Preparation and characterization of graphite films with high thermal conductivity

Graphite films were prepared from DuPon polyimide films with different thicknesses by carbonization and graphitization treatments at a certain press. The micro-structural evolution of PI films during the process of high-temperature treatments was characterized by polarized light microscope, scanning electron microscope, X-ray diffraction and Raman spectrum. The results show that the PI graphite films (with a thickness of 50 μm for raw films) possess a three-dimensional structure of graphite layers with preferred orientation and prefect graphite crystals after graphitization at 3000℃. The corresponding interlayer spacing and stacking height of (002) crystal plane of the PI graphite film are 0.336 and 65.94 nm, respectively. The degree of graphitization of the PI graphite film is as high as 93%, and the electrical resistivity and thermal conductivity of the PI graphite films at room temperature in the main plane direction are measured to be 0.48 μΩ·m and 994 W/(m·K), respectively. The higher heat-treated temperature, the more easily transformation from the turbostratic carbon to ordered graphite, resulting in the better growth and crystallization of graphite microcrystals, and the more orientation of graphite layers. However, the microcrystals in the thick PI graphite films grow and crystallize difficultly, and their preferred orientation of carbon layers is very low.