X-ray study of the twinning and phase transformation of phosphocristobalite (AlPO4)

1977 ◽  
Vol 55 (7-8) ◽  
pp. 677-683 ◽  
Author(s):  
H. N. Ng ◽  
C. Calvo
Keyword(s):  
Phase Transformation ◽  
Transition Temperature ◽  
Short Range ◽  
X Ray ◽  
First Order ◽  
Β Phase ◽  
Α Phase ◽  
Short Range Correlations

Crystals of the cristobalite polymorph of AlPO4 (phosphocristobalite) up to 3 mm in breadth were grown from a V2O5 flux. In the α phase (C2221), the presence of twin domains prevents an accurate resolution of the structure as a function of temperature. The six twin components of this phase readily lead to a disordered β phase [Formula: see text] with short range correlations as suggested previously. The α–β transformation is first order with a substantial hysteresis in the transition temperature.

Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems

1988 ◽  
Vol 133 ◽  
Author(s):  
K. S. Kumar ◽  
S. K. Mannan
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
Crystalline Compound ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.

scholarly journals X-Ray Investigations of the Low-Temperature Phases of the Organic Metals α- and β-(BEDT-TTF)2I3

1986 ◽  
Vol 41 (11) ◽  
pp. 1319-1324 ◽  
Author(s):  
H. Endres ◽  
H. J. Keller ◽  
R. Swietlik ◽  
D. Schweitzer ◽  
K. Angermund ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Slight Variation ◽  
X Ray ◽  
Organic Metals ◽  
Β Phase ◽  
Α Phase

The structure of single crystals of the organic metals α- and β-(BEDT-TTF)2I3* was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis. In the α-phase no unusual change of the room temperature unit cell but a slight variation in the triiodide network and especially a more pronounced dimerization in one of the two donor stacks have been found. The β-phase develops a superstructure with a unit cell volume three times as large as that at room temperature and with pronounced distortions of the I3--ions.

2.45 GHz Microwave Sintering of Silicon Nitride

2008 ◽  
Vol 403 ◽  
pp. 27-30
Author(s):  
S. Chockalingam ◽  
J.P. Kelly ◽  
V.R.W. Amarakoon ◽  
James R. Varner
Keyword(s):  
Phase Transformation ◽  
Oxidation Behavior ◽  
Microwave Sintering ◽  
Sintered Sample ◽  
Microstructure Development ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Structurally Stable

Microwave sintered Si3N4-MgO system that contains 2, 4 and 10 wt% of ZrO2 as secondary particulates were investigated with respect to phase transformation and microstructure development. The experimental results of microwave sintered samples were compared with conventional methods. Complete α to β phase transformation was observed in the case of microwave sintered samples due to the volumetric nature of microwave heating. High temperature X-ray diffraction (HTXRD) analysis was performed to study in-situ the oxidation behavior of Si3N4 specimens. Si3N4 specimens with 10 wt % ZrO2 were exposed to air at temperature between 25°C and 900°C for up to 24 hours. Microwave sintered sample were structurally stable in air 25°C and 900°C for up to 24 hours of testing.

Phase Transformations of the Ti-40% Nb Alloy Under External Influence

2016 ◽  
Vol 683 ◽  
pp. 174-180 ◽  
Author(s):  
Yuri P. Sharkeev ◽  
Zhanna G. Kovalevskaya ◽  
Margarita A. Khimich ◽  
Vladimir A. Bataev ◽  
Qi Fang Zhu ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Phase Transformation ◽  
Severe Plastic Deformation ◽  
Phase Transformations ◽  
Optical Metallography ◽  
External Influence ◽  
Β Phase ◽  
Α Phase ◽  
Pressing Operation ◽  
Loading Axis

The phase transformations of the alloy Ti-40 mas % Nb after tempering and severe plastic deformation are studied. The phase transformations of the alloy according to the type and conditions of external influences are analyzed using methods of XRD, SEM and optical metallography. It is determined that inverse phase transformation of the metastable α''-phase to equilibrium β-phase is carried out after severe plastic deformation. Complete phase transformation α'' → β is typical for the mode, which consists of three pressing operation with the change of the loading axis in cramped conditions, followed by a multi-pass rolling in grooved rolls.

Phase Transformation Cycle β→ α′ + α + α"→ β in Ti6Al4V Alloy

2015 ◽  
Vol 828-829 ◽  
pp. 232-238 ◽  
Author(s):  
Kalenda Mutombo ◽  
Siyasiya Charles ◽  
Waldo Stumpf
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
Phase Field ◽  
Xrd Analysis ◽  
External Stress ◽  
Ti6al4v Alloy ◽  
Β Phase ◽  
Α Phase ◽  
Sequential Transformation ◽  
Dsc Thermograms

The β-phase transforms to α′, α and α" within a range of temperature from the β-transus (Tβ) to about 600°C, considering no external stress is applied. Two types of microstructure were obtained: acicular martensite when rapidly cooled and lamellar α/β when slowly cooled from the β phase field. The sequential transformation of β into α′, α-phase, α2, and α" was revealed as peaks on the coefficient thermal expansion (CTE) curves, however, reversed transformations: α"→β, and α→β, were revealed by the DSC thermograms. The presence of β, α′, α, α2 and α" was identified by means of XRD analysis and HRTEM.

Investigation on β-Polypropylene/Talc Composites

2012 ◽  
Vol 182-183 ◽  
pp. 259-264
Author(s):  
Jia Wei Duan ◽  
Qiang Dou
Keyword(s):  
Polarized Light ◽  
Nucleating Agent ◽  
Mechanical Tests ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Melt Compounding ◽  
Β Phase ◽  
Α Phase ◽  
Melting And Crystallization

In this study polypropylene (PP) composites containing β-nucleating agent (NT-C) and talc filler were prepared by melt compounding. The melting and crystallization behavior, morphology and mechanical properties of the composites were studied by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), polarized light microscopy (PLM) and mechanical tests. The results indicate that talc suppresses the formation of β phase, but promotes the formation of α phase. The Izod notched impact strength and tensile strength of β-PP/talc composites are superior to those of PP/talc composites, indicating an outstanding balance of stiffness and toughness of β-PP/talc composites.

Structure and properties of Al–Mg mechanical alloys

2003 ◽  
Vol 18 (8) ◽  
pp. 1827-1836 ◽  
Author(s):  
Mirko Schoenitz ◽  
Edward L. Dreizin
Keyword(s):  
Solid Solution ◽  
Energetic Materials ◽  
Amorphous Material ◽  
Bulk Composition ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Diffraction Microscopy

Mechanically alloys in the Al–Mg binary system in the range of 5–50 at.% Mg were produced for prospective use as metallic additives for propellants and explosives. Structure and composition of the alloys were characterized by x-ray diffraction microscopy (XRD) and scanning electron microscopy. The mechanical alloys consisted of a supersaturated solid solution of Mg in the α aluminum phase, γ phase (Al12Mg17), and additional amorphous material. The strongest supersaturation of Mg in the α phase (20.8%) was observed for bulk Mg concentrations up to 40%. At 30% Mg, the γ phase formed in quantities detectable by XRD; it became the dominating phase for higher Mg concentrations. No β phase (Al3Mg2) was detected in the mechanical alloys. The observed Al solid solution generally had a lower Mg concentration than the bulk composition. Thermal stability and structural transitions were investigated by differential scanning calorimetry. Several exothermic transitions, attributed to the crystallization of β and γ phases were observed. The present work provides the experimental basis for the development of detailed combustion and ignition models for these novel energetic materials.

Phase Constitution and Heat Treatment Behavior of Zr-Nb Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 1435-1440 ◽  
Author(s):  
Masahiko Ikeda ◽  
Tsuyoshi Miyazaki ◽  
Satoshi Doi ◽  
Michiharu Ogawa
Keyword(s):  
Heat Treatment ◽  
Elastic Modulus ◽  
Elastic Moduli ◽  
X Ray Diffraction ◽  
Phase Constitution ◽  
X Ray ◽  
Β Phase ◽  
Ω Phase ◽  
Solution Treated ◽  
Α Phase

Phase constitution in the solution-treated and quenched state and the heat treatment behavior were investigated by electrical resistivity, hardness, and elastic modulus measurements, X-ray diffraction, and optical microscopy. Hexagonal martensite and the β phase were identified in the Zr-5mass%Nb alloy. β and ω phases were identified in the Zr-10 and 15mass%Nb alloys, and only the β phase was identified in the Ti-20Nb alloy. Resistivity at RT, Vickers hardness and elastic modulus increased up to 10Nb and then decreased dramatically at 15Nb. Above 15Nb, these values slightly decreased. The elastic moduli for 15Nb and 20Nb were 59.5 and 55.5 GPa, respectively. On isochronal heat treatment, the isothermal ω phase precipitated between 473 and 623 K and then the α phase precipitated in the 10Nb, 15Nb and 20Nb alloys.

The Flavonoids of Combretum quadrangulare: Crystal structures of the Polymorphic Forms of 5-Hydroxy-2-(4'-hydroxy-3',5'-dimethoxyphenyl)-3,7-dimethoxy-4H-1-benzopyran-4-one

1985 ◽  
Vol 38 (8) ◽  
pp. 1177 ◽  
Author(s):  
IR Castleden ◽  
SR Hall ◽  
S Nimgirawath ◽  
S Thadaniti ◽  
AH White
Keyword(s):  
Least Squares ◽  
Crystal Structures ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Polymorphic Forms

The following substituted 2-phenyl-4H-1-benzopyran-4-ones have been isolated from the dried flowers of Combretum quadrangulare Kurz ( Combretaceae ): 5-hydroxy-3,3′,4′,5′,7-pentamethoxy ( combretol ) (1), 3′,5-dihydroxy-3,4′,7-trimethoxy ( ayanin ) (2) and 4′,5-dihydroxy- 3,3′,5′,7-tetramethoxy (3). The last substance (3) was obtained as a mixture of two polymorphic forms (α and β) each of which was characterized by X-ray diffraction. Diffractometer data at 295 K were refined by full matrix least squares to residuals of 0.043 (1181 'observed' reflections) for the α-phase and 0.044 (1421) for the β phase of (3). Crystals of the α-phase of (3) are triclinic, Pī, a 12.663(6), b 9.592(4), c 7.444(4) Ǻ, α 102.48(3), β 101.39(4), γ 91.72(4)°,Z 2. Crystals of the β-phase of (3) are monoclinic P21/n, a 17.139(8), b 12.728(6), c 7.845(7) Ǻ, β 95.07(6)°, Z 4. An unambiguous synthesis of (3) was also achieved.

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