Al2O3在Al(111)面形核机理的第一性原理

First-Principle Study of Al2O3 Nucleation Mechanism on Al(111)Surface

为了揭示金属Al粉末表面生成无定形Al2O3的反应机理,基于具有周期性边界条件的超晶胞模型,采用第一性原理密度泛函理论中的广义梯度近似计算方法,计算并分析了三氧化二铝(Al2O3)在Al(111)面的形核过程,根据前人的实验结果总结和提出了4条反应路径,对O2和Al2O3分子在Al(111)表面的吸附性质进行了结构和能量分析,分别由3个或4个基元步构成。结果表明,首先O2在Al(111)表面吸附时,O2发生O—O键断裂形成中间产物AlO,该中间产物再继续和Al原子、O原子、AlO进一步反应形成Al2O、AlO2、Al2O2等中间产物,最终形成Al2O3。从这些中间产物之间的自由能变化可以看出,AlO和O2参与反应的中间步能量分别下降8.37和8.08 eV,而形成AlO2和Al2O等中间产物时能量分别上升1.27和0.76 eV,但是整个Al2O3形核反应是放热的,即自由能降低15.19 eV。因此,三基元和四基元反应都易在Al表面生成Al2O3。

In order to reveal the reaction mechanism of amorphous Al2O3 layer on the surface of Al powder,the process of Al2O3 nucleation on Al(111)surface was systematically investigated by the first-principle calculations based on density functional theory(DFT)with generalized gradient approximation(GGA).The energy and geometry behaviors were studied with the adsorption of O2 and Al2O3 molecules onto Al(111)surface.Possible reaction pathways consisting of four or three elementary steps were considered based on previous results.Results show that O2 molecule firstly adsorbs onto Al(111)surface with the break of O—O bond,producing the intermediate of AlO.The intermediate AlO reacts with O,Al and AlO,further giving the intermediates of Al2O,AlO2,Al2O2,and eventually forms Al2O3.As shown in the free energy change of different intermediates,it is found that the elementary steps containing O2 and AlO exhibit downhill in the free energy profiles(-8.37,-8.08 eV),while the steps of forming the intermediates of AlO2 and Al2O are endothermic(1.27,0.76 eV).As a whole,the reaction for Al2O3 nucleation on Al(111)surface is downhill in the free energy profiles(-15.19 eV).Therefore,the reaction pathways irrespective of three elementary steps and four elementary steps are thermodynamically favorable for Al2O3 nucleation on Al(111)surface.