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- Trybula, Marcela E., et al.
(författare)
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Atomic-Level Description of Chemical, Topological, and Surface Morphology Aspects of Oxide Film Grown on Polycrystalline Aluminum during Thermal Oxidation—Reactive Molecular Dynamics Simulations
- 2023
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Ingår i: Crystals. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2073-4352. ; 13:9
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation results in the formation of an oxide film whose properties and structure can be tailored by controlling the oxidation conditions. Reactive molecular dynamics simulations were performed to study thermal oxidation of polycrystalline Al substrates as a function of O2 density and temperature. The structural, chemical, and topological aspects of polycrystalline Al (poly-Al) substrates and oxide films formed upon oxidation were studied. The studies were supported by surface topography and morphology analyses before and after oxidation. An analysis of Al–O atomic pair distribution showed the development of long-range order in the oxide films grown upon exposure to low-density (0.005 g/cm3) and high-density (0.05 g/cm3) O2 gas. The long-range order was more apparent for the high-density environment, as the oxide films formed in low-density O2 gas did not fully cover the poly-Al surface. The dominance of over-coordinated polyhedral units in a tightly packed structure was indicative of medium- and long-range atomic order in the oxide films. The two-phase structure of the oxide was found in the films, with a crystalline phase at the metal/oxide interface and an amorphous phase at the oxide/O2 interface. The combination with topological analyses supported the conclusions of the chemical analysis and enabled us to capture an amorphous-to-crystalline phase transformation in the oxide films with increasing oxygen density and temperature. An important effect of Al surface roughness before oxidation on the behavior of the metal/oxide interface and on the oxide film structure was observed.
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| 2. |
- Trybula, Marcela E., et al.
(författare)
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Structure and Behavior of Oxide-Coated Aluminum in Contact with Acidic and Alkaline Aqueous Solutions─A Reactive Molecular Dynamics Simulation Study
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:5, s. 2493-2507
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Tidskriftsartikel (refereegranskat)abstract
- Aluminum oxide coating is inert to weak acidic and alkaline aqueous solutions and naturally provides a passivation layer on the coated substrate against corrosion. It exhibits good adhesion to the substrate. Reactive molecular dynamics simulations were performed to study the structure, topology, and behavior of the Al/oxide surface upon exposure to strong corrosive media at 363 K. A systematic study of OH- and H3O+ ion concentration on the behavior of Al/oxide surface was performed to describe structural, morphological, and topological differences associated with the mechanism of film growth in aqueous solutions. The difference found in the mechanism of film growth on the Al/oxide surface during corrosion influences the structure, surface topography, and interatomic bond topology of the formed films. Hydroxylation is a major reaction leading to the formation of a pseudoboehmite structure of film developed in alkaline solutions, whereas hydration is the reaction governing the film growth in acidic solutions. The mechanism of observed reactions during corrosion of the Al/oxide surface was confronted with available experimental data. The chemical composition of the developed films is pH-independent, and Al-enriched films form upon contact with both alkaline and acidic media. A higher content of OH group anchored to the Al/oxide surface is found in alkaline solutions, which increases the surface roughness and solvent-accessible surface area (SASA). Topological aspects of the grown films and Al/oxide interface were described performing Voronoi analysis supplemented with n-ring analysis. A dominance of lattice distortions of the Al substrate over crystal defects was observed, and a topologically complex amorphous nature of the films formed on Al/oxide surface.
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