Dissertations / Theses on the topic 'Nucleation and Crystal Growth'
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Biyikli, Kasim. "Nucleation and growth of crystals of pharmaceuticals on functionalized surfaces." Worcester, Mass. : Worcester Polytechnic Institute, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-020606-165721/.
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Patchigolla, Kumar. "Particle process measurements : shape and size with crystal growth and nucleation kinetics." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/2088.
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To deduce particle size information, the majority of particle sizing techniques assume that the particles are spheres. For industrial materials, particles are rarely spherical. Non-sphericity causes discrepancies in different measurement technologies so results vary from the real characteristics of the sample. Applications like crystallisation require .shape information in addition to the size of the particles. The majority of this thesis describes results that have demonstrated that particle shape has a strong influence on particle size distribution measured by different techniques. The effect of shape on measured particle size distribution was investigated by ultrasonic attenuation spectroscopy (VAS) compared with other widely used techniques such as laser diffraction spectroscopy (LDS), microscopic image analysis (MIA) and focused beam reflectance measurement (FBRM). A strategy was applied using different chemical systems to monitor the importance of shape to measured size distribution using different techniques; fragile and non-fragile, .sp-pericaC'crystalline and irregular materials were tested. The measurements were successfully applied to laboratory crystallisation processes of different organic and inorganic chemicals In-situ monitoring of particle size evolution during crystallisation using FBRM has aroused much interest. Therefore it was important to demonstrate the dependence of measured particle size on different operating conditions and more particularly on the hydrodynamic conditions, solvent, temperature and other physical and chemical , properties of the system. In-situ measurement of maximum supersaturation during batch crystallisation and dissolution processes of different chemical systems is presented, through which nucleation kinetics of the crystallisation was retrieved. This was clemonstrated for different organic and inorganic chemical systems using FBRM as a process analytical technique (PAT). Based on crystallisation behaviour and with process analytical techniques, notably FBRM to retrieve the nucleation kinetics, the growth kinetics of different chemical systems are presented based on seeded batch cooling crystallisation. Finally future developments within this area of research are presented.
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Xu, Bao Jiang. "Nucleation and growth of 55% Al-Zn alloy on steel substrate." Faculty of Engineering, 2005. http://ro.uow.edu.au/theses/72.
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The nature of nucleation and growth of the alloy overlay of a 55%A1-Zn alloy on a steel substrate strongly affects the surface appearance of hot dip metal-coated steel in the Zincalume process. The potential nucleation site of the first nucleus that forms in the alloy overlay will contribute to the initial solidification process and subsequent microstructural development. An important issue of industrial interest is the occurrence of localized variations in spangle size or variations in spangle size from coil to coil. Control of spangle size on hot-dip metallic coatings is important both from an aesthetic and functional point of view. From the point of view of surface appearance, a uniform spangle size is required and small spangle size is required for improvement of tension bend rust stain performance. An attempt was made to reveal the nature of nucleation and growth of the A1-Zn overlay by studying early stage nucleation and growth. The effect of cooling rate on spangle formation, the influence of trace element additions, the effects of dipping time, preheat temperature and bath composition were taken into account during experimental immersion tests. Spangle size, dendrite arm spacing and solidification temperature of the alloy overlay were determined under various cooling conditions and a variety of other techniques were used to analyze the progress of solidification.Experiments were conducted in the current study to determine the influence of process variables on spangle size. An experimental immersion simulator was used to test the hypothesis regarding nucleation on intermetallic particles using a quench-interruption technique. Serial sectioning in combination with microprobe studies has been used to quantify the element distribution. Commercial products have been analyzed using a tilt polishing technique combined with EPMA to assess element distribution across the solidified overlay. Also, bulk analysis of the element distribution through the thickness of commercial products has been conducted using Glow Discharge Spectroscopy. These experimental studies provided convincing experimental evidence that 55%A1-Zn spangles nucleate on the intermetallic layer. In an attempt to verify that the experimental observations are scientifically founded, a model was developed to predict the nucleation rate and nucleation temperature. Thermodynamic analyses as well as phase-field modeling have been used to further correlate the experimental findings with theoretical predictions. The rate of nucleation decreases with an increase in wetting angle, and the nucleation temperature decreases with increasing cooling rate. Phase field modeling predicts that an aluminum rich phase forms at the intermetallic layer, acting as the nucleus of a spangle.Experimental studies on spangle size distribution of 55%A1-Zn have indicated that the cooling rate and bath composition are factors that influence spangle size. An attempt to prove that experimental observations are scientifically forwarded, modeling of nucleation rate, nucleation temperature, thermodynamic analysis as well as phase-field modeling have been conducted. An advantage of the modeling techniques is that the rate of nucleation and nucleation temperature as function of undercooling and cooling rate can be extrapolated beyond the experimental findings. A description of heterogeneous nucleation was modeled to elucidate the effect of cooling rate on the rate of nucleation and nucleation temperature. The rate of nucleation decreases with an increase of wetting angle, and the nucleation temperature decreases with increasing the cooling rate, also the microstructural evolution at different nucleation sites during solidification of 55%A1-Zn coating is simulated using a phase-field model. A comparison of this experimental observation with the phase field simulations reveals good correlation with the case where dendrite growth was initiated at the intermetallic layer. Detail examination and thermodynamic analysis explained the occurrence of the different intermetallic phases on the alloy layer that could provide potent nucleation sites and hence lead to variation of spangle size. Consideration of nature of nucleation and growth of 55%A1-Zn alloy on steel substrate was taken to clarify the variation of spangle size. In combination with modified immersion simulator and various measuring techniques and modeling approaches, it concluded that the intermetallic layer is potent nucleation site and results in spangle size variation, also the cooling rate and trace elements play role in the spangle size.
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Uwaha, Makio. "The Classical Nucleation Model : Entire Process of Crystal Growth and Application to Chirality Conversion." AIP, 2010. http://hdl.handle.net/2237/20569.
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Katsuno, Hiroyasu, Hideaki Uemura, Makio Uwaha, and Yukio Saito. "Growth modes in two-dimensional heteroepitaxy on an elastic substrate." Elsevier, 2005. http://hdl.handle.net/2237/7317.
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Back, Kevin. "The crystallisation of conformationally flexible molecules." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/the-crystallisation-of-conformationally-flexible-molecules(e00131ab-f91f-4bc9-902b-421e4d70fd74).html.
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Crystallising large, flexible molecules, which are becoming more common in pharmaceutical development, often presents significant challenges for chemists and particle scientists. These difficulties are sometimes attributed to the flexibility of the molecule, and the existence of multiple conformers in solution. Structurally related impurities, frequently present when crystallising these materials, can also impact on growth and habit, and both these aspects are considered in this thesis. This work considers two pharmaceutical compounds, a relatively small but nonetheless flexible molecule, ethenzamide, and a precursor of Amprenavir, a much larger molecule. Both compounds typically grow as thin needles in a wide variety of solvents, and effort was required to grow suitable crystals for structure determination. Ethenzamide has an unusual structure, the amide group being out-of-plane relative to the ring, while in all known co-crystals of the compound, including three new co-crystal structures determined in this work, it has a planar structure with an intramolecular hydrogen bond not seen in the single component crystal. Theoretical structure generation calculations suggest a second polymorph with a planar conformation may exist, though a screen has not found any further solid phases. ab initio work suggests the planar conformation is the stable arrangement in vacuo. Several structures for the Amprenavir intermediate have been determined, as an ethanol solvate, a methanol solvate and a hydrate. A phase diagram has been measured in the industrial solvent mix, and the nucleation and growth properties of this molecule, both pure and in the presence of several structurally related impurities, have been measured. The Cambridge Structural Database has been searched for similar structures, and conformational searches have been carried out for both molecules, using vacuum phase ab initio energy calculations. Infrared spectroscopy has been used to investigate solution phase structure. These theoretical and practical studies will try to relate conformational properties to crystallisation behaviour.
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Sullivan, Rachel. "Molecules, clusters and crystals : the crystallisation of p-aminobenzoic acid from solution." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/molecules-clusters-and-crystals-the-crystallisation-of-paminobenzoic-acid-from-solution(ec826e71-782f-4bb0-9dc2-48cf94a7c941).html.
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Nucleation is a key step in the crystallisation process, where a new crystalline solid phase is created from a supersaturated solution. The applications of crystallisation as a purification and separation technique span many industries, yet still no definitive molecular mechanism for nucleation exists. This PhD is part of a critical mass research project involving researchers from both the Universities of Manchester and Leeds. The aim is to reveal the relationship between structural components of the nucleation transition state, solution phase molecular self-assembly and nano cluster formation, through to critically sized crystalline nuclei which then grow to crystals. All work has been carried out on a small organic molecule, p-aminobenzoic acid (PABA). This PhD has delivered successful characterisation of PABA in the solid and solution state, along with a detailed understanding of its nucleation kinetics and growth rates from a range of solvents. PABA has two enantiotropically related polymorphs, α and β, with the former constructed of carboxylic acid dimers and the latter of a hydrogen bonded tetramer network linking alternate acid and amine functionalities. New determinations of the crystal structures of both forms were submitted to the CCDC with Ref codes of AMBNAC07 and 08 for α and β PABA respectively. A detailed morphological study on both forms of PABA employing modelling and experimental methods has revealed the effect of solvent on the growth habit. In all polar solvents, α PABA displays a more important or slower growing (002) face than the calculated morphology implies. In water, β PABA has a much smaller (101 ̅) face in comparison to β PABA grown from alcohols. Crystallisation experiments demonstrate a clear solvent effect on the appearance of the two polymorphs. From organic solvents only α PABA is obtained, from water both α and β PABA are crystallised. A database search (CCDC) suggests that water may play an important role in the stabilisation of the nucleation transition state for both α and β PABA. This is not possible in organic solvents. Detailed nucleation and crystal growth kinetics have been measured for α PABA at 20°C in water, acetonitrile, ethyl acetate and 2-propanol. A clear solvent trend was observed in both the derived rates of molecular attachment and crystal growth. These were fastest in water, followed by acetonitrile, then ethyl acetate and finally slowest, in 2-propanol. This can be explained by the solvation of the carboxylic acid functional group, where 2-propanol is deemed the most effective solvator of building units in solution and on a crystal surface. This conclusion is supported by the solution FTIR spectroscopy, which clearly confirms strong solvation.
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Gaines, Etienne. "The nucleation and growth of meta-aminobenzoic acid : a density functional theory and molecular dynamics study." Thesis, Queen Mary, University of London, 2018. http://qmro.qmul.ac.uk/xmlui/handle/123456789/54056.
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Controlling crystal polymorphism, the ability of a molecule to crystallise in different solid forms, is one of the grand, ongoing challenges in materials science. In the pharmaceutical industry particularly, where up to half of the active pharmaceutical active ingredients exhibit polymorphic behaviour, it is of paramount importance to rationalise the impact of experimental conditions, such as the nature of the solvent, on the obtainment of a specific c crystal form. As strategies for the selection of polymorphs is still, by and large, based on a trial-and-error approach, it is necessary to acquire a fundamental understanding of the factors controlling the formation of a speci fic solid-state structure during crystallisation from solution. During this doctoral research project, we have conducted a computer simulation study of the early stages of crystallisation of meta-aminobenzoic acid, an important model system in the investigation of polymorphic phenomena. This molecule can in fact form five different polymorphic forms whose selective crystallisation from solution chiefly depends on the nature of the solvent. Molecular models and computational chemistry methods, based on density functional theory and molecular dynamics, have been developed and applied to quantify the processes surrounding the crystallisation of meta-aminobenzoic acid: solvent-solute separation, solute aggregation and surface reactivity. The aim was to identify what controls, at the molecular level, the polymorphic selection process during crystallisation from solution of this important active pharmaceutical ingredient. The results show that the solvent play a signi cant role during the key stages of meta-aminobenzoic acid crystallisation by controlling both the kinetics and thermodynamics of solute desolvation, formation of prenucleation clusters and surface reactivity. This work represents a paradigm of the role of molecular processes during the early stages of nucleation in affecting polymorph selection during crystallisation from solution.
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Hutchinson, Adrian Paul. "The effect of additives on the growth of benzophenone." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/the-effect-of-additives-on-the-growth-of-benzophenone(41b9d82d-644d-4e19-9035-8b6b239d1842).html.
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The effect of impurities on crystal morphology is a challenging problem, since even at low concentrations they can have drastic effects on the final habit. Industrially this causes problems with downstream processes such as filtration, processability and even storage. Conversely, structurally related additive molecules may be introduced to a system in order to mimic the effect of an impurity resulting in a beneficial effect on problematic crystal morphologies. The work presented here considers the design and use of tailor made additives on a nonhydrogen bonded crystal, benzophenone. This compound is typical of many agrochemical materials in that the major intermolecular interactions are of the nondirectional van der Waals type. Using crystal packing analysis a selection of additives has been chosen with the intent of specifically hindering certain directions of crystal growth. From an initial group of nine molecules two additives, 4ABP and 4MBP were found tobe particularly effective, both strongly hindering growth. Measured kinetic data suggests that these additives bind to steps in the growth spirals, drastically slowing growth of specific crystal faces altering the crystal morphology to a needle shape. Through nucleation experiments and product analysis the additives were shown to effect only crystal growth becoming incorporated into the crystal structure. Computational modelling of the binding of additives to the crystal surfaces of benzophenone has been used in an attempt to rationalise the experimental effects. In many cases calculated binding energies were in agreement with experimental observation. However, modified attachment energies did not match well with experimental observations.
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Carr, Matthew William. "A study of the kinetics of nucleation, growth and detachment of carbon dioxide and chlorine bubbles using pressure release nucleation and the quartz crystal microbalance." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335381.
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Dennis, Shelli R. "Nucleation and growth of inorganic crystals at the organic-inorganic interface /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/8050.
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Jiang, Haiyang. "Molecular-scale effects of additives on the nucleation, growth and crystal properties of long-chain alkyl methyl-esters." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598018.
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Biodiesel is a diesel-related fuel manufactured from vegetable oils, recycled grease, or animal fats. It is technically competitive with, or offers technical advantages when compared to, conventional diesel fuel. However, the freezing and gelling behaviour of many biodiesel formulations are potentially limiting their applications. It is known that the use of additives is an efficient way to improve the cold flow properties of formulated, so it is very important to clarify the mechanism and effect of additives. Molecular cluster modelling work has been explored to study the effect of additives on crystallization temperature, meta-stable zone width and solubility. A new method has been developed for the prediction of crystallisability through the comparison of structural variability of molecular clusters of pure naphthalene, pure biphenyl, and naphthalene in the presence of biphenyl and vice versa. The approach has been validated through the experimental determination of crystallization temperatures and meta-stable zone width. The predicted growth morphologies of methyl stearate have been derived through attachment energy calculations and the resulting surface chemistry of the morphological habit faces characterized. Molecular simulations using grid search methods combined with experimental observed images were used to investigate the solvent-mediated effect on crystal habits of methyl stearate. Tubidometric studies employing a 100ml batch crystallizer operating in a polythermal mode confirmed the change of crystallization temperature and the meta-stable zone width of methyl stearate with or without additives. Related crash-cooling studies enabled the characterization of crystallization kinetics with or without additives through examination of set paints as a function of supersaturation.
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Storey, Richard Anthony. "The nucleation, growth and solid state properties of particulate pharmaceuticals : studies of the molecular clustering, nucleation and crystal growth of ibuprofen and the role of the crystallisation environment ... mechanical properties of particles." Thesis, University of Bradford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.734450.
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Nwanosike, Quinta M. "Effect of divalent cations and solubilizers in apoferritin and gamma D-crystallin solutions nucleation, crystallization and light scattering studies /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31736.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Ronald Rousseau; Committee Co-Chair: Athanassios Sambanis; Committee Member: Amyn Teja; Committee Member: Athanasios Nenes; Committee Member: Ingeborg Schmidt-Krey. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Li, Huayu. "Process measurements and kinetics of unseeded batch cooling crystallization." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53503.
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This thesis describes the development of an empirical model of focus beam reflectance measurements (FBRM) and the application of the model to monitoring batch cooling crystallization and extracting information on crystallization kinetics.
Batch crystallization is widely used in the fine chemical and pharmaceutical industries to purify and separate solid products. The crystal size distribution (CSD) of the final product greatly influences the product characteristics, such as purity, stability, and bioavailability. It also has a great effect on downstream processing. To achieve a desired CSD of the final product, batch crystallization processes need to be monitored, understood, and controlled.
FBRM is a promising technique for in situ determination of the CSD. It is based on scattering of laser light and provides a chord-length distribution (CLD), which is a complex function of crystal geometry. In this thesis, an empirical correlation between CSDs and CLDs is established and applied in place of existing first-principles FBRM models. Built from experimental data, the empirical mapping of CSD and CLD is advantageous in representing some effects that are difficult to quantify by mathematical and physical expressions. The developed model enables computation of the CSD from measured CLDs, which can be followed during the evolution of the crystal population during batch cooling crystallization processes.
Paracetamol, a common drug product also known as acetaminophen, is selected as the model compound in this thesis study. The empirical model was first established and verified in a paracetamol-nonsolvent (toluene) slurry, and later applied to the paracetamol-ethanol crystallization system. Complementary to the FBRM measurements, solute concentrations in the liquid phase were determined by in situ infrared spectra, and they were jointly implemented to monitor the crystallization process.
The framework of measuring the CSD and the solute concentration allows the estimation of crystallization kinetics, including those for primary nucleation, secondary nucleation, and crystal growth. These parameters were determined simultaneously by fitting the full population balance model to process measurements obtained from multiple unseeded paracetamol-ethanol crystallization runs.
The major contributions of this thesis study are (1) providing a novel methodology for using FBRM measurements to estimate CSD; (2) development of an experimental protocol that provided data sets rich in information on crystal growth and primary and secondary nucleation; (3) interpretation of kinetics so that appropriate model parameters could be extracted from fitting population balances to experimental data; (4) identification of the potential importance of secondary nucleation relative to primary nucleation. The protocol and methods developed in this study can be applied to other systems for evaluating and improving batch crystallization processes.
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Euhus, Daniel D. "Nucleation in bulk solutions and crystal growth on heat-transfer surfaces during evaporative crystallization of salts composed of NaCO and NaSO." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5401.
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Fernando, Joseph F. S. "Crystal seeding and photochemistry of gold-zinc oxide hybrid nanoparticles." Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/101206/1/Joseph_Fernando_Thesis.pdf.
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This project investigated the synthesis of hybrid nanoparticles of gold and zinc oxide by using photodeposition and crystal seeding approach. The study extended our understanding of the factors that determine nanocrystal size, shape and ratio of gold and zinc oxide in the hybrid system. Control at this scale is important from a materials-engineering viewpoint and for technological applications such as nonlinear optics, photocatalysis and photovoltaics. This research found that nonlinear optical absorption of zinc oxide can be enhanced by several orders of magnitude by coupling zinc oxide nanoparticles to gold nanoparticles.
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Nguyen, Thai Thu Hien. "Influence of crystallisation environment on the nucleation and growth of single crystals of (RS)-ibuprofen." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5771/.
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The crystal growth of ibuprofen as a function of crystallisation environment is presented. Measurement of solubility as a function of solvent (ethanol 95%, ethyl acetate, acetonitrile and toluene) and temperature using UV/Vis spectroscopy and gravimetric analysis reveals less than ideal behaviour, consistent with strong solute-solute interactions, particularly in the case of acetonitrile. Examination of the nucleation kinetics reveals a comparatively small metastable zone width (MSZW) (ΔT = 10.0 - 13.9oC) with interfacial tensions in the range 2.56 – 5.52.10-3 (J/m2). The growth rates for the {001} and {011} faces of spontaneously nucleated single crystals are precisely measured in-situ using optical microscopy revealing that their growth rates increase with increasing supersaturation to different extents, depending on the solvent type with concomitant impact on the crystal habit. For similar supersaturations, the growth rate of {011} is lowest in ethanol and highest in acetonitrile, whilst that of {001} is lowest in toluene and highest in ethanol. The aspect ratios, as a function of supersaturation, are generally higher at the 15 mL than the 0.5 mL crystalliser scale size. The data is consistent with a 2-D Birth and Spread growth model for both surfaces and scale sizes. This is in good agreement with the calculated surface entropy α factor. The measured growth rate dispersion for these faces is much less for these spontaneously nucleated crystals in stagnant, supersaturated solutions when compared to the literature data obtained for a stirred batch crystalliser. Additional higher index re-entrant faces are found at high levels of supersaturation consistent with their alignment either parallel to the {012} or {112} face. The growth rate in the non-agitated jacketed vessel is found to be slightly higher than that for the agitated reactors with both being in quite in a good agreement with literature data suggesting that these results on single crystals will have utility in representative the growth rates of a population of crystals in an agitated crystallizer. Observations are is rationalised using molecular and crystallographic modelling revealing e.g. that polar protic solvents inhibit the growth rate of faces containing available hydrogen bonding binding sites, such as carboxylic acid groups. Molecular conformational searching reveals the molecular structure in the solid-state to be close to that of molecules minimum intra-molecular energy. Conformer population analysis as a function of solvent reveals no significant solvent effect on the low energy conformer distribution indicative a low likelihood of polymorphic behaviour for this compound in good agreement with literature.
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Euhus, Daniel D. "Nucleation in bulk solutions and crystal growth on heat-transfer surfaces during evaporative crystallization of salts composed of Na₂CO₃ and Na₂SO₄." Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180136/unrestricted/euhus%5Fdaniel%5Fd%5F200312%5Fphd.pdf.
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Muterspaw, Taylor M. "The Formation of Prenucleation Clusters for Calcium Fluoride." Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1630356298649522.
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Davey, Roger J. "The nucleation and growth of crystals from solution - molecular self assembly, materials science and process technology." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525976.
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FU, QIANG FU. "POLYMER-TEMPLATED NUCLEATION AND CRYSTAL GROWTH OF PEROVSKITE FILM AND CONDUCTIVE IONOMER DOPED PEROVSKITE FILLM FOR HIGH PERFORMANCE OF ORGANIC-INORGANIC HYBRID PEROVSKITE SOLAR CELLS." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1495207539153854.
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Lid, Steffen [Verfasser], Ciacchi Lucio [Akademischer Betreuer] Colombi, Ciacchi Lucio [Gutachter] Colombi, and Dominik [Gutachter] Horinek. "Molecular mechanisms of crystal nucleation and growth at ferritin/oxide Interfaces : a theoretical investigation / Steffen Lid ; Gutachter: Lucio Colombi Ciacchi, Dominik Horinek ; Betreuer: Lucio Colombi Ciacchi." Bremen : Staats- und Universitätsbibliothek Bremen, 2018. http://d-nb.info/1166849732/34.
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ER-RAJI, SOURAYA. "Preparation de l'experience spatiale mercuric iodide crystal growth first international microgravity laboratory. Controle de la nucleation de hgi2 dans une cavite et etude de la cinetique de croissance." Clermont-Ferrand 2, 1992. http://www.theses.fr/1992CLF21317.
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Ce travail porte sur la preparation d'une experience spatiale de croissance du diodure mercurique par la methode du flux force. Des etudes de vitesse de transport, des experiences de nucleation et de croissance dans une cavite sont reportees. Une approche theorique du couplage entre la cinetique de croissance et le transport est effectuee afin de mettre en evidence la localisation du gradient de concentration, du a la gravite, autour du cristal en croissance. Cette etude a permis le choix des conditions experimentales utilisees au cours du vol first international microgravity laboratory
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Zhai, Zengqiang. "Molecular dynamics simulation of uni and bi-modal semicrystalline polymers : Nucleation, chain topology and microstructure." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI069.
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Les polymères semi-cristallins (comme le polyéthylène, l'acide polylactique, le polyamide, etc.) sont utilisés dans un large éventail d'applications (automobiles, tuyaux, engrenages, etc.) en raison de propriétés mécaniques promues. Il existe un lien étroit entre les propriétés mécaniques et la microstructure du polymère semi-cristallin, comme la bimodalité, la topologie moléculaire (la façon dont les chaînes de polymères passent à travers les phases cristallines et amorphes), les enchevêtrements de chaînes, l'épaisseur lamellar, température, et ainsi de suite. Cependant, ces microstructures ne peuvent pas être accédées quantitativement à l'expérience. Il existe quelques études de dynamique moléculaire, mais la cristallisation homogène est très difficile à réaliser et n'a pas fait l'objet de discussions approfondies. Ainsi, le mécanisme de cristallisation des polymères et la dépendance de la microstructure restent relativement flous et controversés. Le premier chapitre est une introduction de la recherche générale, qui intègre des polymères semi-cristallins, des nucléations et de la cinétique de croissance cristalline, la théorie classique de la nucléation et des simulations numériques. Dans cette thèse, nous avons effectué la cristallisation homogène des polymères à l'aide d'un modèle de dynamique moléculaire à grain grossier (CG-MD) publié dans notre article précédent, qui favorise l'alignement des chaînes et la cristallisation. L'objectif principal de cette thèse est d'utiliser la technique de simulation CG-MD pour fournir plus d'informations sur la nucléation homogène et le comportement de croissance cristalline des polymères MWD bimodaux et unimod, l'influence de la bimodalité sur la topologie moléculaire (boucle, cravate, cils) et la concentration d'enchevêtrement, le processus de démêlage de chaîne et son influence sur l'épaississement lamellar aussi bien que la dépendance de températureSemicrystalline polymers (such as polyethylene, polylactic acid, polyamide, etc.) are used in a wide range of application (such as automotive, pipes, gearing, etc.) due to promoted mechanical properties. There is strong link between the mechanical properties and microstructure of semicrystalline polymer, such as bimodality, molecular topology (the way polymer chains pass through crystalline and amorphous phases), chain entanglements, lamellar thickness, temperature, and so on. However, these microstructure cannot be access quantitatively in experiment. There exists some molecular dynamics investigations, but the homogeneous crystallization is very difficult to achieve and not extensively discussed. Thus, the crystallization mechanism of polymers and the dependence of microstructure remain relatively unclear and controversy. In this thesis, we have performed the homogeneous crystallization of polymers using a coarse-grained molecular dynamics (CG-MD) model published in our previous article 1, which favors chain alignment and crystallization. The main objective of this thesis is to use CG-MD simulation technique to provide more insights of the homogeneous nucleation and crystal growth behavior of bimodal and unimodal MWD polymers, the influence of bimodality on the molecular topology (loop, tie, cilia) and entanglement concentration, the chain disentanglement process and its influence on lamellar thickening as well the temperature dependence
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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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Parmentier, Delphine. "Étude cinétique de la nucléation primaire et de la croissance cristalline au cours de la coprécipitation de solutions solides d’oxalates d’actinides." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0425.
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Une gestion groupée des actinides est envisagée afin d’améliorer les performances du combustible et de réduire le risque de prolifération. Dans le procédé COEXTM, l’étape de coprécipitation oxalique permet de former un oxalate mixte d’uranium et de plutonium, précurseur de l’oxyde mixte destiné à la fabrication de combustible MOX. Afin de déterminer les cinétiques de nucléation et de croissance de cet oxalate mixte, il est nécessaire de pouvoir calculer la sursaturation. Appliquée à la coprécipitation, différentes théories sont proposées dans la littérature, cependant aucune n’a été vérifiée expérimentalement. Une nouvelle expression de la sursaturation applicable à tous types de solutions solides est alors proposée. La détermination des cinétiques de nucléation primaire est basée sur le principe de Nielsen avec l’utilisation d’un appareil de nucléation assurant un très bon micromélange des réactifs. Les lois cinétiques des solutions solides vérifient la théorie de Volmer et Weber appliquée à la coprécipitation. La méthode de calcul de la sursaturation proposée permet de retrouver le comportement classique de la nucléation. Les résultats expérimentaux permettent de démontrer que la coprécipitation de la solution solide est favorisée par rapport à la précipitation des oxalates simples du fait d’une barrière énergétique plus faible pour la solution solide. La cinétique de croissance est déterminée à partir d’un suivi spectrophotométrique des concentrations des réactifs en solution et en utilisant une semence. La croissance est contrôlée par l’intégration au réseau cristallin selon un mécanisme en spiraleCurrent concepts for future nuclear systems aim at improving the fuel cycle with the co management of actinides in order to enhance the fuel performance and to reduce the proliferation risk. Actinides coconversion processes play an important role by producing mixed actinides compounds used as starting materials for fuel re-fabrication. Oxalic coprecipitation is one investigated way to synthesize solid solutions of actinides – lanthanides mixed oxalates which have to meet strict standards. The nucleation and growth kinetic laws involve a fundamental crystallization parameter such as the supersaturation. For the precipitation of solid solutions, different theories are developed in the literature, however none have been verified experimentally. A new suitable expression for the supersaturation ratio applicable is presented in order to determine a general model for the expression of nucleation and growth rates. The experimental study of the primary nucleation kinetics is based on a “stopped flow” apparatus which provides a very good micromixing of the reactants. The kinetic laws of solid solutions verify the theory of Volmer and Weber applied to the coprecipitation. The method of calculating the supersaturation developed allows to find the typical behavior of nucleation. The experimental results demonstrate that the coprecipitation of the solid solution is kinetically favored over the precipitation of simple oxalates due to a lower energy barrier for the solid solution. The crystal growth rate is determined from a spectrophotometric monitoring of the reactant concentrations using a seed charge. The crystal growth is controlled by the surface integration with a spiral mechanism
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Planteur, Séverine. "Étude thermodynamique et cinétique de nucléation primaire et de la croissance cristalline en vue de la modélisation de la précipitation du peroxyde d'uranium en lit fluidisé." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0019.
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Le procédé de précipitation du peroxyde d'uranium en lit fluidisé breveté par AREVA est actuellement testé à l'échelle pilote sur différents sites miniers en vue d'applications industrielles à court terme. Le yellow cake formé par ce procédé a des qualités très intéressantes en termes de densité, granulométrie et morphologie pour la manipulation et le transport. De plus, le faible taux d'impuretés présents dans le peroxyde d'uranium est un atout important pour la suite du procédé de fabrication du combustible. L'objectif de ce travail est de déterminer la thermodynamique ainsi que les cinétiques de nucléation primaire et de croissance cristalline qui régissent la précipitation du peroxyde d'uranium en vue d'une modélisation globale permettant de simuler le comportement du système. Afin de déterminer la solubilité du peroxyde d'uranium sur une large gamme de conditions opératoires correspondante aux conditions du procédé industriel, un modèle de solubilité a été développé et optimisé à l'aide de mesures expérimentales. Dans le cadre de cette étude, le produit de solubilité a été identifié ce qui a permis la mise en équation et le calcul de la sursaturation, force motrice de la précipitation qu'il est indispensable de connaitre pour l'étude des cinétiques de nucléation et de croissance. Les nucléations primaires sont étudiées par une approche phénoménologique qui met en oeuvre une méthode développée par Bertrand-Andrieu basée sur l'utilisation d'un appareil permettant un micromélange très rapide (~1ms) des réactifs. La cinétique de nucléation primaire du peroxyde d'uranium suit la loi classique de Volmer et Weber. De plus il est démontré que la nucléation primaire est fonction de la concentration de sulfate, la loi correspondante intègre alors cette dépendance via le terme BN lié à la tension interfaciale et ainsi à la quantité de sulfate absorbée. La cinétique de croissance est de même déterminer par une approche phénoménologique. Au vue de la production d'ions H+ au cours de la réaction de précipitation, l'étude expérimentale de la croissance cristalline est effectuée par suivi pH-métrique. Étant indépendante de la vitesse d'agitation, la croissance est contrôlée par l'intégration au réseau cristallin selon un mécanisme en spirale. Il est démontré que la loi de croissance du peroxyde d'uranium est d'ordre un vis-à-vis de la sursaturation, le paramètre cinétique kg étant dépendant de la concentration de sulfate et du pH, une loi empirique fonction des conditions expérimentales est alors proposée pour ce paramètreThe uranium peroxide precipitation in fluidised bed patented by AREVA is currently tested on pilot scale reactor on different mine sites for industrial applications in the short term. The yellow cake produced on this way has very interesting qualities in terms of density, particle size and morphology for handing and transport. In addition, the low level of impurities present in the uranium peroxide is an important advantage for the rest of the manufacturing process fuel. The objective of this work is to determine the thermodynamics and kinetics of primary nucleation and crystal growth governing the uranium peroxide precipitation for a global modelling to stimulate the system behaviour. In order to determine the uranium peroxide solubility over a wide range of operating conditions corresponding to the industrial process conditions, a solubility model has been developed and optimized using experimental measurements. In this study, the solubility product has been identified which allows the calculation of the supersaturation, driving force of the precipitation which is an essential parameter to know in order to study the nucleation and crystal growth kinetics. The primary nucleation is investigated by a phenomenological approach which implements a method developed by Bertrand-Andrieu based on the use of a very fast reagents micromixing device (~1ms). Uranium peroxide primary nucleation kinetics follows the Volmer and Weber law. Furthermore it is shown that the primary nucleation depends on the sulphate concentration, the corresponding law incorporates this link with the BN term related to the interfacial tension and thus the quantity of sulphate absorbed. Crystal growth kinetics is also determined by a phenomenological approach. Due to the hydrogen ion production during the precipitation reaction, the crystal growth experimental study is performed by a pH-metric monitoring. Independent of the impeller speed, crystal growth is surface integration controlled with a spiral mechanism. It is shown that the uranium peroxide crystal growth law is first order with respect to the supersaturation. The kinetic parameter kg is dependent on pH and sulphate concentration, an empirical law function of the experimental conditions is then proposed for this parameter
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Sebastián, Paula. "Surface Influence on the First Stages of Metal Electrodeposition in Ionic Liquids." Doctoral thesis, Universidad de Alicante, 2018. http://hdl.handle.net/10045/79870.
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Esta tesis es un estudio profundo de las propiedades interfaciales Metal|líquido iónico (LI), y como estas influyen en las primeras etapas de formación de electrodepósito metálico. Dos líquidos iónicos, de dos familias diferentes, se han escogido para el análisis: un Room Temperature Ionic Liquid (RTIL): [Emmim][Tf2N]; y un Deep Eutectic Solvent (DES): 1ChCl:2urea. Para estudiar la influencia superficial en los distintos procesos, se empleó monocristales de platino (Pt(111)) y de oro Au(hkl), principalmente. El análisis inicial de las propiedades interfaciales M(hkl)|LI se realizó utilizando, entre otras técnicas, la técnica de salto de temperatura con láser pulsante, técnica que además permitió estimar el valor de potencial de carga (valor característico de la interfase metal|electrolito) en cada caso. Una vez caracterizados electroquímicamente estos sistemas, ambos LIs se utilizaron para estudiar el depósito metálico en distintas superficies tanto orientadas como poliorientadas. En concreto, se investigó el depósito de Ag y Cu en DES y sobre carbono vítreo, obteniendo que el DES influenciaba el mecanismo de nucleación y crecimiento y permitía modular el tamaño de grano. Se analizó la formación de ad-capas UPD de Cu en Au(hkl) y en DES, observándose dependencia del proceso con la orientación del sustrato y el tipo de electrolito. Finalmente, se evaluó la aplicabilidad de estos dos solventes para modificar un sustrato orientado de platino (Pt(111)) con Ni, y la sensibilidad superficial del proceso, para ello combinando técnicas clásicas como voltametría cíclica y cronoamperometría con técnicas ex-situ como SEM y AFM (para recubrimientos de baja cobertura). El presente trabajo doctoral muestra el potencial de estos solventes para modificar una superficie con distinto metales y de forma sencilla, a través de la técnica formación de depósito electroquímico, abriendo la posibilidad de utilizar estos novedosos solventes para el diseño de nuevos materiales.
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Sheridan, Andrew Keith. "Kinetics and temperature- and pressure-induced polymorphic phase transformations in molecular crystals." Thesis, King's College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322597.
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Rabeony, Haveloma Manese. "Phenomenes de nucleation en phase vapeur : condensation a basse temperature et en presence d'ions." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13012.
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Etude experimentale de la germination homogene de vapeurs organiques a basse temperature a l'aide d'une chambre a diffusion thermique en vue de tester sur le plus grand intervalle possible de temperature la theorie classique de la germination homogene et de confronter les resultats obtenus avec ceux d'autres techniques experimentales. Etude theorique et experimentale de la germination heterogene en presence d'ions : l'etude theorique permet de verifier l'aptitude des differentes theories a prevoir correctement l'influence de l'ion central, puis les predictions sont confrontees aux resultats experimentaux obtenus a l'aide de la chambre a diffusion thermique
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Hirschler, Joachim. "Influence des impuretés sur la cristallisation d'une protéine modèle dans différents milieux." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10020.
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La cristallisation du lysozyme de dinde (ld) en presence du contaminant rajoute lysozyme de poule (lp, structure tridimensionnelle similaire) mene aux cristaux a morphologie raccourcie (meme symmetrie hexagonale). La selectivite d'interactions des molecules de lp avec les differentes faces du cristal de ld a ete demontree par des mesures de la cinetique de croissance. La spectrometrie de masses des cristaux dissous nous a montre que les taux du contaminant dans les cristaux sont tres eleves, en effet tres proches de ceux de la solution de depart. La modelisation basee sur l'analyse des contacts intramoleculaires a permis de largement reproduire les principaux aspects des observations experimentales. Repetant les memes experiences de contamination dans un milieu de cristallisation gelifie, le raccourcissement des cristaux s'avere moins important qu'en milieu non-gelifie. Le milieu gelifie etant considere comme modele pour les conditions en apesanteur, nous avons compare l'effet de lp sur la cristallisation de ld dans ces deux milieux. Les cristaux obtenus en microgravite montrent un l'effet contaminateur qui est intermediaire entre ceux dans les milieux non-gelifie et gelifie sur sol. Des futures experiences sont proposees pour mieux comprendre ces observations. Un projet des mesures detaillees de la mosaicite cristalline par la radiation synchrotron a ete aborde afin de mieux caracteriser les repercussions des differents milieux de cristallisation sur la qualite des cristaux proteiques. Les premiers resultats ont montre la fiabilite des telles mesures par cette demarche. En etudiant des phenomenes de nucleation, nous avons trouve que la filtration de la solution de ld peut empecher sa cristallisation par une retention des agents nucleateurs, dont la taille est d'environ 0. 17 m. Le milieu gelifie semble moins sensible a l'elimination de ces agents nucleateurs par la filtration.
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Lay, Philippe. "Elaboration et caracterisation de lingots de silicium polycristallin polix." Caen, 1987. http://www.theses.fr/1987CAEN2001.
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Le but de cette etude est le developpement du procede d'elaboration de lingots de si polycristallin polix, par caracterisation de ces lingots et correlation avec l'arrangement experimental. Les proprietes du materiau dependent des conditons de germination et de croissance. L'encapsulation du lingot et les conditons thermiques limitent le nombre de cristaux est contribuent a leur developpement. Les plans de macle (111) jouent un role predominant dans le mecanisme de germination. La croissance est controlee par les transferts thermiques et la qualite chimique. Un modele thermique a permis d'isoler les parametres principaux influencant la vitesse de solidification et l'extrapolation a de grands lingots. Mise en place de methodes de caracterisation pour optimiser les conditions d'elaboration
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Schneider, Jana. "Beitrag zur Wirkungsweise von Verzögerern beim Abbinden von Stuckgipsen." Doctoral thesis, TU Bergakademie Freiberg, 2009. https://tubaf.qucosa.de/id/qucosa%3A22717.
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In dieser Arbeit wurde der Einfluss verschiedener Additive (Carbonsäuren, Phosphonsäuren und Retardan P) auf die einzelnen Teilprozesse des Abbindens von Gips an technischen und synthetischen Halbhydraten unter vergleichbaren Bedingungen untersucht. Vorrangig bei der Keimbildung und beim Kristallwachstum wurde ein Einfluss der Additive beobachtet. Das pH-abhängige Wirkungsoptimum kann mit der Speziation der Additive erklärt werden. Ihre Wirkung wird durch Adsorption auf CaSO4-Oberflächen verursacht. Die Untersuchungen ergaben eine bevorzugte Ca-Affinität mit den Flächen (120) und (001) zunehmend von Citronensäure über Weinsäure, HEDP zu HDTMP. Die in verdünnten homogenen Lösungen erhaltenen Ergebnisse sind nicht direkt auf den Abbindeprozess in Pasten übertragbar. In-situ Ramanspektroskopie und Auswaschexperimente weisen in Pasten auf irreversible Adsorption und ein Überwachsen der Additive hin, was zur Abnahme ihrer Wirkung führt. Auf die Festigkeit der abgebundenen Gipskörper zeigen die Additive kaum Einfluss.
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Schneider, Jana. "Beitrag zur Wirkungsweise von Verzögerern beim Abbinden von Stuckgipsen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-27696.
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In dieser Arbeit wurde der Einfluss verschiedener Additive (Carbonsäuren, Phosphonsäuren und Retardan P) auf die einzelnen Teilprozesse des Abbindens von Gips an technischen und synthetischen Halbhydraten unter vergleichbaren Bedingungen untersucht. Vorrangig bei der Keimbildung und beim Kristallwachstum wurde ein Einfluss der Additive beobachtet. Das pH-abhängige Wirkungsoptimum kann mit der Speziation der Additive erklärt werden. Ihre Wirkung wird durch Adsorption auf CaSO4-Oberflächen verursacht. Die Untersuchungen ergaben eine bevorzugte Ca-Affinität mit den Flächen (120) und (001) zunehmend von Citronensäure über Weinsäure, HEDP zu HDTMP. Die in verdünnten homogenen Lösungen erhaltenen Ergebnisse sind nicht direkt auf den Abbindeprozess in Pasten übertragbar. In-situ Ramanspektroskopie und Auswaschexperimente weisen in Pasten auf irreversible Adsorption und ein Überwachsen der Additive hin, was zur Abnahme ihrer Wirkung führt. Auf die Festigkeit der abgebundenen Gipskörper zeigen die Additive kaum Einfluss.
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Campbell, James Matthew. "On topography and crystal nucleation." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/6829/.
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The influence of topography on crystal nucleation is investigated, mostly with regards to nucleation from vapour but also regarding nucleation from the melt and from solution. Two mechanisms are discussed for acute features to promote nucleation: a thermodynamic reduction in the free energy barrier provided by a favourable geometry, and the formation of a confined condensate of a metastable phase which then transitions to the crystalline phase. Organic compounds nucleating from vapour are used to demonstrate the efficacy of scratches and mineral steps as preferable nucleation sites. A study of various compounds on mica demonstrates that highly acute features provide the most favourable nucleation sites. High-magnification study of the growth of crystals from such features reveals the presence of small condensates prior to the appearance of bulk crystals, and the growth of these is studied quantitatively. Ice is shown to have a similar nucleation site preference to the organic compounds, although no condensate was seen prior to bulk nucleation. Well-defined 100 nm-wide trenches were milled into silicon substrates and shown to have a great ability to direct ice nucleation. The freezing of picolitre droplets of water was studied on smooth and roughened silicon, glass and mica substrates, and the roughening was shown to have little to no effect. Calcium carbonate growth and its dependence on topography was investigated, and found to be broadly anomalous and greatly dependent on surface chemistry.
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Breuer, Steffen. "Molecular beam epitaxy of GaAs nanowires and their suitability for optoelectronic applications." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16457.
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Thema dieser Arbeit ist die Synthese von GaAs Nanodrähten mittels Molekularstrahlepitaxie. Dabei wird das Wachstum mittels Au- und jenes mittels selbst-induziertem VLS-Mechanismus verglichen. Die Au-induzierte Methode ist als vielseitiger Ansatz für die Herstellung von Nanodrähten bekannt. Darüberhinaus wird seit Neuerem der selbst-induzierte Mechanismus untersucht, bei dem Galliumtropfen die Rolle des Goldes übernehmen, um eine etwaige Verunreinigung mit Au von vornherein auszuschliessen. Mit beiden Wachstumsmethoden erzielen wir GaAs Nanodrähte mit großem Aspektverhältnis und epitaktischer Beziehung zum Si(111) Substrat. Während des Au-induzierten Wachstums entsteht eine parasitäre Schicht zwischen den Drähten, die mittels des selbst-induzierten Mechanismus vermieden werden. Alle GaAs Drähte sind vollständig relaxiert. Die durch die Gitterfehlanpassung (4,1\% zwischen GaAs und Si) verursachte Verspannung wird durch Versetzungen an der Grenzfläche abgebaut. Selbst-induzierte Drähten zeigen ausschließlich unpolare Seitenfacetten, während verschiedene polare Facetten für Au-induzierte Nanodrähte beschrieben werden. Mittels VLS-Nukleationstheorie könnne wir den Einfluss des Tropfenmaterials auf die Stabilität der verschiedenen Seitenfacetten erklären. Optoelektronische Anwendungen benötigen lange Minoritätsladungsträgerlebensdauern bei Raumtemperatur. Daher wurden mit (Al,Ga)As Hüllen ummantelte GaAs Nanodrähte mittels zeitaufgelöster PL vermessen. Das Ergebnis sind 2,5 ns für die selbst-induzierten aber nur 9 ps für die Au-induzierten Nanodrähte. Durch temperaturabhängige PL Messungen kann eine charakteristische Aktivierungsenergie von 77 meV nachgewiesen werden, die nur in den Au-induzierten Nanodrähten vorliegt. Dies suggeriert, dass sich Au aus den Tröpfchen in die GaAs Nanodrähte einbaut und dort als tiefes, nichtstrahlendes Rekombinationszentrum fungiert.In this work the synthesis of GaAs nanowires by molecular beam epitaxy (MBE) using the vapour-liquid-solid (VLS) mechanism is investigated. A comparison between Au- and self-assisted VLS growth is at the centre of this thesis. While the Au-assisted method is established as a versatile tool for nanowire growth, the recently developed self-assisted variation results from the exchange of Au by Ga droplets and thus eliminates any possibility of Au incorporation. By both methods, we achieve nanowires with epitaxial alignment to the Si(111) substrates. Caused by differences during nanowire nucleation, a parasitic planar layer grows between the nanowires by the Au-assisted method, but can be avoided by the self-assisted method. Au-assisted nanowires grow predominantly in the metastable wurtzite crystal structure, while their self-assisted counterparts have the zincblende structure. All GaAs nanowires are fully relaxed and the strain arising from the lattice mismatch between GaAs and Si of 4.1\% is accommodated by misfit dislocations at the interface. Self-assisted GaAs nanowires are generally found to have vertical and non-polar side facets, while tilted and polar nanofacets were described for Au-assisted GaAs nanowires. We employ VLS nucleation theory to understand the effect of the droplet material on the lateral facets. Optoelectronic applications require long minority carrier lifetimes at room temperature. We fabricate GaAs/(Al,Ga)As core-shell nanowires and analyse them by transient photoluminescence (PL) spectroscopy. The results are 2.5 ns for the self-assisted nanowires as well as 9 ps for the Au-assisted nanowires. By temperature-dependent PL measurements we find a characteristic activation energy of 77 meV that is present only in the Au-assisted nanowires. We conclude that most likely Au is incorporated from the droplets into the GaAs nanowires and acts as a deep, non-radiative recombination centre.
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Ward, Martin Robert. "Non-photochemical laser-induced nucleation (NPLIN) : an experimental investigation of crystal nucleation." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8966.
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NPLIN was studied in supersaturated solutions (S = 1.06) of potassium chloride (KCl) and bromide (KBr). The fraction of samples nucleated (f) follows a nonlinear dependence on peak power density that approaches f = 1 at higher incident powers. It is shown that a lower threshold power is required for nucleation using 532 nm laser pulses than at 1064 nm, and that a higher fraction of samples nucleate when exposed to 532 nm pulses at a given laser power. Comparison with KCl shows higher fractions of KBr samples nucleate with lower threshold values at both wavelengths. Samples of KCl of equal supersaturation at two different temperatures (23 and 33 °C) exposed to 1064 nm pulses show that those at 33 °C are significantly more labile to nucleation. The ratio of samples nucleated at 33 °C compared to those at 23 °C was 2.11 ± 0.47. A classical nucleation model based on activation of subcritical solute clusters accounts remarkably well for the experimental data and provides phenomological values of the crystal–solution interfacial tension (γ) at 23 °C for KCl and KBr of 5.283 and 4.817 mJ m-2. At 33 °C, the model yields a best-fit value of γ = 5.429 mJ m-2 for KCl. As an extension of this work the use of an evanescent wave (ew) generated by total internal reflection was investigated as a method to cause nucleation in supersaturated KCl solution. Evanescent wave NPLIN (ew-NPLIN) was shown to cause nucleation. The results showed a higher laser-power threshold required for nucleation and sample lability greater than that of bulk NPLIN. In a second approach to understanding NPLIN, the structures of concentrated solutions were probed by a series of laser scattering experiments. Evidence showing populations of particles in solution was provided by Rayleigh laser scattering (RLS) experiments. Scattering in solutions prepared to be nearly saturated (S = 0.95) was observed using a low magnification (×10) microscope objective; almost all solutions showed the presence of scattering objects moving freely in solution. For those that showed no particles, it was noted that the solutions were typically of higher solute concentration (> 11 mol% solute). Ammonium nitrate solution showed no particles using ×10 magnification, however particles were identified when higher magnification was used (×50 and ×100). Video footage of the Rayleigh scattering observed in aqueous solutions of glycine, urea and ammonium nitrate obtained using ×50 magnification were analysed using a custom nanoparticle tracking software. The results showed a population of particles in aqueous urea and glycine solutions with particle concentrations of the order 108 particles cm-3 and mean hydrodynamic diameter of approximately 267 ± 1 and 173 ± 2 nm respectively. Not enough particles were identified in ammonium nitrate solution to complete the tracking analysis; however a fluctuating background scatter suggested a population of particles with sizes below the limit of resolution of the optical system. Using aqueous urea solution as a model system the structure of the particles identified in solution was investigated using scanning microscopy. The second-harmonic scattering (SHS) signal measured in concentrated aqueous urea solution was measured as a function of solution concentration (C) over a range of saturation conditions from undersaturated (S = 0.15) to supersaturated (S = 1.86). The results show a non-linear increase in SHS signal with local maxima near S = 0.95 and 1.75 suggesting a change in solution structure near these points. Rayleigh scattering images indicate the presence of particles in nearly saturated (S = 0.95) urea solutions. Time-dependent SHS measurements indicate that signals originate from individual events encountered during scanning of the sample through the focal volume of the probe laser, consistent with second harmonic generation (SHG) from particles. SHG from aqueous dispersions of barium titanate (BaTiO3) nanoparticles with diameters < 200 nm, showed signals ~20 times larger than urea solutions. The results suggest the existence of a population of semi-ordered clusters of urea that changes with solution concentration.
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Briuglia, Maria Lucia. "Primary and secondary crystal nucleation of pharmaceutics." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28867.
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Control of the crystallisation process is essential in the consistent and reliable production of many particulate materials in the pharmaceutical and chemical industries. Crystal Nucleation defines the crystal size distribution of the obtained crystal population affecting downstream operations. The literature agrees on crystal nucleation division as primary and secondary nucleation depending on the conditions of the used supersaturated solution. Primary nucleation occurs in a clear supersaturated solution, while secondary nucleation is induced by at least one parent crystal present in the solution. Despite the large amount of research conducted on this field, several challenges for primary and secondary nucleation fundamental understanding are still identifiable. The aim of this thesis is to develop meticulous and accurate methods to measure primary and secondary nucleation in order to systematically study nucleation mechanisms relevant to industrial scales. This thesis is constituted of two main parts: one part studies primary nucleation and develops a method for control and measure primary nucleation rate within the metastable zone width (Chapter 2) using different volumes and hydrodynamics (Chapter 3). The second part concerns studies of secondary nucleation under well-controlled conditions providing a systematic method to measure secondary nucleation rates (Chapter 4), which can be integrated in industrial workflows (Chapter 5) and applied to study the chiral outcomes (Chapter 6). The developed methods decouple primary and secondary nucleation events improving crystallisation processes understanding. The reliability and reproducibility of the novel proposed methods offer an appropriate process control strategy to address existing challenges on crystal nucleation.
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Benissad, Farida. "Elaboration de fibres de carbone à partir du mélange méthane-hydrogène." Grenoble INPG, 1986. http://www.theses.fr/1986INPG0121.
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On etudie l'elaboration de fibres de carbone par pyrolyse d'un melange h::(2)-ch::(4) a 950-1150**(o)c en presence de particules de fer deposees sur un support en carbone. Les observations se font par microscopies electroniques a balayage et transmission et par microscopie optique. On determine les conditions operatoires optimales (composition et debit du melange gazeux) et on etudie les mecanismes des etapes sucessives: germination, croissance catalytique et croissance pyrolytique
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Merlin, Aurore. "Cinétiques de concentration de suspensions colloïdales par évaporation microfluidique : de la solution diluée aux cristaux colloïdaux." Phd thesis, Bordeaux 1, 2010. http://tel.archives-ouvertes.fr/tel-00564692.
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Cette thèse est consacrée à l'étude de processus de concentration de solutions colloïdales par voie microfluidique, pour former des matériaux denses et structurés. A partir d'un outil basé sur la perméation de l'eau à travers le PDMS : le microévaporateur, nous proposons de contrôler le séchage de solution pour maîtriser la concentration de solutés afin de former des états denses organisés au choix, alternant cristaux et états amorphes de colloïdes. En adaptant les outils de microévaporation à différentes techniques d'observations, la nucléation et la croissance d'états denses ont été finement étudiées et correlées à un modèle simple de la microévaporation. Ces études expérimentales ont montré le contrôle précis qu'apporte le microévaporateur sur les cinétiques de concentration d'espèces chimiques pour la formation d'états denses de particules. Des études complémentaires ont aussi mis en évidence l'existence d'une dynamique de construction de cristaux colloïdaux avec des réorganisations au niveau du front ainsi qu'un effet de compaction présents lors de la croissance de l'état dense.
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Warren, Dale Ross Seinfeld John H. "Nucleation and growth of aerosols /." Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-03212008-085926.
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Pino-García, Osvaldo. "Influence of Admixtures on Crystal Nucleation of Vanillin." Doctoral thesis, KTH, Chemical Engineering and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3800.
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Admixtures like reactants and byproducts are solublenon-crystallizing compounds that can be present in industrialsolutions and affect crystallization of the main substance.This thesis provides experimental and molecular modellingresults on the influence of admixtures on crystal nucleation ofvanillin (VAN). Seven admixtures: acetovanillone (AVA),ethylvanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxy-acetophenone (HAP), 4-hydroxy-benzaldehyde (HBA), andvanillic acid (VAC) have been used in this study. Classicalnucleation theory is used as the basis to establish arelationship between experimental induction time andsupersaturation, nucleation temperature, and interfacialenergy. A novel multicell device is designed, constructed, andused to increase the experimental efficiency in thedetermination of induction times by using 15 nucleation cellsof small volumes simultaneously. In spite of the largevariation observed in the experiments, the solid-liquidinterfacial energy for each VAN-admixture system can beestimated with an acceptable statistical confidence. At 1 mole% admixture concentration, the interfacial energy is increasedin the presence of GUA, GUE, and HBA, while it becomes lower inthe presence of the other admixtures. As the admixtureconcentration increases from 1 to 10 mole %, the interfacialenergy also increases. The interfacial energies obtained are inthe range 7-10 mJ m-2. Influence of admixtures on metastable zone widthand crystal aspect ratio of VAN is also presented. Theexperimental results show that the admixtures studied arepotential modifiers of the nucleation of VAN. Molecularmodelling by the program Cerius2 is used to identify the likelycrystal growth faces. Two approaches, the surface adsorptionand the lattice integration method, are applied to estimatequantitatively the admixture-crystal interaction energy on thedominating crystal faces of VAN,i.e., {0 0 1} and {1 0 0}. However, a simple and clearcorrelation between the experimental values of interfacialenergy and the calculated interaction energies cannot beidentified. A qualitative structural analysis reveals a certainrelationship between the molecular structure of admixtures andtheir effect on nucleation. The determination of the influenceof admixtures on nucleation is still a challenge. However, themolecular and crystal structural approach used in this thesiscan lead to an improved fundamental understanding ofcrystallization processes. Keywords: Crystallization,nucleation, vanillin, admixtures, additives, impurities,induction time, interfacial energy, molecular modelling,interaction energy.
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Parker, Alexander S. "Quantitative crystal investigations : surface dissolution and nucleation processes." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/88282/.
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The aim of this thesis is twofold with both elements related to industrially relevant crystal systems and processes. The first element utilized a combined scanning electrochemical cell microscope (SECCM) and atomic force microscopy (AFM) method to study the dissolution of enamel surfaces with controlled proton flux to the surface. This was then extended to investigate the effect of both known surface treatments, fluoride and zinc ions, but also a novel treatment of calcium silicate and its methods of action. The second element investigated the use of a nanopipette to investigate the early nucleation and initial growth of calcium carbonate crystals. For the dissolution of enamel, an SECCM probe to selectively etch a surface for a defined period of time with a high spatial resolution was used. The extent of the etching in the resultant pits was then monitored through AFM to measure the volume of material removed along with other pit dimensions. The method allowed for multiple independent measurements on a single sample, which could be selectively treated to eliminate comparability issues associated with measurements on multiple samples. The system could be modelled via finite element method (FEM) to calculate an intrinsic rate of reaction for the proton induced dissolution of enamel. A proton induced rate constant of dissolution of k0= 0.099 ± 0.008 cm s-1 for bare untreated enamel was established, whereas treatment with 1000 ppm sodium fluoride (NaF) and/or zinc chloride (ZnCl2) decreased this rate constant. The work also characterised the use of calcium silicate as a novel additive in toothpaste and to determine its effect as both a remineralising agent and as a dissolution inhibitor. The release of Ca2+ ions into solution was measured which acts to promote the remineralisation of tooth enamel. The addition of phosphate buffer into this solution combined with micro-Raman spectroscopy was then used to confirm the formation of hydroxyapatite (HAP (Ca10(PO4)6(OH)2)) material. The extent of adhesion of calcium silicate onto rough and polished samples was also observed, showing the preference of particles to adhere to rough surfaces, and was quantified by investigating the effect of infilling of etch pits formed via the SECCM method above, which showed an average pit volume reduction of 77±12%. The second element of the thesis involved investigation into the initial phase of nucleation, nanoprecipitation and growth of calcium carbonate crystals using voltage driven ion migration within a nanopipette (~50 nm opening) geometry to control the mixing of constituent ions to selectively control and induce the nucleation and dissolution of crystals and monitor their growth. This was achieved using oppositely charged CO32- and Ca2+ ions, inside and outside the pipette respectively, which could be either driven together or apart depending on the applied polarity. This process was modelled using FEM to give quantitative information about the growth rate and nanocrystal size during growth as well as analysis of the saturation levels within the probe geometry. The nanocrystals formed were studied in situ using micro-Raman spectroscopy to give information about the polymorph of calcite produced. The effect of the driving bias was demonstrated and rationalised through simulation along with the effect of constituent ion concentration. This method was used to assess the effect of maleic acid as an inhibitor to the formation of calcium carbonate. Its potent effect was shown by the significantly larger time taken to block the pipette by crystal growth. This also provided evidence for the mechanism of crystal growth inhibition by comparison with ion concentrations expected as a result of a pure chelation effect.
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Green, David John. "Controls on concretion nucleation and growth." Thesis, University of Exeter, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426140.
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Schindler, Manon. "Deracémisation du chlorate de sodium avec et sans l’influence du dithionate de sodium." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMR004.
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Dans le domaine pharmaceutique, la séparation des énantiomères est souvent effectuée par des méthodes de cristallisation. L’avantage de la déracémisation est la possibilité d’obtenir un rendement théorique de 100% grâce à la conversion du contre énantiomère en l’énantiomère désiré en solution. Le mécanisme de la déracémisation par cycles de température (TCID), a été étudié dans ce manuscrit. Les recherches se sont concentrées sur le développement d’un procédé de TCID pour NaClO3. Ce composé modèle pour la déracémisation est achiral à l’état solvate, ce qui permet de se focaliser sur les mécanismes de cristallisation impliqués dans le procédé de déracémisation. Après la caractérisation complète de l’état solide de Na2S2O6, ce composé a été utilisé comme une impureté nonchirale dans le procédé de TCID du NaClO3 et a permis de mettre en évidence le rôle important de la nucléation secondaire dans le procédé. Ainsi, le succès du TCID dépend d’un bon équilibre entre la croissance des cristaux et la nucléation secondaire. A des fins industrielles, les réacteurs du type Couette Taylor sont des appareils prometteurs pour le développement de procédés de déracémisation en continu. Les premiers tests de déracémisation réalisés dans ce type de réacteur ont montré que la brisure de symétrie et la déracémisation du NaClO3 ont été réalisés avec succès. Néanmoins, le ≪ recyclage de cristaux ≫, soit par attrition soit par la nucléation secondaire, doit être amélioré pour obtenir un procédé de déracémisation plus performant avant de considérer l’implémentation d’un procédé en continuIn the field of pharmaceutical chemistry, crystallization based methods are used to obtain pure enantiomers. The advantage of deracemization is the conversion of the unwanted enantiomer into the desired enantiomer by means of racemization in liquid phase, giving rise to a theoretical yield of 100%. The mechanism of Temperature Cycling Induced Deracemization (TCID) process, still matter of debate, has been investigated in this thesis. Research was focused on the development of the TCID process for sodium chlorate (NaClO3). This model compound is achiral at the solvated state which enables to focus investigation on crystallization mechanisms involved during deracemization. After the full solid state characterization of sodium dithionate (Na2S2O6), this compound has been used as a nonchiral impurity in the TCID process of NaClO3 and highlighted the key role of secondary nucleation in the process. Thus, the success of the TCID process depends on the right balance between growth and secondary nucleation. From an industrial perspective, the Couette Taylor reactor has been considered as a promising device for the development of continuous deracemization process. Attempts to deracemize NaClO3 in this kind of reactor showed that symmetry breaking and deracemization of NaClO3 were successful. Nonetheless, crystal recycling, via either attrition or secondary nucleation, has to be improved to enhance deracemization process before considering the execution of continuous process
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Uwaha, Makio, and Katsunobu Koyama. "Transition from nucleation to ripening in the classical nucleation model." Elsevier, 2010. http://hdl.handle.net/2237/13867.
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Cooper, Sharon. "Nucleation beneath monolayer films." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238881.
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Kananagh, A. "The crystal growth and crystal growth inhibition of calcium carbonate." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383820.
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Gong, Li. "Selective external oxidation of Fe-Mn (1 wt.%) binary alloys during continuous annealing." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC014.
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Ce travail est axé sur le comportement de l'oxydation sélective d'un alliage binaire Fe-Mn (1% en poids) lors d'un recuit continu dans les conditions de galvanisation industrielle, pour comprendre la diffusion du manganèse et de l'oxygène et le mécanisme de formation d'oxyde à la surface.Un modèle analytique a d'abord été développé pour décrire les réactions de surface et la thermodynamique impliquant la vapeur d'eau et la diffusion de O et Mn dans l'alliage, ainsi que la germination et la croissance hétérogènes des oxydes de MnO à la surface. Des équations théoriques ont été établies et analysées pour calculer le rayon critique et le taux de germination des embryons de MnO ainsi que la taille et les taux de couverture de surface des oxydes de MnO en fonction du recuit.Des expériences de recuit ont ensuite été menées et les surfaces recuites ont été analysées par: des cartographies EBSD pour déterminer l'orientation du grain de ferrite; Analyse EDS pour déterminer la nature chimique; SEM et AFM pour étudier les caractéristiques géométriques des oxydes; TEM/STEM sur des lames extraites des échantillons massifs pour observer la forme latérale des oxydes; XPS pour étudier la nature des oxydes et les profils de concentration de Mn en fonction de la profondeur et des modèles de diffraction pour déterminer la relation d'orientation du MnO et du substrat de ferrite.Le logiciel Wulffmaker a été utilisé pour simuler le cristal d'équilibre de MnO. Les observations par SEM, AFM et TEM/STEM permettent de réaliser les facettes composant les cristaux de MnOThis work is focused on the selective oxidation behavior of Fe-Mn (1 wt.%) binary alloy during continuous annealing under the industrial galvanizing conditions, to understand the diffusion of manganese and oxygen and the mechanism oxide formation on the surface.An analytical model was first developed to describe the surface reactions and thermodynamics involving water vapor and diffusion of O and Mn in the alloy, and the heterogeneous nucleation and growth of MnO oxides on the surface. Theoretical equations were established and sovled to calculate the critical radius and nucleation rate of MnO embryos and the size and surface coverage fractions of MnO oxides as a function of annealing.Annealing experiments were then conducted and the annealed surfaces were analyzed by: EBSD maps to determine the ferrite grain orientation; EDS analysis to determine the chemical nature; SEM and AFM to study the geometrical characteristics of oxides; TEM/STEM on the crosee-sections to observe the lateral shape of oxides; XPS to study the oxide nature and Mn concentration profiles as a function of depth and diffraction patterns to determine the orientation relationship of MnO and ferrite substrate.Wulffmaker software was used to simulate the equilibrium crystal of MnO. Observations by SEM, AFM and TEM/STEM make it possible to realize the facets composing MnO crystals