Studies of Thermal Conductivity of Graphite Foil-Based Composite Materials.

We have proposed and developed a method for measuring the thermal conductivity of highly efficient thermal conductors. The measurement method was tested on pure metals with high thermal conductivity coefficients: aluminum (99.999 wt.% Al) and copper (99.990 wt.% Cu). It was demonstrated that their thermal conductivities at a temperature of T = 22 ± 1 °C were <λ> = 243 ± 3 W/m·K and <λ> = 405 ± 4 W/m·K, which was in good agreement with values reported in the literature. Artificial graphite (ρG1 = 1.8 g/cm) and natural graphite (ρG2 = 1.7 g/cm) were used as reference carbon materials; the measured thermal conductivities were <λ> = 87 ± 1 W/m·K and <λ> = 145 ± 3 W/m·K, respectively. It is well established that measuring the thermal conductivity coefficient of thin flexible graphite foils is a complex metrological task. We have proposed to manufacture a solid rectangular sample formed by alternating layers of thin graphite foils connected by layers of ultra-thin polyethylene films. Computer modelling showed that, for equal thermal conductivities of solid products made of compacted thermally exfoliated graphite and products made of a composite material consisting of 100 layers of thin graphite foil and 99 layers of polyethylene, the differences in temperature fields did not exceed 1%. The obtained result substantiates our proposed approach to measuring thermal conductivity of flexible graphite foil by creating a multi-layer composite material. The thermal conductivity coefficient of such a composite at room temperature was <λ> = 184 ± 6 W/m·K, which aligns well with measurements by the laser flash method.