Heat capacity and phonon mean free path in the biocarbon matrix of beech

摘要

The heat capacity at constant pressure C_p of the biocarbon matrix prepared at a beech wood carbonization temperature of 1000°C has been measured in the temperature range 80-300 K. It has been shown that, in the temperature range 90-180 K, the heat capacity is C ~ T~(0. 8) and, at T = 190-300 K, it is C_p ~ T~(1. 2). The phonon mean free path l(T) in the biocarbon matrix has been calculated using the obtained dependences C_p(T), our previous results on the phonon thermal conductivity of the carbon framework of this biocarbon matrix, and data available in the literature on the sound velocity in the matrix. It has been demonstrated that, in the temperature range 200-300 K, the mean value of l is ~ 15 ?, which is close to the sizes of nanocrystallites ("carbon fragments") of ~ 12?, obtained earlier from X-ray diffraction data for the carbon matrix under consideration. These nanocrystallites participate in the formation of the carbon framework of the beech wood biocarbon matrix.