Thermal conductivity of high-porosity biocarbon precursors of white pine wood

Abstract

This paper reports on measurements of the thermal conductivity κ and the electrical conductivity σ of high-porosity (cellular pores) biocarbon precursors of white pine tree wood in the temperature range 5–300 K, which were prepared by pyrolysis of the wood at carbonization temperatures (T_(carb)) of 1000 and 2400°C. The x-ray structural analysis has permitted the determination of the sizes of the nanocrystallites contained in the carbon framework of the biocarbon precursors. The sizes of the nanocrystallites revealed in the samples prepared at T_(carb) = 1000 and 2400°C are within the ranges 12–35 and 25–70 A, respectively. The dependences κ(T) and σ(T) are obtained for samples cut along the tree growth direction. As follows from σ(T) measurements, the biocarbon precursors studied are semiconducting. The values of κ and σ increase with increasing carbonization temperature of the samples. Thermal conductivity measurements have revealed that samples of both types exhibit a temperature dependence of the phonon thermal conductivity κ_(ph), which is not typical of amorphous (and amorphous to x-rays) materials. As the temperature increases, κ_(ph) first varies proportional to T, to scale subsequently as ∼T ^(1.7). The results obtained are analyzed.