite/PW composites have the best value for given graphite loading and molding pressure. The l of the graphite/PW composites with the same size of PW spheres increases with increasing DTCN. When the amount of graphite is 10 wt%, the molding pressure is 200 MPa, and the PW spheres size is 2.08 +/- 0.08 mm, the graphite/PW composites have the maximum l (1.81 W/(m.K), the l enhancement rate per unit mass fraction (El/wt) of graphite is 45, about 6 times of that of pure PW (0.33 W/(m.K)), also obviously higher than that of the freely dispersed R-graphite/PW composites with the same amount of graphite and molding pressure (0.79 W/(m.K), El/wt is 14). The higher DTCN, the more uniform distribution and integrity of the thermal conduction networks, and ultimately the higher l of graphite/PW composites. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Thermal conduction networks formed by thermally conductive fillers play a crucial role in determining the thermal conductivity coefficients of composites. In this study, graphite/PW thermally conductive composites with high thermal conductivity were prepared by a special fabrication process, demonstrating the importance of high density, uniform distribution, and integrity of the thermal conduction networks for enhancing the thermal conductivity performance.