Non-isothermal Oxidation Kinetics and Mechanisms of Polycrystalline Graphite

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 microstruc- ture 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 (α20%),oxidation is controlled by chemical reaction;in middle stage (20%α60%), oxidation is controlled by chemical reaction and gaseous diffusion;in final stage (α60%),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.