The Kinetics and Mechanism of Oxidation of Superpurity Aluminum in Dry Oxygen

Dignam, M. J.; Fawcett, W. Ronald; Böhni, H.

doi:10.1149/1.2424086

Cited by 94 publications

(55 citation statements)

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“…Several researchers have studied the thermal oxidation of aluminum and found that an air-formed oxide film develops when aluminum is heated in air or oxygen to a temperature above 723 K. An amorphous oxide film is formed initially and then -alumina crystals develop at the metal-oxide interface. [1][2][3][4] As the oxidation temperature increases, the crystallinealumina is gradually transformed from the amorphous aluminum oxide by the inward diffusion of oxygen.…”

Section: Introductionmentioning

confidence: 99%

Thermally-Formed Oxide on Aluminum and Magnesium

Shih

Liu

2006

Mater. Trans.

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Pure aluminum and magnesium cube samples were heated at a specific temperature for a given time after being polished by abrasive papers. The amorphous layer that formed on the sample surface was transformed into a crystallized oxide film during the heating and holding period. We discuss how this thermally-formed oxide film progressively developed on the surface of the cubic samples. Gibbsite (Al(OH) 3 ) forms on pure aluminum during the initial stage of heating, after which it is then transformed to complex oxides, diaspore and -alumina. After an extended holding time at 883 K, the thermally-formed oxide film will be comprised of gibbsite, diaspore, -Al 2 O 3 and -alumina. This thermally-formed oxide film is compact and contains evenly-distributed microchannels. With pure magnesium, the transformation of periclase from brucite is associated with the formation of microcracks. In this study we use TGA (thermo-gravimetric analysis) to describe the progressive development of complex oxides and periclase films on pure Al and Mg respectively.

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Section: Introductionmentioning

confidence: 99%

Thermally-Formed Oxide on Aluminum and Magnesium

Shih

Liu

2006

Mater. Trans.

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“…The oxide film formed is initially amorphous and -alumina crystals develop at the metaloxide interface. [2][3][4][5] Shih et al conducted thermogravimetric analysis (TGA) and X-ray powder diffractometer analysis on pure aluminum samples that had been heated in an air atmosphere from room temperature to 883 K. They found an apparent weight gain at 832 K due to the transformation of gibbsite to diaspore. They found the thermally formed oxide films to be comprised of complex oxides: gibbsite, diaspore, -Al 2 O 3 , and -Al 2 O 3 .…”

Section: Introductionmentioning

confidence: 99%

Thermally Formed Oxides on Al-2 and 3.5 mass% Mg Alloys Heated and Held in Different Gases

Chen

Shih

2009

Mater. Trans.

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Weight changes in Al-2 and 3.5 mass% Mg alloy samples were measured by thermogravimetric analysis. X-ray diffractometer tests were used to investigate the progressive development of thermally formed oxide films on the samples. Both samples were first heated in a dry air atmosphere. The oxide film formed on the Al-2 mass% sample comprised -alumina, MgO, MgAl 2 O 4 , and gibbsite. The film formed on the Al-3.5 mass% sample contained large quantities of MgO, but no MgAl 2 O 4 .The samples were then heated in a nitrogen gas atmosphere for <1:9 h. The Al-3.5 mass% sample contained greater amounts of gibbsite and -alumina than did the Al-2 mass% sample. The latter yielded a greater amount of AlN (and/or MgO). After an extended holding time ($6 h), the Al-3.5 sample contained a greater amount of AlN (and/or MgO), and its weight increased remarkably. The as-cast samples containing the Al-3.5 mass%Mg cube had a higher percentage of foggy film compared to those containing an Al-2 mass%Mg cube. Oxide films that are readily formed during melting tend to be trapped in aluminum alloy castings.

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“…When it comes to the oxidation of pure aluminium, the literature is primarily focussed on oxidation in the solid state (see, e.g. [24,31,[49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66]). …”

Section: Microstructural Observations Of Oxide Filmsmentioning

confidence: 99%

“…In solid-state oxidation of aluminium, it is generally observed that the initial oxide to form is amorphous [49][50][51][52][53][54][55]. When held at an elevated temperature, a crystalline oxide is observed [31,51,[54][55][56][57], often identified to be γ-alumina [31,51,54,55,[58][59][60][61].…”

Section: Microstructural Observations Of Oxide Filmsmentioning

confidence: 99%

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A microstructural and kinetic study of molten aluminium oxidation in relation to dross formation

Bonner¹

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Oxidation and dross formation on molten aluminium is estimated to directly cause losses of tens of millions of dollars per annum to the Australian smelting industry. Although there has been significant study of molten aluminium oxidation over the past few decades, the formation mechanisms are still not fully understood. There is also lack of reliable and useful kinetic data that can be applied to computational simulations of industrial melt handling processes involving the oxidation of either quiescent pools or turbulent transfers of molten aluminium. There is additional uncertainty in the literature relating to the physical processes underlying molten aluminium oxidation, and the microstructural evolution of the growing oxide film. Past oxidation studies have been confounded by the detrimental effect of the pre-existing oxide ubiquitously present on aluminium specimens. Recent studies conducted at The University of Queensland have indicated a way forward in this respect, with the development of an experimental technique that enables the melt surface to be skimmed free of pre-existing oxide prior to each oxidation experiment. This project is based on previous outcomes and expands on them to create new insights into the oxidative behaviour of molten aluminium in response to various key parameters, such as melt temperature and isothermal holding time. It also aims to resolve some ambiguities in the literature.Melts of commercial purity aluminium were isothermally held at various temperatures ranging from 750°C to 900°C, and exposed to ambient air for times ranging up to ~20 h. The oxide grown on each melt was removed and treated to separate the oxide itself from the underlying aluminium metal, using a molten salt flux. The mass of oxide was then determined as a function of melt temperature and exposure time. These gravimetric experiments were complemented by morphological and microstructural characterization of grown oxide films, using scanning electron microscopy, transmission electron microscopy, and electron diffraction. These two approaches were combined to develop a simple kinetic model based on the parabolic rate law.The amount of oxide formed was found to be significantly lower than what has previously been reported, and was attributed to the removal of the pre-existing oxide. The amount of oxide that formed increased with increasing temperature, and the oxidation rate continuously decreased with increasing exposure time. These observations are consistent with diffusion-limited growth.Microstructural characterisation showed two stages of oxidation. In the early stage, nano-sized, planar, polyhedral crystallites of γ-alumina nucleate at the metal/oxide interface. In the later stage, flake-like γ-alumina crystallites were observed to grow outwards from the oxide/air interface. The time at which the second stage of growth became active decreased with increasing temperature, and the flake-like crystallites continued to increase in size with increasing exposure time.iii Crystallographic texture was obser...

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The Kinetics and Mechanism of Oxidation of Superpurity Aluminum in Dry Oxygen

Cited by 94 publications

References 11 publications

Thermally-Formed Oxide on Aluminum and Magnesium

Thermally-Formed Oxide on Aluminum and Magnesium

Thermally Formed Oxides on Al-2 and 3.5 mass% Mg Alloys Heated and Held in Different Gases

A microstructural and kinetic study of molten aluminium oxidation in relation to dross formation

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