通过热重分析技术用模式函数和无模式函数法研究了多晶石墨材料的非等温氧化动力学, 并利用扫描电镜观察了该材料同一表面不同氧化程度的微观结构. 研究表明, 石墨氧化过程中, 活化能(E)随着氧化程度(α)增加而变化. 氧化从石墨表面的颗粒界面开始, 在氧化初期阶段, 表面原始空隙的尺寸随氧化程度的增加几乎不变. 石墨的非等温氧化过程主要分三个阶段: 氧化前期(α<20%), 氧化主要由碳氧化学反应控制; 氧化中期(20%<α<60%), 氧化为化学反应和气体扩散共同控制; 氧化后期(α>60%), 氧化主要由气体扩散控制. 运用无模式函数法研究石墨非等温氧化更具有可信度.
With the help of thermogravimetric analysis technique, non-isothermal oxidation kinetics of polycrystalline graphite was investigated by model-fitting and model-free methods, and the microstructure of the same surface of different weight loss was observed by SEM. Results show that the activation energy (E) depends strongly on weight loss fraction (α). Oxidation starts from grain boundary, and the pore size on observed surface almost does not change with the increase of weight loss at the initial stage of oxidation. The non-isothermal oxidation of polycrystalline graphite exhibites three regimes: in the initial stage (α<20%), oxidation is controlled by chemical reaction; in middle stage (20%<α<60%), oxidation is controlled by chemical reaction and gaseous diffusion; in final stage (α>60%), oxidation is controlled by gaseous diffusion. The model-free method is recommended as a trustworthy way for obtaining reliable kinetic information from non-isothermal oxidation of graphite.
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