Crystal graphite of graphite powder
At room temperature, lambda A is about 200 times larger than lambda C. As the temperature increases, this ratio decreases, but remains large. Therefore, the thermal conductivity of polycrystalline graphite composed of microcrystalline is controlled by the thermal conductivity of microcrystalline layer lambda a, and lambda C can hardly be considered. The lambda a of natural flake graphite is between 280 and 500W/ (m * K) at room temperature. The ratio of lambda a/ lambda C is between 3~5, so the perfection of crystal is far better than that of high directional pyrolytic graphite.
The crystal structure of highly structured pyrolytic graphite, La above 2000Nm, from low temperature to high temperature, the thermal conductivity changes with the temperature is bell shaped, see Figure 1, figure 2.
Pure graphite flake graphite and high directional pyrolytic graphite, which have less defects and larger sizes, can generally be considered as perfect graphite single crystals. Considerable research has been done on the thermal conductivity of such graphite. Under compressive stress, the pyrolytic graphite above 3000K processing, the bulk density is 2.25g/cm, 2.266g/cm is close to the theoretical density of the single crystal, the half width of the diffraction peak (002) show only 0.4 degree angle (mosaic angle), is also very close to the theoretical value of zero. The thermal conductivity of this graphite is shown in table 1. These values are generally considered to represent the corresponding values for single crystal graphite. The thermal conductivity along two principal directions is denoted as lambda a along the layer, and is marked by lambda C along the vertical plane.
