scholarly journals Barium oxide as a modifier to stabilize the γ-Al2O3 structure

2016 ◽  
Vol 18 (4) ◽  
pp. 1-4 ◽  
Author(s):  
Shahram G. Pakdehi ◽  
Maryam Rasoolzadeh ◽  
Ali Saberi Moghadam
Keyword(s):  
Phase Transition ◽  
Barium Oxide ◽  
Exothermic Peak ◽  
X Ray ◽  
Α Phase ◽  
Aluminum Ions ◽  
Porous Properties ◽  
Dta Curves ◽  
Octahedral Cations

Abstract This research concentrated on the structural stability of γ-alumina (γ-Al2O3) was investigated by a combination of differential thermal analysis, X-ray diffractometry and surface-area measurements. The γ –to– θ and then α phase transitions were observed as an exothermic peak at 1000°C–1400°C in the DTA curves. The role of barium oxide as a modifier to stabilize γ-Al2O3 structure has been investigated. XRD measurements show that after calcination at 1000°C for 2 h, a significant fraction of the pure γ-Al2O3 (BaO-free) transformed to θ-Al2O3 while that the transition phase in alumina samples modified by BaO have been reduced significantly. Barium oxide, eliminate pentacoordinated aluminum ions through coordinative saturation and alter these ions into octahedral cations and effectively suppressed the γ –to– α phase transition in Al2O3, which concluded as improving the thermal stability and porous properties of the experimental samples.

The role of π-bonding on the high temperature structure of the double perovskites Ba2CaUO6and BaSrCaUO6

2015 ◽  
Vol 44 (36) ◽  
pp. 16036-16044 ◽  
Author(s):  
Emily Reynolds ◽  
Gordon J. Thorogood ◽  
Maxim Avdeev ◽  
Helen E. A. Brand ◽  
Qinfen Gu ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Neutron Diffraction ◽  
Temperature Structure ◽  
Double Perovskites ◽  
Phase Transition Behavior ◽  
X Ray ◽  
Progressive Loss ◽  
Octahedral Tilting

High temperature synchrotron X-ray and neutron diffraction powder diffraction studies of the uranium perovskites Ba2CaUO6and BaSrCaUO6reveal unusual phase transition behavior associated with the progressive loss of cooperative octahedral tilting.

X-ray investigation of the α-α' phase transition of hydrogen in Pd1-xAgxalloys

1982 ◽  
Vol 12 (9) ◽  
pp. 1897-1906 ◽  
Author(s):  
W Fenzl ◽  
H Zabel ◽  
H Peisl
Keyword(s):  
Phase Transition ◽  
X Ray ◽  
Α Phase

Brillouin scattering near the α–β phase transitions of N2 and CO

1988 ◽  
Vol 66 (4) ◽  
pp. 541-548 ◽  
Author(s):  
V. Askarpour ◽  
H. Klefte ◽  
M. J. Clouter
Keyword(s):  
Phase Transition ◽  
Single Crystals ◽  
Elastic Constants ◽  
Brillouin Scattering ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Mode Softening ◽  
Cubic Structure

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of single crystals of β-N2 and β-CO as a function of temperature, in an effort to study the α–β phase transition. For all elastic constants, there is an increase of approximately 1%/K on cooling and there is no evidence of further mode softening, even within 0.5 K of the phase transition. Three large single crystals of α-CO were grown. The orientations were determined, by Laue X-ray diffraction, and correlated to the orientations of the parent β-crystals. The β-phase hexagonal basal planes appear to transform to planes of the form {110} in the α-phase cubic structure.

Development of Robot System and X-ray Powder Diffraction for Combinatorial Materials Research

2001 ◽  
Vol 700 ◽  
Author(s):  
Ikuo Yanase ◽  
Kenjiro Fujimoto ◽  
Kazunori Takada ◽  
Takugo Ohtaki ◽  
Mamoru Watanabe
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Exothermic Peak ◽  
Robot Arm ◽  
Robot System ◽  
X Ray ◽  
Materials Research ◽  
Combinatorial Materials ◽  
Dta Curve

AbstractWe developed a combinatorial robot system as the first step of combinatorial approach to wet and dry synthesis of ceramics. In this study, nanoparticles mixtures having maghemite and a small amount of Y2O3 were prepared successively by using the combinatorial robot system. maghemite and Y2O3 slurries were volumetrically and automatically measured and mixed by repetition of sucking and injecting with a micro-pipette attached to the robot arm. The structural phase transition temperature of maghemite to hematite, which was investigated from the exothermic peak in the DTA curve, increased from ca.813K to ca.1093K by 2atom%Y2O3 addition. It was considered that Y2O3 dissolution into the crystal structure of maghemite had an important role on increasing the temperature of the structural phase transition for stabilizing maghemite phase. (Combinatorial, Slurries, Maghemite, Nanoparticles, Phase transition)

Stretching Induced Crystalline-Phase Transition in Energy-Conversion Poly(Vinylidene Fluoride) (PVDF) Films

2014 ◽  
Vol 1070-1072 ◽  
pp. 589-593
Author(s):  
Fei Peng Wang ◽  
Zheng Yong Huang ◽  
Jian Li
Keyword(s):  
Phase Transition ◽  
Crystalline Phase ◽  
High Speed ◽  
Vinylidene Fluoride ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Poly Vinylidene Fluoride ◽  
Crystalline Phase Transition

Commercial poly (vinylidene fluoride) (PVDF) films are uniaxially stretched with varying rates at 110 °C in order to endow PVDF piezo-and pyroelectric by crystalline-phase transition from α to β during the stretching. The crystalline phases are determined by infrared spectroscopy. The β-phase content and its fraction in films increase as a result of stretching with high rates. In addition, higher stretching rates yield a slight increase of γ phase. The crystallite size is evaluated by means of X-ray diffraction. It is found that the β-phase crystallites become smaller with fast stretching, whereas the α-phase crystallites are cracked and disappear at high-speed stretching of 2.5 /min.

scholarly journals Ultrafast disordering of vanadium dimers in photoexcited VO2

Science ◽  
2018 ◽  
Vol 362 (6414) ◽  
pp. 572-576 ◽  
Author(s):  
Simon Wall ◽  
Shan Yang ◽  
Luciana Vidas ◽  
Matthieu Chollet ◽  
James M. Glownia ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Space ◽  
Vanadium Dioxide ◽  
Solid Phase ◽  
Rapid Evolution ◽  
X Ray ◽  
Transition Mechanism ◽  
Unit Cells ◽  
Phonon Oscillation

Many ultrafast solid phase transitions are treated as chemical reactions that transform the structures between two different unit cells along a reaction coordinate, but this neglects the role of disorder. Although ultrafast diffraction provides insights into atomic dynamics during such transformations, diffraction alone probes an averaged unit cell and is less sensitive to randomness in the transition pathway. Using total scattering of femtosecond x-ray pulses, we show that atomic disordering in photoexcited vanadium dioxide (VO2) is central to the transition mechanism and that, after photoexcitation, the system explores a large volume of phase space on a time scale comparable to that of a single phonon oscillation. These results overturn the current understanding of an archetypal ultrafast phase transition and provide new microscopic insights into rapid evolution toward equilibrium in photoexcited matter.

CH3CN: X-ray structural investigation of a unique single crystal. β → α phase transition and crystal structure

2002 ◽  
Vol 58 (6) ◽  
pp. 1005-1010 ◽  
Author(s):  
Renée Enjalbert ◽  
Jean Galy
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Temperature ◽  
Transition Temperature ◽  
Single Crystal ◽  
Structural Investigation ◽  
X Ray ◽  
Α Phase ◽  
First Time

The phase transition from the low- (β) to the high-temperature (α) form of acetonitrile, CH3CN, has been directly observed and studied on a unique single crystal. Both the β and α structures have been determined at temperatures close to the transition temperature (206 K and 201 K), taking advantage of the hysteresis. A single crystal of the β form was obtained for the first time.

scholarly journals Surface adsorption of stearic acid by natural calcite

2009 ◽  
Vol 63 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Slavica Mihajlovic ◽  
Aleksandra Dakovic ◽  
Zivko Sekulic ◽  
Deana Iles ◽  
Milan Kragovic
Keyword(s):  
Stearic Acid ◽  
Active Sites ◽  
Solution Method ◽  
Surface Adsorption ◽  
Exothermic Peak ◽  
Test Results ◽  
Dry Coating ◽  
X Ray ◽  
Dta Curves ◽  
Hydrophobic Material

In order to obtain hydrophobic material, the surface of natural limestone with the high content of calcite (>95%), was treated with 0.5, 1, 1.5, 2, 3 and 4% of stearic acid. Two methods were used for modification: the solution method and the dry coating. The obtained products were characterized using the thermal analysis (DT/TG), X-ray powder diffraction analysis (XRPD), scanning electron microscopy (SEM) and by the evaluation of floating test. Results of floating test showed that when the solution method was applied, the hydrophobicity arrived at above 99% when the amount of stearic acid was 1.5%, while with the dry coating the same hydrophobicity was achieved with 3% of stearic acid. From the position of the principal exothermic peak (> 310 ?C) at DTA curves, for calcites modified with dry coating and with the solution method, it can be concluded that with both modification processes, the same active sites exist at the calcite surface onto which stearic acid may be chemisorbed. However, the position and the intensity of the other exothermic peaks, indicate the differences in bonding of stearic acid at the calcite surface during the solution method and the dry coating.

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