Oxidation kinetics and nanostructure of model carbons based on TGA data

Oxidation kinetics and fringe analysis studies of three "model" carbons, ranging from amorphous to onionlike nanostructures were performed in a thermogravimetric analyzer (TGA). The carbons were oxidized isothermally at temperatures ranging from 575 to 775 o C in air using a TGA Q600. Multiple tests were performed to obtain the most favorable operating conditions to minimize mass-transfer diffusion limitations. 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 ranged from 124 to 204 kJ/mol. The onion-like structure exhibited a slower kinetic rate compared to the amorphous M1300. For Regal 250 carbon, the kinetic rate changed during oxidation and Differential Scanning Calorimeter (DSC) analysis suggested the formation of a new compound (still to be identified) at higher conversions. The fringe analysis explained the differences in the kinetic parameters between carbon samples studied. The onion ike nascent sample had a longer range of fringe lengths and smaller tortuosity, suggesting a flatter structure; the nascent M1300, had a much shorter fringe length and broader tortuosity, suggesting more curvature. The nascent R250 nanostructure was between the other two carbons.