Kinetic model and mechanisms of oxidation of 2D-C/C composite

The isothermal oxidation of a two-dimensionally reinforced carbon/carbon (2D-C/C) composite was investigated by thermogravimetric analysis, and a kinetic model was proposed. The microstructure of 2D-C/C composite with different mass loss was studied by SEM, and isothermal oxidation mechanisms were discussed. The oxidation exhibits two stages: a linear oxidation stage with mass loss from 0 to 65%, during which the oxidation rate is almost stable; and a non-linear oxidation stage with mass loss between 65% and 100%, in which the oxidation rate decreases. The oxidation Arrhenius curve for 2D-C/C composite consists of two straight lines, the intercept of which is at about 800~850℃. At the linear oxidation stage, the activation energy is 217.2 kJ/mol and 157.0kJ/mol respectively; at the non-linear oxidation stage, the reaction order is 0.55 and 0.65, and the activation energy is 219.3 kJ/mol and 182.0 kJ/mol respectively. By comparing the experimental and theoretical TG curves, the kinetic model can be used to predict the isothermal oxidation of 2D-C/C composite. The oxidation starts from the fiber/matrix interface, and the matrix is oxidized much more rapidly than the carbon fibers, and only the fibers are being attacked in the final stage of oxidation. At 750~800℃, the oxidation is controlled by chemical reaction; at 850~905℃, it is controlled by chemical reaction and gaseous diffusion, but the contribution of gaseous diffusion to oxidation in the non-linear stage is less than that in the linear stage.