Evolution of the two-phase microstructure L12 + DO22 in near-eutectoid Ni3(Al,V) alloy

1994 ◽  
Vol 9 (12) ◽  
pp. 3068-3082 ◽  
Author(s):  
L.A. Bendersky ◽  
F.S. Biancaniello ◽  
M.E. Williams
Keyword(s):  
Stage Iv ◽  
High Angle ◽  
X Ray Diffraction ◽  
Two Phase ◽  
Fast Kinetics ◽  
X Ray ◽  
Transmission Electron ◽  
Discontinuous Coarsening ◽  
Fcc Phase ◽  
Kinetics Of

Transmission electron microscopy and powder x-ray diffraction methods have been used to investigate the evolution of two-phase (L12 + DO22) microstructures from the quenched fcc phase of the Ni-5Al-20V (at. %) alloy. The microstructure after annealing in a temperature range from 650 to 900 °C differs from the eutectoid structure which might be expected for the alloy according to the eutectoid-type phase diagram of the Ni3Al-Ni3V section. This structure results from fast kinetics of ordering in the fcc → L12 and fcc → DO22 phase transitions. Four main stages in the microstructural evolution were observed. Stage I is the formation of spheroidal coherent L12 clusters in a disordered fcc matrix. During stage II the L12 clusters transform into cuboidal precipitates, and the fcc matrix orders into three DO22 variants (which may have interfaces that are wetted by thin fcc layers). In stage III accommodation of misfit (elastic energy) between different phases and variants occurs by formation of (110) twins or a single variant of the DO22 phase and tetragonally strained lamellae of the L12 phase. Stage IV is a discontinuous coarsening process in which a coarse incoherent two-phase structure replaces the fine coherent one. Grains of the coarse structure are nucleated on high-angle boundaries of primary fcc or other surfaces. Many of the grains are found twinned.

Microstructures of two-phase Ti–Cr alloys containing the TiCr2 Laves phase intermetallic

1997 ◽  
Vol 12 (6) ◽  
pp. 1472-1480 ◽  
Author(s):  
Katherine C. Chen ◽  
Samuel M. Allen ◽  
James D. Livingston
Keyword(s):  
Laves Phase ◽  
X Ray Diffraction ◽  
Orientation Relationships ◽  
Phase Growth ◽  
Two Phase ◽  
X Ray ◽  
Lattice Constants ◽  
Annealing Temperatures ◽  
Transmission Electron ◽  
Phase Intermetallic

Microstructures of two-phase Ti–Cr alloys (Ti-rich bcc + TiCr2 and Cr-rich bcc + TiCr2) are analyzed. A variety of TiCr2 precipitate morphologies is encountered with different nominal alloy compositions and annealing temperatures. Lattice constants and crystal structures are determined by x-ray diffraction (XRD) and transmission electron microscopy (TEM). Orientation relationships between the beta bcc solid solution and C15 TiCr2 Laves phase are understood in terms of geometrical packing, and are consistent with a Laves phase growth mechanism involving twinning.

Transformation kinetics for mullite in kaolin–Al2O3 ceramics

2003 ◽  
Vol 18 (6) ◽  
pp. 1355-1362 ◽  
Author(s):  
Yung-Feng Chen ◽  
Moo-Chin Wang ◽  
Min-Hsiung Hon
Keyword(s):  
Glassy Phase ◽  
Avrami Equation ◽  
Mullite Formation ◽  
Transformation Kinetics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Energy Dispersion Spectrometry ◽  
Two Stages ◽  
Kinetics Of

Transformation kinetics of mullite formation in kaolin–Al2O3 ceramics was studied by x-ray diffraction, transmission electron microscopy, and energy dispersion spectrometry. The mullitization process of kaolin–Al2O3 ceramics is described by two stages; one is the primary mullite transformation at 1273 to 1573 K, and the other is the secondary mullite formation at 1573 to 1873 K. The activation energy of 1164.6 kJ mol-1 obtained for the secondary mullite formation is lower than 1356.9 kJ mol-1 for the primary mullite transformation by the general form of the Johnson–Mehl–Avrami equation. The lower value of growth morphology parameter strongly supports that in the secondary mullite formation the added alumina is dissolved into glassy phase and the mullite is then precipitated.

Characterization of Nanocrystalline γ–Fe2O3Prepared by Wet Chemical Method

1999 ◽  
Vol 14 (4) ◽  
pp. 1570-1575 ◽  
Author(s):  
G. Ennas ◽  
G. Marongiu ◽  
A. Musinu ◽  
A. Falqui ◽  
P. Ballirano ◽  
...  
Keyword(s):  
Isothermal Treatment ◽  
X Ray Diffraction ◽  
Ferrous Chloride ◽  
Scanning Calorimetry ◽  
Direct Transformation ◽  
X Ray ◽  
Transmission Electron ◽  
Xrd Techniques ◽  
Kinetics Of

Homogeneous maghemite (γ–Fe2O3) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe2O3), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.

Crystallization kinetics of yttrium aluminum garnet (Y3Al5O12)

2001 ◽  
Vol 16 (6) ◽  
pp. 1795-1805 ◽  
Author(s):  
Bradley R. Johnson ◽  
Waltraud M. Kriven
Keyword(s):  
Yttrium Aluminum Garnet ◽  
Three Dimensional ◽  
Constant Number ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Yttrium Aluminum ◽  
Temperature Transformation ◽  
Kinetics Of ◽  
Dimensional Crystal

The kinetics and pathways for crystallization of solid, amorphous, yttrium aluminum garnet (YAG) were studied using isothermal differential thermal analysis, x-ray diffraction, and transmission electron microscopy. The activation energy for crystallization was 437 KJ/mol and the measured Avrami exponent was 2.74, which corresponded to three-dimensional crystal growth with a constant number of nuclei. Time–temperature–transformation (T–T–T) curves were developed from the data to predict crystallization rates as a function of temperature. The crystallization pathway for YAG in this system is compared to others reported in the literature.

Interdiffusion Kinetics and Magnetic Properties of TA-Permalloy Multilayers

1991 ◽  
Vol 232 ◽  
Author(s):  
I. Hashim ◽  
H. A. Atwater ◽  
K. T. Y. Kung ◽  
R. M. Valletta
Keyword(s):  
Magnetic Properties ◽  
Isothermal Annealing ◽  
Lattice Diffusion ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Short Period ◽  
Interface Roughening ◽  
Interdiffusion Kinetics ◽  
Kinetics Of

ABSTRACTThe interdiffusion kinetics of ultrahigh vacuum deposited Ta/Ni81Fe19 short-period multilayers films have been investigated, and changes in microstructure were related to magnetic properties. Small angle X-ray diffraction and transmission electron microscopy were used to study layer morphology evolution and interdiffusion during post-growth isothermal annealing in the temperature range 300 – 600°C. The kinetic analysis suggests that interface roughening due to grain growth, and grain-boundary mediated diffusion of Ta occurs concurrently at early anneal times in the Ni81Fe19 films. Subsequent grainboundary and lattice diffusion of Ta lead to a reduction of magnetization and increase in coercivity of Ni81Fe19.

Effect of film composition on the orientation of (Ba,Sr)TiO3 grains in (Ba,Sr)yTiO2+ythin films

1999 ◽  
Vol 14 (12) ◽  
pp. 4657-4666 ◽  
Author(s):  
Debra L. Kaiser ◽  
Mark D. Vaudin ◽  
Lawrence D. Rotter ◽  
John E. Bonevich ◽  
Igor Levin ◽  
...  
Keyword(s):  
Amorphous Phase ◽  
Composition Dependence ◽  
Compressive Strain ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
X Ray Diffraction ◽  
Two Phase ◽  
Film Composition ◽  
X Ray ◽  
Transmission Electron

Thin films of composition (Ba,Sr)yTiO2+y with 0.43 ≤ y ≤; 1.64, were deposited by metalorganic chemical vapor deposition on (100) MgO substrates at various growth conditions. X-ray diffraction and transmission electron microscopy studies showed that the films were composed of epitaxial Ba1–xSrxTiO3 (x ≈0.06) grains and an amorphous phase. The orientation of the tetragonal Ba1–xSrxTiO3 grains (pure a axis, pure c axis, or a mix of the two) was found to be strongly dependent upon film composition. This composition dependence is explained for the majority of the Ti-rich films by an analysis of average strains in the two-phase films, assuming a compressive strain of ≈1% in the amorphous phase.

scholarly journals Electrochemical oxidation of methanol on Pt/(RuxSn1-x)O2 nanocatalyst

2013 ◽  
Vol 78 (11) ◽  
pp. 1703-1716 ◽  
Author(s):  
Mila Krstajic ◽  
Maja Obradovic ◽  
Biljana Babic ◽  
Velimir Radmilovic ◽  
Uros Lacnjevac ◽  
...  
Keyword(s):  
Electrochemical Oxidation ◽  
Methanol Oxidation ◽  
Pt Nanoparticles ◽  
Atomic Ratio ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Oxidation Of Methanol ◽  
Potentiodynamic Polarization Curves ◽  
Transmission Electron

The Ru-doped SnO2 powder, (RuxSn1-x)O2, with the Sn:Ru atomic ratio of 9:1 was synthesized and used as a support for Pt nanoparticles (30 mass% loading). The (RuxSn1-x)O2 support and Pt/(RuxSn1-x)O2 catalyst were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy (TEM). (RuxSn1-x)O2 was found to be two-phase material consisting of probably solid solution of RuO2 in SnO2 and pure RuO2. The average Pt particle size determined by TEM was 5.3 nm. Cyclic voltammetry of Pt/(RuxSn1-x)O2 indicated good conductivity of the sup-port and displayed usual features of Pt. The results of the electrochemical oxidation of COads and methanol on Pt/(RuxSn1-x)O2 were compared with those on commercial Pt/C and PtRu/C catalysts. Oxidation of COads on Pt/(RuxSn1-x)O2 starts at less positive potentials than on PtRu/C and Pt/C. Potentiodynamic polarization curves and chronoamperometric curves of methanol oxidation indicated higher initial activity of Pt/(RuxSn1-x)O2 catalyst compared to PtRu/C, but also a greater loss in the current density over time. Potentiodynamic stability test of the catalysts revealed that deactivation of the Pt/(RuxSn1-x)O2 and Pt/C was primarily caused by the poisoning of Pt surface by the methanol oxidation residues, which mostly occurred during the first potential cycle. In the case of PtRu/C the poisoning of the surface was minor and deactivation was caused by the PtRu surface area loss.

The early stages of phase formation during mechanical alloying of Ti–Al

1994 ◽  
Vol 9 (1) ◽  
pp. 47-52 ◽  
Author(s):  
T. Klassen ◽  
M. Oehring ◽  
R. Bormann
Keyword(s):  
Mechanical Alloying ◽  
Phase Formation ◽  
X Ray Diffraction ◽  
Annealing Behavior ◽  
Early Stages ◽  
Transmission Electron ◽  
Fcc Phase ◽  
Multilayered Thin Films ◽  
Kinetics Of ◽  
Structural Disordering

The early stages of phase formation during mechanical alloying of Ti/Al powder blends were investigated using x-ray diffraction and transmission electron microscopy. After the initial formation of an hep solid solution by the diffusion of Al into Ti, the first phase nucleated at the Ti/Al interface is a (partially) Ll2-ordered fcc phase with a crystallite size of about 10–30 nm. This observation is ascribed to the kinetics of phase formation and the energetic destabilization of the equilibrium intermetallic compounds during milling due to chemical and structural disordering. A mechanism of phase formation during mechanical alloying is proposed, and comparisons are made with the thermal annealing behavior of Ti/Al multilayered thin films.

The concentration quenching of photoluminescence in Eu3+-doped La2O3

2013 ◽  
Vol 37 (1) ◽  
pp. 47-54 ◽  
Author(s):  
V. Đorđević ◽  
Ž. Antić ◽  
M. G. Nikolić ◽  
M. D. Dramićanin
Keyword(s):  
Room Temperature ◽  
Hexagonal Phase ◽  
Average Particle Size ◽  
Average Particle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Maximum Lifetime ◽  
Transmission Electron ◽  
Lifetime Value ◽  
Kinetics Of

Abstract This work explores the influence of dopant concentration on photoluminescent emission and kinetics of Eu3+-doped (0.2−10 at.%) nanocrystalline lanthanumoxide powders. The X-ray diffraction analysis confirmed that all samples crystallize in La2O3 hexagonal phase with space group P3¯ m1. Transmission electron microscopy showed particles with non-uniform shape and diverse size distribution with an average particle size of (95 ± 5) nm. The room temperature photoluminescence spectra of all samples contain characteristic Eu3+ luminescence lines with the most pronounced red 5D0 →7F2 emission at about 626 nm. The maximum intensity of red emission is observed for the sample containing 5at.% of Eu3+ ions. The emission kinetics was recorded in the temperature range from 10K to 300 K. The maximum lifetime value of 0.98 ms obtained for the sample with 0.5at.% Eu3+ at room temperature increases up to 1.3ms at 10 K.

scholarly journals On the kinetics of the hydrogen evolution reaction on Ni-MoOx composite catalysts in alkaline solutions

2012 ◽  
Vol 77 (2) ◽  
pp. 211-224 ◽  
Author(s):  
Borka Jovic ◽  
Uros Lacnjevac ◽  
Vladimir Jovic ◽  
Ljiljana Gajic-Krstajic ◽  
Nedeljko Krstajic
Keyword(s):  
Electron Microscopy ◽  
Constant Current ◽  
Catalyst Stability ◽  
Alkaline Solutions ◽  
High Catalytic Activity ◽  
X Ray Diffraction ◽  
X Ray ◽  
Composite Catalysts ◽  
Transmission Electron ◽  
Kinetics Of

MoO3 particles were co-deposited with Ni onto smooth or rough Ni supports from modified Watt?s baths of different compositions. Morphology and composition of the electrodeposits were characterized by means of cyclic voltammetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic activity of the composite catalysts for H2 evolution in alkaline solutions was determined by quasi-stationary polarization curves. Activity increases with MoOx content in the Ni deposit up to a limiting value. Composite Ni-MoOx catalyst performed high catalytic activity, similar to that of commercial Ni-RuO2 catalyst. Stability tests showed that Ni-MoOx codeposits are stable under condition of constant current and exhibit excellent tolerance to repeated short-circuiting.

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