Microstructure dependence of the mechanical and thermal behavior of pyrolytic carbonaceous char

The mechanical and thermal properties of carbonaceous char, obtained through ultrahigh-temperature pyrolysis using molecular dynamics simulations with the Brenner reactive empirical bond-order potential, are reported in this work. The main focus is on the effects of microstructure and microtopology on the mechanical and thermal response properties of pyrolytic char. The Young's modulus of char is found to follow an ∼(n̄ - n_T) ^γ dependence on the average coordination number, n̄, for n̄ values below ≈2.97, with n_T being a threshold coordination number for transition between soft and solid phases of the material. This behavior is characteristic of a random network model of glassy systems, in which case γ ≈ 1.5. As the average coordination number n̄ increases from ≈2.97 to ≈3.10, deviations from the simple power-law behavior are observed. We show that these deviations are due to a microtopological transition associated with the formation of buckled graphene-sheet-like microstructures in the char. The thermal conductivity of pyrolytic char is also investigated in a wide range of temperatures and shown to follow a behavior described by the modified Einstein heat transfer theory, corrected for the presence of buckled graphene-sheet-like features in the pyrolyzed char.