Oxygen and aluminum diffusion in α-Al2O3: How much do we really understand?

doi:10.1016/j.jeurceramsoc.2007.12.020

Journal of the European Ceramic Society

Volume 28, Issue 7, 2008, Pages 1495-1507

https://doi.org/10.1016/j.jeurceramsoc.2007.12.020 Get rights and content

Abstract

The major diffusion processes in α-Al₂O₃ have been reviewed, including oxygen and aluminum lattice diffusion, D_oxy and D_Al, respectively; oxygen grain boundary diffusion, D_b-oxy; and pipe diffusion, D_p. Their relevance to creep of Al₂O₃ and oxidation of Al₂O₃ scale-forming alloys is briefly considered.

It is concluded that the answer to the question included in the title is “not a great deal”. Eight major questions and issues have been identified that would constitute fitting subjects for future research:

(i)
What is the nature of the “buffering” that appears to control D_oxy?
(ii)
What process(es) are occurring during annealing that eliminate non-Fickian behavior when measuring D_oxy?
(iii)
How should the magnitude of the measured activation energies for D_oxy be interpreted?
(iv)
Have all the defect types involved in oxygen diffusion been identified?
(v)
Does oxygen diffusion occur by an interstitialcy mechanism?
(vi)
What is the order of magnitude of D_Al/D_oxy?
(vii)
What is the order of magnitude of D_b-Al/D_b-oxy?
(viii)
It appears that the activation energy for D_b-oxy is greater than that for D_oxy. How should this be understood?

Introduction

Self-diffusion of oxygen and aluminum in Al₂O₃ has been of scientific and technological interest for nearly half a century. Alumina in both single crystal and polycrystalline form is arguably the most important structural ceramic, and knowledge of lattice, grain boundary, and pipe diffusion is crucial for understanding a host of important high temperature processes: plastic deformation of single crystals, diffusional creep and sintering of polycrystals, oxidation of Al₂O₃-scale forming alloys, etc. (Al₂O₃ scales provide the very best oxidation resistance for structural alloys in oxidizing environments.) Furthermore, Al₂O₃ is often considered a model material for many oxide ceramics and other refractory non-metallic substances, and the database of its properties, fabrication, and areas of application is probably unequaled among modern ceramics.

This writer had earlier pointed out¹ the difficulty of understanding the activation energy for oxygen lattice diffusion in Al₂O₃ in the context of traditional point defect chemistry considerations (“Oxygen diffusion in corundum (α-Al₂O₃): a conundrum”, Philos. Mag. Lett. 79 p. 629 (1999)). In this paper, a tribute to Sir Richard Brook on the occasion of his 70th birthday, this issue is revisited. Some considerations of pipe diffusion and grain boundary diffusion are also included, as well as some brief comments on the applicability of these data to diffusional creep of alumina and oxidation of Al₂O₃-scale forming alloys. Attention is restricted to the stable corundum polymorph, α-Al₂O₃, with space group $R \bar{3} c$ .

In addition to the conundrum regarding the activation energy for lattice diffusion¹ (the values deduced for the migration energy, about 5 eV, are very much larger than the calculated migration energies, which are of the order of 1.5–2.0 eV2, 3); it is concluded that there are major difficulties in understanding: (i) the processes that occur during annealing of single crystal specimens prior to diffusion experiments that eliminate non-Fickian behavior; (ii) whether the lattice diffusivities of oxygen and aluminum are similar or not; (iii) the magnitude of the pre-exponential and activation energy for oxygen grain boundary diffusion in alumina polycrystals; and (iv) the defects and defect equilibria controlling oxygen diffusion in this scientifically interesting and technologically important material. It turns out that we do not understand a great deal about diffusion in α-Al₂O₃!

Section snippets

Lattice diffusion

Oxygen self-diffusion in Al₂O₃ single crystals and polycrystals was first measured in 1960 using gaseous exchange of ¹⁸O-enriched oxygen by Oishi and Kingery,⁴ who annealed Verneuil-grown single crystals spheres, crushed Verneuil rods, and crushed polycrystals which had been sintered at 1900 °C. Some of the latter were made into spherical particles by dropping through a three-phase carbon arc. After the ¹⁸O diffusion anneal, the amount of ¹⁸O exchange was determined from mass spectrometric

Aluminum lattice diffusion

In contrast to the extensive literature just reviewed dealing with oxygen diffusion in Al₂O₃, there have been only two reports of aluminum self-diffusion in Al₂O₃. The first was Paladino and Kingery's early work⁵⁵ on coarse-grained 130–200 μm polycrystals, and the second a more recent study by Le Gall et al.,²¹ who used Verneuil single crystals. The paucity of data reflects the difficulty involved in determination of aluminum self-diffusion coefficients. The only available tracer is ²⁶Al, which

Diffusional creep in polycrystalline Al₂O₃ and oxidation of Al₂O₃-scale-forming alloys

Some years ago, Cannon et al.⁵⁶ deduced D_bδ values for hot pressed and sintered MgO-doped Al₂O₃ from diffusional creep data (Table 1 and Fig. 5); they were convinced that the rate controlling process involved aluminum, rather than oxygen grain boundary diffusion, because the latter was deemed to be very rapid. The comparison of D_b-oxyδ data with the creep-derived values of D_bδ (Fig. 5) casts doubt on this assumption.

What else can be said about the atomistic processes dominating creep and

Concluding remarks

We really do not understand a great deal about oxygen and aluminum diffusion in aluminum oxide. The following questions and issues have been identified in this review:

(i)
What is the nature of the buffering that makes D_oxy in Al₂O₃ single crystals so (relatively) insensitive to impurities, even intentionally added aliovalent dopants?
(ii)
What process(es) are occurring during annealing of single crystal specimens that eliminate non-Fickian behavior? (Although the effect of annealing has been demonstrated

Note added in proof

Fielitz et al.⁶¹ performed simultaneous ¹⁸O and ²⁶Al tracer diffusion measurements in the temperature range 1230–1500 °C on Ti-doped Al₂O₃ single crystals and demonstrated that D_Al is orders of magnitude higher than D_oxy. Extrapolation of their data to the temperature range used by Paladino and Kingery (1670–1905 °C) reveals very good agreement with the absolute magnitude of D_Al, although the D_o and Q parameters differed. Fielitz, et al. report D_o and Q values of 7.2 × 10⁻⁶ m²/s and 375 kJ/mol,

Acknowledgements

The writer acknowledges long friendship with Sir Richard Brook, useful conversations with J.D. Cawley on non-Fickian oxygen diffusion, D.B. Hovis, who prepared the figures and Table 1, and J. Castaing, M. P. Harmer, and B. Lesage, who provided useful criticism of an earlier draft of this manuscript. K.P.D. Lagerlöf suggested that peroxide ions might be involved in oxygen transport, while G. Wei (Osram Sylvania) suggested that (OH)⁻ ions might be important. K.P.R. Reddy encouraged publication of

References (61)

T. Nakagawa et al.
Yttrium doping effect on oxygen grain boundary diffusion in Al₂O₃
Acta Mater.
(2007)
B.J. Inkson
Dislocations twinning activated by abrasion of Al₂O₃
Acta Mater.
(2000)
J. Cho et al.
Role of segregating dopants on the improved creep resistance of aluminum oxide
Acta Mater.
(1999)
S.J. Dillon et al.
Multiple grain boundary transition in ceramics: a case study of alumina
Acta Mater.
(2007)
S.J. Dillon et al.
Complexion: a new concept for kinetic engineering in material science
Acta Mater.
(2007)
A. Nakamura et al.
Control of dislocation configuration in sapphire
Acta Mater.
(2005)
B.J. Pletka et al.
Work hardening in sapphire (α-Al₂O₃)
Acta Met.
(1977)
K. Messaoudi et al.
Diffusion and growth mechanisms in Al₂O₃ scales on kinetic Fe–Cr–Al alloys
Mater. Sci. Eng. A
(1998)
P. Fielitz et al.
Al-26 diffusion measurement in 2/1-mullite by means of secondary ion mass spectrometry
Solid State Ionics
(2006)
A.H. Heuer et al.
Oxygen self-diffusion in corundum (α-Al₂O₃): a conundrum
Philos. Mag. Lett.
(1999)

C.R.A. Catlow et al.

Defect energetics in α-Al₂O₃ and rutile TiO₂

Phys. Rev. B

(1982)

P.W.M. Jacobs et al.

Defect energies for pure corundum and for corundum doped with transition metal ions

Philos. Mag.

(1993)

Y. Oishi et al.

Self-diffusion of oxygen in single crystal and poly-crystalline aluminum oxide

J. Chem. Phys.

(1960)

Y. Oishi et al.

Self-diffusion of oxygen in single crystal alumina

J. Chem. Phys.

(1980)

Y. Oishi et al.

Effect of surface condition on oxygen self-diffusion coefficients for single crystal Al₂O₃

J. Am. Ceram. Soc.

(1983)

D.J. Reed et al.

Ion-probe measurement of oxygen self-diffusion in single crystal Al₂O₃

J. Am. Ceram. Soc.

(1980)

J.D. Cawley et al.

Oxygen tracer diffusion in single crystal alumina

J. Am. Ceram. Soc.

(1991)

D. Prot et al.

Self-diffusion in Al₂O₃. II. Oxygen diffusion in “undoped” single crystals

Philos. Mag. A

(1996)

T. Nakagawa et al.

Oxygen pipe diffusion in sapphire basal dislocations

J. Ceram. Soc. Jpn.

(2006)

K.P.R. Reddy et al.

Oxygen diffusion in sapphire

J. Am. Ceram. Soc.

(1982)

K.P.D. Lagerlöf et al.

Lattice diffusion kinetics in undoped and impurity-doped sapphire (α-Al₂O₃): a dislocation loop annealing study

J. Am. Ceram. Soc.

(1989)

J.D. Cawley et al.

Dopant distribution in nominally yttrium-doped sapphire

J. Am. Ceram. Soc.

(1986)

M. Le Gall et al.

Self-diffusion in α-Al₂O₃ III oxygen diffusion in single crystals doped with Y₂O₃

Philos. Mag.

(1996)

H. Haneda et al.

Oxygen self-diffusion in Magnesium-or Titanium-doped alumina single crystals

J. Am. Ceram. Soc.

(1989)

Reddy, K. P. R., Oxygen diffusion in close packed oxides, Ph.D. thesis, Case Western Reserve Univ., Cleveland, OH,...

J.H. Harding et al.

Experiment and theory in alumina

J. Am. Ceram. Soc.

(2003)

R.H. Doremus

Oxidations of alloys containing aluminum and diffusion in Al₂O₃

J. Appl. Phys.

(2004)

R.H. Doremus

Diffusion in alumina

J. Appl. Phys.

(2006)

M. Le Gall et al.

Self-diffusion in Al₂O₃. I. Aluminum diffusion in single crystals

Philos. Mag.

(1994)

B.A. Pint et al.

Comment on “Oxidation of alloys containing aluminum and diffusion in Al₂O₃” [J. Appl. Phys. 95, 3217 (2004)]

J. Appl. Phys.

(2005)

Cited by (246)

Effect of post-annealing on the oxidation behavior of hot rolled ODS-FeCrAl steel in liquid lead
2024, Corrosion Science
The microstructure of the hot-rolled and annealed ODS-FeCrAl steels and related oxide scales formed in the oxygen-containing liquid lead at 600 °C was investigated by SEM-EDS, EBSD and TEM. The post-annealing caused partial recrystallization of hot-rolled ODS steel, which significantly reduced the intense θ-fiber (<001>||ND) and local dislocation density. After corrosion, the hot-rolled ODS steels exhibited complex and locally uneven oxide scales while the annealed ODS steels formed a uniform triple-layered oxide scale. A new insight into the relationship between oxidation depth and grain orientation was proposed, highlighting the significance of orientation-dependent dislocations on the transition of external/internal oxidation mechanisms.
A promising high temperature self-lubricating Cu-based superalloy with coherent cuboidal L1<inf>2</inf>-γʹ phases
2023, Composites Part B: Engineering
High temperature self-lubricating materials including composites or coatings exhibit remarkable tribological property but typically suffer from poor ductility. Therefore, striking a fine balance between these two properties is a great challenge. In this work, series of high-temperature self-lubricating Cu_100-x(Ni₃Al₁)_(x/4) superalloys were obtained, and it possesses both good tensile strength at room temperature or high temperature and appreciable elongation value (its elongation can reach up to 3%). Compared with other high temperature self-lubricating materials, it has already made great progress in the aspect of mechanical property. The results showed that the source for remarkable high temperature tribological properties derives from the synergistic effect of naturally formed oxide scale and high temperature bearing capacity. In the naturally formed oxide scale, the CuO layer provides excellent lubrication action due to those unique advantages, such as easy to shear, formation of twinning and brittle-ductile transition at high temperature. Additionally, the existence of substantial coherent interfaces hinders the crack initiation. The dense and continuous γ-Al₂O₃ protective layer can hinder the diffusion of the oxygen anions and metal cations, which is beneficial to inhibit the further oxidation of the alloy. The work provides a novel strategy for the design and preparation of high temperature self-lubricating materials.
Experimental and thermodynamic modeling of Al<inf>2</inf>O<inf>3</inf> corundum and TiO<inf>2</inf> rutile structures forming on Ti-6Al-4V powder during oxidation
2023, Acta Materialia
The high affinity of Ti-6Al-4 V (Ti64) powder to oxygen impacts the quality of the powder during additive manufacturing. The oxide scale consists of a double layer with α-Al₂O₃ in the outer part and TiO₂ in the inner one. Experimental and thermodynamic results are used to further understand the formation of these two oxide layers. Inert marker revealed the anionic growth of the duplex oxide scale. The thermodynamic results highlighted that interstitial aluminum enters and diffuses fast within TiO₂ (rutile) to form Al₂O₃ as the surface layer. Moreover, α-Al₂O₃ is considered as a non-stoichiometric oxide with a very small excess of oxygen as dumbbells at high partial pressures of oxygen. A remarkable effect of the impurities on the concentration of native point defects is observed in this phase. Finally, a reactional mechanism with elementary steps for the oxidation of Ti64 powder is proposed.
Evolving corundum nanoparticles at room temperature
2023, Acta Materialia
Metals and ceramics in nanometric forms attract much attention due to their unique properties, yet their stability is often questioned. Nevertheless, the shape and size instabilities are thought to be suppressed at ambient conditions, especially for refractory materials with high melting points. Contrary to this notion, here we report gradual coarsening of sub-10 nm corundum (α-Al₂O₃) nanoparticles during room-temperature storage, indicating active surface diffusion at a surprisingly low temperature (13% of the absolute melting point). Prolific surface diffusion is confirmed by in-situ transmission electron microscopy mechanical deformation, performed at room temperature and demonstrating remarkable high-strain-rate Coble pseudoelasticity. Anomalously small activation energy and growth stagnation are found in high-temperature coarsening experiments, suggesting additional chemical driving forces beyond purely physical capillarity. We expect similar phenomena may also exist in other ceramic materials, which is an important factor to consider for quality control, storage, and applications of ultrafine nanomaterials.
Water-aluminum reaction by MD simulations and its interpretation defect formation
2023, Computational Materials Science
Many of the aluminum and its alloys are produced by casting methods. During casting, aluminum is heated to temperatures above melting point. In the liquid state, aluminum reacts with water vapor to form aluminum oxide on the surface and hydrogen is dissolved in the melt. These are the two most critical defects that deteriorate the properties of the cast part. Therefore, it is important to investigate the possible reactions of water vapor with liquid aluminum in order to understand the formation of these defects. In this work, Molecular Dynamic (MD) analysis was used to evaluate the reactions of water vapor with aluminum at various temperatures (300, 500, 700, 900 and 1100 K). It was found that when aluminum reacts with water vapor, aluminum oxide layers form on the surface of the aluminum block. In addition, mono and di-atomic hydrogen are released due to the reaction between aluminum and water. These free hydrogen atoms are distributed homogeneously and rapidly in the aluminum block and gap between two aluminum blocks.
In-situ Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> enhances comprehensive properties of alumina-based ceramic cores by vat photopolymerization 3D printing
2023, Additive Manufacturing
Ceramic cores are an essential part to produce aeroengine turbine blades by investment casting. In recent years, vat photopolymerization (VPP) 3D printing has emerged as a promising technique for fabricating ceramic cores with complex structures due to its advantages of being moldless, low cost, etc. However, how to improve the properties of VPP 3D printed ceramic cores has always been a key bottleneck in industry. In this study, in-situ Y₃Al₅O₁₂ (YAG) enhanced alumina-based ceramic cores with excellent comprehensive properties were fabricated by VPP 3D printing. Alumina-based ceramic core with in-situ generated YAG phase during the sintering process could reduce the high-temperature deflection to almost one-tenth of a pure alumina ceramic core without decreasing the apparent porosity. Furthermore, the lattice characteristics of the YAG phase and Y³⁺ segregation were clarified as the main factors in the improvement of the high-temperature deflection resistance and apparent porosity of ceramic cores. The microstructure demonstrated that the increase of fine powders could narrow down the interlayer gap, and the irregular arrangement of ceramic particles could result in the diversification of sintering grain morphologies. With optimal process parameters, the sintering shrinkage of VPP 3D printed alumina-based ceramic cores in X, Y, and Z directions were 3.8 %, 3.7 %, and 4.8 %, respectively. The apparent porosity, flexural strength, and high-temperature deflection were 40.8 %, 16.1 MPa, and 0.63 mm, respectively. This study has reached an excellent balance between high apparent porosity and low high-temperature deflection of ceramic cores, which provides an important reference for the industrialization of 3D printed ceramic cores.

View all citing articles on Scopus

View full text

Oxygen and aluminum diffusion in α-Al2O3: How much do we really understand?

Abstract

Introduction

Section snippets

Lattice diffusion

Aluminum lattice diffusion

Diffusional creep in polycrystalline Al2O3 and oxidation of Al2O3-scale-forming alloys

Concluding remarks

Note added in proof

Acknowledgements

Acta Mater.

Acta Mater.

Acta Mater.

Acta Mater.

Acta Mater.

Acta Mater.

Acta Met.

Mater. Sci. Eng. A

Solid State Ionics

Oxygen self-diffusion in corundum (α-Al2O3): a conundrum

Philos. Mag. Lett.

Defect energetics in α-Al2O3 and rutile TiO2

Phys. Rev. B

Defect energies for pure corundum and for corundum doped with transition metal ions

Philos. Mag.

Self-diffusion of oxygen in single crystal and poly-crystalline aluminum oxide

J. Chem. Phys.

Self-diffusion of oxygen in single crystal alumina

J. Chem. Phys.

Effect of surface condition on oxygen self-diffusion coefficients for single crystal Al2O3

J. Am. Ceram. Soc.

Ion-probe measurement of oxygen self-diffusion in single crystal Al2O3

J. Am. Ceram. Soc.

Oxygen tracer diffusion in single crystal alumina

J. Am. Ceram. Soc.

Self-diffusion in Al2O3. II. Oxygen diffusion in “undoped” single crystals

Philos. Mag. A

Oxygen pipe diffusion in sapphire basal dislocations

J. Ceram. Soc. Jpn.

Oxygen diffusion in sapphire

J. Am. Ceram. Soc.

Lattice diffusion kinetics in undoped and impurity-doped sapphire (α-Al2O3): a dislocation loop annealing study

J. Am. Ceram. Soc.

Dopant distribution in nominally yttrium-doped sapphire

J. Am. Ceram. Soc.

Self-diffusion in α-Al2O3 III oxygen diffusion in single crystals doped with Y2O3

Philos. Mag.

Oxygen self-diffusion in Magnesium-or Titanium-doped alumina single crystals

J. Am. Ceram. Soc.

Experiment and theory in alumina

J. Am. Ceram. Soc.

Oxidations of alloys containing aluminum and diffusion in Al2O3

J. Appl. Phys.

Diffusion in alumina

J. Appl. Phys.

Self-diffusion in Al2O3. I. Aluminum diffusion in single crystals

Philos. Mag.

Comment on “Oxidation of alloys containing aluminum and diffusion in Al2O3” [J. Appl. Phys. 95, 3217 (2004)]

J. Appl. Phys.

Oxygen and aluminum diffusion in α-Al₂O₃: How much do we really understand?

Diffusional creep in polycrystalline Al₂O₃ and oxidation of Al₂O₃-scale-forming alloys

Oxygen self-diffusion in corundum (α-Al₂O₃): a conundrum

Defect energetics in α-Al₂O₃ and rutile TiO₂

Effect of surface condition on oxygen self-diffusion coefficients for single crystal Al₂O₃

Ion-probe measurement of oxygen self-diffusion in single crystal Al₂O₃

Self-diffusion in Al₂O₃. II. Oxygen diffusion in “undoped” single crystals

Lattice diffusion kinetics in undoped and impurity-doped sapphire (α-Al₂O₃): a dislocation loop annealing study

Self-diffusion in α-Al₂O₃ III oxygen diffusion in single crystals doped with Y₂O₃

Oxidations of alloys containing aluminum and diffusion in Al₂O₃

Self-diffusion in Al₂O₃. I. Aluminum diffusion in single crystals

Comment on “Oxidation of alloys containing aluminum and diffusion in Al₂O₃” [J. Appl. Phys. 95, 3217 (2004)]