Atomistic modeling of ultra-thin surface oxide growth on a ternary alloy : oxidation of Al-Ni-Fe.
- Center for Nanoscale Materials
By employing variable-charge molecular dynamics, surface oxide film growth on aluminum-nickel-iron alloys has been studied at 300 and 600 K. The dynamics of oxidation and oxide growth is strongly dependent on the composition of the initial alloy and the ambient temperature. Higher content of Ni and Fe in Al alloys is found to reduce the oxide growth kinetics; 15% Ni + 15% Fe Al alloy yielded 30-40% less growth at 400 ps oxygen exposure compared to pure Al. We observe dopant segregation, which disrupts the interaction between O atoms and Al atoms in the alloy, leading to a nonlinear oxide growth profile in the case of ternary Al-Ni-Fe alloy. Compared to oxidation at 300 K, 30% more oxide layer was yielded at 600 K, due to the elevated temperature. The simulated oxide kinetics indicates that the growth rate of anion surpasses the cation rate with higher sensitivity to the stoichiometry of the base metal substrate. Charge state analysis provides insights into the evolution of cation and anion species as the oxide layer grows. In particular, due to higher correlation, Fe shows a high rate of oxidation when the content is high, whereas the rate of Ni oxidation is consistently low. Density profile analysis suggests the segregation of dopant atoms below the growing ultrathin oxide layer, showing the presence of a layer-by-layer mode of oxide layer even with disordered structure. Coordination number (Z, the number of oxygen atoms around an aluminum atom) of aluminum oxide has been used to identify how the initial oxidation transitions into equilibrated states. Z = 3 is dominant in the early stages of oxidation and at the interface between oxide and bulk substrate, but it transitions quickly to Z = 4 (45%) and 5 (35%) as the oxide equilibrates and approaches its self-limiting thickness. Even though growth kinetics is dependent on the base metal stoichiometry, the composition of the oxide microstructure is not significantly affected, primarily segregating dopant elements, i.e., Ni and Fe outside of the oxide layer.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- ORN; USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 1020665
- Report Number(s):
- ANL/CNM/JA-68589; TRN: US201116%%563
- Journal Information:
- J. Phys. Chem. C, Vol. 115, Issue 14 ; Apr. 14, 2011
- Country of Publication:
- United States
- Language:
- ENGLISH
Similar Records
Oxygen Transport Membranes
Al deposition on Fe: Formation of an iron aluminide surface alloy