Kinetic Analysis of Oxidation of Carbon Nanotubes, C_(60) and Graphite Using Mechanism-Function Method

摘要

The oxidation of carbon nanotubes, C_(60) and graphite was studied by thermogravimetric (TG) analysis and differential thermal analysis (DTA) technique, and the oxidation kinetic models of three carbon materials studied were analyzed by mechanism-function method. The results indicate that three carbon species adopt different oxidation mechanisms due to their different structures. The oxidation of carbon nanotubes with cylindrical structure follows contracting volume reaction mechanism [R_3 mechanism, 1 - (1 - α)~(1/3) = kt], indicating that the oxidation of carbon nanotubes takes place from the ends to the center. For graphite with planar sandwich structure, the oxidation starts at the edges initially and gradually moves toward the center, which corresponds to contracting area phase boundary reaction mechanism [R2 mechanism, 1 - (1 - α)~(1/2) = kt]. The oxidation of C_(60) with spherical structure, however, is complex and apparently cannot be illustrated with a single kinetic model. The values of apparent, activation energy obtained by the mechanism-function method are (145 ± 5)kJ·mol~(-1) for carbon nanotubes and (193±7)kJ·mol~(-1) for graphite, respectively, while the value of apparent activation energy for C_(60) determined using Kissinger method is 91 kJ·mol~(-1).