• Magarino, E. Enrique
• Orlova, T. S.
• Popov, V. V.
• Martínez-Fernández, J.

Abstract

This paper reports on comparative investigations of the structural and electrical properties of biomorphic carbons prepared from natural beech wood, as well as medium-density and high-density fiberboards, by means of carbonization at different temperatures T <SUB>carb</SUB> in the range 650-1000°C. It has been demonstrated using X-ray diffraction analysis that biocarbons prepared from medium-density and high-density fiberboards at all temperatures T <SUB>carb</SUB> contain a nanocrystalline graphite component, namely, three-dimensional crystallites 11-14 Å in size. An increase in the carbonization temperature T <SUB>carb</SUB> to 1000°C leads to the appearance of a noticeable fraction of two-dimensional graphene particles with the same sizes. The temperature dependences of the electrical resistivity ρ of the biomorphic carbons have been measured and analyzed in the temperature range 1.8-300 K. For all types of carbons under investigation, an increase in the carbonization temperature T <SUB>carb</SUB> from 600 to 900°C leads to a change in the electrical resistivity at T = 300 K by five or six orders of magnitude. The dependences ρ( T) for these materials are adequately described by the Mott law for the variable-range hopping conduction. It has been revealed that the temperature dependence of the electrical resistivity exhibits a hysteresis, which has been attributed to thermomechanical stresses in an inhomogeneous structure of the biocarbon prepared at a low carbonization temperature T <SUB>carb</SUB>. The crossover to the conductivity characteristic of disordered metal systems is observed at T <SUB>carb</SUB> ≳ 1000°C.

Topics

• porous
• density
• impedance spectroscopy
• Carbon
• resistivity
• x-ray diffraction
• two-dimensional
• wood