Anisotropy of skeleton structure of highly porous carbonized bamboo and yucca related to the pyrolysis temperature of the precursors

- Properties of continuous matrix (skeleton) of porous carbonised plants were studied.
- Anisotropy of carbons structure was discussed on macro- and microscopic levels.
- Knudsen formula and series model of two-component system were used.
- Skeleton stiffness exhibits sharp changes at pyrolysis temperatures 300 °C and 600 °C.
- High increase of skeleton stiffness at high pyrolysis temperatures evidences structure ordering.

In this work, anisotropic properties of skeleton of highly porous monolithic blocks of carbonized stems of bamboo and yucca are discussed in relation to temperature of pyrolysis ranging between 300 °C and 950 °C. Elastic moduli of skeleton, i.e. of continuous matrix of porous block were calculated using two models: the series model of two-component system and the Knudsen formula relating elastic modulus to bulk porosity. Two models of pore shape were assumed: cuboid and cylindrical. The experimental data of the physical properties previously presented: bulk porosity and dynamic elastic modulus were applied for calculations. The dependence of the skeleton elastic moduli on the temperature of pyrolysis exhibited wide minimum at temperatures ∼300-400 °C. Sharp increase of skeleton stiffness found at temperature ∼600 °C could be interpreted as the phase transition from disordered to ordered structure of pore wall.Anisotropy of structure of carbonized plants studied was discussed on two levels: (i) macroscopic-description using physical parameters measured along basic directions of a block sample and (ii) microscopic-anisotropy of skeleton structure. Ultrasonic measurements supported an information similar to that obtained previously by means of different methods (XRD, EPR and optical microscopy): ordering of aromatic structures develops with increasing temperature of pyrolysis. However because of their random arrangement solid carbon skeleton is nearly isotropic-anisotropy of carbonized plant structure is mostly due to pore system.

195Marta Krzesińska, Anisotropy of skeleton structure of highly porous carbonised bamboo and yucca related to the pyrolysis temperature of the precursors.