The Spinel/Alumina Phase Boundary

The formation of spinel during solid-state reactions between two oxides of the type A0 (e.g. Mg0) and B203 (e.g. A1203), has been extensively studied both from a theoretical viewpoint and an experimental one. The present paper will illustrate the structural aspects of the study of the spinel/sesquioxide interface. It has recently been shown by Carter and Schmalzried, that, when Co0 and A1203 react to form Co-Al spinel, the {111} oxygen planes in the spinel do not lie parallel to the (0001) oxygen planes in the parent alumina even though the oxygen ions are almost close-packed in both planes. The small rotation which is present implies that the mechanism whereby the alumina is transformed to spinel is not simply the glide of either isolated, or bundles of, Shockley partial-like transformation dislocations as had previously been assumed, but rather involves a new defect which causes a rotation of the oxygen sublattice.

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The wustite-spinel interface

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126226 ◽

1987 ◽

Vol 45 ◽

pp. 268-269

Author(s):

S.R. Summerfelt ◽

C.B. Carter

Keyword(s):

Solid State ◽

Solid State Reaction ◽

Strain Energy ◽

Matrix Material ◽

Lattice Misfit ◽

Solid State Reactions ◽

Oxygen Sublattice ◽

Large Particles ◽

Small Lattice ◽

Coherent Interfaces

The wustite-spinel interface can be viewed as a model interface because the wustite and spinel can share a common f.c.c. oxygen sublattice such that only the cations distribution changes on crossing the interface. In this study, the interface has been formed by a solid state reaction involving either external or internal oxidation. In systems with very small lattice misfit, very large particles (>lμm) with coherent interfaces have been observed. Previously, the wustite-spinel interface had been observed to facet on {111} planes for MgFe2C4 and along {100} planes for MgAl2C4 and MgCr2O4, the spinel then grows preferentially in the <001> direction. Reasons for these experimental observations have been discussed by Henriksen and Kingery by considering the strain energy. The point-defect chemistry of such solid state reactions has been examined by Schmalzried. Although MgO has been the principal matrix material examined, others such as NiO have also been studied.

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The Structure of Spinel/Oxide Reaction Fronts During Spinel-Forming Solid State Reactions

MRS Proceedings ◽

10.1557/proc-357-325 ◽

1994 ◽

Vol 357 ◽

Cited By ~ 4

Author(s):

D. Hesse ◽

R. Scholz ◽

S. Senz ◽

H. Sieber ◽

P. Werner ◽

...

Keyword(s):

Solid State ◽

Reaction Front ◽

Lattice Misfit ◽

Solid State Reactions ◽

Interface Plane ◽

Misfit Dislocations ◽

Spinel Oxide ◽

Oxygen Sublattice ◽

Cross Sectional ◽

Reaction Fronts

AbstractA series of spinels were grown by topotaxial solid state reaction on MgO(001) and sapphire(11.2) substrates. The structure of the various spinel/oxide reaction fronts was investigated by cross-sectional high resolution electron microscopy and other methods. While for extremely low misfit the reaction front is completely coherent, different interfacial defects form in other cases, depending on sign and amount of the spinel/oxide lattice misfit. For a large positive misfit, a network of misfit dislocations occured all running along <100<, with Burgers vectors of types a/2[101] and a/2[011] pointing out of the interface. The perpendicular Burgers vector component along [001] permits these dislocations to glide in order to cope with the advancing reaction front, avoiding kinetically unfavourable climb processes. The latter have, however, been observed in negative misfit, where the interfacial dislocations run along <110>, with their Burgers vectors lying in the interface plane. At the sapphire/MgAl2O4 front the structure is completely different. Here the h.c.p.-type oxygen sublattice of sapphire is reconstructed into the f.c.c-type oxygen sublattice of the spinel, which requires a tilt of the MgAl2O4 lattice and the formation of interfacial ledges.

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Structural Aspects of Phase Transitions

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.112.1 ◽

2006 ◽

Vol 112 ◽

pp. 1-20

Author(s):

Maciej Kubicki

Keyword(s):

Phase Transitions ◽

Solid State ◽

Gas Phase ◽

Molecular Complexes ◽

Structural Transformations ◽

Solid State Reactions ◽

Crystalline Solid ◽

Polymorphic Transitions ◽

Polymorphic Modifications ◽

Structural Aspects

There are two kinds of structural transformations in the crystalline solid state: solid state reactions, in which the product chemically different from the starting material can be isolated, and polymorphic transitions, when the phases have different organization of identical molecules in the crystal structures. As a consequence, the starting and the final phases of a solid state reaction differ in the melt and vapor, while different polymorphic modifications are identical in melt or gas phase. Some examples of the different phase transitions in the solid state are described in detail: the π-molecular complexes, the hydrogen-bond transformations and the reversible single crystal - twin transition.

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Synthese und Kristallstruktur des Lanthan-Titanat-Tellurats LaTi(Ti0,25Te0,75)O6 und seine Verwandtschaft mit PbSb2O6 und Sr(MnTe)O6/Synthesis and Crystal Structure of the Lanthanum Titanate Tellurate LaTi(Ti0.25Te0.75)O6 and its Relationship to PbSb2O6 and Sr(MnTe)O6

Zeitschrift für Naturforschung B ◽

10.1515/znb-1998-0203 ◽

1998 ◽

Vol 53 (2) ◽

pp. 149-152 ◽

Cited By ~ 3

Author(s):

L. Wulff ◽

Hk. Müller-Buschbaum

Keyword(s):

Crystal Structure ◽

Solid State ◽

Single Crystals ◽

Solid State Reactions ◽

Synthesis And Crystal Structure ◽

X Ray ◽

Oxygen Ions ◽

Lanthanum Titanate ◽

Symmetry Space ◽

Symmetry Space Group

Abstract Single crystals of LaTi(Ti0.25Te0.75)O6 have been prepared by solid state reactions. X-ray investigations led to trigonal symmetry, space group C31-P3 , a = 5.141(10), c = 5.218(10) Å, Z = 1. The compound is characterized by a predominantly ordered distribution of Ti4+ and Te6+. Typical features of the crystal structure are staggered layers containing edge connected TiO6 and (Ti,Te)O6 octahedra. The layers are connected by La3+ ions receiving an octahedral coordination by the surrounding oxygen ions. The relationships to the PbSb2O6 type and the recently described compound Sr(MnTe)O6 are discussed.

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Microstructural Variations in Melt-Spun Rapidly Solidified Ribbons

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117340 ◽

1985 ◽

Vol 43 ◽

pp. 54-55

Author(s):

L. A. Bendersky ◽

W. J. Boettinger

Keyword(s):

Solid State ◽

Processing Parameters ◽

Heat Extraction ◽

Solid State Reactions ◽

Careful Examination ◽

Ion Milling ◽

Melt Spun ◽

Wheel Side ◽

Rapidly Solidified ◽

Heat Extraction Rate

Rapid solidification produces a wide variety of sub-micron scale microstructure. Generally, the microstructure depends on the imposed melt undercooling and heat extraction rate. The microstructure can vary strongly not only due to processing parameters changes but also during the process itself, as a result of recalescence. Hence, careful examination of different locations in rapidly solidified products should be performed. Additionally, post-solidification solid-state reactions can alter the microstructure.The objective of the present work is to demonstrate the strong microstructural changes in different regions of melt-spun ribbon for three different alloys. The locations of the analyzed structures were near the wheel side (W) and near the center (C) of the ribbons. The TEM specimens were prepared by selective electropolishing or ion milling.

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Growth of spinel into alumina

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126317 ◽

1987 ◽

Vol 45 ◽

pp. 294-295

Author(s):

Y. Kouh Simpson ◽

C. B. Carter

Keyword(s):

Misfit Dislocations ◽

Phase Boundaries ◽

Large Rotation ◽

Alumina Phase ◽

Metallic Interfaces ◽

Small Rotation

The structure of spinel/alumina phase boundaries has recently been studied using the selected- area diffraction technique. It has been found that there exist several dominant topotactic relationships; of these, the two most common situations are when the {111} plane of spinel is parallel to either the (0001) plane or the {1120} plane of alumina. In both of these cases, it has been found that there is often a small rotation from exact topotaxy (typically 0° to 2° but with larger rotations possible) which partially eliminates the need for misfit dislocations. This rotation is a special phenomenon that may be unique to non-metallic interfaces such as phase boundaries in ceramics. In this report, a special spinel/alumina interface in which a large rotation from the exact topotaxy exists between the (111) plane of spinel and the (OOOl) plane of alumina is discussed.

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TEM study of amorphization of Cu and Ti foils by cold-rolling

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173868 ◽

1990 ◽

Vol 48 (4) ◽

pp. 146-147

Author(s):

W. A. Chiou ◽

N. L. Jeon ◽

Genbao Xu ◽

M. Meshii

Keyword(s):

Solid State ◽

Cold Rolling ◽

High Energy ◽

Rapid Quenching ◽

Vapor Condensation ◽

Metallic Alloys ◽

Solid State Reactions ◽

High Energy Particle ◽

Amorphous Metallic Alloys ◽

Thin Foils

For many years amorphous metallic alloys have been prepared by rapid quenching techniques such as vapor condensation or melt quenching. Recently, solid-state reactions have shown to be an alternative for synthesizing amorphous metallic alloys. While solid-state amorphization by ball milling and high energy particle irradiation have been investigated extensively, the growth of amorphous phase by cold-rolling has been limited. This paper presents a morphological and structural study of amorphization of Cu and Ti foils by rolling.Samples of high purity Cu (99.999%) and Ti (99.99%) foils with a thickness of 0.025 mm were used as starting materials. These thin foils were cut to 5 cm (w) × 10 cm (1), and the surface was cleaned with acetone. A total of twenty alternatively stacked Cu and Ti foils were then rolled. Composite layers following each rolling pass were cleaned with acetone, cut into half and stacked together, and then rolled again.

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The use of high-resolution FESEM to study solid-state phase transformations and reactions

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100172875 ◽

1994 ◽

Vol 52 ◽

pp. 1028-1029

Author(s):

P. G. Kotula ◽

D. D. Erickson ◽

C. B. Carter

Keyword(s):

Solid State ◽

High Resolution ◽

Phase Transformations ◽

High Efficiency ◽

Sol Gel ◽

Quantitative Information ◽

Solid State Reactions ◽

Critical Dimensions ◽

Backscattered Electrons ◽

Backscattered Electron

High-resolution field-emission-gun scanning electron microscopy (FESEM) has recently emerged as an extremely powerful method for characterizing the micro- or nanostructure of materials. The development of high efficiency backscattered-electron detectors has increased the resolution attainable with backscattered-electrons to almost that attainable with secondary-electrons. This increased resolution allows backscattered-electron imaging to be utilized to study materials once possible only by TEM. In addition to providing quantitative information, such as critical dimensions, SEM is more statistically representative. That is, the amount of material that can be sampled with SEM for a given measurement is many orders of magnitude greater than that with TEM.In the present work, a Hitachi S-900 FESEM (operating at 5kV) equipped with a high-resolution backscattered electron detector, has been used to study the α-Fe2O3 enhanced or seeded solid-state phase transformations of sol-gel alumina and solid-state reactions in the NiO/α-Al2O3 system. In both cases, a thin-film cross-section approach has been developed to facilitate the investigation. Specifically, the FESEM allows transformed- or reaction-layer thicknesses along interfaces that are millimeters in length to be measured with a resolution of better than 10nm.

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TEM studies of solid-state reactions in sputter-deposited Nb/Al multilayer thin films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167561 ◽

1996 ◽

Vol 54 ◽

pp. 1020-1021

Author(s):

F. Ma ◽

S. Vivekanand ◽

K. Barmak ◽

C. Michaelsen

Keyword(s):

Thin Films ◽

Solid State ◽

Stoichiometric Composition ◽

Analytical Electron Microscopy ◽

Grain Structure ◽

Solid State Reactions ◽

Multilayer Thin Films ◽

X Ray Diffraction ◽

X Ray ◽

Sputter Deposited

Solid state reactions in sputter-deposited Nb/Al multilayer thin films have been studied by transmission and analytical electron microscopy (TEM/AEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The Nb/Al multilayer thin films for TEM studies were sputter-deposited on (1102)sapphire substrates. The periodicity of the films is in the range 10-500 nm. The overall composition of the films are 1/3, 2/1, and 3/1 Nb/Al, corresponding to the stoichiometric composition of the three intermetallic phases in this system.Figure 1 is a TEM micrograph of an as-deposited film with periodicity A = dA1 + dNb = 72 nm, where d's are layer thicknesses. The polycrystalline nature of the Al and Nb layers with their columnar grain structure is evident in the figure. Both Nb and Al layers exhibit crystallographic texture, with the electron diffraction pattern for this film showing stronger diffraction spots in the direction normal to the multilayer. The X-ray diffraction patterns of all films are dominated by the Al(l 11) and Nb(l 10) peaks and show a merging of these two peaks with decreasing periodicity.

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