The thermal oxidation characterization and its dynamic mechanism of micron-Al powders in air were investigated by simultaneous thermal analysis.Three kinds of micron-sized aluminum powders were heated up to 1110 ℃ at 10 K · min-1 heating rate in air.The kinetic parameters of the oxidation reaction were calculated by Satava-Sestak integral method.By analyzing the obtained TG-DTG-DTA curves and using SEM and XRD to observe the oxidation products of different stages,it can be found the thermal reactivity of aluminum has size effect:the smaller the particle size is,the deeper the degree of oxidation is.The oxidation process of micron-Al powder is divided into three distinct stages.During stage Ⅰ,below 550 ℃,the oxidation rate is the lowest,the natural amorphous alumina layer on the particle surface grow slowly.During stage Ⅱ,550-670 ℃,the oxide transformed into γ-Al2O3 which can't form a continuous shell on the surface of Al particles completely,the oxidation rate increases rapidly at the beginning of the stage Ⅱ,but decreases to the minimum when γ-Al2O3 layer completely covers the particle surface again.During stage Ⅲ,670-1110 ℃,because of the volume expansion of molten Al and the shrinkage of the surface area caused by the transition from γ-Al2O3 to α-Al2O3,the alumina layer produces cracks or breaks,the oxidation reaction is the most dramatic and produced only α-Al2O3 finally.Calculations prove that the smaller the particle size is,the lower the apparent activation energy of the oxidation reaction is,and the easier the reaction is.The most probable mechanism functions of thermal oxidation of the samples is the boundary control model function R3 ∶G(α) =G(α) =1-(1-α) 1/3 in the temperature range from 550 ℃ to 1110 ℃.%利用同步热分析技术,以10 K·min-1的加热速率将3种微米铝粉从室温加热至1110℃,分析获得的热重-微商热重-差热分祈曲线,并通过Satava-Sestak积分法计算得到氧化反应的动力学参数及最可几机理函数;利用扫描电镜(SEM)、X射线衍射(XRD)对不同阶段的氧化产物进行观察分析.结果表明,粒径越小的铝粉,越容易被氧化,其氧化程度也越深.微米铝粉的氧化过程可分为三个阶段:阶段Ⅰ,温度低于550℃,反应非常缓慢,Al颗粒表面的无定形氧化铝层缓慢生长;阶段Ⅱ,550 ～ 670℃,氧化层由无定形氧化铝向γ-Al2O3转变,新形成的y-Al2O3层不能在Al颗粒表面形成一个连续完整的外壳,裸露的Al与氧气接触,因此在阶段Ⅱ开始时,氧化速率迅速增大,当γ-Al2O3层完全覆盖Al核后,氧化速率迅速降低;阶段Ⅲ,670～1110 ℃,在内部熔融态Al受热体积膨胀及氧化铝由γ-Al2O3向α-Al2O3转变引起表面积收缩的共同作用下,颗粒表面氧化壳层产生裂缝或破碎,活性Al释放,氧化反应非常剧烈,最终生成稳定的α-Al2O3.粒径越小的Al粉,其氧化反应的表观活化能越低,反应越容易进行;3种样品的热氧化反应均符合边界控制模型函数R3∶G(α)=G(α)=1-(1-α)1/3,温度适用范围550 ～1110℃.
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