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Pint, B.A.; Garratt‐Reed, Anthony J.; Hobbs, Linn W.

doi:10.1023/a:1010347504052

Cited by 51 publications

(34 citation statements)

References 26 publications

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“…On the contrary, for P O2 ðIIÞ/P O2 ðIÞ = 10 5 Pa/10 ¹9 10 ¹7 Pa, the oxygen permeability constant was larger than for lines a and b because of the larger ÁP O2 , and its slope was between the slopes of the lines. Figure 2 shows the effect of the equilibrium P O2 in the upper chamber on the oxygen permeability constants of polycrystalline Al 2 Pa in the upper chamber, the oxygen permeability constants increased with increasing P O2 at 1773 and 1923 K. The slopes of the curves correspond to a power constant of n = 3/16, which is applicable to the defect reaction given in Eq. (1) and is related to the first term [A Al · P O2 ðIIÞ 3/16 ] in Eq.…”

Section: ¹1mentioning

confidence: 98%

Mutual grain-boundary transport of aluminum and oxygen in polycrystalline Al2O3 under oxygen potential gradients at high temperatures

Wada

Matsudaira

Kitaoka

2011

J. Ceram. Soc. Japan

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The oxygen permeability of non-doped polycrystalline Al 2 O 3 wafers under steep oxygen potential gradients (ÁP O2 ) was evaluated at temperatures of up to 1973 K. The oxygen permeation occurred by grain boundary (GB) diffusion of oxygen from the higher oxygen partial pressure (P O2 ) side to the lower P O2 side and by the simultaneous GB diffusion of aluminum in the opposite direction. The exposed Al 2 O 3 was an electronic conductor, and both the aluminum and oxygen ions migrated without any acceleration or inhibition due to the interdiffusion. The ratios of the aluminum and oxygen flux to the oxygen permeation under ÁP O2 conditions at which mutual GB transport of the ions occurred depended strongly on ÁP O2 . The chemical potentials, GB diffusion coefficients, and the flux of aluminum and oxygen were estimated as functions of position in the depth direction of the wafers.

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Section: ¹1mentioning

confidence: 98%

Mutual grain-boundary transport of aluminum and oxygen in polycrystalline Al2O3 under oxygen potential gradients at high temperatures

Wada

Matsudaira

Kitaoka

2011

J. Ceram. Soc. Japan

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“…(15), whereas, the permeability constant for a P O 2 range of n ¼ 3=16 is dominated by P O 2 ðIIÞ in accordance with eq. (19). Figure 5 shows SEM micrographs of the two surfaces of an Al 2 O 3 wafer exposed at 1923 K for 10 h under a ÁP O 2 produced by P O 2 ðIÞ ¼ 10 À8 Pa in the upper chamber and P O 2 ðIIÞ ¼ 1 Pa in the lower chamber.…”

Section: )mentioning

confidence: 99%

“…These REs segregate at grain boundaries in growing Al 2 O 3 scales during oxidation of the alloys and diffuse toward the scale/gas interface, resulting in the precipitation of RE-rich particles. 19) The REs are thought to affect the scale growth by altering both the outward grain boundary diffusion of aluminum and the inward grain boundary diffusion of oxygen.…”

Section: Introductionmentioning

confidence: 99%

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

2009

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The oxygen permeability of an undoped polycrystalline -Al 2 O 3 wafer that was exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. Oxygen preferentially permeated through the grain boundaries of -Al 2 O 3 . The main diffusion species, which were attributed to oxygen permeation, depended on oxygen partial pressures (P O2 ), forming oxygen potential gradients. Under oxygen potential gradients generated by P O2 below about 1 Pa, oxygen permeation occurred by oxygen diffusing from regions of higher P O2 to regions of lower P O2 . By contrast, under oxygen potential gradients generated by P O2 above about 1 Pa, oxygen permeation proceeded by aluminum diffusing from regions of lower P O2 to regions of higher P O2 . In other words, O 2 molecules were adsorbed onto a surface at higher P O2 and subsequently dissociated into oxygen ions (forming Al 2 O 3 ), while oxygen ions on the opposite surface at lower P O2 were desorbed by association into O 2 molecules (decomposition of Al 2 O 3 ). The grain-boundary diffusion coefficients of oxygen and aluminum as a function of P O2 were determined from the oxygen permeation constants.

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“…In addition, the REs are considered to inhibit scale growth by effectively blocking the GB diffusion of aluminum due to an ionic-size mismatch because the ionic sizes of the REs are larger than that of Al 3+ . However, the GB segregated REs diffused toward the scale surface together with aluminum during high-temperature oxidation for long periods, which resulted in the precipitation of RE-rich particles on the surface [9]. The addition of 0.05 at% Hf to a Fe-Cr-Al alloy was more effective for a reduction of the scale growth rate during oxidation of the alloy at 1427 K than a similar amount of Y-dopant [14].…”

Section: Introductionmentioning

confidence: 99%

“…The REs segregate to GBs during alumina scale growth by oxidation of the alloys [9]. The REs have been considered to primarily decrease the aluminum GB diffusivity with respect to the oxygen diffusivity, according to 18 O depth profiling in scale after two-stage oxidation experiments [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Engineering of Alumina Ceramics

et al. 2018

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Oxygen permeability through alumina wafers was evaluated at high temperatures up to 1923 K to elucidate the mass-transfer mechanisms of polycrystalline alumina and serve as a model for protective alumina film formed on heat-resistant alloys. Oxygen permeation proceeded via grain boundary (GB) diffusion of oxygen from the higher oxygen partial pressure (P O2 ) surface side to the lower P O2 surface side, along with the simultaneous GB diffusion of aluminum in the opposite direction to maintain the Gibbs-Duhem relationship. Oxygen GB diffusion coefficients in the vicinity of the P O2 (hi) surface were lower than those of oxygen GB self-diffusion without an oxygen potential gradient (dµ O ). When dµ O was applied to the wafer, the oxygen and aluminum fluxes at the outflow side of the wafer were significantly larger than those at the inflow side. Ln (Y and Lu) and Hf segregation at the GBs selectively reduced the diffusivity of oxygen and aluminum, respectively. Thus, the mesoscopic arrangements of segregating dopants, which were selected by taking into consideration the behavior of the diffusion species and the role of dopants, enabled the alumina film to have enhanced oxygen shielding capability and structural stability at high temperatures. Furthermore, the GB diffusion data derived from the oxygen permeation experiments were compared to those for alumina scale formed by the so-called two-stage oxidation of alumina-forming alloys.

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Cited by 51 publications

References 26 publications

Mutual grain-boundary transport of aluminum and oxygen in polycrystalline Al2O3 under oxygen potential gradients at high temperatures

Mutual grain-boundary transport of aluminum and oxygen in polycrystalline Al2O3 under oxygen potential gradients at high temperatures

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

Grain Boundary Engineering of Alumina Ceramics

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