Size effect on the oxidation of aluminum nanoparticle: Multimillion-atom reactive molecular dynamics simulations

Abstract

The size effect in the oxidation of aluminum nanoparticles (Al-NPs) has been observed experimentally; however, the mechano-chemistry and the atomistic mechanism of the oxidation dynamics remain elusive. We have performed multimillion atom reactive molecular dynamics simulations to investigate the oxidation dynamics of Al-NPs (diameters, D = 26, 36, and 46 nm) with the same shell thickness (3 nm). Analysis of alumina shell structure reveals that the shell of Al-NPs does not break or shatter, but only deforms during the oxidation process. The deformation depends slightly on the size of Al-NP. This reaction from the oxidation heats the Al-NP to a temperature of T > 5000 K. Ejection of Al atoms from shell starts earlier in small Al-NPs - at t0 = 0.18, 0.28 and 0.42 ns for D = 26, 36 and 46 nm, when they all have the same shell temperature of 2900 K. As the oxidation dynamics proceeds, the total system temperature (including the environmental oxygen) increases monotonically; however, the time derivative of the total temperature, (dTsystem/dt), reaches a maximum at t1 = 0.20, 0.32 and 0.51 ns for D = 26, 36 and 46 nm. At this peak value of (dTsystem/dt), the shell temperature for the three Al-NPs are 3100 K, 3300 K, and 3500 K, respectively. The time lag between t1 and t0 is 0.02, 0.04 and 0.09 ns for D = 26, 36 and 46 nm clearly indicates the size effect. © 2013 © 2013 Author(s).