密度泛函理论预测微量元素在Al(100)表面的偏聚

通过周期性层状模型, 利用密度泛函理论预测了微量杂质元素原子M(M=Fe, Si, Mg, Cu, Mn, Ga, In, Sn, Pb)在高纯铝箔(100)表面的偏聚趋势. 计算得到表面偏聚能与已有实验结果相吻合. 表面偏聚能由表面取代的微量元素原子M的位置、原子半径和金属的表面能决定. 当表面偏聚能为负时, 微量元素原子M在表面偏聚, 反之则杂质原子不发生表面聚集. 微量元素原子在铝箔表面偏聚可以使铝箔表面产生大量的缺陷和位错, 它们在铝箔腐蚀时容易成为腐蚀的形核起点, 进而增加铝箔的腐蚀发孔密度.

Prediction of the Surface Segregation of Trace Elements on the Al(100) Surface by Density Functional Theory

A simplified 9-layer slab model was created using periodic density functional theory calculation to predict the tendency of trace elements to undergo surface segregation. Using this approach, nine different trace element atoms (Fe, Si, Mg, Cu, Mn, Ga, In, Sn, and Pb) were substituted into the (100) plane in a pure aluminum foil surface and the surface segregation energies were calculated. The results were in very good agreement with the available experimental data. There were various correlations between the segregation energy and the relaxed position on the surface of the substituted atom, the radius of the substitute atom and the experimental surface energy of the metal. A negative segregation energy indicated that the trace element atoms were able to segregate and move to the surface while a positive segregation energy implied a tendency to move into the bulk material. Trace element atoms segregated on the Al foil surface and led to many defects and dislocations which can increase initial pitting nucleation sites and enhance the density of pitting for Al foils.