Sintering of Chromium Borides Synthesized by Solid-State Reaction Between Metallic Chromium and Amorphous Boron.

Fe–N alloys with crystalline structures different from those obtained at atmospheric pressure were produced by solid-state reaction between Fe and amorphous boron nitride under high pressure. Two new paramagnetic Fe–N phases were obtained at temperatures above 800 K under pressures between 2.0 and 4.0 GPa. One is of cubic structure with lattice constant of 6.114 Å, and another is of orthorhombic structure with lattice constants of a = 4 8.443, b = 4 4.749, and c 4 3.993 Å. ε–Fe3Nx with N contents of 18.1 to 21.4 at.%, which could not be obtained at atmospheric pressure, was produced at pressures of 3.0 to 4.0 GPa and temperatures of 690 to 800 K. The mechanism of formation of ε–Fe3Nx under high pressure is discussed.

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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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Observation of solid-state reaction between a thin yttria film and a (0001) α-alumina substrate

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100170955 ◽

1994 ◽

Vol 52 ◽

pp. 644-645

Author(s):

J. R. Heffelfinger ◽

C. B. Carter

Keyword(s):

Electron Microscopy ◽

Solid State ◽

Solid State Reaction ◽

Yttrium Aluminum Garnet ◽

Secondary Phase ◽

Ceramic Composites ◽

Alumina Substrate ◽

Transmission Electron ◽

Alumina Fibers ◽

Optical Applications

Transmission-electron microscopy (TEM), scanning-electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to investigate the solid-state reaction between a thin yttria film and a (0001) α-alumina substrate. Systems containing Y2O3 (yttria) and Al2O3 (alumina) are seen in many technologically relevant applications. For example, yttria is being explored as a coating material for alumina fibers for metal-ceramic composites. The coating serves as a diffusion barrier and protects the alumina fiber from reacting with the metal matrix. With sufficient time and temperature, yttria in contact with alumina will react to form one or a combination of phases shown by the phase diagram in Figure l. Of the reaction phases, yttrium aluminum garnet (YAG) is used as a material for lasers and other optical applications. In a different application, YAG is formed as a secondary phase in the sintering of AIN. Yttria is added to AIN as a sintering aid and acts as an oxygen getter by reacting with the alumina in AIN to form YAG.

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