Thermal conductivity of carbon nanofiber mats

The anisotropic thermal conductivity of novel vapor grown carbon nanofiber (VGCNF) based paper-like mats was measured for increasing volume fraction and at different stages of heat-treatment. These nanofiber mats were prepared to exhibit high in-plane and low through-plane thermal conductivities with the goal of assessing their potential as 2-D heat spreaders. The in-plane thermal conductivity of the mats varied from 12 W/m-K to 157 W/m-K for volume fractions of 0.067 and 0.462, respectively, while the corresponding through-plane thermal conductivities were measured to be 0.428 W/m-K and 0.711 W/m-K. Heat treatment to temperatures above 3000 °C increased the through-plane thermal conductivity of the mats by an order of magnitude. However, the in-plane thermal conductivity, at best, was only seen to double. A model is proposed to describe the arrangement of nanofibers in the mats, and analytical expressions were used to estimate the thermal conductivity of an individual nanofiber using experimental results. Thermal conductivities of approximately 1400 W/m-K and 1600 W/m-K were calculated for individual VGCNFs heat treated to temperatures of around 1100 °C and above 3000 °C, respectively.

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► Characterization of thermal conduction in mats made with a new type of VGCNFs, termed PR-25, at two different stages of heat treatment.
► Layered structure of the mats resulted in the in-plane thermal conductivity being two to three orders of magnitude higher than the through-plane values.
► Estimation of thermal conductivity of an individual nanofiber based on the experimental results obtained for the mats.
► Increase in thermal conductivity due to graphitization of nanofibers is negligible compared to the increase seen in conventional carbon fibers.