Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

Thermal oxidation of carbon/carbon composites in an oxidizing atmosphere is a multistep process regulated by the intrinsic heterogeneity of the solid–gas reaction, the additional heterogeneity of the compositional and structural characteristics of the composite, and how these two properties change as the reaction progresses. By focusing on the overlapping features of the component reaction steps, the kinetic characterization of the multistep kinetic process was studied to reveal the correlation between the thermal oxidation behavior and the compositional and structural characteristics of carbon/carbon composites. Using commercially available mechanical pencil leads as a typical model system for a carbon/carbon composite, the thermal behaviors of two different leads manufactured by different companies were investigated comparatively via thermoanalytical techniques and morphological observations. On the basis of a reaction model considering the different reactivities of the main (graphite) and secondary (carbonized polymer) carbon components, the kinetic features of two partially overlapping reaction steps were revealed via a kinetic deconvolution analysis of the thermoanalytical data for the thermal oxidation process. The kinetic results were correlated with the compositional and structural characteristics of carbon/carbon composites using morphological observations of the partially reacted samples. Herein, the practical usefulness of the kinetic analysis in characterizing carbon/carbon composites is discussed.