Academic literature on the topic 'High temperature crystal structurephase transition'
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Journal articles on the topic "High temperature crystal structurephase transition"
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Khan, Humayun, and A. H. Khan. "High temperature phase transition in KH2PO4 crystal." Bulletin of Materials Science 16, no. 5 (October 1993): 357–63. http://dx.doi.org/10.1007/bf02759548.
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Połomska, M., J. Wolak, and L. Szcześniak. "High temperature phase transition of β-LiNH4SO4single crystal." Ferroelectrics 159, no. 1 (September 1994): 179–84. http://dx.doi.org/10.1080/00150199408007569.
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Yan, Feng, and Ye-Ning Wang. "Phase transition of C60 crystal in high temperature regime." Applied Physics Letters 73, no. 4 (July 27, 1998): 476–77. http://dx.doi.org/10.1063/1.121905.
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Bento, I. C. V., P. T. C. Freire, F. E. A. Melo, J. Mendes Filho, A. J. D. Moreno, M. R. Joya, and P. S. Pizani. "High temperature phase transition in monohydrated L-asparagine crystal." Solid State Communications 141, no. 1 (January 2007): 29–32. http://dx.doi.org/10.1016/j.ssc.2006.09.041.
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Chen, Xianhui, Pengcheng Dai, Donglai Feng, Tao Xiang, and Fu-Chun Zhang. "Iron-based high transition temperature superconductors." National Science Review 1, no. 3 (July 3, 2014): 371–95. http://dx.doi.org/10.1093/nsr/nwu007.
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Abstract In a superconductor electrons form pairs and electric transport becomes dissipation-less at low temperatures. Recently discovered iron-based superconductors have the highest superconducting transition temperature next to copper oxides. In this article, we review material aspects and physical properties of iron-based superconductors. We discuss the dependence of transition temperature on the crystal structure, the interplay between antiferromagnetism and superconductivity by examining neutron scattering experiments, and the electronic properties of these compounds obtained by angle-resolved photoemission spectroscopy in link with some results from scanning tunneling microscopy/spectroscopy measurements. Possible microscopic model for this class of compounds is discussed from a strong coupling point of view.
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Xia, Zhang, Wan Song-Ming, Yin Shao-Tang, and You Jing-Lin. "High-Temperature Raman Investigation on Phase Transition of LBO Crystal." Chinese Physics Letters 26, no. 11 (October 29, 2009): 113301. http://dx.doi.org/10.1088/0256-307x/26/11/113301.
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Scheel, H. J., and F. Licci. "Crystal Growth of High Temperature Superconductors." MRS Bulletin 13, no. 10 (October 1988): 56–61. http://dx.doi.org/10.1557/s0883769400064204.
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The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.
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Masciocchi, Norberto, and William Parrish. "New Crystal Data for High Temperature Hexagonal Silver Sulfate." Powder Diffraction 5, no. 1 (March 1990): 50–52. http://dx.doi.org/10.1017/s0885715600015232.
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AbstractPowder data for Ag2SO4were obtained with a conventional diffractometer equipped with a vacuum heating chamber. The transition from the low-temperature orthorhombic phase occurs over a temperature range of about 415° to 425°C and forms a hexagonal phase plus metallic silver. The lack of a sharp transition must be taken into account in high-temperature X-ray diffraction or DSC/DTA studies. The lattice parameters of the high-temperature hexagonal phase are a = 5.531(3), c = 7.456(5)Å at 440°C, λ = 1.540562 Å. Crystal structure determination was not completed because of uncertainty in the chemical composition.
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Sist, Mattia, Jiawei Zhang, and Bo Brummerstedt Iversen. "Crystal structure and phase transition of thermoelectric SnSe." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 72, no. 3 (May 13, 2016): 310–16. http://dx.doi.org/10.1107/s2052520616003334.
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Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram–Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperatureCmcmphase is not pseudo-tetragonal as commonly assumed.
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Igartua, J. M., M. I. Aroyo, E. Kroumova, and J. M. Perez-Mato. "Search for Pnma materials with high-temperature structural phase transitions." Acta Crystallographica Section B Structural Science 55, no. 2 (April 1, 1999): 177–85. http://dx.doi.org/10.1107/s0108768198013342.
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A systematic search for structures having a high-temperature structural phase transition can be carried out through the identification in the structural databases of those structures that can be considered pseudosymmetric. Pseudosymmetry in a crystal structure indicates the possibility of a similar configuration of higher symmetry. If the distortion relating both structures is small enough, it can be expected that the crystal acquires the more symmetric configuration through a Landau-type phase transition at a higher temperature. Here, we present the results of such a search among inorganic structures with space group Pnma retrieved from the Inorganic Crystal Structure Database. Pseudosymmetry has indeed been detected in those compounds with a known (displacive) Landau-type phase transition at higher temperatures. This is measured by a parameter Δ, which measures the maximal atomic displacement relating the pseudosymmetry-transformed structure and the original one. In most of these compounds with a known phase transition, this parameter was smaller than 1.0 Å for at least one minimal supergroup of Pnma. The database contains 144 additional structures with pseudosymmetry features under the same quantitative limit. A comparison of the Δ distributions in both sets of compounds suggests a smaller Δ window (with 0.7 Å as maximal value) for selecting the materials having maximal probability of exhibiting a phase transition at higher temperatures. A set of 58 compounds fulfils this criterion.
Dissertations / Theses on the topic "High temperature crystal structurephase transition"
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Schmidt, Marek Wojciech, and Marek Schmidt@rl ac uk. "Phase formation and structural transformation of strontium ferrite SrFeOx." The Australian National University. Research School of Physical Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20020708.190055.
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Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different
gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical
applications in oxygen conducting devices such as pressure driven oxygen
generators, partial oxidation reactors in electrodes for solid oxide fuel cells
(SOFC).
¶
This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental
techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer
spectroscopy. Changes in the oxide were induced using conventional thermal
treatment in various atmospheres as well as mechanical energy (ball milling).
The first experimental chapter examines the formation of the ferrite from
a mixture of reactants.It describes the chemical reactions and phase transitions that lead to the formation of the oxide. Ball milling of the reactants prior to annealing was found to eliminate transient phases from the reaction route and to increase the kinetics of
the reaction at lower temperatures.
Examination of the thermodynamics of iron oxide (hematite) used for the
reactions led to a new route of synthesis of the ferrite frommagnetite and
strontium carbonate.This chapter also explores the possibility of synthesis
of the material at room temperature using ball milling.
¶
The ferrite strongly interacts with the gas phase so its behaviour was studied under different pressures of oxygen and in carbon dioxide.The changes in ferrite composition have an equilibrium character and depend on temperature and oxygen concentration in the
atmosphere. Variations of the oxygen
content x were described as a function of temperature and oxygen partial
pressure, the results were used to plot an equilibrium composition diagram.
The heat of oxidation was also measured as a function of temperature and oxygen partial pressure.
¶
Interaction of the ferrite with carbon dioxide below a critical temperature
causes decomposition of the material to strontium carbonate and SrFe12O19 .
The critical temperature depends on the partial pressure of CO2 and above
the critical temperature the carbonate and SrFe12O19 are converted back into
the ferrite.The resulting SrFe12O19 is very resistant towards carbonation and
the thermal carbonation reaction does not lead to a complete decomposition
of SrFeOx to hematite and strontium carbonate.
¶
The thermally induced oxidation and carbonation reactions cease at room
temperature due to sluggish kinetics however,they can be carried out at ambient temperature using ball milling.The reaction routes for these processes are different from the thermal routes.The mechanical oxidation induces two
or more concurrent reactions which lead to samples containing two or more
phases. The mechanical carbonation on the other hand produces an unknown
metastable iron carbonate and leads a complete decomposition of the ferrite
to strontiumcarbonate and hematite.
¶
Thermally and mechanically oxidized samples were studied using Mossbauer
spectroscopy. The author proposes a new interpretation of the Sr4Fe4O11
(x=2.75) and Sr8Fe8O23 (x=2.875)spectra.The interpretation is based
on the chemistry of the compounds and provides a simpler explanation of
the observed absorption lines.The Mossbauer results froma range of compositions
revealed the roomtemperature phase behaviour of the ferrite also
examined using x-ray diffraction.
¶
The high-temperature crystal structure of the ferrite was examined using
neutron powder diffraction.The measurements were done at temperatures
up to 1273K in argon and air atmospheres.The former atmosphere protects
Sr2Fe2O5 (x=2.5) against oxidation and the measurements in air allowed
variation of the composition of the oxide in the range 2.56 ≤ x ≤ 2.81.
Sr2Fe2O5 is an antiferromagnet and undergoes phase transitions to the paramagnetic
state at 692K and from the orthorhombic to the cubic structure
around 1140K.The oxidized formof the ferrite also undergoes a transition
to the high-temperature cubic form.The author proposes a new structural
model for the cubic phase based on a unit cell with the Fm3c symmetry.
The new model allows a description of the high-temperature cubic form of
the ferrite as a solid solution of the composition end members.The results
were used to draw a phase diagramfor the SrFeOx system.
¶
The last chapter summarizes the findings and suggests directions for further research.
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SANFILIPPO, STEPHANE. "Effets des plans de macles sur les propriétés physiques du supraconducteur YBa2Cu3O(7-(delta) : étude sur des échantillons massifs texturés monodomaines." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10300.
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Par quatre methodes de mesures, mesures de courant critique de transport, mesures d'aimantation, mesures de resistivite, et mesures de diffusion de neutrons, un effet important des plans de macles (tb) sur les proprietes supraconductrices d'echantillons d'yba#2cu#3o#7#-#x textures monodomaines est mis en evidence. Les proprietes etudiees sont essentiellement celles le long de l'axe c, avec un champ b evoluant dans les plans ab et faisant un angle variable avec une direction de tb. A t = 77k, l'ancrage des vortex par les plans de macles se traduit pour b 1t par des pics de densite de courant critique selon c (j#c) lorsque est inferieur a un angle critique t8-10. Pour b < 1t, j#c est isotrope car l'ancrage est completement domine par les plans de macles. L'angle d'accommodation devient maximal (t45). Ceci est compatible avec un reseau de vortex qui se decompose en deux sous reseaux, chacun piege par une direction de plans de macles. De plus lorsque b tb, le courant critique suivant c est insensible a l'intensite du champ magnetique jusqu'a 8t. Les plans de macles pourraient induire une supraconductivite heterogene : a forts champs, le courant critique serait domine par le courant circulant pres des tb. La supraconductivite et les proprietes de piegeage apparaissent heterogenes dans nos echantillons des que t < t#l#o#c = 87 k et b > 3t. Pres de t#c, les plans de macles localisent les vortex dans l'etat liquide. Les courbes r() et r(b) indiquent une reduction de resistivite importante lorsque < t. Cet effet se manifeste jusqu'a des champs de 20t. La localisation augmente la coherence de phase dans la direction de b et minimise le depiegeage thermique. Lorsque le piegeage est domine par les defauts etendus, le liquide pourrait geler en un verre appele <<<>verre de bose<>>>. Ceci se traduit en aimantation par une augmentation de la ligne d'irreversibilite lorsque < t et t < t#l#o#c. Les mesures de diffusion de neutrons a 4 k confirment que pour b < 1t, les vortex s'adaptent au reseau de plans de macles et forment un reseau carre lorsque b est suivant l'axe c. Il devient hexagonal pour un angle de desorientation eleve, autour de 50. Les preuves que nous apportons de l'influence des plans de macles sur les proprietes supraconductrices d'ybacuo indiquent que la maitrise de ces defauts au cours de la synthese, pourrait etre importante en vue de certaines applications futures.
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Schwerdtfeger, Michael. "Elaboration et caractérisation de multicouches supraconductrices YBaCuO/LaSrCuO." Grenoble 1, 1993. http://www.theses.fr/1993GRE10179.
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Ce travail est consacre a l'elaboration et a la caracterisation structurale et electrique de multicouches supraconductrices de type yba#2cu#3o#7#-#/la#2#-#xsr#xcuo#4 (ybco/lasrcuo). Deux dopages differents en strontium ont ete choisis afin de separer les couches d'ybco soit par des couches semi-isolantes de la#2cuo#4 (lco) pour x=0, soit par des couches metalliques de la#1#,#8#5sr#0#,#1#5cuo#4 (lsco) pour x=0,15. Le principal objectif de ce travail est donc d'etudier comment l'intercalation de couches de lasrcuo, de nature et d'epaisseur differentes, affecte la dimensionnalite et l'anisotropie de ces systemes. Les echantillons sont elabores par photo-ablation avec un laser excimere d'une longueur d'onde de 248 nm (krf). Une etude prealable, portant sur les proprietes structurales et electriques de couches minces d'ybco, de lco et de lsco, a permis de constituer une base de reference pour l'etude du comportement des multicouches. Les proprietes structurales et morphologiques ont ete analysees par diffraction de rayons x, par rbs et par microscopie electronique. En particulier les figures de poles x ont revele la rotation des axes a et b des couches de lco de 45 par rapport aux axes des substrats de srtio#3. L'etude de la magnetoresistance et des fluctuations de conductance des couches d'ybco a montre que ce compose est moderement anisotrope et qu'il ne presente pas un comportement purement bidimensionnel. La derniere partie de ce memoire est consacree a l'etude des proprietes des multicouches. Ainsi, la diffraction de rayons x a permis de constater la bonne qualite epitaxiale des echantillons, avec une rotation de 45 des axes a et b des couches de lco par rapport aux axes des substrats et des couches d'ybco. Cette etude a egalement revele la presence probable de contraintes aux interfaces entre les couches d'ybco et les couches de lasrcuo. A partir de l'analyse de la transition resistive, des fluctuations de conductance et de la magnetoresistance, il a ete montre que le decouplage des couches d'ybco par des couches de lasrcuo d'epaisseur croissante resulte en un abaissement de la temperature critique, la suppression du passage d'un regime bidimensionnel a un regime tridimensionnel et une anisotropie accrue
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Schmidt, Marek Wojciech. "Phase formation and structural transformation of strontium ferrite SrFeOx." Phd thesis, 2001. http://hdl.handle.net/1885/48187.
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Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical applications in oxygen conducting devices such as pressure driven oxygen generators, partial oxidation reactors in electrodes for solid oxide fuel cells (SOFC). ¶ This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer spectroscopy. Changes in the oxide were induced using conventional thermal treatment in various atmospheres as well as mechanical energy (ball milling). ¶ ...
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Tasi, Jhen-Ming, and 蔡鎮名. "High-Temperature, High-Pressure Hydrothermal and Flux Synthesis, Crystal Structures and Properties of Transition Metal and Lanthanide Silicates." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/85580246397732734352.
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碩士國立中央大學
化學研究所
96
Two series of transition metal and lanthanide silicates. Three metal silicates were synthesized by the high-temperature, high-pressure hydrothermal method. The series A denotes transition metals silicates, Rb2(Nb2O4)(Si2O6)·H2O (A1), Rb2(Nb2O4)(Si2O6) (A2) and Rb2(Ta2O4)(Si2O6)．H2O (A3). Five metal silicates were synthesized by the flux-growth method. The series B denotes lanthanide silicates, Rb2YFSi4O10 (B1), Rb2GdFSi4O10 (B2), Rb2TbFSi4O10 (B3), Rb2Tb0.9Eu0.1FSi4O10 (B4) and Rb2Eu0.67Tb0.33FSi4O10 (B5). All structures of those compounds are determined by single-crystal X-ray diffraction. The purity of each compound was confirmed by the good agreement between observed powder X-ray pattern and the calculated pattern based on single-crystal X-ray diffraction. The properties of these compounds were further characterized by different physical measurements respectively according to their structural features : the dehydration of A1 by thermogravimetric analysis (TGA) and the luminescence spectra of lanthanide silicates. A1 and A3 are isostructural, representing a novel structure. Upon heating to 500 oC, A1 loses the lattice water molecules, while the framework structure retains to give the anhydrous compound A2. If A2 is exposed to air for several hours, the water molecules can be restored based on powder X-ray diffraction, and structure will be changed into A1. All compounds of series B have similar structures, representing a novel structure. These materials have been characterized by photoluminescence spectroscopy, including emission and excitation spectra. Mixed lanthanide samples B4 and B5 have also been prepared and efficient Tb →Eu energy transfer has been observed for B4.
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Chyuan, Chen，Sheng, and 陳勝全. "The crystal structure of triammonium hydrogen disulphate and trisodium hydrogen disulphate at room temperature and phase transition at high temperature." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/78160828330938467935.
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碩士國立師範大學
物理研究所
81
We observe the shape and optic nature of X■H(SO■)■ (X=Na，NH ■) by polarizing microscope．We also study X■H(SO■)■(X=Na， NH■) single crystal both room and high temperature structures by x-ray precession meth- od ．At room temperature Na■H(SO■)■ grows two kinds of single crystal．The one is irregular long shape，the other is swallow twin ．The irregular long sh- ape crystal’s bm axis is lying on (001) surface．We can cut swallow twin by knife into single crystal(as figure 1)．Its shape is parallelogram． Its bm axi- s is perpendicular to crysatl surface．Two kinds of crystal are both optic biaxials． The single crystals’ room temperature structure are monoclinic ． Their space group are P2■/c．When temperature are added． Crystal occurs structural phase transition ．Their space group may turn into P3．(NH■)■H(SO■)■is also single crystal．The shape of (NH■)■H(SO■)■is para- llelogram ． Its cm■axis is perpendicular to (001) surface ．The room temperature structure is monocl- inic with the space group A2/a．When temperature is added to 140℃．It occurs structural phase transition．The space group may turn into R■m．
Book chapters on the topic "High temperature crystal structurephase transition"
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Tiwari, Sandip. "Light interactions with semiconductors." In Semiconductor Physics, 454–92. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198759867.003.0012.
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This chapter examines how electromagnetic waves—light, photons—interact with semiconductors through coupling between the electromagnetic wave and dipoles of various kinds and analyzed via a dipole interaction Hamiltonian. Phenomena in the energy range of micro eV to several eVs are explored, stressing surface interactions, absorption, emission and luminescence. The first involves coupled plasmon interactions. Absorption and emission arise across energy and through multiple mechanisms. Free carrier processes are pronounced for low energy. Direct electron-photon interactions—a direct transition—can involve allowed transitions and forbidden transitions across the gap. Indirect transitions of both these varieties can arise in phonon-assisted processes. Oscillator strength is fleshed out. Field dependence, doping dependence and temperature dependence are analyzed, broadening the discussion to the Franz-Keldysh effect as well as dependence due to impurities, excitons, plasmons and crystal oscillations, to unravel the dielectric function and reflectivity’s behavior at high frequencies and restrahlen often observed.
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Jolivet, Jean-Pierre. "Titanium, Manganese, and Zirconium Dioxides." In Metal Oxide Nanostructures Chemistry. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190928117.003.0011.
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The dioxides of titanium (TiO2), manganese (MnO2), and zirconium (ZrO2) are important materials because of their technological uses. TiO2 is used mainly as white pigment. Because of its semiconducting properties, TiO2, in its nanomaterial form, is also used as an active component of photocells and photocatalysis for self-cleaning glasses and cements . MnO2 is used primarily in electrode materials. ZrO2 is used in refractory ceramics, abrasive materials, and stabilized zirconia as ionic conductive materials stable at high temperature. Many of these properties are, of course, dependent on particle size and shape (§ Chap. 1). Dioxides of other tetravalent elements with interesting properties have been studied elsewhere in this book, especially VO2, which exhibits a metal–isolator transition at 68°C, used, for instance, in optoelectronics (§ 4.1.5), and silica, SiO2 (§ 4.1.4), which is likely the most ubiquitous solid for many applications and uses. Aqueous chemistry is of major interest in synthesizing these oxides in the form of nanoparticles from inorganic salts and under simple, cheap, and environmental friendly conditions. However, as the tetravalent elements have restricted solubility in water (§ 2.2), metal–organic compounds such as titanium and zirconium alkoxides are frequently used in alcoholic solution as precursors for the synthesis of TiO2 and ZrO2 nanoparticles. An overview of the conversion of alkoxides into oxides is indicated about silica formation (§ 4.1.4), and since well-documented works have already been published, these compounds are not considered here. The crystal structures of most MO2 dioxides are of TiO2 rutile type for hexacoordinated cations (e.g., Ti, V, Cr, Mn, Mo, W, Sn, Pb) and CaF2 fluorite type for octacoordinated, larger cations (e.g., Zr, Ce), but polymorphism is common. Some dioxides of elements such as chromium and tin form only one crystalline phase. So, hydrolysis of SnCl4 or acidification of stannate [Sn(OH)6]2− leads both to the same rutile-type phase, cassiterite, SnO2. Many other dioxides are polymorphic, especially TiO2, which exists in three main crystal phases: anatase, brookite, and rutile; and MnO2, which gives rise to a largely diversified crystal chemistry.
Conference papers on the topic "High temperature crystal structurephase transition"
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Vasilyev, Boris. "Stress–Strain State Prediction of High-Temperature Turbine Single Crystal Blades Using Developed Plasticity and Creep Models." In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25229.
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This paper discusses a novel approach to calculating inelastic strain that incorporates elastic anisotropy in combination with ANSYS finite element analysis (FEA) software to predict the stress–strain state kinetics of a single crystal (SX) nickel-based turbine blade. The approach is based on using “equivalent direction” and allows us to correctly define the critical load value and plastic strain field in SX details for different load types. The suggested approach is simple and generic and requires only a few standard experimental material properties. This should allow for an easy transition to actual blade design application. Predictions of plastic field distribution obtained using the suggested approach with anisotropic specimens are compared with experimental data as well as with the results obtained using a crystallographic approach. Good correlation was achieved. The second goal of this study is to develop a physically based, readily implementable creep model SX superalloy that accurately represents the creep phenomena of these materials under complex, thermomechanical loading conditions.
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de Villiers, Johan P. R., Noko Ngoepe, James Roberts, and Alison S. Tuling. "Evaluation of the Phase Composition, Crystallinity and Trace Isotope Variation of SiC in Experimental TRISO Coated Particles." In Fourth International Topical Meeting on High Temperature Reactor Technology. ASMEDC, 2008. http://dx.doi.org/10.1115/htr2008-58208.
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The silicon carbide layers in experimental TRISO coated particles with zirconia kernels were evaluated for their phase composition, their impurity levels and the crystal perfection and twinning of the crystallites in the layers. This evaluation was necessary to compare the different SiC layers and to relate these properties to various quality tests and ultimately to manufacturing parameters in the CVD coater. Identification of the various polytypes was done using electron diffraction methods. This is the only method for the unequivocal identification of the different polytypes. The 3C, and 6H polytypes were positively identified. A feature of the SiC in some samples is the disordered nature of the phase. The disorder is characterised by planar defects, of different width and periodicity, giving rise to streaking in the diffraction pattern along the [111] direction of the 3C polytype. Polarised light microscopy in transmission is a useful tool to easily distinguish between the cubic (beta) and non-cubic (alpha) SiC in the layers. It also provides valuable information about the distribution of these phases in the layers. Raman spectroscopy was used to examine the distribution of Si in the SiC layers of the different samples. Two samples contain elevated levels of Si, of the order of 50%, with the highest levels on the inside of the layers. The elevated Si levels also occur in most of the other samples, albeit at lower Si levels. This was also confirmed by use of SEM electron backscatter analysis. Rietveld analysis using X-ray diffraction is presently the only reliable method to quantify the polytypes in the SiC layer. It was found that the SiC layer consists predominantly (82% to 94%) of the 3C polytype, with minor amounts of the 6H and 8H polytypes. Impurities in the SiC and PyC could be measured with sufficient sensitivity using laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The SiC and PyC layers are easily located from the intensity of the C13 and Si29 signals. In most cases the absolute values are of less concern than the variation of impurities in the samples. Elevated levels of the transition elements Cu, Ni, Co, Cr and Zn are present erratically in some samples. These elements, together with Ag107 and Ag109, correlate positively, indicating impurities, even metallic particles. Elevated levels of these transition elements are also present at the SiC/OPyC (Outer Pyrolytic Carbon) interface. The reasons for this are unknown at this stage. NIST standards were used to calibrate the impurity levels in the coated particles. These average from 1 to 18 ppm for some isotopes.
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Tsukiji, Tetsuhiro, and Shinsuke Tanabe. "Pressure Drop of Liquid Crystal Flowing Between Two Parallel-Plate Electrodes." In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/fed-24921.
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Abstract Liquid crystal is one of homogeneous ER (Electrorheological) fluids in some range of temperature. Transient responses of pressure drop are examined when liquid crystal flows between two parallel-plate electrodes for constant flow rates. When voltages are applied on the liquid crystal and removed, the pressure responses of the inlet of electrodes are measured with the pressure transducer. At the same time, liquid crystal between the transparent electrodes made of glass is visualized with the high-speed video camera to investigate the time history of the director of the liquid crystal. Outlet of the flow channel with two parallel-plate electrodes is atmosphere. Relation between the flow visualization results and changes of pressure drop is investigated especially for transient period. In the present experiment the flow rates change from 0.001cc/sec (velocity is 1mm/sec) to 0.003cc/sec and the electric field intensity is from 0.2kV/mm to 1kV/mm. The gap of the electrodes is 0.2mm. The isotropic-nematic transition is 35.5°C and smectic-nematic transition is 23.1°C. The open-loop test facility with the liquid crystal is set in a pyrostat to keep the temperature constant.
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Zhao, Wanqian. "High Temperature Oxidation Kinetics of Zr-Sn-Nb Alloy and the Effect of Its Oxide Film Growth On Corrosion Resistance." In 2022 29th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icone29-93520.
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Abstract Zirconium-based alloys are widely used for fuel claddings particularly in pressurized water reactor. The high temperature oxidation kinetics of Zr-Sn-Nb alloys in steam in the temperature range of 650°C∼1250°C are studied by a modified thermo-gravimetric analyzer. The oxidation rate exponents and oxidation correlation are calculated. The rate transition of kinetic oxidation for Zr-Sn-Nb occur at 1100°C. The microstructure characteristic of the oxide film formed at 1200°C indicated that the oxide layer is constituted of nanometer exquiaxed grains on the outer surface, columnar grains along perpendicular to the O/M interface and quaisi-equxiaxed grains near the O/M interface. The thickness, crystal distribution and grains size of each layer is measured and analyzed. Furthermore, the correlation among the tetragonal phase fraction, the stress, and the microstructural change of the oxide film is schematized and then analyzed. How to obtain the intact columnar grains structures in the oxide and uniform protective oxide film formation are the key to improve the corrosion resistance of zirconium alloys.
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Stekovic, Svjetlana. "Low Cycle Fatigue of Single Crystal Nickel-Base Superalloy CMSX-4 Coated With a New Coating IC1." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-81065.
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High strength nickel base superalloys have often been used in turbine blades because of their superior performances at high temperatures. One of them is CMSX-4, an ultra high strength, single crystal. CMSX-4 is a second generation rhenium-containing, nickel-base superalloy capable of high temperature and stress operations of at least 1150 °C [1]. The superalloy has limited oxidation and corrosion resistance at the high temperatures and to improve the oxidation and corrosion resistance, the base material is protected with coatings [2]. However, coatings exhibit a ductile-to-brittle transition temperature (DBTT) which causes early cracking of the coating and failure due to fatigue. The paper details low cycle fatigue (LCF) properties and degradation mechanisms of uncoated and IC1 coated single crystal CMSX-4. The tests were performed at two temperatures, 500 °C and 900 °C. Cylindrical solid specimens were cyclically deformed with fully reversed tension-compression loading with total strain amplitude control and at a constant strain rate of 10−4s−5 in air atmosphere without any dwell time. At 500 °C the coating has a detrimental effect on the fatigue life of CMSX-4 while at 900 °C IC1 does improve the fatigue life of the superalloy. The reduction of the fatigue life can be related to early cracking of the coating under its ductile to brittle transition temperature while the beneficial effect of the coating at 900 °C may be due to slower propagation of cracks caused by oxidation at the front of the crack tip.
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Vorobieff, Peter, and Robert E. Ecke. "Flow Structure in a Rayleigh-Bénard Cell Upon Impulsive Spin-Up." In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-1243.
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Abstract We investigate convection in a cylindrical Rayleigh-Bénard cell with radius-to-height ratio Γ = 1/2. The cell is subjected to impulsive spin-up about its vertical axis. We use TLC (thermochromic liquid crystal) for temperature field measurements and PIV (particle image velocimetry) for the velocity reconstruction of the transition in the range of Rayleigh numbers R from 5 × 107 to 5 × 108 and dimensionless rotation rates Ω from 0 up to 8 × 104. The initial (at rest) and the final (in steady rotation) states of the system are those of turbulent convection. The most persistent transient feature is a sharply defined ringlike pattern characterized by a decrease in temperature, axial velocity directed downward and high azimuthal shear. The latter leads to formation of an azimuthally regular structure of Kelvin-Helmholz vortices. During the final stage of the transition, this vortical structure loses azimuthal regularity and an irregular pattern of vortices characteristic of turbulent rotating convection forms.
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Lakshminarasimhan, M. S., D. K. Hollingsworth, and Larry C. Witte. "Boiling Incipience in Narrow Channels." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1506.
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Abstract Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 1 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mass flux varied from 60 to 4586 kg/(m2s). The inlet subcooling varied from 3.0 to 15.3 °C, and the inlet pressure ranged up to 0.20 MPa. Liquid crystal thermography was used to measure distributions of surface temperature from which the heat transfer coefficients on the heated surface were calculated. Observations of the boiling incipience superheat excursion and the hysteresis phenomenon are presented and discussed. In laminar flow, a boiling front was observed that clearly separated the region cooled by single-phase convection from the region experiencing nucleate boiling. A prediction for the wall temperature and heat flux at boiling incipience based on nucleation theory compared favorably with the data. An incipience turning angle was defined to describe the transition process from the point of incipience to fully developed nucleate boiling. Fully developed saturated nucleate boiling was correlated well by Kandlikar’s technique.
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Takauchi, Hideaki, Tomoaki Nakanishi, and Hidenori Nako. "Welding Consumables for 2.25Cr-1Mo-V Refining Reactors." In ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65640.
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Owing to the demands for larger-capacity reactor vessels in petroleum plants and higher temperature processes for the upgrade of heavy oil, enhanced 2.25Cr-1Mo, 2.25Cr-1Mo-V and 3Cr-1Mo-V steels, which suit both high temperatures and pressure operations, have been developed and used for heavy-wall pressure vessels since the 1990s. 2.25Cr-1Mo-V steel, which has very special mechanical properties, resistant to both hydrogen attack and embrittlement under high temperatures and pressure environments in particular, has been used since 2000. The specifications for 2.25Cr-1Mo-V steel pressure vessels, such as ASME Sec. VIII and API RP 934-A, have been established and reviewed to enhance the contents [1–2]. In this report, the transition of materials, the welding techniques for hydrocracking reactors and 2.25Cr-1Mo-V welding materials are introduced. Particularly, for these welding materials, in order to improve the creep rupture and temper embrittlement properties, the effectiveness of precipitates is discussed. It was found that fine carbide (MC) in crystal grains improves creep rupture lifetime and MC at the prior austenite (γ) grain boundaries inhibits temper embrittlement caused by the segregation of impurities.
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Zhuang, Shiqiang, Xuan Shi, and Eon Soo Lee. "A Review on Non-PGM Cathode Catalysts for Polymer Electrolyte Membrane (PEM) Fuel Cell." In ASME 2015 13th International Conference on Fuel Cell Science, Engineering and Technology collocated with the ASME 2015 Power Conference, the ASME 2015 9th International Conference on Energy Sustainability, and the ASME 2015 Nuclear Forum. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/fuelcell2015-49602.
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In recent years, people attach high attention to the energy problem owing to the energy shortage of the world. Since the price of energy resources significantly increases, it is a necessary requirement to develop new alternative sources of energy to replace non-renewable energy resources. Polymer electrolyte membrane (PEM) fuel cell technology is one of the promising fields of clean and sustainable power, which is based on direct conversion of fuel into electricity. However, at the present moment PEM fuel cell is unable to be successful commercialization. The main factor is the high cost of materials in catalyst layer which is a core part of PEM fuel cell. In order to reduce the overall system cost, developing active, inexpensive non-platinum group metal (non-PGM) electrode catalysts to replace currently used Platinum (Pt)-based catalysts is a necessary and essential requirement. This paper reviews several important kinds of non-PGM electro-catalysts with different elements, such as nitrogen, transition metal, and metal organic frameworks (MOF). Among these catalysts, transition metal nitrogen-containing complexes supported on carbon materials (M-N/C) are considered the most potential oxidation reduction reaction (ORR) catalysts. The main synthetic methods are high temperature heat treating (800–1000°C). The mechanical and electrochemical properties of the final product will be analyzed by several characterization methods. For example, a RRDE test will be used to measure electron transfer number and ORR reactivity, which are the most important electrochemical properties of the new catalyst. And the morphology, particle size, crystal phase and specific surface area can be analyzed with SEM, TEM, XRD and BET methods. Although great improvement has been achieved in non-PGM catalyst area of research, there are still some challenges in both ORR activity and stability of non-PGM catalysts. Consequently, how to improve the ORR activity and stability are the major challenge of non-PGM catalyst research and development. Based on the results achieved in this area, our future research direction is also presented and discussed in this paper.
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Curtin, Paul R., Steve Constantinides, and Patricia Iglesias Victoria. "Fracture Toughness of Samarium Cobalt Magnets." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53435.
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Samarium Cobalt (SmCo) magnets have been the magnet of choice for a variety of industries for many years due to their favorable magnetic properties. Their high coercivity, combined with a low temperature coefficient, make them the ideal permanent magnet for demanding high temperature applications. One of the biggest concerns with rare earth magnets is their brittleness. Samarium Cobalt magnets in particular are prone to fracturing during machining and assembly. In manufacturing, great care must be taken to avoid chipping or fracturing these magnets due to their brittle nature. There are two main grades of Samarium Cobalt magnets, 1:5 and 2:17. These ratios define the nominal ratio of rare earth to transition metal content. In this paper, an investigation is performed on the fracture toughness of permanent magnets based on the Samarium Cobalt 2:17 composition. Various techniques are used to characterize the microstructure of the material, and quantify the material properties. Optical microscopy is used to characterize the grain structure of the material and quantify the porosity of the material after sintering. By comparing the average grain size and fracture toughness of several samples, grain size was shown to not affect fracture toughness in standard material. Latent cracks in defective material showed no preference to follow grain boundaries, oxides inclusions or voids. River marks in fracture surfaces are seen through scanning electron microscopy, confirming the transgranular cracking pattern seen by Li et al [1]This suggests that the toughness of the material is an inherent property of the main phase, not of grain boundaries or contaminants. Samarium Cobalt magnets exhibit both mechanical and magnetic anisotropy due to the alignment of their crystal structure in the manufacturing process. Using Palmqvist indentation crack techniques, the magnetic orientation of the grains was seen to greatly influence the direction of crack propagation from the tip of the indenter. Measurements of fracture toughness using this technique produce highly scattered data due to this anisotropic nature of the material. Specimens loaded with the indenter axis parallel to the direction of orientation show normal Palmqvist cracks, while specimens loaded perpendicular to the direction of magnetization exhibit crack propagation initiating from the faces of the indenter. To better quantify the material’s brittleness, fracture testing is performed on specially prepared samples to obtain an absolute measure of fracture toughness (K1c). Results show that SmCo is measurably weaker than other magnetic materials such as neodymium iron boron magnets[2]. Furthermore, neither relative concentration of Samarium nor source of raw material show notable effect on the fracture toughness of the material.