Grain boundary segregation and sintering in alumina

Nanni, Paolo; Stoddart, C. T. H.; Hondros, E. D.

doi:10.1016/0390-6035(76)90031-6

Cited by 59 publications

(14 citation statements)

References 9 publications

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“…One of the most important findings was the direct observation using FEG-STEM / XEDS of RE ionic segregation to the ␣-Al 2 O 3 and ␣-Cr 2 O 3 scale grain boundaries. This result was not entirely unexpected, as foreign ion segregation is a commonly observed phenomenon in oxides, [36][37][38][39][40][41][42][43][44][45] but prior to the experimental work segregation in growing oxide scales had only been hypothesized. 46,47 Initially, some authors felt that this segregation was uncommon, 13,48,49 a surmise perhaps deriving from the fact that instruments with larger electron probes were not able to detect the segregation in some samples.…”

Section: Introductionmentioning

confidence: 87%

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al₂O₃ Grain Boundaries

Pint

Garratt‐Reed

Hobbs

1998

Journal of the American Ceramic Society

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Thermally grown, ␣-Al 2 O 3 external scales formed on alloys after oxidation in pure oxygen at temperatures between 1000°and 1500°C were analyzed using FEG-STEM / XEDS. Alloy dopants such as Y, Zr, La, Hf, and Ti were found to segregate to the ␣-Al 2 O 3 grain boundaries and to the alloyscale interface. With increasing oxidation time and temperature, the amount of segregant on the oxide grain boundaries near the gas interface increases until a critical level is reached and precipitates begin to nucleate and grow. These observations are a result of the outward transport of dopants from the alloy, through the external alumina scale, to the gas interface. The apparent driving force for the dopant diffusion is the oxygen potential gradient in the growing oxide scale.

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Section: Introductionmentioning

confidence: 87%

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al₂O₃ Grain Boundaries

Pint

Garratt‐Reed

Hobbs

1998

Journal of the American Ceramic Society

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“…Results of two-stage oxidation experiments under 16 O 2 and 18 O 2 showed that external diffusion of cations could be blocked by RE additions [23, 28-30, 33, 41-46]. Even if oxygen diffusion is still available in REdoped a-Al 2 O 3 , oxygen diffusion coefficients at oxide grain boundaries decrease [47,48], especially in the presence of Y 2 O 3 .…”

Section: Introductionmentioning

confidence: 99%

High-Temperature Oxidation of Fe3Al and Fe3Al–Zr Intermetallics

et al. 2009

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The oxidation behavior of Fe 3 Al and Fe 3 Al-Zr intermetallic compounds was tested in synthetic air in the temperature range 900-1200°C. The addition of Zr showed a significant effect on the high-temperature oxidation behavior. The total weight gain after 100 h oxidation of Fe 3 Al at 1200°C was around three times more than that for Fe 3 Al-Zr materials. Zr-containing intermetallics exhibited abnormal kinetics between 900 and 1100°C, due to the presence and transformation of transient alumina into stable a-Al 2 O 3 . Zr-doped Fe 3 Al oxidation behavior under cyclic tests at 1100°C was improved by delaying the breakaway oxidation to 80 cycles, in comparison to 5 cycles on the undoped Fe 3 Al alloys. The oxidation improvements could be related to the segregation of Zr at alumina grain boundaries and to the presence of Zr oxide second-phase particles at the metal-oxide interface and in the external part of the alumina scale. The change of oxidation mechanisms, observed using oxygen-isotope experiments followed by secondary-ion mass spectrometry, was ascribed to Zr segregation at alumina grain boundaries.

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“…If anisotropic segregation is present, consistent with previous microanalytical studies. [5][6][7][8][9][10]15,16 Excess the degree of anisotropy is insufficient to be distinguished from dopant that was not accommodated within the Al 2 O 3 grains or this statistical variation. Alternatively, the absence of anisoat the grain boundaries was concentrated in discrete second tropic segregation may be the consequence of high powder phases.…”

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confidence: 99%

Dopant Distributions in Rare‐Earth‐Doped Alumina

Thompson

Soni

Chan

et al. 1997

Journal of the American Ceramic Society

103

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The distribution of yttrium and lanthanum dopants hason the dopant level, Al 2 O 3 grain size, and impurity content of Al 2 O 3 . been mapped in yttrium-and lanthanum-doped polycrystalline aluminas using imaging secondary-ion mass spec-The objective of this work was to map the yttrium distribution in a 1000-ppm-yttrium-doped polycrystalline Al 2 O 3 samtrometry (imaging-SIMS). Both dopants segregate to grain boundaries and pore surfaces. On average, yttrium occupies ple that has exhibited favorable creep properties. 1 In addition, a 500-ppm-lanthanum-doped sample was examined, primarily to 7.1%-9.0% of the available grain-boundary cation sites, whereas lanthanum occupies only 2.0%-5.2%. In 1000-compare the segregation behavior of the two isovalent rareearth elements and partly to assess the potential of lanthanumppm-yttrium-doped alumina, an abundance of yttrium aluminum garnet precipitates also is observed. Implications of doped Al 2 O 3 for improved creep properties. Mapping of the dopant distributions was performed using these observations to the creep behavior of alumina are discussed. The similarity in the segregation behavior of yttrium a high-resolution scanning-ion microprobe developed at the University of Chicago. 17 This unique instrument uses a finely and lanthanum highlights the potential of lanthanum-doped alumina for improved creep properties.focused gallium beam to sputter secondary ions from the uppermost layers of the sample surface. For many elements, this imaging-SIMS system offers excellent analytical sensitivity,

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Grain boundary segregation and sintering in alumina

Cited by 59 publications

References 9 publications

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al₂O₃ Grain Boundaries

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al₂O₃ Grain Boundaries

High-Temperature Oxidation of Fe3Al and Fe3Al–Zr Intermetallics

Dopant Distributions in Rare‐Earth‐Doped Alumina

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Grain boundary segregation and sintering in alumina

Cited by 59 publications

References 9 publications

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al2O3 Grain Boundaries

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al2O3 Grain Boundaries

High-Temperature Oxidation of Fe3Al and Fe3Al–Zr Intermetallics

Dopant Distributions in Rare‐Earth‐Doped Alumina

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Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al₂O₃ Grain Boundaries

Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al₂O₃ Grain Boundaries