Impurity Effects on Alumina Scale Growth

Hou, P.Y.

doi:10.1111/j.1151-2916.2003.tb03355.x

Cited by 141 publications

(82 citation statements)

References 89 publications

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“…Cannon (unpublished) and Hou 12 showed that the oxidation rate constants obtained by Hindam and Whittle 13 (interpreted as being due to inward diffusion of oxygen) are similar to the oxygen grain boundary diffusivity derived from creep experiments on polycrystalline alumina. Both have activation energies of ∼5 eV.…”

Section: Introductionmentioning

confidence: 61%

“…This is especially so for grain boundary diffusion. Cannon (unplublished) and Hou 12 have compared the oxidation rate constant, k p , determined by Hindam and Whittle 13 for a variety of aluminaformers with the diffusivity of oxygen along grain boundaries derived from creep experiments on polycrystalline samples of alumina. From the comparison, they concluded that inward diffusion of oxygen along grain boundaries was the rate-controlling process but this still begs the question as to the diffusing species.…”

Section: Discussionmentioning

confidence: 99%

“…where the number of Al ions is given in terms of the measured grain boundary ridge volume and the unit cell volume of Al 2 O 3 (2.538 × 10 −22 cm 3 ) and the number of Al ions per unit cell (12):…”

Section: Grain Boundary Ridge Volume Measurementsmentioning

confidence: 99%

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Quantification of Aluminum Outward Diffusion During Oxidation of FeCrAl Alloys

2005

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The outward flux of aluminum during the oxidation of four similar aluminaforming alloys is determined using two types of experiments. One is measurement of the total thickness of the oxide and the ratio of the thickness of the characteristic equiaxed layer to the total oxide thickness. The second is measurement of the new oxide formed along the grain boundaries of the oxide upon re-oxidation. The former provides information about the ratio of outward diffusion of aluminum to inward diffusion of oxygen during oxidation. The latter experiment directly quantifies the outward flux of aluminum as a function of oxide thickness. Both the outward aluminum flux and the ratio of inward to outward diffusional fluxes are found to vary with the minor concentrations of "reactive element" alloying additions. Specifically, Y in solution in the alloy is found to limit outward aluminum diffusion more than Zr in solution, with Y 2 O 3 limiting aluminum diffusion more than Zr, Y, and ZrO 2 .

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Section: Introductionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 99%

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Quantification of Aluminum Outward Diffusion During Oxidation of FeCrAl Alloys

2005

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“…It is well known that alloy chemistry can dramatically affect the scale performance, including RE additions and S [17][18][19][20][21]. However, most explanations for such observations are only qualitative.…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

et al. 2017

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It is widely accepted that the growth of protective a-Al 2 O 3 scales on Nibased alloys is governed by the inward diffusion of oxygen through the oxide grain boundaries (GB). However, there is also some outward diffusion of metal ions to the surface, but it is difficult to quantify. In this work we apply atomic force microscopy, scanning electron microscopy and transmission electron microscopy to investigate the outward flux of Al, which manifests as the growth of small ridges along the alumina GBs after the removal of the outermost oxide layer by mechanical polishing or focused ion beam techniques followed by additional oxidation. As a model alumina-former, NiAl with Hf and Zr additions was investigated. In comparison to Zr, Hf was found to reduce the outward Al diffusion. This outward diffusion was six orders of magnitude smaller than the O inward diffusion.

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“…to the alloy leads to a two-layered structure, where the inner layer consists of columnar-and the outer layer of equiaxed crystals [16][17][18][19]. However, the major impurities in the alumina scale are Fe, Cr and other species originating from the base alloy [20][21][22]. As an example, a TEM bright-field image of a cross section through an oxide scale formed on the Kanthal AF alloy at 900°C. It is interesting to study this multilayer-and multiphase structure of the alumina scale by means of IS, because the dielectric and electric properties of the different phases and layers in such a material might be individually characterized by this method.…”

Section: Introductionmentioning

confidence: 99%

In-situ Impedence Spectroscopy Study of Electrical Conductivity and Ionic Transport in Thermally Grown Oxide Scales on a Commercial FeCrAl Alloy

Öijerholm

Pan

et al. 2007

Oxid Met

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In-situ impedance-spectroscopy measurements were performed at temperatures between 600 and 1,000°C to investigate ionic transport in oxide scales formed on Kanthal AF alloy. The samples were pre-oxidized at 800, 900 and 1,000°C in air. The impedance spectra of the oxide formed at 1,000°C exhibited essentially one semicircle, whereas samples oxidized at lower temperatures showed an additional semicircle at high frequencies suggesting a more heterogeneous oxide. The ionic-transference number, derived by measuring the voltage across the oxide scale, indicates that the oxide is a predominant electronic conductor. Ionic diffusivity in the oxide scales formed at different pre-oxidizing temperatures was calculated, using the ionic-transference number. The ionic diffusivities obtained in this way are in reasonable agreement with literature data acquired by other methods. The oxide-formation temperature has a significant influence on the conductivity and ionic-transport properties of the oxide scale.

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Impurity Effects on Alumina Scale Growth

Cited by 141 publications

References 89 publications

Quantification of Aluminum Outward Diffusion During Oxidation of FeCrAl Alloys

Quantification of Aluminum Outward Diffusion During Oxidation of FeCrAl Alloys

Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

In-situ Impedence Spectroscopy Study of Electrical Conductivity and Ionic Transport in Thermally Grown Oxide Scales on a Commercial FeCrAl Alloy

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