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1
Miller, Wayne. "Negative Thermal Expansion Materials." Thesis, University of Exeter, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531676.
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Hansen, Glenn Alexander. "TWO ULTRAPRECISE THERMAL EXPANSION INVESTIGATIONS: SODIUM SILICATE - A LOW-EXPANSION CEMENT, AND THERMAL EXPANSION UNIFORMITY OF ZERODUR." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291814.
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Maksimova, E. M., and A. I. Zamkovskaya. "Visualization of Thermal Crystals Expansion." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/40672.
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Greyling, Guillaume Hermanus. "Negative thermal expansion of organic compounds." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/6896.
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Thesis (MSc)--Stellenbosch University, 2011.ENGLISH ABSTRACT: The primary objective of the work was to investigate the negative thermal expansion of organic materials and to determine the mechanisms governing this phenomenon by using the principles of crystal engineering. To this end, the following three compounds were studied in detail: • 4,4'-Diiodobiphenyl • 4-Iodobenzoic acid • Methyl Paraben The rationale behind this work was to determine the mechanisms responsible for the observed negative thermal expansion and to uncover the structural factors that induce negative thermal expansion. Single-crystal X-ray diffraction was employed as the primary analytical tool, owing to the unique information it can provide regarding intermolecular interactions in the solid state. A total of twenty organic compounds were analysed, of which three exhibited negative thermal expansion. Each compound employs a specific mechanism for negative thermal expansion, two of which are closely related and the third distinct.
AFRIKAANSE OPSOMMING: Die hoof doel van hierdie studie was om ondersoek in te stel in die verskynsel van ‘negative thermal expansion’ in organiese materiale en gevolglik die meganisme vas te stel deur die beginsels van kristalmanipulsie (‘crystal engineering’) te gebruik. Gevolglik was drie organise stowwe ondersoek: • 4,4'-Diiodobiphenyl /4,4'-Diiodobifeniel • 4-Iodobenzoic acid /4-Iodobensoësuur • Methyl Paraben Die redenasie hieragter is om die meganisme verantwoordelik vir die ‘negative thermal expansion’ vas te stel en die verskillende faktore wat bydra tot dit te bevestig. Enkel-kristal diffraksie word benut as die primêre analitiese tegniek as gevolg van die unieke inligting wat verkry kan word met betrekking tot die intermolekulêre interaksies. 'n Totaal van twintig stowwe is geanaliseer waarvan drie die spesifieke termisie eienskap besit. Elk van die drie stowwe het ‘n ander meganisme te vore laat kom waarvan twee baie ooreenstem en die derde verskil.
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Tu, Jie. "Thermal expansion of chemically modified mullite." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43063.
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Solid-state reaction and sol-gel, processing techniques were used extensively to form
chemically-modified mullite solid solutions in an effort to lower their thermal expansion
coefficients. TiO2, B203, CrPO4, P205, Ga203, Cr203, and WO3 and the half-breed
Si02 compounds AlPas, BPO4, GaPO4, BAsO4, AIAsO4, GaAsO4, and Ge02 were chosen as the modifiers.
The results indicate that, apart from Ti02, none of the substitutions made in mullite
significantly change the thermal expansion properties. The solubility of 3 wt% TiO2 in
mullite reduces the coefficient of thermal expansion by about 10%; That corresponds
to a reduction in A1203/Si02 molar ratio ( < 1.5) compared to stoichiometric mullite
(3A1203â ¢2Si02). The formation of Ti02-modified mullite depends on processing condition and heat treatment.
The possible mechanism of lowering the CTE of mullite by the addition of TiO2 is discussed in terms of the bond strength. The axial expansion of a Ga203-modified
mullite was measured' up to 1200°C to show that the expansion is increased along the c-axis compared with that of the stoichiometric mullite.Master of Science
6
Greve, Benjamin K. "Exploring the thermal expansion of fluorides and oxyfluorides with ReO₃-type structures: from negative to positive thermal expansion." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43753.
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This thesis explores the thermal expansion and high pressure behavior of some materials with the ReO₃ structure type. This structure is simple and has, in principle, all of the features necessary for negative thermal expansion (NTE) arising from the transverse thermal motion of the bridging anions and the coupled rotation of rigid units; however, ReO₃ itself only exhibits mild NTE across a narrow temperature range at low temperatures. ReO₃ is metallic because of a delocalized d-electron, and this may contribute to the lack of NTE in this material. The materials examined in this thesis are all based on d⁰ metal ions so that the observed thermal expansion behavior should arise from vibrational, rather than electronic, effects.
In Chapter 2, the thermal expansion of scandium
fluoride, ScF₃, is examined using a
combination of in situ synchrotron X-ray and neutron variable temperature diffraction. ScF₃ retains the cubic ReO₃ structure across the entire temperature range examined (10-1600 K) and exhibits pronounced negative thermal expansion at low temperatures. The magnitude of NTE in this material is comparable to that of cubic ZrW₂O₈, which is perhaps the most widely studied NTE material, at room temperature and below. This is the first report of NTE in an ReO₃ type structure across a wide temperature range.
Chapter 3 presents a comparison between titanium oxyfluoride, TiOF₂, and a vacancy containing titanium hydroxyoxyfluoride, Tiₓ(O/OH/F)₃. TiOF₂ was originally reported
to adopt the cubic ReO₃ structure type under ambient conditions, therefore the initial
goal for this study was to examine the thermal expansion of this material and determine
if it displayed interesting behavior such as NTE. During the course of the study, it was
discovered that the original synthetic method resulted in Tiₓ(O/OH/F)₃, which does adopt
the cubic ReO₃ structure type. The chemical composition of the hydroxyoxyfluoride is
highly dependent upon synthesis conditions and subsequent heat treatments. This material
readily pyrohydrolyizes at low temperatures (~350 K). It was also observed that TiOF₂ does not adopt the cubic ReO₃ structure; at room temperature it adopts a rhombohedrally
distorted variant of the ReO₃ structure. Positive thermal expansion was observed for TiOF₂
from 120 K through decomposition into TiO₂. At ~400 K, TiOF₂ undergoes a structural
phase transition from rhombohedral to cubic symmetry. High pressure diffraction studies
revealed a cubic to rhombohedral phase transition for Tiₓ(O/OH/F)₃ between 0.5-1 GPa.
No phase transitions were observed for TiOF₂ on compression.
In Chapter 4, an in situ variable pressure{temperature diffraction experiment examining the effects of pressure on the coefficients of thermal expansion (CTE) for ScF₃ and TaO₂F is presented. In the manufacture and use of composites, which is a possible application for low and NTE materials, stresses may be experienced. Pressure was observed to have a negligible effect on cubic ScF₃'s CTE; however, for TaO₂F the application of modest pressures, such as those that might be experienced in the manufacture or use of composites, has a major
effect on its CTE. This effect is associated with a pressure-induced phase transition from
cubic to rhombohedral symmetry upon compression. TaO₂F was prepared from the direct
reaction of Ta₂O₅ with TaF₅ and from the digestion of Ta₂O₅ in hot hydro
uoric acid. The
effects of pressure on the two samples of TaO₂F were qualitatively similar. The slightly
different properties for the samples are likely due to differences in their thermal history
leading to differing arrangements of oxide and
uoride in these disordered materials.
In Chapter 5, the local structures of TiOF₂ and TaO₂F are examined using pair distribution
functions (PDFs) obtained from X-ray total scattering experiments. In these materials,
the anions (O/F) are disordered over the available anion positions. While traditional X-ray
diffraction provides detailed information about the average structures of these materials,
it is not suffcient to fully understand their thermal expansion. Fits of simple structural
models to the low r portions of PDFs for these materials indicate the presence of geometrically
distinct M{X{M (M = Ti, Ta; X = O, F) linkages, and a simple analysis of the TaO₂F variable temperature PDFs indicates that these distinct links respond differently to temperature.
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Ruschman, Chad. "Chemical tuning of thermal expansion in oxides." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34778.
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This work focuses on the chemical substitution of cations and anions in the frameworks of materials that have been known to exhibit negative thermal expansion (NTE). Zr2(PO4)2(SO4) is a member of the A(2)M(3)O(12) family which has been known to exhibit NTE. We have shown that Zr2(PO4)2(SO4) exhibits anisotropic positive thermal expansion. We have also shown that this material has been characterized in the wrong space group. Hf2(PO4)2(SO4) behaves similarly to Zr2(PO4)2(SO4) and follows this trend. Under pressure, Hf2(PO4)2(SO4) appears to undergo a phase transition. We have still yet to determine what space group the materials transitions to. While many members of the AX(2)O(7) family of frameworks have been fully characterized, the thermal expansion of PbP2O7 has yet to be reported. We were unable to obtain a reproducible procedure for synthesis of PbP2O7 from its precursor. Finally, variable temperature and variable pressure studies were performed on ZrMo2O8 in an attempt to learn more about the local structure. We found that space groups P213 and Pa-3 gave poor fits of the local structure at low r. Behavior of the nearest neighbor Zr-Mo distance was very similar to the bulk CTE. On compression, pressure induced amorphization is observed in ZrMo2O8. All interatomic correlations above 4 angstroms are washed out. Zr-O-Mo linkages remain well defined and do not massively deform as the pressure is increased. Finally, we we observed that Zr-O-Mo linkages change geometry reversibly as the pressure is increased.
8
Mackenzie, D. S. "Modeling negative thermal expansion in network structures." Thesis, University of Exeter, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441808.
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Rimmer, Leila Heather Najla. "Negative thermal expansion in flexible framework materials." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707927.
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Lind, Cora. "Negative thermal expansion materials related to cubic zirconium tungstate." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/30861.
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Wang, Liran. "Thermal expansion and magnetostriction studies on iron pnictides." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-39895.
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In this work, a 3-terminal capacitance dilatometer was set up and used for measurements of the thermal expansion and magnetostriction of novel superconducting iron pinictides and related materials. In particular, \re~with R\,=\,La, Ce, Pr, Sm, Gd, \laf~and Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ have been investigated.
The data on polycrystalline \laf~are the first published thermal expansion data on this material. The lattice effects at the structural and the magnetic phase transition have been investigated and the phase diagram upon F-doping has been studied. A main result is the observation of a previously unknown fluctuation regime for the doping level $\mathnormal{x}\leqslant$ 0.04 over a large $T$ range above the structural transition temperature \ts. The absence of any structural anomalies in the normal state of the superconducting \laf~samples with $\mathnormal{x}\geqslant$ 0.05 corroborates the discontinuous character of the phase boundary not only for the magnetism but also for the structural degrees of freedom.
Similarly, the presence of high-temperature fluctuations is found for all \re~undoped materials under study. The discussion of the probable origin of the fluctuations as well as the definition of the structural transition temperature \ts~are done. The low temperature features shown by the thermal expansion data for \re~are caused by the onset of long range magnetic order of the $4f$-moments and their different configurations. In particular, \pr, which has a very pronounced anomaly associated with Pr-ordering exhibits a large magnetostriction at low temperatures. By discussing this effect along with the magnetization, resistivity and other measurements, it is found that this large magneto-elastic effect may originate from the correlations between the momentum from Fe$^{3+}$ and Pr$^{3+}$.
Last, the thermal expansion of Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ 122 single crystals is investigated. Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ is one of the first materials where single crystals are available. The thermal expansion results on the undoped compound with $x=0$ show a large anomaly at the combined magnetic and structural transition which is far sharper than that for polycrystalline systems. Upon doping, both transitions are suppressed and their splitting is visible in the thermal expansion data.
The high precision thermal expansion and magnetostriction results presented in this work are among the first data on the novel family of iron-based superconductors. A valuable insight in the respective ordering phenomena and the thermodynamic properties is provided.
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Lu, Xiao-Gang. "Theoretical modeling of molar volume and thermal expansion." Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-252.
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SANO, MONICA ARI. "SYNTHESIS AND CHARACTERIZATION OF LOW THERMAL EXPANSION OXIDES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=11333@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORMateriais que apresentam expansão térmica baixa ou negativa possuem grande potencial de emprego em diversas aplicações que requerem resistência ao choque térmico, assim como para aplicações odontológicas, em placas de circuitos eletrônicos, em componentes ópticos e para produzir compósitos em que compensam a expansão térmica positiva de outros materiais. Por este motivo, o estudo e a produção de materiais com expansão térmica controlada têm crescido nos últimos anos. No presente trabalho, foram estudadas algumas famílias de óxidos com estruturas que apresentam este tipo de comportamento. Foi avaliada a expansão térmica em três sistemas da família A2M3O12 com o intuito de produzir materiais com expansão térmica controlada pela substituição química do cátion A pelos cátions Al, Cr e Fe. Os sistemas produzidos foram: Cr2xFe2-2xMo3O12 (molibdato de cromo - ferro), Al2xCr2- 2xMo3O12 (molibdato de alumínio - cromo) e Al2xFe2-2xMo3O12 (molibdato de alumínio - ferro). Além destes, o composto HfMgMo3O12 foi também sintetizado para testar a viabilidade de substituição dos cátions A trivalentes por um cátion divalente e um tetravalente. Foi possível obter soluções sólidas monofásicas e seus parâmetros de rede variam linearmente com o aumento no conteúdo do cátion de maior tamanho, conforme a lei de Vegard. Análise térmica realizada por DSC permitiu determinar a temperatura de transição de fase da estrutura monoclínica (P21a) à ortorrômbica (Pbcn). Os valores encontrados foram: para o Al2Mo3O12, 200oC, para o Cr2Mo3O12 , 403oC e para o Fe2Mo3O12, 512oC. Coeficientes de expansão térmica intrínsecos foram determinados por difração de raios-X utilizando luz síncrotron, encontrando-se valores bem reduzidos para todos os sistemas estudados, a saber: para o Al2Mo3O12, (alfa)l = 2,32 x 10- 6/oC, para o Cr2Mo3O12 , (alfa)l = 0,65 x 10-6/oC e para o Fe2Mo3O12, (alfa)l = 1,72 x 10-6/oC.
Negative and low thermal expansion materials have important potential applications as resistance to thermal shock, as well as, for odontological applications, printed circuit boards, optical components and to produce composites to compensate the positive thermal expansion of materials. For this reason, the study and production of materials with controlled thermal expansion have increased in the recent years. In the present work, some oxide families with structures that present this type of behavior were investigated. The thermal expansion in three systems of A2M3O12 family was evaluated in order to produce materials with controlled thermal expansion through the chemical substitution of cation A with Al, Cr and Fe. The produced systems were: Cr2xFe2-2xMo3O12 (chromium - iron molybdate), Al2xCr2-2xMo3O12 (chromium - aluminum molybdate) and Al2xFe2-2xMo3O12 (aluminum - iron molybdate). Besides that, HfMgMo3O12 was synthesized to test the viability of substitution of trivalent cations for one divalent plus one tetravalent. It was possible to obtain single- phase solid solutions and their lattice parameters increased linearly with the increase of the largest cation content, following the Vegard`s law. Thermal analysis carried out by DSC allowed the determination of the phase transition temperature from monoclinic (P21a) to orthorhombic (Pbcn) structure. The values were 200oC for Al2Mo3O12, , 403oC for Cr2Mo3O12 , and 512oC for Fe2Mo3O12. Intrinsic thermal expansion coefficients were determined by X-rays diffraction using syncrotron radiation, and low values were found for all studied systems: (alfa)1 = 2,32 x 10- 6/oC for Al2Mo3O12, (alfa)1 = 0,65 x 10-6/oC for Cr2Mo3O12 , and (alfa)1 = 1,72 x 10-6/oC for Fe2Mo3O12.
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Stolk, Jonathan Douglas. "Development of low thermal expansion, high conductivity nanocomposites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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SCANDOLO, LORENZO. "Thermal expansion of mantle mineral inclusions in diamonds." Doctoral thesis, Università degli studi di Pavia, 2016. http://hdl.handle.net/11571/1203287.
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The aim of this PhD thesis is to provide new constraints on the thermoelastic behavior of some minerals phases frequently occurring as inclusions in diamonds. Knowledge of the thermoelastic properties of minerals is a fundamental requirement to enable the estimate of the entrapment pressures for host-inclusion pairs using elastic geobarometry. As it will be shown in the present study precision and accuracy in determining the thermoelastic coefficients can strongly affect the results in terms of calculated entrapment pressures. The new measurements performed on pyroxenes and garnets will be used here also to illustrate the importance of using consistent and homogeneous compressibility and thermal expansion dataset determined using the same measurements protocols on a single sample. This approach allows us to obtain a complete set of thermoelastic coefficients to reliably describe the behavior of a crystalline phase at high-P and T.
A new micro-furnace developed by our research group here at the Department of Earth and Environmental Sciences at the University of Pavia has been described . The furnace allows to perform in situ single-crystal X-ray diffraction experiments at high temperature up to 1200K. The combined use of a K-type small diameter thermocouple together with mineral phases with well characterized lattice expansion (allowed us to determine a very accurate temperature calibration from room temperature to about 1273 K. Furthermore, we could evaluate thermal gradients and stability while performing a simulated experiment.
Thermal expansion behavior from room T to 1073 K of two Pbca orthopyroxene samples has been investigated, donpeacorite and enstatite. The investigation has been performed by single-crystal X-ray diffraction. Data demonstrated that there is no difference in the volume thermal expansion coefficient as a function of composition. The negligible effect of the Fe-Mn substitution on the bulk thermal expansion allows a strong simplification when elastic geobarometry is applied to orthopyroxenes. In fact, even though the compressibility effect is still not known, it is certain that the nearly identical thermal expansion coefficients will not affect the calculated entrapment pressure (Pe).
The elastic behaviour of synthetic single crystals of grossular garnet has been studied in situ as a function of pressure and temperature separately. The same data collection protocol has been adopted to collect both the pressure-volume (P-V) and temperature-volume (T-V) datasets in order to make the measurements consistent with one another. The consistency between the two datasets allows simultaneous fitting to a single pressure-volume-temperature equation of state (EoS).
The evaluation of the possible role of iron oxidation on the lattice parameters thermal expansion for Fe-rich aluminosilicate garnets. The oxidation state of the two garnets recovered after the high-T single crystal X-ray diffraction experiments performed under different fO2 conditions has been evaluated using single-crystal Mössbauer spectroscopy. Mössbauer data confirmed that no oxidation occurs for the Fe-rich garnets up to at least about 1100 K neither for the “no buffer” nor for the “iron-wustite” buffered sample. The thermal expansion data nearly identical (within 2 e.s.d.’s) one to another indicates that there is no evident effect of the different fO2 conditions in the vial on the thermal expansion behavior.
The resulting thermal expansion coefficients and bulk moduli have been combined for each composition into a single pressure-volume-temperature equation of state that allowed us to compare the thermoelastic properties measured on the eclogitic garnet with those calculated from the endmembers EoS. The remarkable agreement between the calculated and measured thermoelastic coefficients will enable us to calculate EoS coefficients and in turn entrapment pressures for virtually any aluminosilicate garnet occurring in diamonds.
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White, Kathleen Madara. "Low Temperature Synthesis and Characterization of Some Low Positive and Negative Thermal Expansion Materials." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11582.
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LOW TEMPERATURE SYNTHESIS AND CHARACTERIZATION OF SOME LOW POSITIVE AND NEGATIVE THERMAL EXPANSION MATERIALS
Kathleen Madara White
151 pages
Directed by Dr. Angus P. Wilkinson
Low temperature non-hydrolytic sol-gel synthesis was used to explore the possibility of lowering the crystallization temperatures of some known AIVMV2O7 compounds. Crystallization temperatures for ZrP2O7 and ZrP2O7 were unaffected by the use of non-hydrolytic sol-gel methods; however, successful synthesis of these compounds broadens the range of materials that can be produced using this method and suggests the possibility of synthesizing solid solutions (or composites) including ZrP2O7 or ZrV2O7.
This research presents for the first time the direct synthesis of ZrP2O7 from separate zirconium and phosphorus starting materials using mild autoclave methods.
Characterization of some AIVMV2O7 compounds, using lab and high resolution synchrotron powder XRD, led to the assignment of a new symmetry for CeP2O7 and to the suggestion that the reported structure for PbP2O7 was inadequate. Studies using in situ high temperature lab and synchrotron powder XRD for PbP2O7 and CeP2O7 provided the opportunity to report their thermal properties for the first time, and to compare their behavior to that of some other AIVMV2O7. High pressure diffraction measurements on CeP2O7 provided data for the estimation of bulk moduli and suggested two possible pressure-induced phase transitions.
A broad range of MIIIMVP4O14 compounds were prepared using low temperature hydrolytic sol-gel synthesis. Thermal studies revealed nearly linear trends in CTEs and lattice constants with respect to the sizes of MIIIMV cations. Some lower ionic radii compounds had CTEs comparable to that of ZrP2O7 at low temperature, suggesting a similar superstructure. Three compounds were found to exhibit temperature-induced phase transitions.
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Okada, Yoshio 1928. "The thermal expansion coefficient of polypropylene and related composites /." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56778.
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The variability of thermal expansion coefficients during the molding of plastics causes the development of frozen thermal stresses in the molded parts. Also, the distribution of thermal expansion coefficients of the material in the molded part plays an important role in controlling shrinkage and warpage. In turn, the distribution of linear thermal expansion coefficients (LTECs) depends on the distributions of crystallinity and orientation in the part. In the case of fibre reinforced polymers, the distributions of fibre concentration and orientation are also important.In this project, a model has been proposed for estimating the LTEC of fibre reinforced plastics as a function of crystallinity, matrix orientation, and fibre concentration and orientation. Also, extensive data have been obtained regarding the LTEC of polypropylene with and without fibre reinforcement. Extruded pellets and injection molded parts were considered. Model predictions have been compared with experimental data.
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Pulham, R. J. "High resolution thermal expansion studies of some magnetic materials." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382186.
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Dolgusheva, E. B., and V. Yu Trubitsin. "Lattice Parameters and Thermal Expansion of Zirconium Thin Films." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35222.
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Using the molecular-dynamics method with many-body potential of interatomic interaction we have studied the polymorphism of zirconium thin films. The conditions for stability of metastable bcc(001) and fcc Zr films are determined at constant zero pressure. The dependences of the lattice parameters and thermal expansion coefficients on the temperature and thickness of bcc, fcc and hcp Zr films are calculated. The peculiarities of their variation near structural transformations are discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35222
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Haverty, Maureen. "The microstructure, texture and thermal expansion of nuclear graphite." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/the-microstructure-texture-and-thermal-expansion-of-nuclear-graphite(5fef7053-d4ca-42b8-a203-d5b2e6d5bedc).html.
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It is proposed to continue operating the graphite moderated Advanced Gas-cooled Reactor (AGR) fleet past its design life. Nuclear graphite's properties change in reactor and our limited mechanistic understanding of the relationship between graphite structure, across different lengthscales, and its properties limits our ability to predict its future behaviour. An improved understanding of the relationship between graphite's structural features, the relationship between features across different lengthscales and their effect on material properties would all contribute to a mechanistic understanding of graphite behaviour. Thermal expansion generates thermal strains and stresses in the graphite core during thermal transients, such as during reactor start-up and shut-down. Thermal expansion is a function of graphite crystal thermal expansion, crystallographic preferred orientation and microstructure, although the exact relationship between these is not understood. It is also altered by neutron irradiation. This thesis investigates graphite microstructure, virgin and irradiated, and its crystallographic preferred orientation, specifically as they pertain to thermal expansion. The microstructure of British nuclear graphites PGA and Gilsocarbon, used in the Magnox and AGR fleet respectively, have been investigated using scanning electron microscopy (SEM). Trepanned AGR graphite, that is, graphite drilled from the reactor brick during routine inspection is examined. These samples are from the 2012 Hinkley Point B inspection campaign and are taken from several points through the brick thickness. This provides a 'snap shot' of current AGR graphite condition. Deep trepan samples removed from further into the brick thickness are observed for the first time. Neutron damage was observed in Magnox graphite, irradiated in an inert environment in the material test reactor programme INEEL. The spatial variation in texture of PGA and Gilsocarbon, and the change in such texture after prestress was observed using synchrotron x-ray diffraction. Numerical models were used to identify the required texture change to produce changes in CTE, observed by other authors, during in-situ stress. PGA filler lamellae are arranged in parallel arrays and Gilsocarbon's smaller platelets are arranged in bunched clusters. Severe radiolytic oxidation is observed at all trepan locations, with oxidation decreasing away from the fuel. Radiolytic oxidation occurs at platelet edges. Texture measurements have indicated that PGA graphite exhibits significant spatial variation in texture. Gilsocarbon exhibits less variation but the variation observed is large enough to cause increased thermal stresses. Texture measurements of prestressed graphite have indicated that texture changes also vary spatially. Texture results and SEM observations indicate that spatial variation in texture is caused by spatial variation in microstructure. Changes to the filler particle during prestress may alter local texture. These results indicate there is a link between nuclear graphite's microstructure and its texture. The texture, a function of lamellae or platelet arrangement, determines its thermal expansion. Spatial variations in microstructure formed during manufacturing leads to spatial variations in CTE and possibly other texture sensitive properties, such as dimensional change. Deformation of the lamellae or platelets during stress; thermal creep or irradiation creep is expected to contribute to the observed change in properties associated with these stimuli.
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Johnson, Jeffrey Keith. "Concrete bridge deck behavior under thermal loads." Thesis, Montana State University, 2005. http://etd.lib.montana.edu/etd/2005/johnson/JohnsonJ0805.pdf.
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Rassi, Erik Michael. "An inverse approach to coefficient of thermal expansion optimization in optical structures." Thesis, Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/rassi/RassiE1207.pdf.
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Sakyi-bekoe, Kwame Opare Schindler Anton K. "Assessment of the coefficient of thermal expansion of Alabama concrete." Auburn, Ala, 2008. http://hdl.handle.net/10415/1435.
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Kutukcu, Mehmet Nuri. "Synthesis and Characterization of Low and Negative Thermal Expansion Materials." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7636.
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The preparation and thermophysical properties of some In(I), Ga(I) and Ag(I) substituted NZP type materials were explored. Many compositions with the NZP framework show low and negative thermal expansion.
Previously reported material, GaZr2(PO4(3, transforms from one NZP related phase into another NZP type phase due to oxidation under air above 300oC. In addition, it exhibits hysteresis under inert atmosphere; the cell parameters are different on heating and cooling cycles for a given temperature. The synthesis, and characterization of a new material, InZr2(PO4)3, is outlined. It crystallizes in space group R -3 c. In addition, as GaZr2(PO4)3, it oxidizes above 300oC under air and exhibits hysteresis under inert atmosphere. Furthermore, the synthesis of AgTixZr2-x(PO4)3 solid solution compositions, their ion exchange characteristics with Ga(I) and their thermophysical properties are described. Thermal expansion anisotropy (the difference between a and c ) of the solid solutions decreases as the bigger ion, Zr4+, is substituted by the smaller one, Ti4+. Thermal expansion characteristics of GaZr2(PO4)3, InZr2(PO4)3 and AgZr2(PO4)3 are compared with MZr2(PO4)3 ( M = Li, Na, K, Rb, Cs). Ionic radii for Ga(I) and In(I) in a six coordinate oxygen environment were proposed.
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Kulkarni, Raghav Shrikant. "Characterization of carbon fibers: coefficient of thermal expansion and microstructure." Texas A&M University, 2004. http://hdl.handle.net/1969.1/3073.
Full textAbstract:
The focus of the research is to develop a consistent and repeatable method to
evaluate the coefficient of thermal expansion (CTE) of carbon fibers at high
temperatures. Accurate measurement of the CTE of carbon fibers is essential to
understand and develop optimal processing procedures as well as computational
simulations to predict properties and allowables for fiber-reinforced composites. The
mismatch between the coefficient of thermal expansion of the fiber and the matrix has a
profound impact on the development of residual stresses and the subsequent damage
initiation and progression, potentially diminishing the performance of composite
structures.
In situ transmission electron microscopy (TEM) is selected to perform the
experimental work on account of the high resolution and the capability of evaluating
both the longitudinal and transverse CTE. The orthotropy in the CTE is tested by
rotating the fibers through 45° about their axis. The method is validated by testing
standard tungsten filaments of known CTE. Additionally, the microstructure of the fibers
is studied in a field emission scanning electron microscope as well as through selected
area diffraction patterns in a TEM to observe presence of any potential orthotropy. The
pitch based P55 fiber revealed a cylindrically orthotropic microstructure, but the PAN
based IM7 and T1000 fibers did not reveal any orthotropy. Finite element models of
hexagonally arranged IM7 fibers in a 977 epoxy matrix are developed using PATRAN
and analyzed using the commercial FEA code ABAQUS 6.4. The fiber properties were
considered temperature independent where as the matrix properties were varied linearly
with temperature. The lamina properties evaluated from the finite element modeling are
in agreement with the experimental results in literature within 10% in the temperature
range of room temperature to the stress free temperature of the epoxy, however at
cryogenic temperatures the difference is greater. The residual stresses developed during
processing of the composite indicated a potential location for fiber matrix debonding to
be in the matrix dominant regions.
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Lemieux, Stephane. "Thermal expansion study of particulate reinforced aluminum matrix composite materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0005/MQ44021.pdf.
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Popovych, Pavlo. "Magnetostriction and thermal expansion of the high-temperature superconductor YBa2Cu3O7." Karlsruhe FZKA, 2006. http://nbn-resolving.de/urn:nbn:de:0005-072072.
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Bettinger, Christopher L. "Effects of thermal expansion on a skewed semi-integral bridge." Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1173468821.
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Lemieux, Stéphane. "Thermal expansion study of particulate reinforced aluminum matrix composite materials." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20505.
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The thermal expansion behavior of Duralcan particle reinforced composite materials was investigated. Initially, the temperature dependence of the CTE of Al-Si alloy containing SiC reinforcement particles ranging from 10 to 40% in volume was experimentally examined and compared with standard theoretical model predictions. In addition, the effects of reinforcement volume fraction and nature of the composite constituents during thermal cycling between 25 and 350ºC were determined for Al-Si alloy containing between 10 and 40% SiC particles and Al alloy having 40% alumina in volume. Accurate experimental CTE measurements were made using a high precision Thermomechanical Analyzer system. Silicon carbide reinforced composite average CTE values were bounded by two elastic CTE theoretical models consisting of Schapery and Kerner predictions over the 25--350ºC interval for reinforcement volume fractions between 10 and 40%. The CTE mismatch between the particles and the matrix does not appear to be the only factor influencing the expansion response of the composites. Indeed, the nature of the composite constituents also plays an important role by influencing the ductility and bonding of the particle-matrix interface.
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Bilbe, Edward. "The structure and negative thermal expansion of low-dimensional compounds." Thesis, University of Reading, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542068.
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Buggakupta, Wantanee. "Microstructure and thermal expansion behaviour of magnesia-magnesium aluminate composites." Thesis, University of Surrey, 2008. http://epubs.surrey.ac.uk/713/.
Full textAbstract:
Knowledge of the coefficient of thermal expansion (CTE) of a ceramic material is important in many application areas. Whilst the CTE can be measured, it would be useful to be able to predict the expansion behaviour of multiphase materials. There are several models for the CTE, however, most require a knowledge of the elastic properties of the constituent phases and do not take account of the microstructural features ·of the material. If the CTE could be predicted on the basis ofmicrostructural information, this would then lead to the ability to engineer the microstructure of multiphase ceramic materials to produce acceptable thermal expansion behaviour. To investigate this possibility, magnesia-magnesium aluminate spinel (MMAS) composites, consisting of a magnesia matrix and magnesium aluminate spinel (MAS) particles, were studied. Having determined a procedure to produce MAS from alumina and magnesia, via solid state sintering, magnesia-rich compositions with various magnesia contents were prepared to make the MMAS composites. Further, the MMAS composites prepared from different powders (i.e. from an alumina-magnesia mixture and from a magnesia-spinel powder) were compared. Com starch was added into the powder mixtures before sintering to make porous microstructures. Microstructural development and thermal expansion behaviour of the MMAS composites were investigated. Microstructures of the MAS and the MMAS composites as well as their porous bodies were quantified from backscattered electron micrographs in terms of the connectivity of solids i.e. solid contiguity by means of linear intercept counting. Solid contiguity decreased with increasing pore content and varied with pore size, pore shape and pore distribution whereas the phase contiguity depended strongly on the chemical composition and was less influenced by porosity. The thermal expansion behaviour of the MAS and the MMAS composites between 100 and 1000 °C was determined experimentally. Variation in the CTE of the MAS relates to the degree of spinel formation while the thermal expansion of the MMAS composites depends strongly on phase content. However, the MMAS composites with similar phase compositions but made from different manufacturing processes showed differences in microstructural features and thermal expansion behaviour. Predictions of the CTE values for composites based on a simple rule-of-mixtures (ROM) using volume fraction were compared with the measured data. A conventional ROM accurately predicted the effective CTE of a range of dense alumina-silicon carbide particulate composites but was not very accurate for porous multiphase structures. It provided an upper bound prediction as all experimental values were lower. Hence, the conventional ROM was modified to take account of quantitative microstructural parameters obtained from solid contiguity. The modified ROM predicted lower values and gave a good agreement with the experimental data. Thus, it has been shown that quantitative microstructural information can be used to predict the CTE of multiphase ceramic materials with complex microstructures.
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LARSSON, FREDRIK. "Evaluation of thermal expansion in busbarsused for battery electric vehicles." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302111.
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Thermal expansion can be an issue in solid busbars, the expansion is caused by several factors and can cause plastic deformation in connection points or structure around it. The expansion occurs due to temperature differences in the busbar as a result of altered ambient temperature and/or joule heating. The environment where a vehicle is used can be harsh and varying in temperatures a lot. For future fast charging systems, a high amount of current will be passed in the conductors. In a stationary installation, this could be solved by increasing the cross-section area. In vehicles, the weight, cost, and space limitations callfor optimization of the conductor. In this thesis, there are several geometrical alterations done to the busbar to investigate the possibility to reduce the amount of stress acting on the connection points. The main geometrical evaluation is to compare a straight busbar to a U-shaped busbar. In the U-shape, the height, bend radius, and cross-section shape are investigated. To investigate this issue a simulation model was developed using Comsol, this software was used to evaluate stress values, max temperature, losses, and displacement. The results from the simulation showed that the U-shape has a large potential to reduce the amount of stress. Also, the cross-section shape tests showed that the steady-state temperature was lower for the more flatter shaped busbar. This is true both for the U-shape and straight busbar. This resulted inreduced amount of thermal expansion causing lower amount of stress, without adding any weight. The weight parameter is extremely important for vehicle implementation. The last test is looking at the busbar material where nickel-plated copper is compared to anodized aluminum. This test is divided into two parts, the first one is looking at an aluminum busbar compared to a copper busbar of the same geometry. This test showed that the losses in the aluminum busbar were much higher, but the steady-state temperature and max stress were lower. The second part of the test investigated the compensated aluminum busbar, this one is modeled by compensating the cross-section area for the higher resistance value of aluminum. The results from this busbar compared to the standard-shaped busbar showed a substantially lower stress, temperature and weight. But the overall dimensions are larger due to the compensated cross-section area. Having this larger Cross section area might hinder the implementation of aluminium busbars in parts of the vehicle where there is a lack of space, like in a battery box.Termisk expansion i solida busbars är ett vanligt problem vid kraftig temperaturvariation. Problemet ökar med längden av busbaren och kan leda till plastisk deformation i infästningen av busbaren. Temperaturvariationen kan ske genom varierad omgivningstemperatur eller genom resistiv uppvärmning. Om en busbar ska användas i ett fordon för kraftöverföring är arbetsmiljön mycket påfrestande. Den termiska uppvärmningen går normalt att motverka genom att öka tvärsnittsarean, men i ett fordon där vikt, kostnad och platsbrist minskar möjligheten för ökad tvärsnittsarea blir optimering av ledaren extra viktig. För att undersöka problemet utvecklades en simuleringsmodell med hjälp av Comsol. Denna programvara använder för att utvärdera spänningskoncentrationer, maxtemperatur, förluster och utböjningar i busbaren. För att undersöka eventuella lösningar togs det fram flera geometriska variationer till busbaren, där möjligheten att använda en “U-form” utgjorde basen i en jämförelse mot en vanlig rakbusbar. För U-formen undersöktes U-höjden, böj-radien samt tvärsnittsformen. Även en jämförelse mellan nickelpläterad koppar och anodiserad aluminiumgenomfördes för att urskilja eventuella för och nackdelar med materialen. Resultaten från simuleringarna visade att U-formen gav klart lägre spänning i kontaktpunkterna. Även tvärsnittsformen påverkade temperaturen och spänningen i busbaren, där den plattare varianten presterade bättre på alla parametrar som undersöktes i simuleringen. För utvärderingen av materialet utfördes två tester, det första testet jämför en busbar i aluminium mot en i koppar med exakt samma geometri, detta testvisade att temperaturen samt spänningen blir lägre i aluminiumvarianten, dock ökar förlusterna kraftigt då aluminium har högre resistans än koppar. I den andra testet användes en kompenserad aluminiumbusbar där tvärsnittsarean har ökats för att ge samma resistans som kopparvarianten. Denna busbar fick en mycket lägre sluttemperatur, spänning och vikt. Förlusterna blev detsamma. Den högre tvärsnittsarean ger dock en fysiskt större busbar.
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DINH, VAN QUY. "LOW THERMAL EXPANSION OF ELECTRODEPOSITED COPPER IN THROUGH SILICON VIAS." Kyoto University, 2020. http://hdl.handle.net/2433/253518.
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Kim, Jinmin. "Synthesis and characterization of ultralow thermal expansion NZP- type compounds." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/54336.
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New ultra-low thermal expansion materials, based on the NZP structure, have been developed and evaluated for future application in ceramic diesel engines which require exceptional thermal shock resistance. Twenty-four cation substitutions, with electron valence ranging from +1 to +5, were used to replace Na⁺ in the NZP skeletal framework. The linear thermal expansion measurements were conducted for ternary systems up to 1000°C. Quarternary & quinternary compounds were processed using combinations of alkali-alkali, alkali-alkaline earth, and alkaline earth alkaline earth instead of Na⁺. These were evaluated for solid solubility. Linear thermal expansion values were obtained for those compositions having single phase composition. Axial thermal expansion measurements were conducted using high temperature XRD for compounds having low linear thermal expansion value from room temperature to 1400°C. Several ultra-low expansion materials (less than 10x10⁻⁷/°C in absolute value) were found, which also had axial thermal expansion anisotropy. ‘ The effects of ionic size and valence of the substitution elements are discussed to explain the linear thermal expansion behavior and thermal expansion anisotropy investigated in these compounds. The effect of crystallinity is discussed, and the unit-cell equilibrium is suggested to interpret the general thermal expansion behavior occurring in crystalline solids. Secondary material properties for the compounds Rb0.5Cs0.5Zr₂(PO₄)₃ & Ca0.5Mg0.5Zr₄(PO₄)₆ with linear thermal expansion values of -0.3x10⁻⁷/°C & -5x10⁻⁷/°C, respectively, have also been characterized.Ph. D.
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Aghajani, Farzaneh. "Additional Thermal Expansion Of Gypsum-Bonded Investment By Rapid Heating." Thesis, The University of Sydney, 1998. http://hdl.handle.net/2123/4842.
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Khan, Zakir. "Energy recovery at thermodynamic expansion and thermal boosting through convection in flat plate solar thermal systems." Thesis, Bournemouth University, 2018. http://eprints.bournemouth.ac.uk/31116/.
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Fossil fuels have served mankind to meet energy needs in both domestic and commercial applications for a considerable length of time. However, fossil fuels have environmental implications such as emission of harmful gases, depletion of ozone layer and climate change. Moreover, the ever rising prices and limited resources of fossil fuels have obstructed the uninterrupted supply of energy. Therefore, there is a dire need to develop renewable energy technologies that can sustain energy supply with increasing demands. Due to inexhaustible amount of clean solar energy, engineers and researchers are engaged in developing technologies to minimise dependency on fossil fuels. Solar collectors are utilised to use solar heat to increase the heat energy of thermo-fluids or heat transfer fluid (HTF), which can operate Organic Rankine Cycle (ORC) to generate electricity. However, the extensive gain from solar energy is restricted due to unreliability of solar energy during changing weathers and lack of availability at nights. Therefore, thermal energy storage (TES) system can provide a viable solution to respond to varying levels of solar energy. Literature review indicated that phase change materials (PCM) based latent heat storage (LHS) systems are promising TES technique due to their high thermal storage density, operation at isothermal conditions and wide range availability of PCMs. However, large-scale practical utilisations of LHS systems are limited due to restrained charging and discharging rates caused by low thermal conductivity of PCM. Hence, this research is focused on numerical and experimental analyses conducted in developing an efficient and effective TES technology with novel heat transfer mechanism and novel thermal storage materials to sustain continuous generation of heat and power for low temperature practical applications. In this research, numerical investigations were conducted to propose an optimum and novel design solution for shell and tube heat exchanger with multiple tube passes and longitudinal fins for improved thermal performance. Parametric investigations were conducted to examine the influence of number and orientations of tube passes in the shell container, geometrical dimensions of longitudinal fins, construction material for shell, tube passes and longitudinal fins, and operating temperature of HTF on phase transition rate and overall enthalpy of LHS system. Further, the proposed design was developed and commissioned with a connection to flat plate solar collector to examine thermal performance at varied operating conditions. Paraffin (RT44HC) was employed as PCM in shell container and water was utilised to circulate in tube passes to transfer thermal energy gained at solar collector to paraffin in shell container. Thermal performance was evaluated by conducting series of charging and discharging cycles at varied operating conditions to examine the charging/discharging rate, accumulative thermal energy gain/release and mean charging/discharging power. Furthermore, numerical and experimental analyses were conducted to evaluate nano-additives enhanced paraffin samples, which were developed by incorporating aluminium oxides (Al2O3), aluminium nitride (AlN) and graphene nano-platelets (GNP) nano-additives in base paraffin. Based on numerical and experimental results and recommendations, numerical simulations were conducted on coupled thermal performance enhancement techniques with longitudinal fins and graphene nano-additives enhanced paraffin samples. It was noticed that phase transition rate for coupled thermal performance enhancement techniques was significantly enhanced by 75.46% as compared to no longitudinal fins orientation with pure paraffin. Likewise, the proposed LHS system can efficiently charge and discharge 14.36 MJ and 12 MJ of thermal energy in as less as 3 h and 1.5 h, which ensures the large-scale practical utilisation in both domestic and commercial applications.
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Cragun, Rebecca. "Thermal Microactuators for Microelectromechanical Systems (MEMS)." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/54.
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Microactuators are needed to convert energy into mechanical work at the microscale. Thermal microactuators can be used to produce this needed mechanical work. The purpose of this research was to design, fabricate, and test thermal microactuators for use at the microscale in microelectromechanical systems (MEMS). The microactuators developed were tested to determine the magnitude of their deflection and estimate their force. Five groups of thermal microactuators were designed and tested. All of the groups used the geometrically constrained expansion of various segments to produce their deflection. The first group, Thermal Expansion Devices (TEDs), produced a rotational displacement and had deflections up to 20 µm. The second group, Bi-directional Thermal Expansion Devices (Bi-TEDs) were similar to the TEDs. The difference, as the name implies, was that the Bi-TEDs deflected up to 6 µm in two directions. Thermomechanical In-plane Micromechanisms (TIMs) were the third group tested. They produced a linear motion up to 20 µm. The fourth group was the Rapid Expansion Bi-directional Actuators (REBAs). These microactuators were bi-directional and produced up to 12 µm deflection in each direction. The final group of thermal microactuators was the Joint Actuating Micro-mechanical Expansion Systems (JAMESs). These thermal microactuators rotated pin joints up to 8 degrees. The thermal microactuators studied can be used in a wide variety of applications. They can move ratchets, position valves, move switches, change devices, or make connections. The thermal microactuator groups have their own unique advantages. The TIMS can be tailored for the amount of deflection and output force they produce. This will allow them to replace some microactuator arrays and decrease the space used for actuation. The Bi-TEDs and REBAs are bi-directional and can possibly replace two single direction micro-actuators. The JAMESs can be attached directly to a pin joint of an existing mechanism. These advantages allow these thermal microactuator groups to be used for a wide variety of applications.
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Gates, Stacy Dione. "Cation influence on negative thermal expansion in the A₂M₃O₁₂ family /." Connect to full text in OhioLINK ETD Center, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1216698704.
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Thesis (Ph. D.)--University of Toledo, 2008.Typescript. "Submitted as partial fulfillment of the requirements for the Doctor of Philosophy in Chemistry." Includes bibliographical references (leaves 168-172).
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Allen, Simon. "Thermoreponsive behaviour of AM₂O₈ materials." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/4008/.
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This thesis investigates the synthesis and structural characterisation of AM(_2)O(_8) phases, many of which show negative thermal expansion (NTE); relevant literature is reviewed in Chapter One. Chapter Two describes the synthesis, structure solution, and mechanistic role of a new family of low-temperature (LT) orthorhombic AM(_2)O(_8) polymorphs (A(^TV) = Zr, Hf; M(^VI) = Mo, W). These materials are key intermediates in the preparation of cubic AM(_2)O(_8) phases from AM(_2)O(_7)(OH)(_2)(H(_2)O)(_2). The structure of LT-AM(_2)O(_8) has been elucidated by combined laboratory X-ray and neutron powder diffraction. Variable temperature X-ray diffraction (VTXRD) studies have shown LT- AM(_2)O(_8) phases exhibit anisotropic NTE. LT-ZrMo(_2)O(_8) has been shown to undergo spontaneous rehydration, allowing preparation of ZrMo(_2)O(_7)(OD)(_2)(D(_2)O)(_2) and assignment of D(_2)O/OD positions within the structure by neutron diffraction. Using this result, a reversible topotactic dehydration pathway from AM(_2)O(_7)(OH)(_2)(H(_2)O)(_2) to LT-AM(_2)O(_8)s is proposed. Chapter Three investigates the order-disorder phase transition with concurrent oxygen mobility in cubic AM(_2)O(_8) materials; studies include comprehensive VT neutron diffraction of cubic ZrMo(_2)O(_8) to reveal a static to dynamic transition at 215 K, and novel quench-anneal/quench-warm variable temperature/time diffraction experiments on ZrMo(_2)O(_8) which lead to an activation energy of 40 kJmol(^-1) for oxygen migration. In Chapter Four (^17)O-labelled cubic ZrW(_2)O(_8) has been prepared to understand the oxygen migration process by VT MAS NMR. In situ hydrothermal studies of cubicZrMo(_2)O(_8) using synchrotron radiation have shown direct hydration to ZrMo(_2)O(_7)(OH)(_2)(H(_2)O)(_2).. In Chapter Five VTXRD of trigonal a-AMo(_2)O(_8) phases reveals a previously unknown second-order phase transition at 487 K (A = Zr) or 463 K (A = Hf) from P31c to P3ml. Rigid-body Rietveld refinements have shown this is due to alignment of apical Mo-O groups with the c axis in the high-temperature, a' phase.
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Varga, Tamas. "Synthesis and Characterization of Some Low and Negative Thermal Expansion Materials." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6905.
Full textAbstract:
Synthesis and Characterization of Some Low and Negative Thermal Expansion Materials
Tamas Varga
370 pages
Directed by Dr. Angus P. Wilkinson
The high-pressure behavior of several negative thermal expansion materials was studied by different methods. In-situ high-pressure x-ray and neutron diffraction studies on several compounds of the orthorhombic Sc2W3O12 structure revealed an unusual bulk modulus collapse at the orthorhombic to monoclinic phase transition. In some members of the A2M3O12 family, a second phase transition and/or pressure-induced amorphization were also seen at higher pressure. The mechanism for volume contraction on compression is different from that on heating.
A combined in-situ high pressure x-ray diffraction and absorption spectroscopic study has been carried out for the first time. The pressure-induced amorphization in cubic ZrW2O8 and ZrMo2O8 was studied by following the changes in the local coordination environments of the metals. A significant change in the average tungsten coordination was found in ZrW2O8, and a less pronounced change in the molybdenum coordination in ZrMo2O8 on amorphization. A kinetically frustrated phase transition to a high-pressure crystalline phase or a kinetically hindered decomposition, are likely driving forces of the amorphization. A complementary ex-situ study confirmed the greater distortion of the framework tetrahedra in ZrW2O8, and revealed a similar distortion of the octahedra in both compounds.
The possibility of stabilizing the low thermal expansion high-temperature structure in AM2O7 compounds to lower temperatures through stuffing of ZrP2O7 was explored. Although the phase transition temperature was suppressed in MIxZr1-xMIIIxP2O7 compositions, the chemical modification employed was not successful in stabilizing the high-temperature structure to around room temperature.
An attempt has been made to control the thermal expansion properties in materials of the (MIII0.5MV0.5)P2O7-type through the choice of the metal cations and through manipulating the ordering of the cations by different heat treatment conditions. Although controlled heat treatment resulted in only short-range cation ordering, the choice of the MIII cation had a marked effect on the thermal expansion behavior of the materials.
Different grades of fluorinert were examined as pressure-transmitting media for high-pressure diffraction studies. All of the fluorinerts studied became nonhydrostatic at relatively low pressures (~1 GPa).
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Seletskaia, Tatiana. "Calculation of thermal expansion of iron-aluminides with transition metal additives." Morgantown, W. Va. : [West Virginia University Libraries], 2002. http://etd.wvu.edu/templates/showETD.cfm?recnum=2684.
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Thesis (Ph. D.)--West Virginia University, 2002.Title from document title page. Document formatted into pages; contains vi, 103 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.
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Liyanage, Chamadari Hemamala Uswatte Kruger Michael B. "High pressure studies of negative thermal expansion materials and nanocrystalline materials." Diss., UMK access, 2007.
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Thesis (Ph. D.)--Dept. of Physics and Dept. of Mathematics. University of Missouri--Kansas City, 2007."A dissertation in physics and mathematics." Advisor: Michael B. Kruger. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed July 16, 2008. Includes bibliographical references (leaves 137-143). Online version of the print edition.
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Amri, Mahrez. "Investigation of thermal expansion behaviour of silicate and phosphate zeotype materials." Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/3766/.
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Carey, Thomas. "Chemical control of thermal expansion in zeolites with the LTA topology." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4258/.
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Zeolites are microporous materials that have been commonly shown to exhibit remarkable negative thermal expansion (NTE) behaviour in their purely siliceous forms, with reported thermal expansion coefficients ranging from −3 x 10–\(_6\) K–\(_1\) to −26.1 x 10–\(_6\) K–\(_1\). In contrast, very little research has been reported on the aluminium-containing structures which are widely used for various commercial applications. Compounds exhibiting this property, which has only been observed in a small number of solids, are of considerable technological interest as their inclusion in devices or composite materials can counterbalance the more usual expansion on heating and contraction on cooling, thereby reducing the incidence of thermally induced failures. Here, we report an investigation into the effect that changing the chemical composition of the zeolite framework and intrapore species has on thermal expansion properties of zeolites with the LTA topology. Variable-temperature powder X−ray diffraction studies were used to determine the thermal expansion coefficients of the chemically modified zeolites over a sub-ambient temperature range and investigate the structural basis behind their thermal behaviour. Dramatic changes in the thermal expansion behaviour (from strong negative to weak positive) of the zeolites were observed as the structures were modified through ion-exchange, dehydration, varying the Al content in the framework and loading the pores with silver nitrate. The zeolitic pores contents have been shown to play a key role in the manner in which LTA-zeolites react to temperature variation, especially in the case of intra-porous water molecules. Detailed atomistic structural mechanisms behind the observed NTE behaviour have been produced for the more simplistic systems. Several key breakthroughs have also been achieved in understanding the formation of the superlattice when silver nitrate is incorporated into the zeolite pores and with regards to solving the unit cell structure.
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Jang, Chang Heui. "Weld development for Incoloy alloy 908, a low thermal expansion superalloy." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/28140.
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Tao, Ju Zhou. "Theory of negative thermal expansion." Thesis, 2002. http://hdl.handle.net/1957/31094.
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Two framework oxide materials of the MO��� network type have been
synthesized and structurally characterized by synchrotron and X-ray powder
diffraction and the Rietveld method in the temperature range 25~500 K. The results
show one of them to be a low thermal expansion material.
Theoretical studies of negative thermal expansion (NTE) in framework oxides
were conducted with two methods, geometrical modeling by Rigid Unit Mode
(RUM) method and lattice dynamic calculations by free energy minimization
(FEM) method, the results are compared with each other as well as with
experimental observations.
RUM analysis of all five types of framework oxide structures negates any
simple and direct correlation between presence or absence of RUMs in a structure
and the sign of its thermal expansion. Instead, results suggest that NTE of a
crystalline solid can not be explained by pure geometrical considerations over its
structure alone, and for a better understanding of structure-relationship in negative
thermal expansion structures, specific interatomic interactions present in each one
must be brought in explicitly.
FEM calculation of two negative thermal expansion structures indicates on a
structure by structure basis NTE could be predicted and understood within the
Gruneisen model, which attributes NTE of a structure to special vibration modes in
a structure that softens when the lattice shrinks. The soft NTE modes are, however,
not necessarily RUM or RUM like vibration motions.Graduation date: 2003
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Lai, Chien-Li, and 賴建利. "Cast Iron Heat Treatment Parameters on The Thermal Expansion Coefficient of Thermal Expansion of The Impact." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/95935370885988844948.
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碩士國立高雄應用科技大學
模具系碩士在職專班
101
Adopted low thermal expansion to produce main materials closed to heat source to reduced deviation caused by thermal expansion is the common consensus with machinery designers and producers。There is about 2%~4% C 、1~3 % Si、20%~40% Ni during low thermal expansion and results indicates that nickel contents is the main effect to α value。 The objective of this research is to study interaction with LT1(FeXNi31Co5-C1Si1)、LT2(FeXNi361-C2Si2)、LT3(FeXNi31Co5-C2Si2) of alloying elements and microstructure、heat treatment 、thermal expansion coefficient 、 change with aging treatments and electropulsing。And result indicates that phase fraction of nickel segregation and graphite phase are large affected by nickel contents, however value of carbon and Si have slightly influence to phase fraction of nickel segregation and graphite。Content of Co is also not significant to increasing of nickel segregation and graphite。At same value of carbon and Si, higher nickel can get more influence to increase percentage of strong nickel segregation and graphite。And we also find there is trend with ordinary carbon can be melted back to matrix in the temperature range of 950℃~1050℃ within heat treatment of 850℃~1200℃。And heat treatment at 1100℃~1200℃ can re-release carbon whose has melted from original matrix. Due to higher temperature can bring more driven power and also can generate new microscopical graphite of Austenite Irons to eliminate nickel aliquation phase thoroughly。 36 % nickel is the highest value of thermal expansion cast iron, and can bring more nickel segregation。 Tempering of heat treatment at 900℃ can get the better result for elimination of nickel segregation。It is not significant between low thermal expansion and temperature of stress relief, assumed that higher temperature can shorten time of stress relief, and experiments show that high temperature can reduce time of stress relief 。moreover，result indicates that reduce temperate at 650℃ can shorten time of stress relief within one hour, and electropulsing also has similar effect to higher heat temperature。Besides there are also new and slightly graphite generated in microstructure to lower thermal expansion , however is not significant to elimination of nickel segregation.
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Gonçalves, Sofia Mendonça. "Customization of Thermal Expansion in Nanowires." Master's thesis, 2021. https://hdl.handle.net/10216/138187.
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Gdoutos, Eleftherios E. "Thin Metastructures with Engineered Thermal Expansion." Thesis, 2013. https://thesis.library.caltech.edu/7765/1/Gdoutos-thesis-final-HQ.pdf.
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The geometry and constituent materials of metastructures can be used to engineer the thermal expansion coefficient. In this thesis, we design, fabricate, and test thin thermally stable metastructures consisting of bi-metallic unit cells and show how the coefficient of thermal expansion (CTE) of these metastructures can be finely and coarsely tuned by varying the CTE of the constituent materials and the unit cell geometry. Planar and three-dimensional finite element method modeling is used to drive the design and inform experiments, and predict the response of these metastructures. We demonstrate computationally the significance of out-of-plane effects in the metastructure response. We develop an experimental setup using digital image correlation and an infrared camera to experimentally measure full displacement and temperature fields during testing and accurately measure the metastructures’ CTE. We experimentally demonstrate high aspect ratio metastructures of Ti/Al and Kovar/Al which exhibit near-zero and negative CTE, respectively. We demonstrate robust fabrication procedures for thermally stable samples with high aspect ratios in thin foil and thin film scales. We investigate the lattice structure and mechanical properties of thin films comprising a near-zero CTE metastructure. The mechanics developed in this work can be used to engineer metastructures of arbitrary CTE and can be extended to three dimensions.
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Madhusoodana, C. D. "Study Of Thermal Expansion Anisotropy In Extruded Cordierite Honeycombs." Thesis, 1997. http://etd.iisc.ernet.in/handle/2005/1824.
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