摘要:
用热重法研究了二维炭/炭(2D-C/C)复合材料的等温氧化, 提出了氧化动力学模型, 用SEM观察了样品不同氧化程度的微观形貌, 并探讨了材料的等温氧化机理。氧化分2个阶段: 线性氧化阶段, 氧化失重率小于约65%, 氧化速率处于稳定状态; 非线性氧化阶段, 氧化失重率约大于65%, 氧化速率急剧减小。Arrhenius曲线由折点在800~850℃之间的2条直线组成。线性氧化阶段, 活化能分别为217.2kJ/mol和157.0kJ/mol; 非线性氧化阶段, 反应级数分别为0.55和0.65, 活化能分别为219.3kJ/mol和182.0kJ/mol。通过实验验证, 氧化动力学模型可以较好地预测材料的恒温氧化。氧化从炭纤维与基体炭的界面开始, 基体氧化快于纤维, 氧化后期主要是纤维的氧化。在750~800℃, 氧化为化学反应控制; 在850~905℃, 氧化由化学反应和气体扩散共同控制, 但非线性氧化阶段气体扩散对氧化的贡献小于线性氧化阶段。
Abstract:
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 157.0kJ/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.
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