Effect of nanostructure, oxidative pressure and extent of oxidation on model carbon reactivity

Oxidation kinetics and fringe analysis studies of three model carbons, ranging from fullerenic to onion-like nanostructures and a reference diesel soot were performed in a thermogravimetric analyzer. The samples were oxidized isothermally at temperatures ranging from 575 to 775 degrees C in air. Multiple tests were performed to obtain the most favorable operating conditions to minimize mass-transfer diffusion limitations in the experiments. First-order reaction kinetics and an Arrhenius-type equation were used to extract the rate constants at each temperature. The activation energies for the oxidation of the carbon samples ranges from 124 to 204 kJ/mol, and it was approximately 140 kj/mol for the reference diesel soot sample. The onion-like structure exhibited a slower kinetic rate compared to the other carbons. Similar kinetic parameters were found for intermediate structure model carbon and reference diesel soot. Fringe analysis explained the differences in the kinetic parameters between carbon samples studied. The onion-like carbon nascent sample had a broader range of lamellae length with smaller tortuosity distribution, suggesting stacking: the nascent fullerenic carbon had much shorter mean lamella length distribution and broader tortuosity, suggesting more curvature. Nanostructure metrics of the reference diesel soot and intermediate model carbon were between the other two carbons. Results confirm a structure-property relationship between oxidative reactivity with carbon nanostructure. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.