Thermal conductivity of Cu-graphite composites

• Nonlinear thermal conductivity on composition was observed in the range of 0–40 vol.% of graphite.
• The average thermal conductivity of used graphite was estimated to be probably between 10 and 80 W/mK.
• Laser flash method gives 5% smaller value of thermal conductivity as comparative cut bar method at 30 vol.% of graphite.
• Different percolation of electrical and thermal conductivity on the identical percolating microstructure.

Cu-graphite composites were prepared in the range of 0–40 vol.% of graphite. Thermal conductivity was measured using comparative cut bar method at room temperature (RT). The observed composition dependence is nonlinear. Mean field approximation with characteristic exponent equal to 1 and percolation threshold of copper phase 0.926 ± 0.039 are the nonlinear fitting results for enlarged experimental data range up to 50 vol.% of graphite. Average thermal conductivity of graphite 80 W/mK was estimated together with used graphite anisotropy values – 10 and 274 W/mK. It was observed that laser flash method gives 5% lower values of thermal conductivity at 30 vol.% of graphite than comparative cut bar method at RT. It was showed that observed percolation threshold and characteristic exponents for thermal and electrical conductivity dependence on composition for the investigated composite system are significantly different on the identical microstructure. It is due to phonon conduction via graphite phase in the case of thermal conductivity.