Thermal analysis of the oxidation of natural graphite: isothermal kinetic studies

The oxidation kinetics of natural graphite particles (2-40 mum average particle size) with a flake-like morphology were investigated at 933, 982 and 1033 K. The reaction rate in air increased with increase in temperature and with a decrease in particle size of natural graphite. The activation energy, derived from the classical Arrhenius relationship, was 188 +/- 2.2 kJ/mol, in good agreement with published results. The activation energies of the natural graphite did not show any systematic trend with particle size. The rate constant, normalized for the area of active sites, is independent of the particle size and Brunauer-Emmet-Teller (BET) surface area, which strongly suggests that the edge sites play a significant role in the oxidation kinetics. This observation is consistent with conclusions reported in the literature that the oxidation kinetics of carbonaceous materials decreases with a decrease in active surface area. (C) 2001 Elsevier Science B.V. All rights reserved.