Effect of h-BN addition on thermo-physical properties and phonon mechanisms of C/C-BN composites

C/C-BN composites containing different contents of h-BN particles were prepared by chemical vapor infiltration (CVI), presenting different microstructures and pyrolytic carbon (PyC) textures. The effects of different micro-structures and PyC textures on the thermo-physical properties and their phonon mechanisms at 30-900 degrees C were investigated. The temperature dependence of heat capacity follows Debye's phonon theory, especially in the low -temperature section (30-300 degrees C) and the temperature dependence of thermal conductivity is determined by heat capacity and mean free length of phonon. Due to the higher texture of h-BN and regenerative laminar PyC (ReL-PyC), h-BN addition causes higher Debye temperature (Theta D) and high sensitivity of thermal conductivity to temperature. Besides, h-BN addition significantly changes the microstructure of composites such as pore struc-ture, PyC morphology, crack distribution and fiber/PyC interface bonding state, causing the transformation of thermal conductivity from anisotropy to isotropy. Finally, based on the different microstructures of composites, the microstructure model and thermal resistance formulas of composites were established and coincident with the experimental results.