Thermal conductivity of the amorphous and nanocrystalline phases of the beech wood biocarbon nanocomposite

Abstract

Natural composites (biocarbons) obtained by carbonization of beech wood at different carbonization temperatures Tcarb in the range of 800–2400°C have been studied using X-ray diffraction. The composites consist of an amorphous matrix and nanocrystallites of graphite and graphene. The volume fractions of the amorphous and nanocrystalline phases as functions of Tcarb have been determined. Temperature dependences of the phonon thermal conductivity κ(T) of the biocarbons with different temperatures Tcarb (1000 and 2400°C) have been analyzed in the range of 5–300 K. It has been shown that the behavior of κ(T) of the biocarbon with Tcarb = 1000°C is controlled by the amorphous phase in the range of 5–50 K and by the nanocrystalline phase in the range of 100–300 K. The character of κ(T) of the biocarbon with Tcarb = 2400°C is determined by the heat transfer (scattering) in the nanocrystalline phase over the entire temperature range of 5–300 K.