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1
Oak, Milind Prabhakar. "Virtual customer driven product design crystallization." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/91722.
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Wollmann, Georgia. "Crystallization Fields of Polyhalite and its Heavy Metal Analogues." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-32906.
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Polyhalite is an abundant distributed mineral in rock salt formations, and considered to respond as a natural heavy metal sink because the Mg2+ ion can be substituted by other bivalent metal ions like Mn2+, Co2+, Ni2+, Cu2+ and Zn2+.
One of the quantities needed to predict mineral solubilities in multi-electrolyte solutions is the solubility constant Ksol. Since polyhalite forms slowly over months or years at 298 K, the solid-liquid phase equilibria experiments were accomplished at 313 K. Enthalpies of dissolution were measured and used to extrapolate lnKsol from 313 K to 298 K. Pitzer’s equations have been applied to describe activities of solute and water, with Pitzer parameters estimated from experimental data.
The solubility constants for the polyhalites were applied to calculate the solubility equilibria in the quaternary systems K+, M2+, Ca2+ / SO42- // H2O (M = Mg, Mn, Co, Cu, Zn) at 298 K and 313 K, and in case of Mg-polyhalite also in the hexary system Na+, K+, Mg2+, Ca2+ / Cl-, SO42- // H2O.
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Boulay, Emilie. "Amorphous phase separation and crystallization in the BaO-TiO2-SiO2 system: experimental approach and thermodynamic study." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209133.
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Glass-ceramics are of growing interest due to their enhanced properties compared to the base glasses. More specifically, the control of microstructures is a major challenge as the properties of glass-ceramics are the direct consequences of microstructures. Microstructures can be modified by forming specific crystal phases or by using a prior amorphous phase separation before crystallization. The PhD thesis objectives are to demonstrate that the properties of silicate glasses can be enhanced by controlling their microstructure genesis with composition and thermal process parameters. More specifically, two systems were studied and compared: the BaO-TiO2-SiO2 system and the soda-lime silica Na2O-CaO-SiO2 used industrially. Both systems exhibit a large zone of immiscibility allowing the study of the influence of phase separation on crystallization.The first system BaO-TiO2-SiO2 has gathered interest from the interesting properties of fresnoite (Ba2TiSi2O8): piezo and pyroelectricity, second harmonic generation and blue/white photoluminescence. Many studies on the stoichiometric composition were conducted to understand and improve those promising properties. However, it was recently suggested that the photoluminescence can be improved with composition exhibiting phase separation. This indicates that the photoluminescence intensity can be improved through a microstructural control. The possible role of a prior amorphous phase separation on the subsequent crystallization has been however the topic of vigorous debates over the last decades and has not yet been clarified, especially regarding the role of the interfaces created by the phase separation. In this PhD, the effect of phase separation on fresnoite crystallization was studied. This had to pass through the calculation of the liquid-liquid immiscibility in the phase diagram in order to select suitable compositions to compare in a systematic study. The systematic study concludes to a surface crystallization mechanism for all non- stoichiometric compositions and shows no influence between amorphous droplets and matrix crystallization. This study was also completed with the investigation of the effect of composition (i.e. SiO2-excess), annealing temperature and prior heat treatment, i.e. heating rate, cooling rate or a prior isothermal step before annealing. It is shown that specific microstructures are obtained depending on the process parameters. Finally, selected compositions and heat treatment show how photoluminescence intensity can be improved by a microstructural control. The highest intensity is obtained with a high crystallization fraction and a maximization of the number of interfaces.
The results obtained in the study of the BaO-TiO2-SiO2 system are extended to the soda-lime-silica system in order to study the effect of phase separation on crystallization. It is shown that cristobalite forma- tion from the surface cannot be avoided and that the involved composition shift inhibits phase separation. It is consequently difficult to observe an interplay. Those studies lead to a general discussion about the criteria allowing to observe an interplay between phase separation and crystallization in oxide glasses.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Zeng, Jianming. "Constrained crystallization and depletion in the polymer medium for transdermal drug delivery system." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5102.
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Transdermal drug delivery systems (TDS) are pharmaceutical devices that are designed to deliver specific drugs to the human body by diffusion through skin. The TDS effectiveness suffers from crystallization in the patch when they are kept in storage for more than two years. It has been reported that there are two types of crystals in the patch: needle and aggregate, and growth of drug crystals in TDS generally occurs only in the middle third of the polymer layer. In our study, fluorescence microscopy, EDS (SEM) and Raman microspectroscopy were used to further characterize the crystals. The results show that the needle crystals most probably contain estradiol and acrylic resin conjugate. The FTIR spectrum of the model sample proved the occurrence of a reaction between estradiol and acrylic resin. Crystal growth in an unstressed matrix of a dissolved crystallizable drug component was simulated using a kinetic Monte Carlo model. Simulation using Potts model with proper boundary condition gives the crystals in the middle of matrix in the higher temperature. Bond fluctuation model is also being implemented to study representative dense TDS polymer matrix. This model can account for the size effect of polymer chain on the crystal growth. The drug release profile from TDS was also studied by simulating the diffusion of drug molecules using Monte Carlo techniques for different initial TDS microstructure. The release rate and profile of TDS depend on the dissolution process of the crystal. At low storage temperature, the grains are evenly distributed throughout the thickness of the TDS patch, thus the release rate and profile is similar to the randomly initiated system. Further work on stress induced crystallization is currently under development. Although the study was specifically done for drug in a polymer medium, the techniques developed in this investigation is in general applicable to any constrained crystallization in a polymer medium.
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Kim, Seong-Jin. "Directional crystallization in the bismuth-strontium-calcium-copper-oxygen system: Effect of phase separation." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/186040.
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Novel unidirectional crystallization was tested in glasses of the Bi-Sr-Ca-Cu-O system to produce highly oriented microstructures. Some evidence of liquid-liquid phase separations on cooling melts of Bi₂Sr₂Ca₁Cu₂Oₓ and Pb₀ͺ₃₂Bi₁ͺ₆₈Sr₁ͺ₇₅Ca₂Cu₃Oₓ is found for the first time from Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), and Transmission Electron Microscope (TEM). This made it difficult to produce highly oriented microstructures through the present route because one of the phases in the phase separated structure is likely close to "R"-phase composition and lead to copious nucleation of "R"-phase on heating. This also resulted in sequential crystallization of the current liquids, first to "R"-phase and then to the Bi₂Sr₂Ca₁Cu₂Oₓ phase. Theoretical modelling was performed to understand general questions in the present route. The model suggests that a liquid with high interfacial energy is a good candidate for the present route to produce highly oriented microstructures. The model was tested in lithium diborate glass and showed a highly oriented microstructure. Thus, unidirectional crystallization is generally an attractive processing option for a liquid free of phase separation.
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Getson, Jacqueline. "Effect of plagioclase crystallization on liquid and magma viscosity in the Anorthite-diopside-dorsterite-quartz system." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4628.
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Thesis (M.S.) University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (June 25, 2007) Includes bibliographical references.
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Taylor, Donald Fulton. "Measurement of binary phase equilibria and ternary/quaternary gas antisolvent (GAS) system measurement and analysis." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-07112004-194307/unrestricted/taylor%5Fonald%5Ff%5F200407%5FMS.pdf.
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Thesis (M.S.)--School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2005. Directed by Charles Eckert.Charles Eckert, Committee Chair ; Amyn Teja, Committee Member ; Pete Ludovice, Committee Member. Includes bibliographical references.
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Stanojevic, Sanja [Verfasser], and Ralf [Akademischer Betreuer] Busch. "Processing, crystallization and oxidation of the Ni-Nb(-Sn) refractory alloy glass system / Sanja Stanojevic. Betreuer: Ralf Busch." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2013. http://d-nb.info/1053681666/34.
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Liu, Lei. "The link between convection and crystallization in a sub-axial magma chamber and heat output in a seafloor hydrothermal system." Thesis, Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-07072007-142506/.
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Xiao, Yi. "Structural study of ExsA, the regulator of Type III Secretion System of Pseudomonas aeruginosa." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/50944.
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The Type III secretion system (T3SS) of Pseudomonas aeruginosa uses a needle-like protein apparatus to detect eukaryotic host cells and translocate effectors directly into the host cell. The effectors are also known as cytotoxins, which cause disruption of a series of signaling events in the host cell, facilitating the infection by P. aeruginosa. As the T3SS is antigenic and the expression of T3SS is energy-consuming, it is highly regulated where several regulatory proteins interact with each other and control the expression of T3SS genes. Among these proteins, ExsA, the master regulator of T3SS in P. aeruginosa, is of great importance as it is a transcriptional activator that activates the expression of all T3SS genes. Also, as ExsA belongs to the AraC protein family which only exists in bacteria and fungi, it makes an excellent potential target for drugs against P. aeruginosa related infections. With a combination of molecular biology tools and structural biology methods, we solved the N-terminal domain structure of the ExsA protein in P. aeruginosa. The model of the ExsA N-terminal domain has enriched our knowledge about ExsA dimerization and can serve as the base for mapping the interaction interfaces on ExsA and ExsD. Further, we have found two homologues of ExsA by structural alignment, which share a lot of similarities and have conserved amino acid residues that are important for ligand binding. The fact that both of these two proteins are regulated by small ligands rather than proteins also raises the possibility that ExsA may have a second regulatory mechanism under which ExsA is regulated by a small ligand, which so far has not been observed or reported by researchers. In order to map the binding site of ExsA on its anti-activator ExsD, we removed the coiled-coil region (amino acid residue 138-202, the potential binding site) of ExsD, based on the structure of ExsD. We surprisingly found that the ExsD variant without the coiled-coil region readily inhibits ExsA-dependent in vitro transcription. This result rules out other possibilities and makes us focus on the N-terminus and adjacent regions of ExsD for the interface with ExsA. Moreover, in order to gain a comprehensive understanding of the dynamics of the regulation of T3SS in P. aeruginosa, we have begun to build a mathematical model of the T3SS regulatory pathways. We are measuring the cellular concentrations of T3SS regulatory proteins with quantitative molecular biology methods such as quantitative western blot, quantitative PCR and quantitative mass spectrometry. We have determined the cellular level of ExsA and ExsD proteins under different physiological conditions, and found that some factors such as temperature have a significant impact on the levels of ExsA and ExsD. This study has thus unveiled some unknown features of the T3SS of P. aeruginosa and its related infections. Master of Science
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Mina-Mankarios, George. "Crystallization kinetics of sodium sulphate in a salting out MSMPR crystallizer system Na₂SO₄/H₂S0₄/H₂O/MeOH /." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/42007.
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The growth and nucleation rates of sodium sulfate
crystals salted out from their solution in a 38% w/w
sulfuric acid solvent by the addition of an 80:20 w/w
methanol : water solution, were determined from measurements
of the steady-state crystal size distribution (CSD)
generated in a continuous mixed-suspension, mixed-product-removal
(MSMPR) salting out crystallizer, and the effect of
the supersaturation, the crystal suspension density and the
temperature on these rates was investigated. The effect of
the Cr+ + + impurity was also briefly studied.
For the pure system, the power-law kinetic rate
equations of crystal growth (G = KGSg ) and crystal
nucleation (B = KBSb ) were fitted to the experimental data
and the fitting parameters were determined at each of 25, 30
and 35°C. In addition, the nucleation and growth rate data
were fitted to the relative kinetic equation (B = KbGi) to
provide a basis for comparison between i and b/g.
Secondary nucleation effects were investigated by testing,
in parallel with the primary nucleation rate equation
B = KBSb, the rate equation B = KNMTJSu which includes a
nucleation dependence on the crystal suspension density.
The relative kinetic equation B = KnMJTGv was also tested for
comparison (v compared with u/g).
No evidence of secondary nucleation could be shown.
The fitted estimates of j were non-positive at all
temperatures and statistically non-different from zero at 35
and 30°C, just approaching significance at 25°C with a
negative point estimate for j. Primary nucleation was shown
to be the dominant nucleating mechanism for this system.
The growth rate kinetic order g was determined to be
essentially unity (G = KGS0.97 ) and was statistically non-changing
with temperature. The nucleation rate kinetic
order b was similarly temperature independent and was
determined as 2.1 (B = KBS2.1). The kinetic rate constants
KG and KB were both a function of temperature and
were fitted to an Arrhenius type temperature dependence to
give
KG = 43960 exp(-24600/RT)
and
KB = 0.064 exp(70870/RT)
where R is in kJ/kmole-K.
The activation energy for growth was positive at 24600
kJ/kmole. The nucleation activation energy was negative and
larger in magnitude at -70870 kJ/kmole. In the presence of the chromium impurity, the kinetic
parameters KG , g, KB , Kb, and i were determined at three
levels of the concentration of the impurity in the
crystallizer feed. An increase in the impurity
concentration was shown to cause an increase in the growth
rate constant KG but had no significant effect on the
nucleation kinetics. The result was a decrease in the
relative rate constant and therefore a larger crystal
size.
The kinetics of crystallization as determined for this
system would indicate that a high temperature, high crystal
suspension density and long residence time are conditions
which are favourable for the production of a large sodium
sulfate crystal.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
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Zheltonozhskaya, T. B., S. V. Partsevskaya, D. O. Klymchuk, and V. F. Gorchev. "Specific Interactions and Crystallization of Drug-Loaded Micelles in the System: Prednisolon/PAAm-b-PEO-b-PAAm Micellar Solutions." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35235.
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Encapsulaton of poorly soluble crystallizing drug prednisolone (PS) in micellar solutions of PAAm-b-
PEO-b-PAAm triblock copolymer (TBC) based on chemically complementary poly(ethylene oxide) and polyacrylamide
(MnPEO = 6 kDa, MnPAAm = 116 kDa) was studied by dynamic light scattering and transmission
electron microscopy. The equilibrium mechanism of the encapsulation process and the effect of specific aggregation
of PS-loaded micelles by their “coronas” that promoted the drug crystallization were established.
The question about the presence of TBC micelles inside crystalline space was discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35235
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Rowland-Smith, Andrea. "The 1630 AD eruption of Furnas Volcano, São Miguel, Azores (Portugal): chemical variations and magmatic processes." Miami University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=miami1186143145.
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Gallo, Leonardo Sant'ana. "Microstructure and mechanical properties of glass-ceramics from the MgO-Al₂O₃-SiO₂ system for ballistic protection." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S063/document.
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Afin d'examiner les effets de la cristallisation sur certaines propriétés mécaniques, l'évolution du module de Young (E), du module de cisaillement (G) et du coefficient de Poisson, ainsi que la séquence des phases cristallines formées au cours d'un traitement thermique en deux étapes ont été accompagnées sur un verre baptisé 75-25, du système MgO-Al2O3-SiO2 (MAS), en utilisant TiO2 comme le principal agent de nucléation. L'évolution de la dureté et de la résistance à la rupture a aussi été examinée. La diffractométrie de Rayons X à haute température a révélé, après cristallisation, la présence de spinelle (MgO.Al2O3) rutile (TiO2), karooite (MgO.2TiO2), sillimanite (Al2O3.SiO2) et la saphirine (4MgO.5Al2O3.2SiO2). Les modules élastiques et de cisaillement des vitrocéramiques (VC) se sont montré environ 20% plus élevés que ceux du verre précurseur. Les valeurs de dureté obtenues sont proches de 10 GPa et KIC proche de 1,2 MPa.m1/2. Dans le but de fabriquer des VCs transparentes et incolores, de nouvelles formulations, dénommées ZT1B4, 75-25/ZT et 75-25/25TI, avec des teneurs en TiO2 réduites et des teneurs en ZrO2 plus élevées, ont été proposées et cristallisées. La formulation ZT1B4 a produit une VC transparente avec une dureté maximale de 8GPa et une ténacité à la fracture (TF) à peu près 40% plus élevée que celle du verre de base. Les formulations 75-25 ZT et 75-25/25Ti ont produit des VC transparentes avec des valeurs de dureté allant jusqu'à 9GPa et une ténacité à la fracture jusqu'à 35% plus élevée que celle du verre de base. Une série de verres ont été fondus en utilisant Ag métallique, au lieu de ZrO2 et TiO2, en tant qu'agent de nucléation. Les traitements thermiques appliqués ont produit des VCs non-homogènes, qui perdent la forme en raison des températures de cristallisation élevées. Ces nouveaux verres précurseurs ont donc été écartés. La transmittance dans la région de l'ultraviolet et visible a été mesurée dans les échantillons de verre et VCs de formulation 75-25, 75-25 / ZT et 75-25 / 25TI. La formulation 75-25 / ZT a présenté la plus haute transmittance soit à l'état vitreux ou en forme de vitrocéramique. En conclusion, parmi les nouvelles compositions, la formulation 75-25 / ZT est la plus adéquate pour une utilisation en tant que protection balistique, lorsque la transparence à la lumière visible est nécessaireIn situ experiments were conducted on a glass dubbed 75-25, of the MgO-Al2O3-SiO2 (MAS) system, using TiO2 as the main nucleating agent, in order to examine the evolution of Young’s modulus (E), shear modulus (G) and Poisson's ratio, and the sequence of the crystalline phases formed during a double-stage heat treatment. The effects of crystallization on hardness and fracture toughness were also examined. High temperature X-ray diffraction experiments revealed the presence of spinel (MgO.Al2O3), rutile (TiO2), karooite (MgO.2TiO2), sillimanite (Al2O3.SiO2) and sapphirine (4MgO.5Al2O3.2SiO2) after crystallization. The elastic and shear moduli of the glass-ceramics (GC) were approximately 20% larger than those of the parent glass. Hardness values were close to 10 GPa and KIC close to 1.2 MPa.m1/2. Aiming to obtain transparent and colorless GC, new formulations, dubbed ZT1B4, 75-25/ZT and 75-25/25Ti, with lower titania content and higher zirconia content, were proposed and crystallized. Formulation ZT1B4 yielded a transparent GC with hardness of up to 8 GPa and an indentation fracture toughness (IFT) about 40% higher than that of the parent glass. Formulations 75-25/ZT and 75-25/25Ti yielded transparent GC with hardness values of up to 9 GPa and an IFT up to 35% higher than that of the parent glass. A series of glasses were also melted using metallic Ag as nucleating agent instead of ZrO2 and TiO2. The applied heat treatments generated non-homogeneous GC, which became warped due to the high crystallization temperatures. These new precursor glasses were therefore discarded. Transmittance in the ultraviolet to visible range was measured in the glass and GC samples of formulations 75-25, 75-25/ZT and 75-25/25Ti. Formulation 75-25/ZT presented the highest transmittance in both glass and GC states. It was concluded that among the new compositions, formulation 75-25/ZT is the most suitable one for use as ballistic protection when transparency to visible light is required
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Araújo, Hugo Valença 1988. "Simulação e análise do desempenho termodinâmico de sistemas de refrigeração por absorção com diferentes configurações." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266566.
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Orientador: José Vicente Hallak d'AngeloDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-23T08:54:55Z (GMT). No. of bitstreams: 1 Araujo_HugoValenca_M.pdf: 2457535 bytes, checksum: cf5a800ee51a5605b7d2cd69248ef52c (MD5) Previous issue date: 2013
Resumo: A refrigeração e o condicionamento de ar representam um campo tecnológico em potencial para a adoção de medidas de economia de eletricidade. Nesse sentido, Sistemas de Refrigeração por Absorção (SRAs) figuram como uma opção interessante por serem adequados à produção de frio mediante um gasto significativamente menor de energia elétrica em comparação a Sistemas de Refrigeração por Compressão Mecânica (SRCMs) de vapor. Com a finalidade de gerar o efeito de refrigeração, o SRCM realiza uma compressão mecânica de vapor à custa do consumo de trabalho elétrico em um compressor; em contrapartida, a compressão no SRA é de natureza termofísica/química e promovida por energia térmica. No segmento de açúcar e álcool brasileiro, a etapa determinante da produção de etanol a partir da cana consiste na fermentação alcoólica do mosto em dornas. Tal etapa é exotérmica e, uma vez que a elevação descontrolada da temperatura desfavorece a produção de álcool, há a necessidade de remover o calor gerado por meio do resfriamento do meio em fermentação. Dessa forma, o objetivo geral do presente trabalho foi simular e analisar o desempenho termodinâmico (energético, COP, e exergético, ?ex) de SRAs com diferentes configurações, trabalhando com o par água/brometo de lítio (H2O/LiBr) e que satisfaçam a carga de refrigeração demandada por um processo fermentativo. Adicionalmente, um dos objetivos específicos foi investigar o risco de ocorrência da cristalização do LiBr, a qual resulta em depósitos, com o auxílio da curva de equilíbrio sólido-líquido (solubilidade) do par H2O/LiBr. As análises dos efeitos de variáveis de projeto e operação (realizadas no software Engineering Equation Solver - EES) demonstraram que os valores de COP das configurações de SRAs de duplo efeito são significativamente maiores do que aquele da configuração de simples efeito; no entanto, as eficiências exergéticas de todas as configurações são equiparáveis, o que pode ser atribuído à quantidade e à qualidade da energia térmica consumida nos respectivos geradores de primeiro efeito. Baixos desempenhos de Segunda Lei são devidos principalmente ao absorvedor, pois esse equipamento apresenta os maiores defeitos de eficiência em todos os SRAs estudados. Adicionalmente, avaliou-se a dependência do desempenho termodinâmico quanto às efetividades de trocadores de calor intermediários, a diferenças de pressão operacional e à cessão direta de calor externo a geradores de segundo efeito. Entre outros resultados, observou-se a existência de máximos do COP e da ?ex em função da temperatura no gerador de primeiro efeito. No que se refere à possibilidade de precipitação do LiBr, verificou-se menor iminência no SRA de duplo efeito com fluxo em paralelo. Em particular, observou-se que aumentos excessivos da temperatura no gerador de primeiro efeito, além de não favorecerem o desempenho termodinâmico, tornam o risco de cristalização do LiBr mais significativo
Abstract: Refrigeration and air conditioning represent a potential technological field for the adoption of measures to save electricity. In this way, Absorption Refrigeration Systems (ARSs) are an interesting option because they are suitable for the production of cold utilities with a significantly lower cost of electric power compared to Mechanical Compression Refrigeration Systems (MCRSs). In order to generate the cooling effect, the MCRS performs a mechanical vapor compression at the expense of the consumption of electrical work in a compressor. On the other side, the nature of the compression in ARSs is thermo physical/chemical and this process is promoted by thermal energy. In the Brazilian sugar and ethanol industry, the main stage of ethanol production from sugarcane is the alcoholic fermentation in vats. This stage is exothermic and since the uncontrolled elevation of temperature results in disadvantages to the ethanol production, it is necessary to remove the heat generated by the cooling of the fermentation medium. Thus, the general objective of this study was to simulate and analyze the thermodynamic performance (energy, COP, and exergy, ?ex) of ARSs with different configurations, working with the water/lithium bromide (H2O/LiBr) mixture, and satisfying the cooling load demanded by a fermentation process. Additionally, one of the specific objectives was to investigate the risk of LiBr crystallization, resulting in deposits, with the aid of the solid-liquid equilibrium (solubility) curve of the H2O/LiBr mixture. Analyses of the effects of design and operating variables (executed in the software Engineering Equation Solver - EES) have shown that the values of COP of the double effect configurations are significantly greater than that of the simple effect configuration; however, the exergetic efficiencies of all configurations are comparable, which can be attributed to the quantity and the quality of the energy consumed in the respective first effect generators. Low Second Law performances are mainly due to the absorber because this equipment has the highest efficiency defects in all ARSs studied. Additionally, it was evaluated the dependence of the thermodynamic performance regarding to the effectivenesses of intermediate heat exchangers, the differences in operating pressures and the direct supply of external heat to second effect generators. Among other findings, it was observed the existence of maximums of COP and ?ex as functions of the temperature in the first effect generator. With regard to the possibility of LiBr precipitation, it was verified lower imminence in the double effect ARS with parallel flow. In particular, it was observed that excessive rises in the temperature in the first effect generator, besides not favor the thermodynamic performance, makes the risk of LiBr crystallization more significant
Mestrado
Sistemas de Processos Quimicos e Informatica
Mestre em Engenharia Química
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Vicard, Céline. "Étude et modélisation de la synthèse du polyamide 6 pour la mise en œuvre de composites thermoplastiques par voie liquide réactive." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2018. http://www.theses.fr/2018EMAC0001/document.
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L’utilisation de procédés de type voie liquide (RTM, LRI) pour l’élaboration de composites thermoplastiques est une des voies prometteuses pour pallier les limitations liées à la haute viscosité des polymères thermoplastiques. Pour cela, la matrice est obtenue par polymérisation in situ de son monomère de faible viscosité après l’imprégnation du renfort fibreux. Cette étude s’est focalisée sur le polyamide 6 (PA6) obtenu par polymérisation anionique par ouverture de cycle de l'ε-caprolactame. La particularité de cette synthèse réside dans le couplage entre la polymérisation des chaînes et leur cristallisation, qui sont des phénomènes tous deux thermodépendants, exothermiques et régissant la viscosité du milieu réactif. La caractérisation cinétique par DSC de ce couplage a permis une meilleure compréhension de l'interaction des phénomènes, en révélant notamment une cinétique de cristallisation particulière à basse température. Cette base de données, complétée par l’étude des propriétés physico-chimiques du PA6 synthétisé, a permis d'alimenter la modélisation des phénomènes. Un nouveau couplage a ainsi été proposé pour rendre compte de la dépendance de la cristallisation à la cinétique de polymérisation et a permis d'éditer des diagrammes Temps-Température-Transformation (TTT) de la synthèse du PA6. En vue de la mise en œuvre de composites thermoplastiques, la simulation du couplage thermocinétique avec un terme source a été réalisée afin de mesurer l’impact de ces phénomènes exothermiques sur les gradients thermiques et cinétiques dans l’épaisseur d’une pièce. Les cinétiques ont de plus été étudiées en présence de fibres de verre et en rhéologie. La présence de fibres engendre un ralentissement de la cinétique de synthèse et le comportement rhéocinétique révèle l’existence d’un point de gel. Ces observations restent à considérer pour simuler l’écoulement du système réactif dans un renfortLiquid type processes (RTM, LRI) for thermoplastic composites manufacturing is one of the most promising routes to overcome the limitations due to the high viscosity of thermoplastic polymers. In this process, the matrix is obtained via in situ polymerization of its low-viscosity monomer after impregnation of the fibrous reinforcement. This study focused on polyamide 6 (PA6) obtained by anionic ring-opening polymerization of ε-caprolactam. The distinctive aspect of this reaction resides in the coupling between chains polymerization and their crystallization, both thermo-dependent, exothermic and driving the viscosity of the reactive mixture.The kinetic characterization of this coupling by DSC allowed for a better understanding of phenomena interaction, revealing notably a specific crystallization kinetic at low temperature. This database, complemented by a study of physicochemical properties of synthesized PA6, has been used to model the underlying phenomena. A new coupling equation has been proposed to take into account the crystallization dependence on the polymerization kinetic, allowing to edit Time-Temperature-Transformation (TTT) diagrams of the PA6 synthesis. Simulations of the thermokinetic coupling with a source term have been performed, highlighting the impact of these exothermic phenomena on thermal and kinetic gradient in the thickness of a part. To reproduce the conditions of the composite manufacturing process, kinetics have also been studied in the presence of glass fibers and in a rheometer. The presence of fibers leads to slower kinetics and the rheokinetic behavior revealed gelation. These observations have to be considered to simulate the reactive system flow in a reinforcement
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Saleemi, Ali Nauman. "Strategic feedback control of pharmaceutical crystallization systems." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8530.
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Crystallization is a widely used purification and separation technique in the pharmaceutical industry. More than 90 % of the active pharmaceutical ingredients are produced in the crystalline form. The quality of the crystalline product greatly affects the downstream processing and bioavailability of the drug. The Food and Drug Administration (FDA) initiated in 2004 the use and implementation of process analytical technology (PAT) in the pharmaceutical development and production and encourages the pharmaceutical industry to adopt quality by design (QBD) approaches. The prime objective of this initiative has been to optimize the drug development and manufacturing process by reducing cost, improving product quality and reducing the number of failed batches. The work presented in this thesis focuses on expanding the use of two PAT tools, namely attenuated total reflection ultra violet/visible spectroscopy (ATR-UV/Vis spectroscopy) and focused beam reflectance measurement (FBRM). ATR-UV/Vis spectroscopy and FRBM are mostly used for process monitoring. The aim here was to develop sophisticated control approaches using these in situ tools for enhancing the product quality. Chemometrics is an integral part of PAT, and can provide valuable information about the system. This tool has also been used in this study for calibration model development and monitoring the cooling and antisolvent crystallization processes for single and muticomponent crystallisations. The development of an accurate and robust calibration model is necessary for qualitative and quantitative analysis of a system using spectroscopy. A systematic methodology was therefore presented for the selection of a suitable calibration model for ATR-UV/Vis spectroscopy. The developed model was then used as part of supersaturation control approach (SSC). SSC uses information from ATR-UV/Vis spectroscopy in a feedback control loop to keep the system at desired supersaturation. The developed approach resulted in the production of crystals of uniform size and can represent the bases for a model-free direct design approach for crystallization systems.
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Sheikh, Ahmad Yahya. "Synthesis, optimisation and control of crystallization systems." Thesis, University College London (University of London), 1997. http://discovery.ucl.ac.uk/1317664/.
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Process systems engineering has provided with a range of powerful tools to chemical engineers for synthesis, optimisation and control using thorough understanding of the processes enhanced with the aid of sophisticated and accurate multi-faceted mathematical models. Crystallization processes have rarely benefited from these new techniques, for they lack in models that could be used to bridge the gaps in their perception before utilising the resulting insight for the three above mentioned tasks. In the present work, first a consistent and sufficiently complex models for unit operations including MSMPR crystallizer, hydrocyclone and fines dissolver are developed to enhance the understanding of systems comprising these units. This insight is then utilised for devising innovative techniques to synthesise, optimise and control such processes. A constructive targeting approach is developed for innovative synthesis of stage-wise crystallization processes. The resulting solution surpasses the performance obtained from conventional design procedure not only because optimal temperature profiles are used along the crystallizers but also the distribution of feed and product removal is optimally determined through non-linear programming. The revised Machine Learning methodology presented here for continual process improvement by analysing process data and representing the findings as zone of best average performance, has directly utilised the models to generate the data in the absence of real plant data. The methodology which is demonstrated through KNO₃ crystallization process flowsheet quickly identifies three opportunities each representing an increase of 12% on nominal operation. An optimal multi-variable controller has been designed for a one litre continuous recycle crystallizer to indirectly control total number and average size of crystals from secondary process measurements. The system identification is solely based on experimental findings. Linear Quadratic Gaussian method based design procedure is developed to design the controller which not only shows excellent set-point tracking capabilities but also effectively rejects disturbance in the simulated closed loop runs.
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Montenegro, Rivelino V. D. "Crystallization, biomimetics and semiconducting polymers in confined systems." Phd thesis, Universität Potsdam, 2003. http://opus.kobv.de/ubp/volltexte/2005/76/.
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populärwissenschaftlicher Abstract:Kristallisation, Biomimetik und halbleitende Polymere in räumlich begrenzten Systemen:
Öl und Wasser mischen sich nicht, man kann aber aus beiden Flüssigkeiten Emulsionen herstellen, bei denen Tröpfchen der einen Flüssigkeit in der anderen Flüssigkeit vorliegen. Das heißt, es können entweder Öltröpfchen in Wasser oder Wassertröpfchen in Öl erzeugt werden. Aus täglichen Erfahrungen, z.B. beim Kochen weiß man jedoch, dass sich eine Emulsion durch Schütteln oder Rühren herstellen lässt, diese jedoch nicht besonders stabil ist. Mit Hilfe von hohen Scherenergien kann man nun sehr kleine, in ihrer Größe sehr einheitliche und außerdem sehr stabile Tröpfchen von 1/10000 mm erhalten. Eine solche Emulsion wird Miniemulsion genannt.
In der Dissertation wurden nun z.B. Miniemulsionen untersucht, die aus kleinen Wassertröpfchen in einem Öl bestehen. Es konnte gezeigt werden, dass das Wasser in diesen Tröpfchen, also in den räumlich begrenzten Systemen, nicht bei 0 °C, sondern bei -22 °C kristallisierte. Wie lässt sich das erklären? Wenn man einen Eimer Wasser hat, dann bildet sich normalerweise bei 0 °C Eis, da nämlich in dem Wasser einige (manchmal ganz wenige) Keime (z.B. Schutzteilchen, ein Fussel etc.) vorhanden sind, an denen sich die ersten Kristalle bilden. Wenn sich dann einmal ein Kristall gebildet hat, kann das Wasser im gesamten Eimer schnell zu Eis werden. Ultrareines Wasser würde bei -22 °C kristallisieren. Wenn man jetzt die Menge Wasser aus dem Eimer in kleine Tröpfchen bringt, dann hat man eine sehr, sehr große Zahl, nämlich 1017 Tröpfchen, in einem Liter Emulsion vorliegen. Die wenigen Schmutzpartikel verteilen auf sehr wenige Tröpfchen, die anderen Tröpfchen sind ultrarein. Daher kristallisieren sie erst bei -22 °C.
Im Rahmen der Arbeit konnte auch gezeigt werden, dass die Miniemulsionen genutzt werden können, um kleine Gelatine-Partikel, also Nanogummibärchen, herzustellen. Diese Nanogummibärchen quellen bei Erhöhung der Temperatur auf ca. 38 °C an. Das kann ausgenutzt werden, um zum Beispiel Medikamente zunächst in den Partikeln im menschlichen Körper zu transportieren, die Medikamente werden dann an einer gewünschten Stelle freigelassen. In der Arbeit wurde auch gezeigt, dass die Gelatine-Partikel genutzt werden können, um die Natur nachzuahnen (Biomimetik). Innerhalb der Partikel kann nämlich gezielt Knochenmaterial aufgebaut werden kann. Die Gelatine-Knochen-Partikel können dazu genutzt werden, um schwer heilende oder komplizierte Knochenbrüche zu beheben. Gelatine wird nämlich nach einigen Tagen abgebaut, das Knochenmaterial kann in den Knochen eingebaut werden.
LEDs werden heute bereits vielfältig verwendet. LEDs bestehen aus Halbleitern, wie z.B. Silizium. Neuerdings werden dazu auch halbleitende Polymere eingesetzt. Das große Problem bei diesen Materialien ist, dass sie aus Lösungsmitteln aufgebracht werden. Im Rahmen der Doktorarbeit wurde gezeigt, dass der Prozess der Miniemulsionen genutzt werden kann, um umweltfreundlich diese LEDs herzustellen. Man stellt dazu nun wässrige Dispersionen mit den Polymerpartikeln her. Damit hat man nicht nur das Lösungsmittel vermieden, das hat nun noch einen weiteren Vorteil: man kann nämlich diese Dispersion auf sehr einfache Art verdrucken, im einfachsten Fall verwendet man einfach einen handelsüblichen Tintenstrahldrucker.
The colloidal systems are present everywhere in many varieties such as emulsions (liquid droplets dispersed in liquid), aerosols (liquid dispersed in gas), foam (gas in liquid), etc. Among several new methods for the preparation of colloids, the so-called miniemulsion technique has been shown to be one of the most promising. Miniemulsions are defined as stable emulsions consisting of droplets with a size of 50-500 nm by shearing a system containing oil, water, a surfactant, and a highly water insoluble compound, the so-called hydrophobe
1. In the first part of this work, dynamic crystallization and melting experiments are described which were performed in small, stable and narrowly distributed nanodroplets (confined systems) of miniemulsions. Both regular and inverse systems were examined, characterizing, first, the crystallization of hexadecane, secondly, the crystallization of ice. It was shown for both cases that the temperature of crystallization in such droplets is significantly decreased (or the required undercooling is increased) as compared to the bulk material. This was attributed to a very effective suppression of heterogeneous nucleation. It was also found that the required undercooling depends on the nanodroplet size: with decreasing droplet size the undercooling increases.
2. It is shown that the temperature of crystallization of other n-alkanes in nanodroplets is also significantly decreased as compared to the bulk material due to a very effective suppression of heterogeneous nucleation. A very different behavior was detected between odd and even alkanes. In even alkanes, the confinement in small droplets changes the crystal structure from a triclinic (as seen in bulk) to an orthorhombic structure, which is attributed to finite size effects inside the droplets. An intermediate metastable rotator phase is of less relevance for the miniemulsion droplets than in the bulk. For odd alkanes, only a strong temperature shift compared to the bulk system is observed, but no structure change. A triclinic structure is formed both in bulk and in miniemulsion droplets.
3. In the next part of the thesis it is shown how miniemulsions could be successfully applied in the development of materials with potential application in pharmaceutical and medical fields. The production of cross-linked gelatin nanoparticles is feasible. Starting from an inverse miniemulsion, the softness of the particles can be controlled by varying the initial concentration, amount of cross-link agent, time of cross-linking, among other parameters. Such particles show a thermo-reversible effect, e.g. the particles swell in water above 37 °C and shrink below this temperature. Above 37 °C the chains loose the physical cross-linking, however the particles do not loose their integrity, because of the chemical cross-linking. Those particles have potential use as drug carriers, since gelatin is a natural polymer derived from collagen.
4. The cross-linked gelatin nanoparticles have been used for the biomineralization of hydroxyapatite (HAP), a biomineral, which is the major constituent of our bones. The biomineralization of HAP crystals within the gelatin nanoparticles results in a hybrid material, which has potential use as a bone repair material.
5. In the last part of this work we have shown that layers of conjugated semiconducting polymers can be deposited from aqueous dispersion prepared by the miniemulsion process. Dispersions of particles of different conjugated semiconducting polymers such as a ladder-type poly(para-phenylene) and several soluble derivatives of polyfluorene could be prepared with well-controlled particle sizes ranging between 70 - 250 nm. Layers of polymer blends were prepared with controlled lateral dimensions of phase separation on sub-micrometer scales, utilizing either a mixture of single component nanoparticles or nanoparticles containing two polymers. From the results of energy transfer it is demonstrated that blending two polymers in the same particle leads to a higher efficiency due to the better contact between the polymers. Such an effect is of great interest for the fabrication of opto-electronic devices such as light emitting diodes with nanometer size emitting points and solar cells comprising of blends of electron donating and electron accepting polymers.
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Succaw, Gary Lee. "Dynamics of crystal growth of self-assembling systems /." view abstract or download file of text, 2004. http://wwwlib.umi.com/cr/uoregon/fullcit?p3136448.
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Thesis (Ph. D.)--University of Oregon, 2004.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 209-215). Also available for download via the World Wide Web; free to University of Oregon users.
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Sultana, Mahmooda. "Microfluidic systems for continuous crystallization of small organic molecules." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59879.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
This thesis presents one of the first demonstrations of continuous crystallization in microfluidic devices, and illustrates their use for various applications related to crystallization of small organic molecules. Crystallization is an important process in a number of industries, including specialty chemicals, food, cosmetics, nutraceuticals and, most importantly, pharmaceuticals. Most small molecule pharmaceuticals are isolated in crystalline form, and more than ninety percent of all pharmaceutical products are formulated in particulate, mainly crystalline form. However, crystallization is not a completely understood process. The sensitivity of the process to synthesis conditions gives rise to serious reproducibility issues. The traditional batch crystallizers suffer from non-uniform process conditions across the reactor, and chaotic, poorly controlled mixing of the reagents, often resulting in polydisperse crystal size distribution and impure polymorphs. This makes it difficult to obtain reliable information on the process kinetics that can be used for scale-up, as well as to study the fundamentals of the process. Microfluidic systems offer a unique toolset for crystallization because of well-defined laminar flow profiles, enhanced heat and mass transfer, better control over the contact mode of the reagents, and optical access for in situ characterization. The better control over the synthesis conditions gives rise to the potential for controlling the crystal size, as well as the polymorphic form. In addition, low consumption of reagents makes it an attractive research tool for expensive pharmaceutical compounds. Some of the advantages of microfluidics have been demonstrated for crystallization in micro-batches, but so far not in continuous devices. Continuous crystallization is difficult to achieve in microchannels as uncontrolled nucleation, crystal growth, agglomeration and sedimentation of crystals easily clog the small channels. The interaction of crystals with channel walls may also contribute to channel plugging in these devices. This thesis has developed microfluidic devices for continuous crystallization of small organic molecules for the first time. We have decoupled nucleation and growth, the two key steps of crystallization, using reaction engineering principles, and have developed two separate continuous devices, one for each of these two processes. We have used seeded crystallization and reactor design to achieve controlled growth, as well as to suppress secondary nucleation, agglomeration and sedimentation of crystals. In addition, we have eliminated any significant interaction of crystals with channel walls by controlling the properties of channel surfaces. We have also integrated microscopy and spectroscopy tools with the device for in-situ characterization of crystal size and polymorphic form. We have illustrated the use of these devices to extract growth kinetics data for crystals of various shapes, including high aspect ratio systems such as that with acicular or plate-like habits. The reproducibility and control in our devices have allowed us to elucidate the growth mechanism and fundamentals of the growth process for difficult crystal systems. In addition, we have demonstrated that continuous microfluidic devices offer a unique advantage over the current state-of-the art technology to measure the size, size distribution and growth kinetics of high aspect ratio crystal systems more accurately. Moreover, we have demonstrated the use of microfluidic devices for understanding crystal habit modification in the presence of impurities. We take advantage of the high spatiotemporal resolution of microfluidic devices to study the evolution of crystal habit over time, and to obtain information on the kinetics of habit modification in the presence of different impurities. We have developed an understanding of the habit modification mechanism for alpha glycine in the presence of alpha amino acids. Such information may not only provide insights into impurity-crystal interactions, but also serve as a powerful tool for the design of impurities that can be deliberately added to improve the crystallization process. Furthermore, we have designed and developed a second microfluidic device for continuous supercritical crystallization for the first time. Using supercritical fluid as an antisolvent, we have demonstrated continuous spontaneous nucleation of acetaminophen. We have shown the ability to produce micron-sized crystals, which may be useful for increasing the bioavailability of drugs with lower solubility, as well as for inhalable and highly potent drugs with stringent size requirements. The developed platform can also be used as a high-throughput device for safely screening crystallization conditions in the supercritical domain. We have demonstrated such use by screening the effects of pressure and various solvents on the habit, size and polymorphic form of acetaminophen crystals.
by Mahmooda Sultana.
Ph.D.
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Angelin, Marcus. "Discovery-Oriented Screening of Dynamic Systems: Combinatorial and Synthetic Applications." Doctoral thesis, KTH, Organisk kemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12524.
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This thesis is divided into six parts, all centered around the development of dynamic (i.e., reversibly interacting) systems of molecules and their applications in dynamic combinatorial chemistry (DCC) and organic synthesis. Part one offers a general introduction, as well as a more detailed description of DCC, being the central concept of this thesis. Part two explores the potential of the nitroaldol reaction as a tool for constructing dynamic systems, employing benzaldehyde derivatives and nitroalkanes. This reaction is then applied in part three where a dynamic nitroaldol system is resolved by lipase-catalyzed transacylation, selecting two out of 16 components. In part four, reaction and crystallization driven DCC protocols are developed and demonstrated. The discovery of unexpected crystalline properties of certain pyridine β-nitroalcohols is used to resolve a dynamic system and further expanded into asynthetic procedure. Furthermore, a previously unexplored tandem nitroaldol-iminolactone rearrangement reaction between 2-cyanobenzaldehyde and primarynitroalkanes is used for the resolution of dynamic systems. It is also coupled with diastereoselective crystallization to demonstrate the possibility to combine several selection processes. The mechanism of this reaction is investigated and a synthetic protocol is developed for asymmetric synthesis of 3-substituted isoindolinones. Part five continues the exploration of tandem reactions by combining dynamic hemithioacetal or cyanohydrin formation with intramolecular cyclization to synthesize a wide range of 3-functionalized phthalides. Finally, part six deals with the construction of a laboratory experiment to facilitate the introduction of DCC in undergraduate chemistry education. The experiment is based on previous work in our group and features an acetylcholinesterase-catalyzed resolution of a dynamic transthioacylation system.QC 20100628
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Bayuadri, Cosmas. "Stability of sodium sulfate dicarbonate (~2Na₂CO₃• Na₂SO₄) crystals." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11507.
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Research on salts species formed by evaporation of aqueous solution of Na2 in the early 1930s. The thermodynamic, crystallographic and many other physical and chemical properties of most of the species formed from this solution has been known for decades. However, there was no complete information or reliable data to confirm the existence of a unique double salt that is rich in sodium carbonate, up until five years ago when a research identified the double salt (~2Na ₂ CO ₃ • Na ₂ SO ₄) from the ternary system Na₂CO ₃Na₂SO ₄ H₂O. Crystallization of this double salt so called sodium sulfate dicarbonate (~2Na ₂ CO ₃ • Na ₂ SO ₄) is known to be a primary contributor to fouling heat transfer equipment in spent-liquor concentrators used in the pulp and paper industry. Therefore, understanding the conditions leading to formation of this double salt is crucial to the elimination or reduction of an industrial scaling problem. In this work, double salts were generated in a batch crystallizer at close to industrial process conditions. X-ray diffraction, calorimetry, and microscopic observation were used to investigate the stability of the salts to in-process aging, isolation and storage, and exposure to high temperature. The results show that care must be taken during sampling on evaporative crystallization. Two apparent crystal habits were detected in the formation of sodium sulfate dicarbonate; the favored habit may be determined by calcium ion impurities in the system. The results also verify that sodium sulfate dicarbonate exists as a unique phase in this system and that remains stable at process conditions of 115-200℃
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Xie, Zhong Jian. "Effet élastocalorique dans le caoutchouc naturel." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI025/document.
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Les effets caloriques représentent la capacité d’un matériau à voir son entropie varier sous l’effet d’une sollicitation externe et peuvent être utilisés pour des systèmes de refroidissement à l'état solide en remplacement (ou complément) des dispositifs traditionnels à base de fluides frigorifiques. Dans cette thèse, nous avons cherché à étudier l'effet élastocalorique du caoutchouc naturel. Après une présentation des différents matériaux caloriques et du caoutchouc naturel, le chapitre 2 détaille la caractérisation élastocalorique du caoutchouc naturel, et les résultats sont interprétés à partir de la notion de cristallisation induite par la déformation. Le changement de température adiabatique élastocalorique et la variation d’entropie associée atteignent 9K et 50kJ.m-3.K-1, ce qui est très important comparé aux autres matériaux caloriques. L’effet élastocalorique étant maximum pour une déformation voisine de 4,5, une pré-déformation peut être appliquée pour éviter la zone moindre activité élastocalorique. La mesure directe de l’effet élastocalorique est ensuite comparée à une méthode indirecte déduite du facteur de Clapeyron, et les divergences sont discutées. Dans le chapitre 3, la contrainte et la température élastocalorique sont simulées par un modèle de Flory modifié sur la base de la cristallisation. Il est possible de prédire le comportement contrainte-déformation à différentes températures, ainsi que les variations de température élastocaloriques à température ambiante. Dans le chapitre 4, les effets de la fatigue sur l’effet élastocalorique du caoutchouc naturel sont ensuite étudiés. La résistance à la fatigue pour de grandes amplitudes de déformation est très faible (< 800 cycles). Trois régimes de déformation intermédiaire sont ensuite testés : 0-3, 2-5, et 4-7, et permet d’établir que le régime 2-5 est le plus performant (jusqu’à 100 000 cycles). Dans le dernier chapitre, un modèle de système régénératif de refroidissement à base de matériaux caloriques est développé afin d’établir des lignes directrices pour le choix des matériaux élastocaloriquesIn this thesis, we aimed to study the eC effect of natural rubber (NR) and to prove its potential to act as an eC material primarily. The method for improving the eC effect efficiency and fatigue life of NR were also proposed. The eC effect of NR is characterized directly, and interpretation based on the theory of strain-induced crystallization/crystallite (SIC) is proposed. The eC adiabatic temperature change and isothermal entropy change of NR can be up to 9 K and 50 kJ.m-3.K-1 (56 J.kg-1.K-1), which are larger than most of caloric materials. Two coefficients, eC strain coefficient and eC stress coefficient , are defined for evaluating the eC performance at different strains, where is the specific entropy, is the engineering strain, is the temperature and is the stretching stress. It’s found that both coefficients are maximum for a strain around 4.5, indicating that the highest eC performance occurred at middle strain, which is attributed to the occurrence of SIC. To improve the eC performance, it is proposed to apply a pre-strain, so that the low strain regime where eC performance is low can be skipped. Moreover, the large needed deformation can be reduced by the pre-strain and thus the possibility of a compact cooling system designed based on NR is improved. The fatigue property of eC effect of NR is then investigated. The fatigue life at large deformation strain amplitudes (strain of 1-6) is about 800 cycles for the tested NR, which is too short to be used for a cooling system. Decreasing strain amplitude is necessary to extend fatigue life up to requirement of a cooling device. For the same small strain amplitude of 3, the fatigue property is compared at amorphous strain regime (strain of 0-3), onset strain of melting (strain of 2-5) and high strain of SIC (strain of 4-7). It’s found that a larger eC temperature change and a better fatigue property can be obtained at two SIC strain regimes (strain of 2-5 and 4-7) than amorphous strain regime. Especially, the fatigue property at the onset strain of melting (strain of 2-5) is better than that at high strain of SIC (strain of 4-7). A high-cycle fatigue was applied at the strain of 2-5 (most promising strain regime) up to 1.7×105 cycles. It was observed that there is no crack of the sample, as well as a degradation degree of 12% of the eC temperature change. Furthermore, the eC stress coefficient (4.4 K/MPa) at onset strain of melting is larger than that at high strain of SIC (1.6 K/MPa). As a result, the middle strain regime (onset strain regime of melting) can get a higher eC performance, larger temperature change, and better fatigue life, which should be chosen for eC cooling system
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Chavez, Krystle J. "Crystallization of pseudopolymorphic forms of sodium naproxen in mixed solvent systems." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29759.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Rousseau, Ronald; Committee Member: Meredith, Carson; Committee Member: Prausnitz, Mark; Committee Member: Teja, Amyn; Committee Member: Wilkinson, Angus. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Uccheddu, Basile. "Observateurs pour un procédé de cristallisation en batch." Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00751922.
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Ce travail a pour but la réalisation d'un outil permettant d'estimer la germination et la distribution en taille de cristaux d'un procédé de cristallisation. Pour ce faire un modèle de cristallisation a été développé et nous a permis de réaliser un observateur de dimension finie afin d'estimer la germination. Par la suite, un observateur de dimension infinie a été mis au point dans le but d'estimer la distribution de taille des cristaux à partir de la germination et de la mesure d'une taille de la distribution. Les deux observateurs ont été validés expérimentalement sur un procédé "batch" de cristallisation de l'oxalate d'ammonium.
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Simba, Bruno Galvão. "Caracterização da vitrocerâmica de Li2Si2O5 em função do tratamento térmico e da análise da usinagem /." Guaratinguetá, 2019. http://hdl.handle.net/11449/182096.
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Orientador: Marcos Valério RibeiroResumo: O dissilicato de lítio, Li2Si2O5, é um material vitrocerâmico muito utilizado na fabricação de próteses dentárias, possui grande destaque por ser biocompatível e devido suas propriedades estéticas, químicas e mecânicas, permite a confecção de próteses a partir da usinagem CAD/CAM (COMPUTER-AIDED DESIGN / COMPUTER-AIDED MANUFACTURING), com elevada precisão dimensional e a possibilidade de restauração imediata em pacientes. Os materiais comerciais são disponibilizados com estrutura Li2SiO3 (metassilicato de lítio) cujas características são: alta usinabilidade e baixa tenacidade à fratura. Após a usinagem das próteses, o material sofre tratamento térmico visando à conversão do Li2SiO3 em Li2Si2O5 (dissilicato de litio), fase de melhor tenacidade e excelente apelo estético. A compreensão desta transformação de fase, seus efeitos na usinabilidade e nas propriedades mecânicas é de interesse tecnológico e científico, pois o material será utilizado como prótese dentária após este processamento. Este trabalho visou à avaliação do Li2Si2O5 em relação as propriedades químicas, físicas e mecânicas quando submetido a diferentes tratamentos térmicos. Foram empregados métodos de caracterização por difração de raios X (DRX), microscopia eletrônica de varredura (MEV), massa específica aparente, além da determinação da dureza, tenacidade à fratura, constantes elásticas e resistência à flexão biaxial sob diferentes condições de tratamento térmico. Também foram analisados a distribuição de partí... (Resumo completo, clicar acesso eletrônico abaixo)
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Antonello, Alice [Verfasser]. "Crystallization of complex inorganic systems within the confinement of miniemulsion droplets / Alice Antonello." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1136638776/34.
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Shank, Dale. "Evaluating carbon dioxide as a causative agent of otolith crystallization in recirculating aquaculture systems." Bowling Green State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1603716784275007.
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Carlert, Sara. "Investigation and Prediction of Small Intestinal Precipitation of Poorly Soluble Drugs : a Study Involving in silico, in vitro and in vivo Assessment." Doctoral thesis, Uppsala universitet, Institutionen för farmaci, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-178053.
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The main objectives of the present project were to increase the understanding of small intestinal precipitation of poorly soluble pharmaceutical drugs, investigate occurrence of crystalline small intestinal precipitation and effects of precipitation on absorption. The aim was to create and evaluate methods of predicting crystalline small intestinal drug precipitation using in vivo, in vitro and in silico models. In vivo small intestinal precipitation from highly supersaturated solutions of two weakly basic model drugs, AZD0865 and mebendazole, was investigated in humans and canine models. Potential precipitation of AZD0865 was investigated by examining dose dependent increases in human maximum plasma concentration and total exposure, which turned out to be dose linear over the range investigated, indicating no significant in vivo precipitation. The small intestinal precipitation of mebendazole was investigated from drug concentrations and amount of solid drug present in dog jejunum as well as through the bioavailability after direct duodenal administration in dogs. It was concluded that mebendazole small intestinal precipitation was limited, and that intestinal supersaturation was measurable for up to 90 minutes. In vitro precipitation methods utilizing simulated or real fasted gastric and intestinal fluids were developed in order to simulate the in vivo precipitation rate. The methods overpredicted in vivo precipitation when absorption of drug was not simulated. An in vitro-in silico approach was therefore developed, where the in vitro method was used for determining the interfacial tension (γ), necessary for describing crystallization in Classical Nucleation Theory (CNT). CNT was evaluated using a third model drug, bicalutamide, and could successfully describe different parts of the crystallization process of the drug. CNT was then integrated into an in silico absorption model. The in vivo precipitation results of AZD0865 and mebendazole were well predicted by the model, but only by allowing the fundamental constant γ to vary with concentration. Thus, the in vitro-in silico approach could be used for small intestinal precipitation prediction if the in vitro concentration closely matched in vivo small intestinal concentrations.
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Böbel, Alexander [Verfasser], and Gregor [Akademischer Betreuer] Morfill. "Crystallization and demixing: morphological structure analysis in many-body systems / Alexander Böbel ; Betreuer: Gregor Morfill." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1173616233/34.
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Erdiller, Emrah Salim. "Investigation Of Solidification And Crystallization Of Iron Based Bulk Amorphous Alloys." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/1096585/index.pdf.
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The aim of this study is to form a theoretical model for simulation of glass forming ability of Fe �
Based bulk amorphous alloys, to synthesize Fe &
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based multicomponent glassy alloys by using the predictions of the theoretical study, and to analyze the influence of crystallization and solidification kinetics on the microstructural features of this amorphous alloys. For this purpose, first, glass forming ability of Fe &
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(Mo, B, Cr, Nb, C) &
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X ( X = various alloying elements, selected from the periodic table) ternary alloy systems were simulated for twenty different alloy compositions by using the electronic theory of alloys in pseudopotential approximation and regular solution theory. Then, by using the results of the theoretical study, systematic casting experiments were performed by using centrifugal casting method. The alloying elements were melted with induction under argon atmosphere in alumina crucibles and casted into copper molds of different shapes. Characterization of the cast specimens were performed by using DSC, XRD, SEM, and optical microscopy. Comparison of equilibrium and nonequilibrium solidification structures of cast specimens were also performed so as to verify the existence of the amorphous phase. Good agreement of the results of experimental work, with the predictions of the theoretical study, and the related literature was obtained.
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Simone, Elena. "Application of process analytical technology (PAT) tools for the better understanding and control of the crystallization of polymorphic and impure systems." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/20098.
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This work presents a comprehensive study on the application of PAT tools to study, monitor and control polymorphism during batch cooling crystallization processes. For the first time, the same techniques were used to control and adjust polymorphic purity of the solid phase but also to investigate the relation between chemical equilibrium in solution and polymorphic outcome of cooling crystallization. Crystallization is an important unit operation used as separation and purification technique. It is widely employed in the pharmaceutical, chemical, agrochemical, food and cosmetics industries but also in the electronic, metallurgic and material industries. More than 90% of the APIs on the market are produced by crystallization, therefore, monitoring and control this process is fundamental to ensure the quality of the final product. The implementation of process analytical technology (PAT) tools during the development stage of APIs has largely helped in better understanding and optimizing both batch and, more recently, continuous crystallization. Polymorphism is the capacity of a compound to crystallize in more than one different crystalline structure, which can have different properties such as density, melting point, bioavailability and solubility. The choice of solvent, pH, kinetic conditions and presence of impurities has very strong effect on the polymorphic outcome of a cooling crystallization in solution. Understanding this phenomenon as well as being able to monitor and control it during industrial crystallization is one the biggest challenges for pharmaceutical industries.
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Carr, Joel Matthew. "CONFINED LAYERED POLYMERIC SYSTEMS FOR PACKAGING ANDCAPACITOR APPLICATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1363104386.
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Lundin, Josefin. "Investigation of How Different Fat Systems and Other Ingredients Affect the Properties of Whipping Creams Based on Vegetable Fat." Thesis, Linnéuniversitetet, Institutionen för kemi och biomedicin (KOB), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-27209.
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Whipping creams are oil-in-water emulsion which by whipping can be formed to a foam by the incorporation of air into the system. Traditionally whipping creams are made out of milk but today imitation whipping creams based on vegetable fat has gained a large share of the marked due to their many benefits compared to traditionally whipping creams. Imitation whipping creams are both cheaper and more flexible than traditionally creams. By vary the characteristics of the fat system and the cream recipe the properties of the imitation creams can be adapted to fit the purpose of a specific product. The aim of this thesis was to increase the understanding of how different types of fat systems and other ingredients affect the properties of imitation whipping creams based on vegetable fat. This was done by studying three vegetable fat systems with different physicochemical properties. The properties of the fat systems were characterized and the three fat systems were then used for making different imitation whipping creams. The properties of the creams were characterized and the properties of the fat systems and the creams were assessed and compared with each other. The study showed that the fat characteristics that generally seem to have the highest impact on the properties of whipping creams are the structure, the solid fat content and the crystallization temperature of the fat. A fat solution with a hard structure, a high crystallization temperature and a high solid fat content at a wide range of temperatures overall seem to provide the whipping creams with the best properties. This as these fat properties provide the creams with a high foam stability, a high overrun and a short whipping time. This study has also shown that other ingredients than the fat systems provide the creams with diverging properties. This is best shown by the results of the freeze-thaw stability which indicate that a recipe with a high amount of sugar seem to provide the whipping creams with good freeze-thaw stability. Other properties of the whipping creams also seem to be very much influenced by other ingredients than the fat systems but further studies are needed to provide clarity to the complexity of the interplay of the ingredients in whipped creams.
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Yoshida, Yukihiro. "Effet élastocalorique dans le caoutchouc naturel et le terpolymère : Mécanismes responsables de la variation de température et bilan énergétique sous déformation." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI070.
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Les effets électrocaloriques, qui se traduisent par une variation de température induite par une variation d’entropie ont été étudiés comme alternative aux systèmes de réfrigération utilisant un cycle de compression/détente. Le travail de thèse se focalise sur l’étude de l’effet élastocalorique dans le caoutchouc naturel et le terpolymère (P(VDF-TrFE-CTFE). En premier lieu, l’effet élastocalorique dans le caoutchouc naturel qui compte parmi les meilleurs candidats, a été évalué pour des cycles de déformation réalisés avec différentes valeurs d’allongement. Une variation de température de 4 °C a pu être observée. Il est usuel d’utiliser la relation déformation/contrainte en fonction de la variation de température pour évaluer l’effet élastocalorique. Il a été démontré que cette méthode ne peut pas être utilisée dans le cas du caoutchouc naturel et qu’elle doit être remplacée par la mesure de la variation de l’énergie mécanique en fonction de la température. Et dans ce cas, une variation linéaire entre ces deux dernières grandeurs a été observée. En réalisant un bilan d’énergie pendant l’essai, non seulement, le rendement énergétique a pu être évalué mais il a été aussi possible de prendre en compte l’effet Mullins et la cristallisation induite par la déformation pour le caoutchouc naturel. Dans un second temps, l’effet élastocalorique a été étudié sur le terpolymère (P(VDF-TrFE-CTFE), ce qui a permis de montrer qu’il était possible d’obtenir une variation de température de 2.1 °C sous réserver de pré-déformer le terpolymère à plus de 1050 % avant. Par comparaison avec d’autres matériaux présentant une bonne conversion élastocalorique, le fort potentiel de ce matériau a pu être mis en évidence. Enfin, il a été mis en évidence que la plus grande partie de l’énergie mécanique était bien convertie en énergie thermiqueCaloric effects (CEs), which are the phenomena that temperature variation is caused by entropy change, have been investigated for the novel system which might be able to replace conventional vapor compression refrigeration system. In the present thesis, the elastocaloric effect (ElCE) of natural rubber (NR) and terpolymer, poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)), was focused. First of all, NR, which is an excellent candidate material for ElCE, was evaluated in cyclic deformation with different strain levels. It was found that NR exhibits temperature variation of around 4.0 °C. In general, the relation between stress/strain versus temperature variation is used to evaluate ElCE. The unsuitability of such evaluation method for NR was demonstrated. The evaluation method for ElCE which uses energy balance was then proposed. A linear relation between the temperature variation caused by ElCE and the applied mechanical energy by deformation was experimentally found. This fact verifies the suitability of the proposed method. Using the energy balance, besides, not only the conversion efficiency but also the influences of the Mullins effect and the strain-induced crystallization on the ElCE of NR were discussed. ElCE of P(VDF-TrFE-CTFE) was also evaluated in order to find out the potential of polymer. It was found that present terpolymer which is not one of the elastomers can also exhibit a large temperature variation, 2.1 °C, caused by ElCE if a large pre-stretch such as more than 1050 % is applied in advance. By comparison with other materials for ElCE, it was demonstrated that P(VDF-TrFE-CTFE) can be a high potential material for ElCE. It was also shown that P(VDF-TrFE-CTFE) converts most of the applied mechanical energy into the heat energy
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Hu, Yushan. "OXYGEN TRANSPORT AS A STRUCTURE PROBE FOR HETEROGENEOUS POLYMERIC SYSTEMS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1112902488.
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Clogston, Jeffrey. "Applications of the lipidic cubic phase from controlled release and uptake to in meso crystallization of membrane proteins /." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1117564268.
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Thesis (Ph.D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxii, 352 p.; also includes graphics. Includes bibliographical references (p. 346-352). Available online via OhioLINK's ETD Center
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Vialetto, Jacopo. "Interface-driven soft matter systems : from 2D particle crystallization and light-responsive assemblies to magnet-guided fluid transport." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS358.
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Les matériaux mous impliquant des interfaces liquides présentent un grand intérêt scientifique en raison des multiples forces faibles en jeu qui dictent leur disposition et leur comportement, souvent surprenants. Dans cette thèse, nous avons étudié de nouveaux phénomènes et principes d'actuation pour le contrôle de la structure (organisation) et de la dynamique (mouvement) des systèmes de matière molle aux interfaces liquides, de l'assemblage dirigé de particules solides à la manipulation de gouttes flottantes. Nous avons établi une méthode pour adsorber et cristalliser des particules, de taille micro- ou nanométrique, à l'interface air/eau, mettant en évidence un nouveau rôle des tensioactifs pour contrôler l'organisation bidimensionnelle (2D) des particules à une concentration de tensioactif extraordinairement faible. Nous avons ensuite programmé ces assemblages en 2D afin de contrôler l'organisation des particules avec la lumière, en élaborant deux stratégies innovantes. L'utilisation de particules absorbant la lumière nous a permis de construire des structures ordonnées reconfigurables. Avec des particules ordinaires et des surfactant photosensibles, nous avons démontré un nouveau type de cristaux 2D dissipatifs (organisation induite par la lumière grâce à un apport constant en énergie). En parallèle, nous avons conçu une nouvelle méthode d'actuation magnétique pour la manipulation de petites entités liquides (gouttes, billes liquides) au moyen de substrats liquides paramagnétiques déformables, permettant de diriger, à l'aide de simples aimants permanents, le mouvement de gouttes d'huile ou d'eauSoft materials interacting at/with liquid interfaces are of great scientific interest because of the multiple weak forces at play that dictate their, often surprising, arrangement and behaviour. In this thesis, we studied novel phenomena and actuating principles for the control of the structure (organization) and dynamics (motion) of soft matter systems at liquid interfaces, from the directed assembly of thousands of solid particles, to the manipulation of small floating drops. We established the first method to both adsorb and crystallise nm- to µm-sized particles at air/water interface, evidencing a new role of surfactants to control two-dimensional (2D) particle organization at extremely low surfactant concentration. We then programmed such 2D assemblies in order to control particle organization with light stimulation, devising two innovative strategies. Using light-absorbing particles allowed us to construct reconfigurable ordered structures (light-controlled inter-particle distance and disassembly). With ordinary particles and photosensitive surfactant, we demonstrated a new kind of dissipative 2D crystals (light-induced organization through continuous consumption of energy). In parallel, we conceived a novel magnetic actuation method for the manipulation of small liquid entities (drops, liquid marbles) by means of deformable paramagnetic liquid substrates, shaping the liquid surface with small permanent magnets and in turn directing the motion of water and oil drops in a user-defined fashion
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Esposito, Rosario. "Studies of volatile evolution in magmatic systems using melt inclusions." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/28287.
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Understanding volatile evolution associated with active volcanic magmatic systems is of paramount importance because volatiles control and determine the magnitude of an eruption owing to the large change in molar volume that volatile species show depending on their physical state (volatiles dissolved in silicate melts vs. volatiles exsolved as vapor). For active volcanic systems studying the volatile evolution can help to assess the potential hazard associated to a certain locality. Also, volatile evolution in magmatic system controls the formation of certain ore deposits.
Despite the importance of understanding volatile evolution of magmatic systems, concentrations of volatiles of evolving magmas are not easily available especially for magmas originated in the deep crust. Fortunately, sample of melts can be entrapped as melt inclusion (MI) into growing igneous minerals in crystalizing magma chamber. After the entrapment, the crystal works as an insulating capsule from the external magmatic environment.
Researchers have started to use MI because they provide some advantages in respect to the classical whole rock approach to petrological studies. One of the most important advantages is that MI often represent sample of a deep and non-degassed melt (glass) available at Earth's surface. In fact, with the exception of deep ocean basalts, igneous whole rocks found at the Earth's surface are degassed magmas.
This dissertation is a compilation of four publications produced during six years of research and is addressed to give a contribution in understanding the volatile evolution in magmatic systems and also to improve the present understanding of information that can be obtained using the melt inclusions technique.
In the first chapter, I present an alternative interpretation of H₂O-CO₂ trends obtained from MI. In this study, we demonstrate that these trends can be due to post entrapment crystallization on the wall of the MI and not to magma ascent. This alternative view is more realistic especially for cases where in the same phenocrysts MI show strongly different CO₂ concentrations.
In the second chapter, I present a study to test for the MI reliability in recording volatile concentrations. We used the approach of the melt inclusion assemblage (MIA) that consists of analyzing groups of MI presumably entrapped at the same time and, thus, at same chemical and physical conditions. The results show that most of the MIA studied show consistent volatile concentrations corroborating the reliability of the MI technique. CO₂ shows the highest degrees of variability and we have assessed this behavior mostly to C-contamination in the surface of the sample.
The third chapter is a study case (the Solchiaro eruption in Southern Italy) that shows the potential uses of MI to understanding the volatile evolution. I present a model showing the dynamic of the magma based on MI. This study also discusses the origin of anomalous MI and which MI provide the best information.
The final chapter is dedicated to test the applicability of the new Linkam TS1400XY heating stage. I was able to show how this new microthermometric tool is capable of homogenizing MI at high temperature and to quench MI to a homogeneous glass state.Ph. D.
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Lucas, Bruce. "Fundamental Modeling of Solid-State Polymerization Process Systems for Polyesters and Polyamides." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29378.
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The dissertation describes and assembles the building blocks for sound and accurate models for solid-state polymerization process systems of condensation polymers, particularly poly(ethylene terephthalate) and nylon-6. The work centers on an approach for modeling commercial-scale, as opposed to laboratory-scale, systems. The focus is not solely on coupled polymerization and diffusion, but extends to crystallization, physical properties, and phase equilibrium, which all enhance the robustness of the complete model.
There are three applications demonstrating the utility of the model for a variety of real, industrial plant operations. One of the validated simulation models is for commercial production of three different grades of solid-state PET. There are also validated simulation models for the industrial leaching and solid-state polymerization of nylon-6 covering a range of operating conditions. The results of these studies justify our mixing-cell modeling approach as well as the inclusion of all relevant fundamental concepts.
The first several chapters discuss in detail the engineering fundamentals that we must consider for modeling these polymerization process systems. These include physical properties, phase equilibrium, crystallization, diffusion, polymerization, and additional modeling considerations. The last two chapters cover the modeling applications.Ph. D.
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Sharma, Satyajeet. "AMORPHOUS PHASE FORMATION IN MECHANICALLY ALLOYED FE-BASED SYSTEMS." Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2484.
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ABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on amorphization, effect of Carbon addition on GFA, and observation of mechanical crystallization in Fe-based systems have been discussed. The subsequent chapter briefly mentions about the consolidation of amorphous powders and presents results of hot pressing and spark plasma sintering on one of the alloy systems. The final chapter summarizes the Dissertation and suggests some prospective research work that can be taken up in future. The Dissertation emphasizes the glass-forming ability, i.e., the ease with which amorphization can occur. In this work the milling time required for amorphization was the indicator/measure of GFA. Although the ultimate aim of this work was to consolidate the Fe-based amorphous alloy powders into bulk so as to undertake mechanical characterization, however, it was first necessary to study the glass forming aspect in the different alloy systems. By doing this a stage has been reached, where different options are available with respect to amorphous phase-forming compositions and the knowledge to improve glass-forming ability via the mechanical alloying technique. This will be ultimately useful in the powder compaction process into various shapes and sizes at optimum pressure and temperature. The study on mechanical crystallization indicates, or in a way defines, a limit to the process of amorphization, and it was also demonstrated that this phenomenon is more common in occurrence than and not as restricted as it was earlier reported to be.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD
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Shah, Zulfiqar Hussain. "Synthesis and Characterizations of Fe-based Metallic Glassy Systems." Thesis, KTH, Materialvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37395.
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This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.
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Tam, Le Minh [Verfasser]. "Designing crystallization based-enantiomeric separation for chiral compound-forming systems in consideration of polymorphism and solvate formation / Le Minh Tam." München : Verlag Dr. Hut, 2014. http://d-nb.info/1052374735/34.
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[Verfasser], Le-Minh-Tam. "Designing crystallization based-enantiomeric separation for chiral compound-forming systems in consideration of polymorphism and solvate formation / Le Minh Tam." München : Verlag Dr. Hut, 2014. http://nbn-resolving.de/urn:nbn:de:101:1-2014062022375.
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Achour, Zeineb. "Étude structurale et thermodynamique du système n-tétracosane : n-hexacosane." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL033N.
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Des dépôts de cristaux d'hydrocarbures, se forment dans les gazoles à basse température. Ceux-ci sont principalement constitués de n-alcanes qui forment entre eux des solutions solides. Pour prévoir cette cristallisation, il est nécessaire de connaitre les propriétés thermodynamiques des mélanges solides. Le but de ce travail est l'étude du système binaire de n-alcanes pairs n-tétracosane (n-C24H50): n-hexacosane (n-C26H54), dont le diagramme est incomplet. Après une description des méthodes expérimentales utilisées, et une revue bibliographique sur les n-alcanes purs et en mélanges binaires, le diagramme de phases n-tétracosane: n-hexacosane est établi expérimentalement par analyse thermique différentielle, enthalpimétrique différentielle et radiocristallographie. Il est mis en évidence à 293 K et en fonction de la concentration molaire en n-hexacosane, la présence de deux solutions primaires de structure triclinique et de trois solutions solides intermédiaires de structure orthorhombique. Le comportement des mélanges en fonction de la température fait apparaitre quatre ou cinq séquences de phases selon la solution solide considérée. Une systématique de diagrammes binaires de n-alcanes pairs différents de deux carbones est établie par analogie avec le système n-docosane (n-C22H46): n-tetracosane (n-C24H50) et le systeme n-eicosane (n-C20H42): n-docosane (n-C22H46). Le traitement des mesures enthalpimétriques est ensuite effectué. Les variations d'enthalpie en fonction de la température des solutions solides qui apparaissent à température ambiante sont traitées par une expression dérivée du solide d'EINSTEIN. Les enthalpies et les entropies d'excès, des différentes phases sont représentées par un modèle de MARGULES à deux termes. Celles-ci jointes aux températures et aux enthalpies de transition des corps purs permettent de calculer les courbes limites de phases des différents équilibres. Le diagramme ainsi calculé coïncide avec celui établi expérimentalement
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Marchand, Jean-Pierre. "Relaxation magnétique nucléaire dans les solutions ternaires de polyacrylonitrile ou de polyacrylonitrile-co-méthallylsulfonate de sodium : détermination et caractérisation du diagramme de phases." Grenoble 1, 1993. http://www.theses.fr/1993GRE10193.
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Ce travail concerne l'etude des proprietes des solutions de polyacrylonitrile (pan) et des copolymeres d'acrylonitrile et de methallylsulfonate de sodium observees a l'equilibre ou hors equilibre thermodynamique. Utilisees dans la fabrication de membranes de dialyse renale, ces solutions ont ete explorees par rmn a une echelle d'espace caracteristique des processus physiques (cristallisation, demixtion) responsable des proprietes de permeabilite de ces membranes. Le pan et son copolymere presentent en solution un diagramme de phases typiques d'un polymere semi-cristallin; les conditions d'etablissement de la transition de phase solide-liquide et de la transition liquide-liquide ont ete precisees pour des solutions en solvant binaire dmf-eau equimolaire. La presence de charges ioniques sur la chaine polymere provoque un elargissement du domaine de la demixtion; cet effet a ete modelise dans le cadre de description des solutions proposees par flory. La cinetique de mise en ordre de ces polymeres en solution peut etre decrite comme un processus gouverne par une nucleation heterogene et sporadique, sans etape de croissance; cette cristallisation conduit a la formation de domaines ordonnes dont la taille moyenne a ete evaluee a l'aide de donnees thermodynamiques. Les membranes de dialyse renale realisees a partir de ces solutions peuvent etre decrites comme des gels physiques composes de domaines ordonnes interconnectes par des chaines polymeres a l'etat amorphe. La presence de ces domaines gouverne les proprietes de permeabilite et de selectivite de ces membranes
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Querniard, Florian. "Thermodynamic study of organic heterogeneous systems : improvement of discontinuous isoperibolic thermal analysis, and use of phase diagrams to design enantiomeric resolutions by crystallization." Rouen, 2010. http://www.theses.fr/2010ROUES026.
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Ce travail de thèse traite de l'étude thermodynamique des systèmes hétérogènes organiques. L'analyse thermique isopéribolique discontinues (DITA), une technique expérimentale permettant l'étude des diagrammes de phases a été améliorée dans trois de ses aspects. Tout d'abord, il a été montré que le signe des ruptures de pente, qui sont caractéristiques du franchissement des limites de domaines, indique le comportement direct ou rétrograde de ces limites. Ensuite, l'incertitude des résultats fournis par la DITA a été estimée grâce à un inventaire des sources d'erreur et à des tests de répétabilité. Enfin, un nouveau logiciel d'automatisation et d'exploitation des résultats a été mis au point pour rendre la technique plus accessible. L'influence de la quantité d'agent dédoublant sur la résolution d'énantiomères par sels diastéréomériques a été étudiée sur la base des diagrammes de phase. Il a été montré que, dans les cas favorables, la quantité d'agent dédoublant peut-être diminuée en dessous d'un demi équivalent sans perte d'efficacité. Cela s'accompagne d'une économie en solvant et d'une réduction de la taille du réacteur pour un résultat équivalent. La résolution de la CF361H par l'αMBA dans l'éthanol est donnée en exemple expérimental. Un nouveau procédé de résolution du phencyphos a été mis au point. La cristallisation préférentielle de son monohydrate a été développée et optimisée à l'aide de diagrammes de phase. Ce procédé a été porté avec succès à l'échelle de 35 litres et 30kg de chaque énantiomère ont été produitsThe work presented consists of thermodynamic study of organic heterogeneous systems. Discontinuous Isoperibolic Thermal Analysis (DITA), an experimental technique dedicated to phase diagram investigation has been improved in three aspects. First, it has been demonstrated that the sign of slope breaks, which are characteristic of phase domain boundary crossing, indicates the direct or retrograde behaviour of these boundaries. Then, the uncertainty of DITA results has been estimated through an inventory of error sources and repeatability tests. Finally, a new automation and processing software has been developed to make the technique more accessible. The influence of resolving agent amount on enantiomer resolution by diastereomeric salts has been studied based on phase diagrams. It has been demonstrated that on favourable cases, the amount of resolving agent can be reduced to less than a half equivalent without efficiency loss. This reduction comes with an economy of solvent and reactor size. The resolution of (±)-CF361H by various amount of αMBA in ethanol is given as experimental example. A new resolution route for phencyphos has been found through preferential crystallization of its monohydrate. This new process has been designed and optimized with the help of phase diagram knowledge. It has been upscaled successfully to 35 litres. 30kg of each enantiomer have been produced
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Hernandez, Lindsey Danielle. "Magma Plumbing Systems along the Juan de Fuca Ridge." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587630136962186.
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[Verfasser], Le-Minh-Tam, and Andreas [Akademischer Betreuer] Seidel-Morgenstern. "Designing crystallization based-enantiomeric separation for chiral compound-forming systems in consideration of polymorphism and solvate formation / Tam Le Minh. Betreuer: Andreas Seidel-Morgenstern." Magdeburg : Universitätsbibliothek, 2014. http://d-nb.info/105791391X/34.
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