Why some carbons may or may not graphitize? The point of view of thermodynamics

Not all carbons graphitize in equal measure. Some will develop a structure which approaches the one of perfect graphite (graphitizable carbons) upon heat treatment, while others will not (non-graphitizable carbons). The present work develops a phenomenological model for the conceptual understanding of graphitizability (capacity to graphitize). To support this model, a mathematical formalism, inspired from thermodynamics, is proposed to calculate the Ultimate Graphitizability (eta(g)) of some graphitizable and non-graphitizable carbon materials. eta(g) is the average interlayer spacing (d(002)) of a graphenic carbon following graphitization at similar to 3400 K. eta(g) can be estimated assuming a topological graphitization mechanism operating between 1700 K and 3400 K. Two independent variables define eta(g): d(002) (T alpha) and d(002) (T beta). T alpha and T beta are arbitrarily selected temperatures between 1700 K and 2550 K (the graphitization threshold). In order to better understand the parameters affecting d(002) (T-alpha) and d(002) (T-beta), new carbonization/ graphitization experimental results are presented. These suggest that d(002)(T-alpha) and d(002) (T-beta) are correlated to the oxygen/hydrogen composition ratio and the relative mesoscale crystallite orientation of some graphitizable carbons following the end of primary carbonization. (C) 2019 The Authors. Published by Elsevier Ltd.

Mots clés

• transmission electron-microscopy
• x-ray-diffraction
• electrochemical properties
• coke crystallites
• phase-transitions
• heat-treatment
• carbonization
• microtexture
• sulfur
• behavior