Acknowledgments Preface Introduction 1. Methods of investigation 2. Thermodynamic fundamentals 3. Mechanisms of oxidation 4. Oxidation of pure metals 5. Oxidation of alloys 6. Oxidation by oxidants other than oxygen 7. Reactions of metals in mixed environments 8. Hot corrosion 9. Erosion-corrosion of metals in oxidizing atmospheres 10. Protective coatings 11. Atmosphere control for the protection of metals during production processes Appendix A. Solution to Fick's second law for a semi-infinite solid Appendix B. Rigorous derivation of the kinetics of internal oxidation Appendix C. Effects of impurities on oxide defect structure Index.

Introduction to the high-temperature oxidation of metals

Structure and nanostructure in ionic liquids.

The available literature on the crystal structure of the metastable alumina polymorphs and their associated transitions is critically reviewed and summarized. All the metastable alumina structures have been identified as ordered or partially ordered cation arrays on the interstitial sites of an approximately close-packed oxygen sublattice (either face-centered cubic or hexagonal close packed). The analysis of the symmetry relations between reported alumina polymorphs having an approximately face-centered cubic packing of the oxygen anions allows for an exact interpretation of all the complex domain structures that have been observed experimentally. Possible mechanisms for the phase transitions between the different alumina polymorphs also are discussed.

Metastable alumina polymorphs : Crystal structures and transition sequences

Hydrogen autotransfer in the N-alkylation of amines and related compounds using alcohols and amines as electrophiles.

Corundum, α-Al 2 O 3 , is the thermodynamically stable phase of coarsely crystalline aluminum oxide, but syntheses of nanocrystalline Al 2 O 3 usually result in γ-Al 2 O 3 . Adsorption microcalorimetry, thermogravimetric analyses, and Brunauer-Emmett-Teller adsorption experiments, coupled with recently reported high-temperature solution calorimetry data, prove that γ-Al 2 O 3 has a lower surface energy than α-Al 2 O 3 and becomes energetically stable at surface areas greater than 125 square meters per gram and thermodynamically stable at even smaller surface areas (for example, 75 square meters per gram at 800 kelvin). The results are in agreement with recent molecular dynamics simulations and provide conclusive experimental evidence that differences in surface energy can favor the formation of a particular polymorph.

https://science.sciencemag.org/content/sci/277/5327/788.full.pdf

Surface Energies and Thermodynamic Phase Stability in Nanocrystalline Aluminas

High temperature corrosion in energy systems

The total structure factor, S(Q), and the corresponding radial distribution function, G(r), for supercooled and stable liquid aluminum oxide have been measured with x-ray synchrotron radiation. The specimens were levitated in a conical nozzle and melted with a laser, achieving temperatures in the range of 2200{endash}2700K. The first two peaks in S(Q) reveal intermediate-range order and dense random packing of atoms, similar to that observed in many network liquids. The first two peaks in G(r) are consistent with AlO{sub 4}{sup 5-} structural units and show that Al{sub 2}O{sub 3} undergoes a major structural rearrangement on melting with an Al coordination change from octahedral to tetrahedral. The structure does not change appreciably with temperature in the stable and supercooled liquid. Implications of these results are discussed in connection with the solidification of aluminum oxide. {copyright} {ital 1997} {ital The American Physical Society}

Structure of Liquid Aluminum Oxide

Optical fibres doped with lanthanide or transition-metal elements can serve as in-line lasers and amplifiers for fibre-optic telecommunications systems. In general, most such fibre lasers use conventional silica-glass fibres doped with erbium or neodymium. But silicon dioxide absorbs strongly in the infrared for wavelengths of greater than 4 µm or so, limiting the infrared range over which such lasers can operate. Some other oxide materials do not absorb significantly until longer wavelengths—the absorption coefficient of crystalline silica at 4 µm is equal to that of yttrium oxide at 7.1 µm and of sapphire (a form of alumina) at 5.1 µm, for example1. Glass fibres made from these materials would therefore expand the range of fibre lasers into the mid-infrared. But molten oxides that do not contain silica typically have a viscosity too low to support fibre-pulling processes. Here we demonstrate that containerless processing, in which a molten sample is levitated by a flow of inert gas, permits sufficient undercooling of molten yttrium aluminium garnet (YAG:Y3Al5O12) to access a viscosity range conducive to fibre-pulling. The process is particularly effective if the molten material of stoichiometric YAG composition is doped with Nd2O3 in place of Y2O3, or with excess Al2O3; and it should also work with other dopants, because molten oxides are good solvents. Fibres could be drawn from a melt doped with Er2O3 in the presence of excess Al2O3. These fibres have the potential to extend the operating range of oxide glass-fibre lasers.

Glass fibres of pure and erbium- or neodymium-doped yttria–alumina compositions

A method for containerless liquid‐phase processing was developed which has practical application in process and property research on virtually any material which is involatile at the melting point. It combines aerodynamic and acoustic forces to support and position the levitated material. The design provides forced convection control of the thermal boundary in the gas surrounding beam‐heated specimens, which stabilizes the acoustic forces and allows acoustic positioning necessary to stabilize the aerodynamic levitation forces on molten materials. Beam heating and melting at very high temperatures was achieved. Experiments were conducted on specimens with diameters in the range 0.25–0.4 cm, of density up to 9 g/cm3, at temperatures up to 2700 K, and in oxygen, air, or argon atmospheres. Unique liquid‐phase processing results included deep undercooling of aluminum oxide, glass formation at exceptionally small cooling rates, complete melting and undercooling of YBa2Cu3Ox superconductor materials, direct form...

Aero‐acoustic levitation: A method for containerless liquid‐phase processing at high temperatures

We report formation of single- and two-phase glasses from rare-earth oxide–alumina materials. Liquids with the Y3Al5O12 and Er3Al5O12 compositions underwent a liquid–liquid phase transition which resulted in glasses with a cloudy appearance due to spheroids of one glass in a matrix of a second glass. The two glasses were isocompositional within the limits of experimental error. Clear, brilliant, single-phase glasses were obtained from La3Al5O12, ErLaYAl5O12, and compositions containing ≥5 mol% La2O3 substituted for the other rare-earth oxides. Formation of two glasses is attributed to nucleation and growth of the second liquid at a temperature below the equilibrium liquid–liquid transition temperature. Addition of lanthanum depresses the phase transition temperature below the glass transition temperature and the liquid–liquid phase transition is not observed. The results are discussed in the context of first-order liquid–liquid phase transitions (polyamorphism) and formation of single-phase glass from liquids that contain a high proportion of 4-coordinate aluminum ions.

Paul C. Nordine

Papers

High temperature corrosion in energy systems

Structure of Liquid Aluminum Oxide

Glass fibres of pure and erbium- or neodymium-doped yttria–alumina compositions

Aero‐acoustic levitation: A method for containerless liquid‐phase processing at high temperatures

Glass Formation and Polyamorphism in Rare‐Earth Oxide–Aluminum Oxide Compositions