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1
Sweed, Muhamed. "Co-crystallization in polyolefin blends studied by various crystallization analysis techniques". Thesis, Link to the online version, 2006. http://hdl.handle.net/10019.1/2733.
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Patki, Rahul P. "Quench Crystallization of Linear Polyethylene: Crystallization Kinetics, Morphology and Structure Investigation". Cincinnati, Ohio : University of Cincinnati, 2008. http://rave.ohiolink.edu/etdc/view.cgi?acc_num=ucin1227282696.
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3
Núñez, Eugenia. "Crystallization in Constrained Polymer Structures : Approaching the Unsolved Problems in Polymer Crystallization". Doctoral thesis, KTH, Fiber- och polymerteknik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4041.
Testo completoAbstract (sommario):
The knowledge regarding certain issues in polymer crystallization e.g. the possible existence of short–lived mesophases remains inconclusive due to experimental limitations. Polymers undergo chain folding upon crystallization, which introduces some complications that are not found in crystallization of low molar mass materials. Chain–folded crystals are far from their equilibrium shape and they rearrange rapidly at the crystallization temperature. This, together with the slow experimental techniques traditionally used, impedes the observation of the originally formed structures. To approach this problem, molecularly constrained polymer structures (in which the crystallizing chains are fixed at one end whereas the other end is free to move) have been studied by X–ray diffraction, differential scanning calorimetry, polarized optical microscopy, transmission electron microscopy and atomic force microscopy. The crystallization studies performed in star–branched polyesters showed that the dendritic cores have a pronounced effect on the crystallization of the linear poly(ε–caprolactone) (PCL) arms attached to them. The star–branched polymers showed slower crystal rearrangement, higher equilibrium melting point, higher fold surface free energy, moderately lower crystallinity, and a greater tendency to form spherulites in comparison with linear PCL. The crystal unit cell was the same in both linear and star–branched PCL. Single crystals of the star–branched polymers were more irregular and showed smoother fold surfaces than linear PCL crystals. No sectorial preference was observed in the crystals of the star–branched polymers upon melting while the single crystals of linear PCL showed earlier melting in the {100} sectors than in the {110} sectors. Some of the differences observed can be attributed to the dendritic cores, which must be placed in the vicinity of the fold surface and thus influence the fold surface structure, the possibility of major crystal rearrangement and the presence of a significant cilia phase during crystal growth causing diverging crystal lamellae and consequent spherulite formation. The attachment of the many crystallizable chains to a single core reduces the melt entropy, which explains the higher equilibrium melting point of star–branched PCL. The crystallization behavior of a series of poly(ethylene oxybenzoate)s was also studied. The polymers showed a profound tendency for crystal rearrangement during melting even at high heating rates. The Hoffman–Weeks extrapolation method was found to be unsuitable to calculate the equilibrium melting point of the samples studied because the melting point vs. crystallization temperature data were sensitive to the variations in crystallisation time, which led to significant variations in the equilibrium melting points obtained.QC 20100914
4
Suzuki, Yasuhito [Verfasser]. "How different is water crystallization from polymer crystallization under confinement? / Yasuhito Suzuki". Mainz : Universitätsbibliothek Mainz, 2015. http://d-nb.info/1078386684/34.
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Robertson, Divann. "Studying crystallization kinetics using solution crystallization analysis by laser light scattering (Scalls)". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20112.
Testo completoAbstract (sommario):
Thesis (MSc)--Stellenbosch University, 2012.ENGLISH ABSTRACT: This study involved the analysis of crystallization kinetics by means of a unique and newly developed Solution crystallization analysis by laser light scattering (Scalls) technique. In the main study we compared two commercial linear low-density polyethylene (LLDPE) polymers (PE-1- octene and PE-1-hexene) and studied the effect of short-chain branching on the solution crystallization of these complex polymer systems. Characterization of the polymers was done by nuclear magnetic resonance spectroscopy (NMR) and high-temperature gel permeation chromatography (HT-GPC). The second study involved the fractionation of a PE-1-hexene copolymer by temperature rising elution fractionation (Tref) and analyzing the solution crystallization of the different temperature fractions. This resulted in important details on the different molecular regions present in the polymer. A third additional study was done on the compatibility in polyolefin blends. Two different blends were prepared: isotactic polypropylene (iPP) – low density polyethylene (LDPE) blend and iPP – polypropylene impact copolymer (PPIC) blend. It was found that co-crystallization only occurred for the iPP - PPIC blends. Phase separation occurred for the iPP – LDPE blends, resulting in the formation of two phases for all blend compositions. Solution crystallization analysis is usually measured by the conventional Crystallization Analysis Fractionation (Crystaf) technique. In this study all crystallization data were compared with Crystaf results and a good correlation was found between the results obtained by Crystaf and Scalls. The major advantages of the Scalls technique are that, results similar to that of Crystaf can be acquired with much shorter analysis times and Scalls also allows for the measurement of solution melting of the crystallized polymer solutions.
AFRIKAANSE OPSOMMING: Hierdie studie het die analise van kristallisasie kinetika behels met behulp van die unieke en nuut ontwikkelde oplossing kristallisasie analise deur laser lig verstrooiing (Scalls) tegniek. In die hoof studie het ons twee kommersïele liniêre lae-digtheid polietileen (LLDPE) polimere (PE-1-okteen en PE-1-hekseen) vergelyk en die effek van kort-ketting vertakking op kristallisasie in oplossing van hierdie komplekse polimeer sisteme bestudeer. Karakterisering van die polimere was gedoen met kern magnetiese resonans spektroskopie (KMR) en hoë-temperatuur gel permeasie kromatografie (HT-GPC). Die tweede studie het die fraksionering van ‘n PE-1-hekseen ko-polieer met behulp van temperatuurstyging eluering fraksionering (Tref) behels asook die analisering van kristallisasie in oplossing van die verskillende temperatuur fraksies. Belangrike informasie oor die verskillende molekulêre areas teenwoordig in die polimeer was verkry. ‘n Derde addisionele studie was gedoen op die versoenbaarheid in poliolefin mengsels. Twee verskillende mengsels was voorberei: isotaktiese polipropileen (iPP) – lae digtheid polietileen (LDPE) mengsel en iPP – polipropileen impak ko-polimeer (PPIC) mengsel. Daar was gevind dat ko-kristallisasie slegs in die iPP – PPIC mengsel plaasgevind het. Fase skeiding het plaasgevind in die iPP – LDPE mengsels wat tot twee fases gelei het vir alle mengsel komposisies. Kristallisasie in oplossing word gewoonlik gemeet met die konvensionele kristallisasie analise fraksionering (Crystaf) tegniek. In hierdie studie was al die kristallisasie data met Crystaf resultate vergelyk en ‘n goeie korrelasie was gevind tussen die resultate van Crystaf en Scalls. Die grootste voordele van die Scalls tegniek is dat resultate soortgelyk aan diè van Crystaf kan verkry word met baie korter analises en Scalls laat ook toe vir die meting van smeltpunt van die gekristalliseerde polimeer oplossings.
6
Walter, Thomas S. "Methodology for macromolecular crystallization". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542989.
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Pridmore, Derik A. (Derik Arnold) 1978. "Online polymer crystallization experiment". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33335.
Testo completoAbstract (sommario):
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (leaves 119-120).
An architecture for online remote operation of a polymer crystallization experiment was refined, beta tested in actual use conditions, and extended based on feedback from those tests. In addition, an application for graphically simulating macroscopic crystal spherulite growth was developed for use as an educational tool. Finally, the experiment was used in the design process for modifying the generic iLab framework to incorporate interactive functionality. Specifically, a reservation model and design changes to the experiment storage and service broker were proposed based on the Polymerlab, and the experiment was used as a testbed for initial implementation of some of the proposed systems.
by Derik A. Pridmore.
M.Eng.
8
Yang, Li-yin 1952. "Crystallization kinetics of diphenylhydantoin". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277190.
Testo completoAbstract (sommario):
The crystallization kinetics of diphenylhydantoin (DPH) has been studied at constant conditions in a small mixed suspension mixed product removal (MSMPR) crystallizer. Supersaturation is created by changing the pH of a DPH solution in the crystallization vessel. Crystal size distributions (CSD's) are measured by an in situ zone sensing method. Effects of pH and supersaturation on crystallization kinetics and CSD are summarized. The effect of an additive on the crystal growth of DPH has been studied in a batch system. Avoidance of nucleation in the early stages of crystallization is essential to the effect investigated.
9
Jana, Sarbojeet. "Crystallization behavior of waxes". Thesis, Utah State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10239292.
Testo completoAbstract (sommario):
Crystallization behavior of different waxes such as beeswax (BW), paraffin wax (PW), ricebran wax (RBW), sunflower wax (SFW) was studied individually and in different oil solutions. Binary mixture at various proportions of the individual waxes was also explored in this study. Soybean oil is used in most of the study but olive, corn, sunflower, safflower, and canola oils were also explored. Lipid crystalline networks were characterized by several physical properties such as melting profile, solid fat content, viscoelastic parameters, cooling rate, phase behavior, crystal morphology. High intensity ultrasound (HIU) was used to change processing conditions of lipid crystallization. Instruments used to analyze the physical characteristics were differential scanning calorimeter, nuclear magnetic resonance spectroscopy, rheometer, temperature controlled water-bath, turbiscan light scattering device, and polarized light microscopy. The use of high intensity ultrasound showed that HIU technology can be used to delay the phase separation in beeswax/ oil system (canola, corn, olive, safflower, sunflower and soybean oil). Crystal sizes were reduced in beeswax/oil system at 0.5 and 1% concentration with the application of HIU technology. A study on binary waxes showed different phase behavior: eutectic behavior in BW/PW, SFW/PW, SFW/ BW, and RBW/BW; monotectic behavior in RBW/PW and continuous solid solution in RBW/SFW. Binary waxes in oil system (2.5% binary waxes) showed different physical properties when a range of binary blends were analyzed. Phase diagrams using iso-solid lines in binary wax/oil study show similarity when binary waxes without oil were studied using melting profile data. From all the above study it is understood that the physical properties of wax/oil systems are affected not only by the concentration and type of wax used, but also by the type of oil and application of HIU which induces wax crystallization and retards phase separation in wax/oil systems. Studies performed on all the topics suggest that understanding wax crystallization could help develop product formulation in food, pharmaceuticals, cosmetics, medicine and other industries.
10
Taffs, Jade. "Local structure in crystallization". Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685975.
Testo completoAbstract (sommario):
In the work presented here, we use simulations of hard and nearly-hard spheres to examine the role of local structures in crystallisation. We are motivated by the work of Sir Charles Frank, who suggested that locally favoured structures, if incommensurate with crystalline ordering, could potentially suppress nucleation [1). Structural analysis is carried out using the topological cluster classification [2], which identifies those local arrangements of 5 < n < 13 particles which are structurally equivalent to the ground state structure for 11 particles considered in isolation. Initial work compares homogeneous crystallisation in simulation and experiment at the single particle level. Brownian dynamics simulations are carefully matched to a system of colloidal 'hard' spheres, taking both poly-dispersity and charge into account. In the regimes accessible, we find a reasonable agreement in the crystallisation rates, although the larger system size in experiments allows crystallisation to be observed at lower supersaturations than in simulation. Structural analysis of the metastable fluid finds a strong similarity between simulation and experiment, and in both we find large populations of five-fold symmetric local structures. We then move to examine what effect energetically favourable, five-fold symmetric local structures have on nucleation. A model hard sphere system with a novel many-body biasing potential is developed, which can be tuned to favour or disfavour the formation of pentagonal bipyramidal structures in the fluid . When the kinetic and thermodynamic effects of the biasing are decoupled, we find that Frank is correct, and that increasing the number of five-fold symmetric structures suppresses nucleation. Finally, in light of this finding, we explore the possibility of employing the structural biasing technique as a novel mechanism for a one component glass-former. Strongly biasing towards formation of five-fold symmetric structures results in unexpected phase behaviour and formation of an icosahedra-rich, Frank-Kasper phase is observed.
11
Núñez, Eugenia. "Crystallization in molecularly constrained polymer structures : approaching the unsolved problems in polymer crystallization /". Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4041.
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12
Sohn, Seungman. "Crystallization Behavior of Bisphenol-A Polycarbonate: Effects of Crystallization Time, Temperature, and Molar Mass". Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/26980.
Testo completoAbstract (sommario):
Crystallization and multiple melting behavior of bisphenol-A polycarbonate (PC) was investigated using differential scanning calorimetry (DSC) for the monitoring of thermal behavior and atomic force microscopy (AFM) for the morphology study. The exceedingly slow crystallization kinetics of PC and the feasibility of obtaining near monodisperse fractions provide distinct advantages for the elucidation of the effects of crystallization time, temperature, and molar mass on crystallization kinetics.
The effects of molar mass on the glass transition temperature (Tg) and heat capacity change at Tg, and the amorphous density of PC were investigated.
Similar to many semicrystalline polymers, PC exhibits a multiple melting behavior upon heating. While for each PC sample, the coexistence of low and high temperature endothermic regions in the DSC heating traces is explained by the melting of populations of crystals with different stabilities, melting-recrystallization-remelting effects are observed only for the lowest molar mass samples.
The effects of crystallization temperature and molar mass distribution on overall crystallization kinetics were studied for some of the fractions, including the commercial PC-28K (Mw = 28,000 g.mol-1) sample. Regarding the kinetics of secondary crystallization, particular attention was placed on understanding the effects of molar mass, initial degree of crystallinity prior to the secondary crystallization, and secondary crystallization time and temperature. The secondary crystallization of PC follows the same laws discovered in previous studies of PEEK, PET, it-PS and ethylene copolymers, and the results are discussed in the context of a bundle-like secondary crystallization model.
During isothermal annealing of semicrystalline PC-28K around the high melting endotherm, a significant increase of melting temperature along with peak broadening with time was observed. Independently, morphological studies using AFM showed that mean lamellar thickness increases with time during isothermal annealing. These results are discussed in light of isothermal thickening of lamellar crystals.
Lastly, almost 200 DSC melting traces of varying molar mass PC samples thermally treated under various conditions were analyzed to calculate crystallinity (Xc), rigid fraction (RF), and rigid amorphous fraction (RAF). The correlation between RAF vs Xc, Tg, and Tg broadening are discussed.Ph. D.
13
Thati, Jyothi. "Spherical Crystallization of Benzoic Acid". Licentiate thesis, Stockholm : Skolan för kemivetenskap, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4602.
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Sura, Ravi Kishore. "Oriented crystallization of syndiotactic polypropylene". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/8293.
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Kimble, Walter Lee. "Mineral induce crystallization of lysozyme". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/11266.
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Gambrel, Timothy Wayne. "Batch crystallization and crystal purity". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/11831.
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Ronca, Gladys. "Heterogeneous nucleation in polymer crystallization". Thesis, Brunel University, 1985. http://bura.brunel.ac.uk/handle/2438/7285.
Testo completoAbstract (sommario):
The effect of talc, sodium benzoate, boron nitride, saccharin and sorbitol on the nucleation and crystallisation of PP, PE, PB, POM, PHB, PET and Nylon 66 has been investigated by DSC, light microscopy and electron microscopy. The effectiveness of the nucleating agent has been evaluated by the study of the interfacial layer between the polymer and the substrate of densely packed particles using light microscopy and by quantitative analysis of the DSC cooling exotherms, obtained from polymers with homogeneously dispersed nucleating agent. It has been found that the crystallisation temperature of the nucleated polymer is exponentially dependent on the concentration of the nucleating particles. This has been explained solely by the decrease in the average distance between the nuclei, with no changes in the crystallization kinetics. The extent of the shift in the crystallisation temperature of a heterogeneously nucleated polymer has been found to be related to the initial number of spherulites present in the un-nucleated polymer. The highest shift in the crystallization temperature has been obtained from partially molten polymers (self nucleation); the shift which can be obtained with the best nucleating agents is approaching this level. Electron microscopy studies, especially the diffraction patterns obtained from the nucleating interface, have shown a good crystallographic correlation between the polymer matrix and the nucleant. Thus, the correlation between the growth direction of the spherulite lamellae and the nucleating facet is good for all active nucleants, but a perfect match of the molecular spacing in this plane (epitaxy) has been observed only for very strong nucleants.
18
Barker, Phil. "Crystallization of hydroxybutyrate/hydroxyvalerate copolymers". Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317156.
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Goldbeck-Wood, E. Gerhard. "Computer simulation of polymer crystallization". Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317157.
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Hillmann, William C. (William Carmen). "Crystallization studies of Pictet-Spenglerases". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43812.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.Vita.
Includes bibliographical references.
Natural products are a rich source of medicinally important molecules. Monoterpene indole alkaloids from plants are an especially important source of therapeutic molecules. Due to the complexity of these molecules, biosynthesis of derivatives is an attractive way of obtaining molecules with potentially new or improved functionality. The rational design of mutants with altered/expanded substrate scope is an important step in engineering organisms to produce such compounds. In monoterpene indole alkaloid biosynthesis, the enzyme strictosidine synthase catalyzes the first committed reaction. This reaction is a Pictet-Spengler coupling between tryptamine and secologanin and produces the biosynthetic intermediate strictosidine, common to all monoterpene indole alkaloids. To better understand the structural features that impart binding selectivity, crystallization studies of this enzyme were performed. The native enzyme and several interesting mutants were studied; co-crystallization experiments with inhibitors and substrates were also performed. Diffraction quality crystals of the native enzyme were obtained following optimization by grid screening, additive screens, and macroseeding. Data on the optimized crystals was collected at the Argonne National Labs synchrotron radiation source. In addition to monoterpene indole alkaloids, the benzylisoquinoline alkaloids are another class of medicinally important plant derived natural products. In a reaction analogous to that catalyzed by strictosidine synthase, the first committed step of benzylisoquinoline biosynthesis is a Pictet-Spengler reaction between 4-hydroxyphenylactetaldehyde and dopamine, catalyzed by the enzyme norcoclaurine synthase. Two different forms of this enzyme have been identified, neither of which shows any homology to strictosidine synthase.
(cont.) Structural information for these enzymes could provide general structural features required for enzymatic Pictet-Spengler reactions. Before crystallization, the enzymes were expressed and tested for activity. Once active preparations of protein were available, crystallization studies were performed and crystals were obtained.
by William C. Hillmann.
S.M.
21
Silver, Barry R. "New approaches to protein crystallization". Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/55616/.
Testo completoAbstract (sommario):
This thesis was focussed toward providing new approaches to protein crystallization. Herein, we describe three new such approaches. Firstly, we describe proof-of-concept studies which demonstrate that simple DC electrochemical systems may be used to enhance and/or control the growth of lysozyme protein crystals on the surface of platinum disc electrodes. Secondly, we demonstrate how various oil/water interfaces provide both novel and unique environments for the study and enhancement of protein crystallization studies. In particular, we show how some oil/water interfaces greatly enhance the extent of lysozyme crystallization in comparison to the air/water interface whilst others do not. Thirdly, we show for the first time, that by application of small magnitude potentials to the ITIES, large increases in lysozyme crystal growth can be achieved (on the ITIES) in short time. Additionally, and unrelated to protein crystallization, we find that large potential-dependent changes in surface tension may be achieved by probable reversible adsorption/desorption of proteins to and from the oil-water interface. The reversible changes in droplet geometry are, in some cases, large and seem controllable. As such, this methodology warrants consideration as means to enhance the performance of alternative liquid/liquid ultra low-voltage and conventional electrowetting systems. The rapid crystallization of TBATPB at the ITIES is also reported for the first time. This work is of importance to theory and experiment regarding ion-transfer mechanisms at the ITIES. Additionally, this work may point towards a new type of crystallization technology for a variety of molecules grounded in methodology developed for liquid/liquid electrochemical systems.
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Ogbuoji, Ebuka. "Protein Crystallization Methods and Apparatus". University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1556924307276754.
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Kesani, Sheshanka. "Crystallization studies of epigallocatechin gallate". [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002100.
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Waechter, David F. (David Francis) Carleton University Dissertation Engineering Electrical. "Crystallization processes in amorphous silicon". Ottawa, 1987.
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Shek, Lai Yung. "Hydrothermal crystallization of organic compounds /". View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202004%20SHEK.
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Konishi, Takashi. "Polymer crystallization through intermediate state". 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144031.
Testo completoAbstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第12346号
工博第2675号
新制||工||1378(附属図書館)
24182
UT51-2006-J338
京都大学大学院工学研究科高分子化学専攻
(主査)教授 金谷 利治, 教授 麹谷 信三, 教授 堀井 文敬
学位規則第4条第1項該当
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Guo, Z. "Ultrasonic effects of crystallization processes". Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1445538/.
Testo completoAbstract (sommario):
This thesis reports a study of the effects of ultrasound on crystal nuclcation from solution and particle breakage. Firstly, the effect of ultrasound on reactive crystallization when nuclcation is consistent with a predominantly homogeneous model is studied by measuring the induction time. Barium sulphate is used as the working substance precipitated by mixing aqueous BaCl2 and Na:S04 solutions. The relationship between amplitude of ultrasonic processor and power input was determined. The experiments were carried with various ultrasonic power inputs. It is observed that increasing ultrasound has a significant effect on reducing the induction time. At a given supersaturation level, the induction time decreases with increasing ultrasonic energy. The relationship between power input (E) and the activation energy of nucleation (E ) is discussed. And the equation between total power input (E) and the nucleation coefficient (A. ) is obtained. A cluster coagulation model, which brings together the current nucleation models and the theories describing the behavior of colloidal suspensions, was applied to estimate the induction time under various power inputs. A comparison between the predictions of the model and the results of experiments shows that the number of monomers in dominating clusters ( ) in the solution remains constant with increasing power input. The mechanism of the ultrasonic effect on homogeneous nucleation is analyzed. It is found that when temperature is kept constant, the main effect of ultrasound is to increase the diffusion coefficient (D,m)- Other parameters change only slightly or remain constant within the ultrasonic field. This suggests that diffusion acceleration is the main reason for the reduction of the induction time. The relationship of DAn and power input is also discussed. A mathematical model of power input and diffusion coefficient is presented, from which it is predicted that diffusivity enhancement (DAB- DAbo) has an exponential relationship with power input. The above relationship is consistent with the results of the experiments. Induction times have also been measured with and without ultrasound to investigate its effect on induction time of spectinomycin hydrochloride, roxithromycin and sucrose during anti-solvent crystallization. The relationship between ultrasonic power input and diffusion coefficient is also investigated. It is found that at the same power input, the ultrasonic effect on DAH decreases with increased solution viscosity. The effect of ultrasound on BaSO.* nucleation is also studied by measuring the induction time when nucleation is consistent with a predominantly heterogeneous model. In these experiments, barium sulphate is used as the working substance precipitated by mixing aqueous BaCb and Na2SC > 4 solutions with relatively low concentrations compared to the experiments of homogeneous nucleation. It is observed that at a given supersaturation level, the induction time significantly decreases with increasing ultrasonic energy during heterogeneous nucleation. The mechanism of the ultrasonic effect on heterogeneous nucleation is analyzed. The effect of ultrasound is to increase the diffusion coefficient (DAb) while reducing the contact angle {0) and geometric factor if). This gives rise to an increase in the heterogeneous nucleation rate and shorter induction time. The ultrasonic effect on critical supersaturation ratio (Sfnf) is also investigated to determine the mechanism of ultrasonic effect on / and 0. It is proposed that both the force from the cavitational bubble implosion and the nucleation process occurring at bubble/solution/foreign solid interface are the predominant reasons why contact angle ( 0) decreases with the increase of power input. In addition, the effects of ultrasound on nucleation order (n) and the nucleation coefficient (ku) are also investigated, and compared with the corresponding effects during homogeneous nucleation. A cluster coagulation model is used to calculate the induction time at different levels of supersaturation when nucleation is consistent with a predominantly heterogeneous model. It is found that the dominant cluster size increases with increasing supersaturation and increasing ultrasonic energy. The effect of ultrasound on nucleation of BaS04 is studied by a Kodak Ektapro Hs motion analyzer. Firstly, the dispersion processes of ink with ultrasound and stirring are used to compare difference of the mixing processes and hydraulic flows. The vessel is divided into several sections to investigate the local mixing process by recording the movement of small silicon carbide crystals. Velocity variance is used to indicate the difference of turbulence when ultrasound is applied and when stirring is applied respectively. The cavitation distribution in different sections is also obtained. BaSC>4 is precipitated by mixing aqueous solutions of BaCb and Na2S04. The nucleation processes are observed by Kodak motion analyzer in different sections. The mechanism of nucleation by ultrasound is analyzed. Then, the induction times at different temperatures are measured with different power inputs at a given supersaturation level. The relationship between the cavitation distribution and temperature is established.
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Fleming, Sean D. "Computer modelling of gibbsite crystallization". Thesis, Curtin University, 1999. http://hdl.handle.net/20.500.11937/1274.
Testo completoAbstract (sommario):
This thesis documents the development and application of a computer model for gibbsite, an aluminium tri-hydroxide polymorph. In particular, the work has emphasized the idea of computer modelling techniques combining with ex- observations to provide greater insight than either could separately. Chapter One provides an overview and introduction to the fields of solid state chemistry, crystallization and computer modelling. These ideas are extended in Chapter Two to include a more detailed discussion of the theoretical principles behind the modelling in this project. The development of transferable oxalate and hydroxide potential models, intended primarily for sodium oxalate and gibbsite, is described in Chapter Three. Both ab initio hypersurface fitting and lattice fitting techniques were utilized, with an average structural fitting error of under two percent. In addition, the potentials were used to successfully reproduce several (related) crystal structures, thus establishing the quality of the model. In Chapter Four, the model for gibbsite was employed in generating equilibrium and growth morphologies. The equilibrium morphology was found to give excellent agreement with experiment, with all observed faces present. However, the importance of the prismatic planes is underestimated. Also discussed in the chapter is a method for predicting the phenomenon of crystalline twinning. This technique was successfully applied to a number of systems, including gibbsite and sodium oxalate. In Chapter Five, the equilibrium morphology calculations performed earlier were extended by probing the effects of cation incorporation on the habit of gibbsite. This study was conducted in order to provide a first step in estimating the role of the crystallizing solution. Calculations of the change in surface energy caused by the replacement of a surface proton with a cation from solution were made. Different crystal habits were constructed by applying a range of defect surface coverage values to each of the faces appearing in the morphology. The resulting defect morphologies were in excellent agreement with crystal habits commonly observed by experimentalists. Also, the work provided an explanation for the earlier underestimation of the prismatic faces. Chapter Six documents molecular simulations of solutions containing the major species known to be present in industrial and experimental Bayer liquors. The structuring in two solutions, one containing sodium hydroxide and the other potassium hydroxide, was probed by constructing graphs of the radial distribution functions. These plots indicated that a significant degree of ion pairing was occurring between the alkali metal cations (Na+ and K+) and the aluminate monomer ([Al(OH)4(subscript)]-). Furthermore, these cations were found to be acting as 'bridges' which stabilize multiple aluminate monomers, allowing them to form clusters. This data was used to assist in explaining vibrational spectra, and to postulate that clustering may be the origin of the fine particle suspensions noted during the induction period.
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Fleming, Sean D. "Computer modelling of gibbsite crystallization". Curtin University of Technology, School of Applied Chemistry, 1999. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10273.
Testo completoAbstract (sommario):
This thesis documents the development and application of a computer model for gibbsite, an aluminium tri-hydroxide polymorph. In particular, the work has emphasized the idea of computer modelling techniques combining with ex- observations to provide greater insight than either could separately. Chapter One provides an overview and introduction to the fields of solid state chemistry, crystallization and computer modelling. These ideas are extended in Chapter Two to include a more detailed discussion of the theoretical principles behind the modelling in this project. The development of transferable oxalate and hydroxide potential models, intended primarily for sodium oxalate and gibbsite, is described in Chapter Three. Both ab initio hypersurface fitting and lattice fitting techniques were utilized, with an average structural fitting error of under two percent. In addition, the potentials were used to successfully reproduce several (related) crystal structures, thus establishing the quality of the model. In Chapter Four, the model for gibbsite was employed in generating equilibrium and growth morphologies. The equilibrium morphology was found to give excellent agreement with experiment, with all observed faces present. However, the importance of the prismatic planes is underestimated. Also discussed in the chapter is a method for predicting the phenomenon of crystalline twinning. This technique was successfully applied to a number of systems, including gibbsite and sodium oxalate. In Chapter Five, the equilibrium morphology calculations performed earlier were extended by probing the effects of cation incorporation on the habit of gibbsite. This study was conducted in order to provide a first step in estimating the role of the crystallizing solution. Calculations of the change in surface energy caused by the replacement of a surface proton with a cation from solution ++were made. Different crystal habits were constructed by applying a range of defect surface coverage values to each of the faces appearing in the morphology. The resulting defect morphologies were in excellent agreement with crystal habits commonly observed by experimentalists. Also, the work provided an explanation for the earlier underestimation of the prismatic faces. Chapter Six documents molecular simulations of solutions containing the major species known to be present in industrial and experimental Bayer liquors. The structuring in two solutions, one containing sodium hydroxide and the other potassium hydroxide, was probed by constructing graphs of the radial distribution functions. These plots indicated that a significant degree of ion pairing was occurring between the alkali metal cations (Na+ and K+) and the aluminate monomer ([Al(OH)4(subscript)]-). Furthermore, these cations were found to be acting as 'bridges' which stabilize multiple aluminate monomers, allowing them to form clusters. This data was used to assist in explaining vibrational spectra, and to postulate that clustering may be the origin of the fine particle suspensions noted during the induction period.
30
FORTUNATI, Andrea. "Crystallization kinetics in Stromboli magma". Doctoral thesis, Università degli Studi di Camerino, 2011. http://hdl.handle.net/11581/401852.
Testo completoAbstract (sommario):
Shoshonitic basalt composition (PST9) has been studied to investigate the kinetics of crystallisation and implications for magma dynamics at Stromboli volcano. A series of decompression experiments over a range of pressure (100 - 5 MPa) at constant temperature (1075°C) show that plagioclase is stable at 50 MPa or less under water saturated conditions. Moreover, these experiments show that plagioclase An content decreases with decreasing P(H2O) reaching the same composition, as the natural plagioclase in Sromboli scoria and that the bulk crystal fraction increases as the experimental conditions tend to lower pressure, associated with water exsolution. Nucleation density increase for lower undercooling whereas for higher decompression the nucleation is almost constant. Growth rate (G+) is observed to increase with undercooling, although at long time (16 hrs), growth rates approach constant values. The values of G+ vary from 10-9 to 10-10 cm/sec for pressure from 50 to 25 MPa, while at pressure from 10 to 5 MPa growth rates are from 10-6 to 10-7 cm/sec (slower in long duration experiments). A series of dissolution experiments at atmospheric pressure and over a range of temperature has been done both for plagioclase (plg) and clinopyroxene (cpx) (temperature range of 1220 - 1240°C and 1140 - 1240°C respectively for plg and cpx). Dissolution rate (G-) for plagioclase (10-7 cm/sec) tends to be slightly higher at higher temperature in the range of 1220 - 1240°C and appears to be time independent for the experimental durations investigated (10 - 30 hrs). For clinopyroxene, we have observed higher dissolution rates (G-) (5 - 6*10-6 cm/sec) at the highest temperatures, whereas the dissolution rates decrease to 1 - 2*10 -6 for longer experimental times. These trends could be related to development of a diffusion limited boundary layer adjacent to the dissolution crystal. By comparison of the experimental data on plagioclase composition, growth rates, nucleation density (Nv), nucleation rate (Jm) and dissolution in Stromboli shoshonitic basalt, it is possible to place the scoria reservoirs in the upper part (from 500 m. to the surface) of volcanic conduit. Furthermore, The results from this work combined with observations on natural samples will help to improve our knowledge of the magma plumbing system and of interactions between resident magma and new magma and in general the dynamics of volcanic activity of Stromboli and the time scale of magmatic processes.
31
Chang, Li-Ching. "Cloning, purification and crystallization of selenophosphate synthetase cloning, purification and crystallization of ERp44 from Mus musculus /". [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980297311.
Testo completo
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Encarnacion-Gomez, Luis G. "Design and operation of enzymatic reactive crystallization: Applications in chiral purity and kinetically controlled synthesis". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54322.
Testo completoAbstract (sommario):
The work presented in this thesis is aimed to design efficient reactive crystallization operations that could potentially be implemented in the manufacture of enantiomerically pure compounds and β-lactam antibiotics. Multiple aspects of solution thermodynamics, reaction engineering and crystallization from complex solutions are involved and will be discussed in detail through the following chapters.
The first piece of this work utilizes reactive crystallization for the manufacture of enantiomerically pure amino acids. Chemo-enzymatic stereoiversion reactions are used to enrich saturated or supersaturated solutions to favor the selection of a desired enantiomer. L-Methionine and L-Phenylalanine were resolve successfully from racemic mixtures by cyclic stereoinversion. r D-amino acids were oxidized by D-amino acid oxidase (D-AAO) and the resulting ketoacid was subsequently reduced by ammonia borane producing a racemic-mixture After the necessary enantiomeric enrichment was reached, system conditions were changed to induce supersaturation and promote crystal formation. In each case crystals with chemical and enantiomeric purities greater than 99% wt. were recovered. experimental information about reaction and crystallization kinetics was used to developed models. Such models were used to design model-based optimizations in which the productivity of the operation was enhanced by selecting an optimal temperature profile.
The second example is a reactive crystallization towards the manufacture of β-lactam antibiotics. One of the major drawbacks of the utilization of enzymes towards the manufacture of β-lactam antibiotics is the fact that the same enzyme that catalyzes the synthesis of the antibiotic also catalyzes its hydrolysis and thus, its degradation. The reaction scheme is a kinetically controlled synthesis in which the desired product is an intermediate within the network. Hence, the focus of this work is to design an efficient reactive crystallization in which the product is crystallized before it is consumed by hydrolysis. In order to accomplish this goal we have study solution equilibria, reaction kinetics, and crystallization kinetics. Even though crystallization kinetics of ampicillin has been previously reported; the reported models are not applicable to a reactive crystallization scheme for a variety of reasons. In this work, we have developed a robust model that can be applied to multiple crystallization protocols that are consistent with the conditions at which the enzymatic reaction can be performed.
Finally, a reactive-crystallization scheme in which ampicillin was successfully recovered from solution was developed. In this work, crystal seeds were used to promote crystallization of the desired product from the complex media. The results indicated that is possible to perform the reaction and crystallization in parallel, and still recover crystals with high purity. This work is the first example in which ampicillin was produced and recovered with high purity in a single stage. Previous work on reaction crystallization of antibiotics reported ampicillin crystallization; however, this was accompanied by precipitation of by-products which greatly reduces the applicability of the operation as product purification is required after the reaction.
33
Lam, Wai Hung. "Chiral resolution by diastereomeric salt crystallization /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?BIEN%202005%20LAM.
Testo completo
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Jibbouri, Sattar al. "Effects of additives in solution crystallization". [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=967410673.
Testo completo
35
Jiang, Yuan. "Precursor phases in non-classical crystallization". Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5246/.
Testo completoAbstract (sommario):
The main objective of this thesis is to understand molecular crystallization as a multistep process with or without polymeric additives, including transient liquid-liquid phase separation, nanocrystal nucleation within the dense phase, and subsequent nanocrystal self-assembly or self-organization in sequence.
The thesis starts with a quaternary model system, containing DL-Glutamic acid (Glu), polyethyleneimine (PEI), water, and EtOH, for the understanding of multistep precipitation of Glu with PEI as an additive. The experiments were performed by mixing Glu-PEI aqueous solution with a non-solvent EtOH. First, the phase diagram of the quaternary system is determined, obtaining precipitate, coacervates, or homogeneous mixtures by varying Glu/PEI w/w and water/EtOH v/v. Coacervation is observed to occur over a wide range of Glu/PEI with various volumes. The composition of coacervates is conveniently characterized by nuclear magnetic resonance spectroscopy. The observed coacervates are thermodynamically stable phases rich in solute, which is different from metastable polymer-induced liquid precursors. The combination of atomic force microscopy, small angle scattering, and ξ-potential measurements confirms the coexistence of monomers and Glu/PEI complexes and the aggregation of complexes in Glu-PEI-water systems. This suggests that there might be a direct structural transformation between the Glu-PEI complexes in aqueous solution and the metastable liquid precursors in a water-EtOH mixture.
The multistep mechanism of Glu precipitation with PEI as an additive is investigated thereafter. The combination of stopped flow and small angle scattering demonstrates that the initially formed liquid precursors pass through an alteration of growth and coalescence. Combined with results from optical microscopy and scanning electron microscopy, the nucleation of nanoplatelets happens within each liquid precursor droplet, and nanoplatelets reorient themselves and self-organize into a radial orientation in the crystalline microspheres.
The recipe was then extended to the precipitation of organics in other oppositely charged amino acid-polyelectrolyte systems.
After the success in preparing hierarchical microspheres in solution, the similar recipe can be extended to the preparation of patterned thin films on substrate. By dipping a quaternary DL-Lys·HCl (Lys)–polyacrylic acid (PAA)–water–EtOH dispersion on a hydrophilic slide, the fast evaporation process of the volatile solvent EtOH is responsible for the homogeneous nucleation of NPs. Then, the following complete evaporation causes the mesocrystallization of a continuous spherulitic thin film along the receding line of the liquid, which again transforms into a mesocrystalline thin film. Furthermore, annealing is used to optimize the property of mesocrystalline thin films. As evaporation is a non-equilibrium process, it can be used to tune the kinetics of crystallization. Therefore, hierarchical or periodical thin films are obtainable by starting the evaporation from microspheres recrystallization, obtaining mesocrystalline thin films with 4 hierarchy levels. The results reveal that evaporation provides an easy but effective way for the formation of patterned structures via the positioning of NPs after their fast nucleation, resulting in different kinds of patterns by controlling the concentration of NPs, solvent evaporation rate, and other physical forces.
Non-classical crystallization is not limited to crystallizations with polymeric additives. We also observed the nucleation and growth of a new molecular layer on the growing DL-Glu·H2O crystals from a supersaturated mother liquor by using an in-situ atomic force microscopy (AFM), where the nucleation and growth of a molecular layer proceed via amorphous nanoparticle (NP) attachment and relaxation process before the observation of the growth of a newly formed molecular layer. NP attachment to the crystal surface is too fast to observe by using in-situ AFM. The height shrinkage of NPs, combined to the structural transformation from 3D amorphous NPs to 2D crystalline layer, is observed during the relaxation process. The nucleation and growth of a newly formed molecular layer from NP relaxation is contradictory to the classical nucleation theory, which hypothesizes that nuclei show the same crystallographic properties as a bulk crystal. The formation of a molecular layer by NP attachment and relaxation rather than attachment of single molecules provides a different picture from the currently held classical nucleation and growth theory regarding the growth of single crystals from solution.Das Hauptziel dieser Arbeit ist das Verständnis der molekularen Kristallisation, sowohl mit als auch ohne polymere Additive, als einen mehrstufigen Prozess. Dieser beinhaltet eine transiente flüssig-flüssig Phasentrennung, die Nukleation von Nanokristallen in der dichten flüssigen Precursor-Phase so wie eine anschließende nanokristalline Selbstorganisation. Die Arbeit beginnt mit Untersuchungen an einem quaternären Modelsystem bestehend aus DL-Glutamat (Glu), Polyethylenimin (PEI), Wasser und Ethanol. Das Phasendiagramm dieses quaternären Systems wird durch Variation der Glu/PEI w/w und Wasser/EtOH v/v Verhältnisse bestimmt, wobei Präzpitat aus polymerinduzierten flüssigen Precursor, Koazervate oder homogene Mischungen erhalten werden Das thermodynamisch stabile Koazervat kann als Referenz für das Verständnis von flüssigen Precursorn angesehen werden, welche in der Natur metastabil und transient sind. Der mehrstufige Mechanismus der Glu-Präzipitation mit PEI als Additiv wird dann mittels Neutronen Kleinwinkelstreuung untersucht. Dies zeigt, dass die ursprünglich gebildeten flüssigen Precursor noch vor der Nukleation von Nanokristallen einen Wechsel von Wachstum und Koaleszenz durchlaufen. Die Ergebnisse aus optischer- und Eletronenmikroskopie zeigen, dass sowohl die flüssigen Precursor Superstrukturen ausbilden als auch, dass die Nukleation von Nanoplättchen in jedem einzelnen Precursor Tropfen von statten geht. Dies geschieht noch bevor sich die Nanoplättchen selbst in einer radialen Orientierung ausrichten. Diese Studie liefert die Kinetik der Präzipitation von organischen Stoffen in Gegenwart von polymeren Additiven. Eine ähnliche Vorgehensweise wie für die Herstellung von Mikrokügelchen kann für die Darstellung von gemusterten Filmen angewandt werden. Die homogene Nukleation von Nanopartikeln (NPs) findet während der Verdampfung einer quarternären DL-Lys·HCl-Polyacrylsäure-Wasser-Ethanol Dispersion auf einer hydrophilen Oberfläche statt. Die darauffolgende vollständige Verdampfung löst die Mesokristallisation eines kontinuierlichen sphärolithischen dünnen Films aus, welcher sich wiederum in einen mesokristallinen dünnen Film umwandelt. Mesokristalline Filme mit 4 Hierarchiestufen bzw. auch periodische Filme werden durch die Verdampfung der Mikrokügelchen-Dispersion erhalten. Die Ergebnisse zeigen, dass die Verdampfung eine einfache aber effektive Methode zur Herstellung von verschieden gemusterten hierarchischen Filmen darstellt. Nicht-klassische Kristallisation wird auch in der Abwesenheit von polymeren Additiven beobachtet. Wir verfolgen mittels Rasterkraftmikroskop (AFM) die Nukleation und das Wachstum einer neuen molekularen Schicht auf wachsenden DL-Glu·H2O Kristallen aus übersättigter Mutterlauge. Die Bildung einer neuen molekularen Schicht verläuft durch die Anlagerung von amorphen Nanopartikeln. Das Schrumpfen der NPs zusammen mit der strukturellen Änderung von dreidimensionalen NPs zu 2D Schichten wird während dieses Relaxationsprozesses beobachtet. Schließlich kommt es zu der Ausbildung einer neuen molekularen Schicht. Die Bildung einer molekularen Schicht durch die Anlagerung von Nanopartikeln aus der Lösung und die darauffolgende Relaxation liefert ein abweichendes Bild zu der bisher gängigen klassischen Theorie des Kristallwachstums.
36
Yang, Huaiyu. "Investigations intothe crystallization of butyl paraben". Licentiate thesis, KTH, Teknisk strömningslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-34051.
Testo completoAbstract (sommario):
In thisproject, solubility of butyl paraben in 7 puresolvents and 5 ethanol aqueous solvents has been determined at from 1 ℃to 50 ℃. Thermodynamic properties of butyl paraben have been measured by DifferentialScanning Calorimetey. Relationship between molar solubility of butyl paraben in6 pure solvents and thermodynamic properties has been analyzed. Thisrelationship suggests a method of estimating activity of solute at equilibrium fromcombining solubility data with DSC measurements. Then, activity coefficient accordingto the solubility at different temperatures can be estimated. Duringthe solubility measurements in ethanol aqueous solvents, it is found that whenbutyl paraben is added into aqueous solutions with certain proportion ethanol,solutions separates into two immiscible liquid layers in equilibrium. Water andethanol are primary in top layer, while the butyl paraben is primary in bottomlayer, but the solution turns to cloudy when two layers of solution are mixed. Theaim of this work was to present the phase behaviour of liquid-liquid-phaseseparation for (butyl paraben + water + ethanol) ternary system from 1 ℃ to 50 ℃at atmospheric pressure. Thearea of liquid-liquid-phase separation region in the ternary phase diagram increaseswith the increasing temperature from 10 ℃to 50 ℃. In thisstudy, more than several hundreds of nucleation experiments of butyl paraben havebeen investigated in ethyl acetate, propanol, acetone and 90% ethanol aqueoussolution. Induction time of butyl paraben has been determined at 3 differentsupersaturation levels in these solvents, respectively. Free energy ofnucleation, solid-liquid interfacial energy, and nuclei critical radius havebeen determined according to the classical nucleation theory. Statistical analysis ofinduction time reveals that the nucleation is a stochastic process with widevariation even at the same experiment condition. Butyl paraben nucleates most difficultlyin 90 % ethanol than in other 3 solvents, and most easily in acetone. The interfacialenergy of butyl paraben in these solvents tends to increasing with decreasemole fraction solubility in these solvents. Coolingcrystallizations with different proportions of butyl paraben, water and ethanolhave been observed by Focused Beam Reflectance Method, Parallel VirtualMachine, and On-line Infrared. The FBRM, IR curves and the PVM photos show someof the solutions appeared liquid-liquid phase separation during coolingcrystallization process. The results suggest that if solutions went throughliquid-liquid phase separation region during the cooling crystallizationprocess the distribution of crystals crystal was poor. Droplets from solutions withsame proportion butyl paraben but different proportions of water and ethanolhave been observed under microscope. Induction time of the droplets has been determinedunder the room temperature. Droplets from top layer or bottom layer of solutionwith liquid-liquid phase separation on small glass or plastic plates were alsoobserved under microscope. The microscope photos show that the opposite flows ofcloudy solution on the glass and the plastic plate before nucleation. The resultsof the cooling and evaporation crystallization experiments both revealed thatnucleation would be prevented by the liquid-liquid phase separation.QC 20110630
37
Derakhshandeh, Maziar. "Crystallization of polypropylene : experiments and modeling". Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55605.
Testo completoAbstract (sommario):
In this study, the quiescent crystallization of several polypropylenes (PPs) with different molecular characteristics was first examined using Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). The Avrami/Nakamura equation was employed to fit and predict crystallization kinetics under isothermal and non-isothermal conditions. The Avrami/Nakamura model was found to predict the non-isothermal crystallization data of the various PPs very well over a range of cooling rates. POM was used in line with a rotational rheometer to further examine the behaviour under quiescent condition at different temperatures and/or cooling rates. The growth rate of crystals was impeded exponentially with increase of temperature. To study the effect of flow on crystallization behaviour of PPs, the Anton Paar MCR-502 rotational rheometer equipped with various fixtures including parallel-plate and POM to induce shear flow was used. Generally, an increase in strain and strain rate or decrease of temperature is found to decrease the thermodynamic barrier for crystal formation and thus enhancing crystallization kinetics at temperatures between the melting and crystallization points. Popular models based on suspension theory, which are often used to relate the degree of crystallinity to normalized rheological functions are validated experimentally. It is found that the constant(s) of various suspension models should be dependent on the flow parameters in order for the suspension models to describe the effect of shear on FIC, particularly at higher shear rates. Finally, a capillary rheometer was used to investigate flow-induced crystallization (FIC) of various resins at high shear rates relevant to polymer processing. It is found that the crystallization kinetics are enhanced with increasing molecular weight indicating the importance of high-end tail of MWD on FIC. Various dies with different physics were used to investigate the effect of flow on FIC. The Cogswell analysis was applied on the capillary data to obtain the apparent extensional strain rate and strain as well as the apparent extensional viscosity. FIC was found to depend strongly on the L/D ratio of the capillary die. Finally, temperature impacted the FIC behaviour extensively since it alters the activation energy needed for the formation of macroscopic structures.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
38
Shore, Mark. "Cooling and crystallization of komatiite flows". Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10267.
Testo completoAbstract (sommario):
Despite their $\sim$2710 Ma age, thin komatiite lava flows in Munro township, NE Ontario have sufficiently well-preserved primary structures, textures, mineralogy, and whole-rock geochemistry to constrain the physical processes of cooling and crystal growth. Seawater convection drove a cooling and fracturing front through the upper surface and was the dominant mechanism of heat loss, leading to pronounced textural asymmetry within flows. Large plate-like crystals of olivine in the upper layers of flows grew by constrained crystallization arising from strong thermal pradients and the high lattice thermal conductivity and near-infrared transparency of olivine (3-5 times greater than that of the surrounding melt). Such crystals exhibit a very strong preferred orientation with the a crystallographic axis perpendicular to flow surfaces. Major and minor-element zoning within olivine crystals is closely modeled by fractional crystallization from the bulk liquid, and whole-rock geochemical variations within flows by crystal fractionation of highly magnesian olivine. The high chromium content of olivine is of mineralogical and technological interest, and is due to two substitutional mechanisms: $\sp{\lbrack 6\rbrack}$Cr$\sp{3+} + \sp{\lbrack 4\rbrack}$Al$\sp{3+} \rightleftharpoons\ \sp{\lbrack 6\rbrack}$Mg$\sp{2+} + \sp{\lbrack 4\rbrack}$Si$\sp{4+}$ and 2 $\sp{\lbrack 6\rbrack}$Cr$\sp{3+} + \sp{\lbrack 6\rbrack}\square \rightleftharpoons 3 \sp{\lbrack 6\rbrack}$Mg$\sp{2+}.$ Dendritic chromian spinel crystals nucleated heteroepitaxially on olivine substrates; the crystallographic relationship between the phases is (111) $\sb{\rm sp} \parallel$ (100) $\sb{\rm ol}$, (110) $\sb{\rm sp}\ \parallel$ (001) $\sb{\rm ol}\ \parallel$, and (211) $\sb{\rm sp}\ \parallel$ (010) $\sb{\rm ol}$. The Cr-spinel crystals have features typical of metallic, ionic, and organic crystal dendrites, but rarely found in minerals. Immobility of Mg and Si and a systematic loss of Ca in these altered rocks is due to a serpentinization reaction buffered by the desilication of glass or fine-grained plagioclase in the groundmass. Serpentinization occurred under conditions of low confining pressure, caused up to 30% expansion of the basal portions of flows, and predated tectonism at $\sim$2700 Ma.
39
Ståhl, Marie. "Process modeling of semibatch reaction crystallization /". Stockholm : Kemiteknik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-538.
Testo completo
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Lee, Chung-Kook. "Crystallization of Nano-sized barium ferrite". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19920.
Testo completo
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Beard, Collen Alana. "Rubredoxin cobalt substitution and crystallization attempts". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/29863.
Testo completo
42
Lungu, Cristian 1968. "Crystallization behavior and kinetics of polyolefins". Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31061.
Testo completoAbstract (sommario):
In order to understand crystallization behavior and to predict polymer resin properties, crystallization kinetics and morphology studies are performed. Thermal analysis of sixteen polyethylene and polypropylene resins was carried out, using Differential Scanning Calorimetry (DSC) to study the crystallization kinetics and mechanism of crystallization. Attention is given to different polyethylene grades, particularly linear low-density polyethylenes (LLDPE) manufactured with Ziegler-Natta and metallocene catalysts. The polymers are obtained with different monomers (1-butene, 1-hexene or 1-octene). Some polymers are based on gas phase polymerization, while others are based on solution polymerization. The isothermal crystallization data were treated to account for transients and to compensate for instrument errors. The data were fitted to the Avrami and Tobin equations, and the corresponding kinetic parameters are reported. The non-isothermal data were fitted to the Ziabicki equation, in order to determine the relevant parameters. Subsequently, the non-isothermal data were compared to the predictions of the Nakamura equation, with good agreement. An effort was made to compare the isothermal and non-isothermal crystallization behavior of the various resins to evaluate the effect of co-monomer and catalyst type. The results indicate significant differences among the resins, and reveal the utility of the DSC as a tool for distinguishing the characteristics of the various resins.
43
Tiang, Jen. "Shear-induced crystallization of nucleated polymers". Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=92255.
Testo completoAbstract (sommario):
Crystallization that occurs during or after a strong shear is important in polymer processing due to its strong effect on product properties and production rate. This study addresses several major gaps in our knowledge of this phenomenon by investigating shear-induced crystallization of nucleated isotactic polypropylenes by simultaneous measurement of light intensity and rheology using a sliding plate rheometer at high, uniform shear rates. An optical fiber probe was devised for the light intensity measurement. For the conditions studied, both measurements were found equally able to detect nascent crystalline structures, but light intensity is more suitable for monitoring changes during the early stages, whereas rheology is more useful for tracking the late kinetics. The relative influence of a melt-insensitive nucleating agent, molecular weight, shear rate, and strain were studied under isothermal, low-supercooling conditions following brief shearing. In contrast to that in quiescent crystallization, the nucleation pathway of nucleated polymers after strong shear was found to be governed not by the nucleating agent but by the molecular weight. The primary effect of shear was confirmed to be in inducing nucleation and is much weaker in changing growth kinetics. Shear and nucleating agent both shorten the induction time, but the effects were found not to be additive. With increasing shear rate or strain, crystallization was found to first accelerate as a result of the increase in the number of point-like nuclei, then saturate due to either slip or consumption of high-molecular weight components for the creation of nuclei, and finally accelerate again at the onset of the transition from spherulitic to highly oriented morphology. Both a critical shear rate and a critical strain are necessary to initiate this morphological transition. The product of shear rate and strain was found useful for describing the acceleration in crystallization associated with the increaseLa cristallisation sous ou après un cisaillement fort est importante dans les procédés de mise en forme des polymères dus à ses effets significatifs sur les propriétés du produit et sur le taux de production. Cette étude traite de plusieurs importantes lacunes dans notre connaissance de ce phénomène en étudiant la cristallisation induite par cisaillement des polypropylènes isotactiques contenant un agent nucléant par une mesure simultanée de l'intensité lumineuse et de la rhéologie en utilisant un rhéomètre à plaques parallèles à des taux de cisaillement élevés et homogènes. Une sonde à fibres optiques a été conçue pour mesurer l'intensité lumineuse. Pour les conditions étudiées, ces deux mesures se sont avérées être aussi bien en mesure de détecter des structures cristallines naissantes, mais l'intensité lumineuse est mieux adaptée pour surveiller les changements au cours des premiers stades de la cristallisation, considérant que la rhéologie est plus utile pour en suivre les derniers stades. L'influence relative d'un agent nucléant ne réagissant pas à la fusion, le poids moléculaire, le taux et la déformation du cisaillement ont été étudiés en conditions isothermes avec faible surfusion après un cisaillement bref. Si on la compare à une cristallisation en condition statique, la voie de la germination des polymères nucléés suite à un fort cisaillement est apparue être régie non pas par l'agent nucléant, mais par le poids moléculaire. Le principal effet du cisaillement a été confirmé être présent durant la germination induite et est beaucoup plus faible en changeant la cinétique de croissance. Le cisaillement et l'agent nucléant ont à la fois réduit le temps d'induction, mais les effets se sont révélés ne pas être cumulatifs. Avec l'augmentation du taux de cisaillement ou de la déformation, la cristallisation s'est avérée tout d'abord accélérée comme une conséquence de l'augmentation du
44
Keats, Clare J. "Crystallization and polymorphism of putative drugs". Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404167.
Testo completo
45
Pratola, Federica. "Micro-mechanics of agglomerative crystallization processes". Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.483559.
Testo completo
46
Leukel, Sebastian [Verfasser]. "Crystallization via Amorphous Intermediates / Sebastian Leukel". Mainz : Universitätsbibliothek Mainz, 2018. http://d-nb.info/1172380783/34.
Testo completo
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Kulkarni, Chandrashekhar V. "In-Cubo Crystallization of Membrane Proteins". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508495.
Testo completo
48
Sinclair, D. M. "Crystallization of high silica molecular sieves". Thesis, University of Edinburgh, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384262.
Testo completo
49
Lai, Tsai-Ta Christopher. "Control of polymorphism in continuous crystallization". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104203.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references.
Continuous manufacturing has gained significant interest in recent years as the ultra-lean mode of pharmaceutical production. Albeit the increasing number of studies on the process dynamics in continuous crystallization, in particular in yield improvement and impurity separation, the research community lacks the systematic understanding of the control of polymorphism in continuous crystallization. Variations in the polymorphism of the active pharmaceutical ingredient can undermine the bioavailability and the downstream processability of the drug substance. Thus, precise control of the drug polymorphism is pivotal for delivering quality drug products to the patients. In this thesis work, we aimed to develop a series of steps forward in understanding the polymorph dynamics in continuous crystallization, notably in mixed-suspension, mixed-product removal (MSMPR) crystallization. We first elucidated the major intrinsic and extrinsic factors which govern the process polymorphism in both monotropic and enantiotropic polymorphic compounds. Using the monotropic L-glutamic acid as the model compound, two temperature regimes each with distinctive kinetic and thermodynamic characteristics were identified. It is found that at high temperatures, the polymorph dynamics is mediated by the relative thermodynamics of the polymorphs. The most stable form is likely to be the dominant form at steady state. On the other hand, at low temperatures, the interplay of the crystal growth and nucleation kinetics is found to play an important role in determining the final polymorphism. Similar results were identified in the enantiotropic p-aminobenzoic acid system where three temperature regimes were identified. The additional regime is located near to the transition temperature where the chemical potential of the two polymorphs are identical. The steady state polymorphism is thereby determined by the kinetic energy barriers for the crystallization of the polymorphs. The study of polymorphism was also conducted in cooling-antisolvent crystallization and the effect of solvent composition on the polymorph dynamics was studied. In addition, the dynamic pathways connecting the startup states to the metastable steady states and the stable steady states were determined. The polymorphic transition between these steady states was observed and analyzed. The fundamental understanding of the kinetic competition and the governing dynamics in polymorphic crystallization forms the backbone for developing the polymorph control strategies in this thesis. Based on the polymorph dynamic studies, we designed MSMPR cascade systems to control the process polymorphism. In addition, systematic procedures are established to facilitate the design and optimization of continuous crystallization with the objectives to control polymorphism, optimize process yield and achieve the target crystal size distribution. The operational window is determined within which these control objectives are achieved. As there are increasing interests in transitioning pharmaceutical manufacturing from batch to continuous processing, the results in this thesis should develop a substantial position in the body of scientific literature.
by Tsai-Ta Christopher Lai.
Ph. D.
50
Nasser, Paola B. (Paola Beatriz) 1979. "Remote microscope for Polymer Crystallization WebLab". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/87281.
Testo completoAbstract (sommario):
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (leaves 65-66).
by Paola B. Nasser.
M.Eng.