13. Kinetics and hysteresis in high-temperature polymorphic transformations under pressure

2013 ◽  
pp. 357-381
Keyword(s):  
High Temperature ◽  
Polymorphic Transformations

Polymorphic transformations and thermal expansion of some modifications in Ag1.5Cu0.5Se and Ag0.4Cu1.6Se

2019 ◽  
Vol 33 (23) ◽  
pp. 1950271 ◽  
Author(s):  
Y. I. Aliyev ◽  
Y. G. Asadov ◽  
A. O. Dashdemirov ◽  
R. D. Aliyeva ◽  
T. G. Naghiyev ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Diffraction Method ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
Polymorphic Transformations ◽  
X Ray

The Ag[Formula: see text]Cu[Formula: see text]Se and Ag[Formula: see text]Cu[Formula: see text]Se compounds have been synthesized and grown as single crystals. High-temperature X-ray diffraction method was used to study polymorphic transformations. It is shown that the Ag[Formula: see text]Cu[Formula: see text]Se crystals of high-temperature FCC modification are decomposed into Ag2Se and AgCuSe when the temperature decreases below T = 488 K and Ag[Formula: see text]Cu[Formula: see text]Se is decomposed into Cu2Se and AgCuSe when the temperature decreases below T = 540 K. Transformations in both compounds are reversible. Crystalline parameters are obtained and the temperature dependence of the lattice parameters for each phase is built.

In situsynchrotron powder diffraction study of active belite clinkers

2007 ◽  
Vol 40 (6) ◽  
pp. 999-1007 ◽  
Author(s):  
Ángeles G. De la Torre ◽  
Khadija Morsli ◽  
Mohammed Zahir ◽  
Miguel A.G. Aranda
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Powder Diffraction ◽  
Polymorphic Transformation ◽  
High Energy ◽  
Dicalcium Silicate ◽  
Polymorphic Transformations ◽  
X Ray ◽  
High Temperature Reactions

The clinkerization processes to form belite clinkers, with theoretical compositions close to 60 wt% of Ca2SiO4, have been studiedin situby high-resolution high-energy (λ = 0.30 Å) synchrotron X-ray powder diffraction. In order to obtain active belite cements, different amounts of K2O, Na2O and SO3have been added. The existence range of the high-temperature phases has been established and, furthermore, Rietveld quantitative phase analyses at high temperature have been performed for all patterns. The following high-temperature reactions have been investigated: (i) polymorphic transformations of dicalcium silicate, \alpha_{\rm L}'-Ca2SiO4↔ \alpha_{\rm H}'-Ca2SiO4from 1170 to 1230 K, and \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4from 1500 to 1600 K; (ii) melting of the aluminates phases, Ca3Al2O6and Ca4(Al2Fe2)O10, above ∼1570 K; and (iii) reaction of Ca2SiO4with CaO to yield Ca3SiO5above ∼1550 K. Moreover, in all the studied compositions the temperature of the polymorphic transformation \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4has decreased with the addition of activators. Finally, active belite clinkers were produced as the final samples contained α-belite phases.

The Bismuth-Barium Oxides

1998 ◽  
Vol 547 ◽  
Author(s):  
K. Müller ◽  
J.K. Meen ◽  
D. Elthon
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Low Temperature ◽  
Phase Relations ◽  
The Other ◽  
Face Centered Cubic ◽  
Polymorphic Transformations ◽  
Face Centered ◽  
T Phase

AbstractPhase relations have been determined for the Bi-Ba oxide pseudobinary up to 50 cat % Ba in 1 atm of oxygen at 640°-1000°C. The low-temperature α-Bi2O3 polymorph does not dissolve appreciable BaO. All other phases in the system have significant ranges of solution. The δ-Bi2O3 polymorph, stable from 730°C to 825°C is an end-member of a face-centered cubic solid solution (FCCss) that dissolves up to 2.7 % Ba. Ba-saturated FCCss and Bi-saturated rhombohedral (ß) solid solution (6.3 % Ba) melt at a eutectic at 753 °C. Less Bi is needed to saturate the ß phase at lower temperatures so α-Bi2O3 coexists with a ß phase containing 11.5 % Ba at 646°C.The amount of Ba required to saturate the ß phase depends less strongly on temperature. Ba-saturated ß phase contains 19 % Ba at 700°C. These ß materials are in equilibrium with an oxide near Bi3BaO5.5 that undergoes two polymorphic transformations: low-temperature cubic (<700°C); orthorhombic (700-730°C); high-temperature cubic (Cht). There is a eutectic between the ß and Cht, at 775±6°C. At T<700°C, 26.5 % Ba saturates the latter but it can take in up to 29.5 % Ba (at 812°C). At T<815°C the coexisting phase is BiBaO3. A tetragonal (T) phase forms by reaction of Ch, and BiBaO3 and has ~35% BaO at 815°C. The composition span of T widens as temperature increases. Cht, melts incongruently at 820°C to a liquid and T with 29.8 % Ba. Above that temperature the Bi-saturated and Ba-saturated T phases both become more Ba-rich as temperature is elevated. T melts incongruently to liquid and BiBaO3.The δ-Bi2O3 and ß, both anion conductors, have structures based on that of fluorite. The other oxides have perovskite-like structures. Half of the Bi in BiBaO3 is pentavalent and half is trivalent. The other oxides appear to have all their Bi in the 3+ state.

Influence of partial substitution of Cu atoms by Zn and Cd atoms on polymorphic transformation in the Cu1.75Te crystal

2019 ◽  
Vol 33 (11) ◽  
pp. 1850128 ◽  
Author(s):  
Y. I. Aliyev ◽  
Y. G. Asadov ◽  
R. D. Aliyeva ◽  
T. G. Naghiyev ◽  
S. H. Jabarov
Keyword(s):  
High Temperature ◽  
Polymorphic Transformation ◽  
Lattice Parameters ◽  
Partial Substitution ◽  
Polymorphic Transformations ◽  
X Ray ◽  
Change Mechanism ◽  
Temperature Modification ◽  
Phase Temperature ◽  
High Temperature Modification

The [Formula: see text], [Formula: see text] and [Formula: see text] compounds have been synthesized and low-temperature modification single crystals obtained from the high temperature modification by polymorphic transformation. The method of high temperature X-ray diffractometer has been used to study [Formula: see text] (x = 0.05 Zn and Cd) layered single crystal. It was established that such a substitution has a significant impact on the number and temperature of polymorphic transformations. Crystallgraphic parameters were determined for each phase. Temperature dependence of lattice parameters were obtained and determined change mechanism of lattice parameters by influence of temperature.

scholarly journals Quantification of High Temperature Transition Al2O3 and Their Phase Transformations

2020 ◽  
Author(s):  
Libor Kovarik ◽  
Mark Bowden ◽  
Amity Andersen ◽  
Nicholas R. Jaegers ◽  
Nancy Washton ◽  
...  
Keyword(s):  
High Temperature ◽  
Structural Disorder ◽  
Study Phase ◽  
Temperature Transition ◽  
Polymorphic Transformations ◽  
Transition Alumina ◽  
Formidable Challenge ◽  
Temperature Exposure ◽  
Xrd Patterns ◽  
High Degree

<p>High temperature exposure of gamma-Al<sub>2</sub>O<sub>3</sub> can lead to a series of polymorphic transformations, including the formation of delta-Al<sub>2</sub>O<sub>3</sub> and theta-Al<sub>2</sub>O<sub>3</sub>. Quantification of the microstructure in the delta/theta-Al<sub>2</sub>O<sub>3</sub> formation range represents a formidable challenge as both phases accommodate a high degree of structural disorder. In this work, we explore the use of XRD recursive stacking formalism for quantification of high temperature transition aluminas. We formulate the recursive stacking methodology for modelling of disorder in delta-Al<sub>2</sub>O<sub>3 </sub>and twinning in theta-Al<sub>2</sub>O<sub>3</sub> and show that explicitly accounting for the disorder is necessary to reliably model the XRD patterns of high temperature transition alumina. In the second part, we use the recursive stacking approach to study phase transformation during high temperature (1050 ºC) treatment. We show that the two different intergrowth modes of delta-Al<sub>2</sub>O<sub>3</sub> have different transformation characteristics, and that a significant portion of delta-Al<sub>2</sub>O<sub>3</sub> is stabilized with theta-Al<sub>2</sub>O<sub>3 </sub>even after prolonged high-temperature exposures. In discussions, we outline the limitation of the current XRD approach and discuss a possible multimodal XRD and NMR approach which can improve analysis of complex transition aluminas.</p>

Effects of Diffusion of Co/Ni Cations on Sol-Gel Derived ZrO2 Polymorphic Transformations

1995 ◽  
Vol 398 ◽  
Author(s):  
H.C. Zeng ◽  
M. Qian
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Tetragonal Phase ◽  
Sol Gel ◽  
Heating Process ◽  
Cubic Phase ◽  
Impregnation Method ◽  
Cooling Process ◽  
Polymorphic Transformations ◽  
Metal Diffusion

ABSTRACTTransition metal incorporated ZrO2 gel matrices have been prepared by impregnation method and investigated with FTIR/DTA/XRD. The metastable tetragonal - monoclinic -tetragonal - cubic phase transformations are revealed in the DTA heating process up to 1400°C for the studied gels. High-temperature tetragonal to monoclinic transition is also observed in the cooling process. It is found that the diffusing metal cations stabilize the low-temperature tetragonal phase. However, for high-temperature (900°C) calcined gels, both as-prepared and metal-stabilized tetragonal phases are reduced substantially. Correlations between metal diffusion and gel polymorphic stabilities are also demonstrated.

scholarly journals Quantification of High Temperature Transition Al2O3 and Their Phase Transformations

2020 ◽  
Author(s):  
Libor Kovarik ◽  
Mark Bowden ◽  
Amity Andersen ◽  
Nicholas R. Jaegers ◽  
Nancy Washton ◽  
...  
Keyword(s):  
High Temperature ◽  
Structural Disorder ◽  
Study Phase ◽  
Temperature Transition ◽  
Polymorphic Transformations ◽  
Transition Alumina ◽  
Formidable Challenge ◽  
Temperature Exposure ◽  
Xrd Patterns ◽  
High Degree

<p>High temperature exposure of gamma-Al<sub>2</sub>O<sub>3</sub> can lead to a series of polymorphic transformations, including the formation of delta-Al<sub>2</sub>O<sub>3</sub> and theta-Al<sub>2</sub>O<sub>3</sub>. Quantification of the microstructure in the delta/theta-Al<sub>2</sub>O<sub>3</sub> formation range represents a formidable challenge as both phases accommodate a high degree of structural disorder. In this work, we explore the use of XRD recursive stacking formalism for quantification of high temperature transition aluminas. We formulate the recursive stacking methodology for modelling of disorder in delta-Al<sub>2</sub>O<sub>3 </sub>and twinning in theta-Al<sub>2</sub>O<sub>3</sub> and show that explicitly accounting for the disorder is necessary to reliably model the XRD patterns of high temperature transition alumina. In the second part, we use the recursive stacking approach to study phase transformation during high temperature (1050 ºC) treatment. We show that the two different intergrowth modes of delta-Al<sub>2</sub>O<sub>3</sub> have different transformation characteristics, and that a significant portion of delta-Al<sub>2</sub>O<sub>3</sub> is stabilized with theta-Al<sub>2</sub>O<sub>3 </sub>even after prolonged high-temperature exposures. In discussions, we outline the limitation of the current XRD approach and discuss a possible multimodal XRD and NMR approach which can improve analysis of complex transition aluminas.</p>

Influence of Thermo-Mechanical Processing on the Microstructure of Beryllia Dispersed Nickel Alloys

1973 ◽  
Vol 31 ◽  
pp. 184-185
Author(s):  
M.S. Grewal ◽  
S.A. Sastri ◽  
N.J. Grant
Keyword(s):  
High Temperature ◽  
Nickel Alloys ◽  
Thermomechanical Processing ◽  
Cold Work ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
Mechanical Processing ◽  
Uniform Dispersion ◽  
Oxide Particles ◽  
Nickel Base

Currently there is a great interest in developing nickel base alloys with fine and uniform dispersion of stable oxide particles, for high temperature applications. It is well known that the high temperature strength and stability of an oxide dispersed alloy can be greatly improved by appropriate thermomechanical processing, but the mechanism of this strengthening effect is not well understood. This investigation was undertaken to study the dislocation substructures formed in beryllia dispersed nickel alloys as a function of cold work both with and without intermediate anneals. Two alloys, one Ni-lv/oBeo and other Ni-4.5Mo-30Co-2v/oBeo were investigated. The influence of the substructures produced by Thermo-Mechanical Processing (TMP) on the high temperature creep properties of these alloys was also evaluated.

Application of TEM to Deformation, Wear, and Fracture of Ceramics

1974 ◽  
Vol 32 ◽  
pp. 472-473
Author(s):  
B. J. Hockey
Keyword(s):  
Wear Resistance ◽  
High Temperature ◽  
Mechanical Behavior ◽  
Brittle Materials ◽  
High Temperature Strength ◽  
Wide Range ◽  
Corrosive Environments ◽  
Further Development

Ceramics, such as Al2O3 and SiC have numerous current and potential uses in applications where high temperature strength, hardness, and wear resistance are required often in corrosive environments. These materials are, however, highly anisotropic and brittle, so that their mechanical behavior is often unpredictable. The further development of these materials will require a better understanding of the basic mechanisms controlling deformation, wear, and fracture.The purpose of this talk is to describe applications of TEM to the study of the deformation, wear, and fracture of Al2O3. Similar studies are currently being conducted on SiC and the techniques involved should be applicable to a wide range of hard, brittle materials.

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