Дисертації з теми "Void nucleation and growth"
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1
Thomson, Ronald D. "Ductile fracture by void nucleation, growth and coalescence." Thesis, University of Glasgow, 1985. http://theses.gla.ac.uk/6487/.
Повний текст джерелаАнотація:
Plastic deformation in ductile metals is limited by a mechanism in which voids, nucleated at second phase particles, grow and coalesce to form a crack. The results of a finite element solution for spherical elastic inclusions in a plastically deforming matrix are discussed. These results have been used in conjunction with experimental work using notched tensile specimens to generate multiaxial states of stress from which the local conditions leading to decohesion of the inclusion/matrix interface were determined. An important feature of these results is the statistical distribution of the interfacial strength. This distribution is bimodal, showing the presence of both weakly and strongly bonded particles. The latter have a modal strength of about 7 times the initial yield stress and the weakly bonded particles are assumed to be pre-existent. Experiments in plane and axisymmetric states of strain indicate that while the stress state is of relevance, the remote strain state is not. The absence of a macroscopic strain state effect is explained in terms of the statistical distribution of the voids nucleated from the population of randomly distributed inclusions. The stress and strain concentrations possible in local patches of high porosity have been investigated by a finite element approach based on the mechanics of a dilating continuum to determine void growth in the porous aggregate and the local conditions at failure. This investigation recognises the importance of the local hardening rate of the aggregate material and leads naturally to the idea of a size scale for failure, in the light of which the concept of a crack-like defect is re-examined.
2
Mukherjee, Sunit. "Quantitative characterization of void nucleation and growth in HY-100 steels." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/19574.
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3
McDermott, Patrick M. "Development and implementation of a shell element with pressure variation through the thickness and void growth and nucleation effects." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA369167.
Повний текст джерелаАнотація:
Thesis (Degree of Mechanical Engineering) Naval Postgraduate School, September 1999."September 1999". Thesis advisor(s): Young W. Kwon. Includes bibliographical references (p. 107-109). Also Available online.
4
Labidi, Sana. "Elaboration des nanoparticules d'oxyde de zirconium par voie sol-gel : mise en forme et application pour la synthèse de biodiesel." Thesis, Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCD085/document.
Повний текст джерелаАнотація:
Actuellement, la stratégie de la production d’énergie repose sur les 3 concepts d’économie, de régénération et d’écologie. La production de biodiesel s’insère dans cette thématique et fait objet de ce travail. Un suivi cinétique de nucléation-croissance est réalisé sur des nanoparticules monodisperses d’oxo-alcoxydes de zirconium (ZOA). Ces nanoparticules sont préparées par voie sol-gel dans un réacteur à T-micro-mélangeur avec deux flux turbulents de ZNP et c dans 1-propanol à 20°C. Les nanodépôts des nanoparticules de ZOA ont été réalisés sur des substrats en silice et comparés aux nanopoudres récupérées après l’induction du sol de ZOA. Les nanodépôts et les poudres subissent un séchage à 80°C puis une imprégnation humide dans une solution aqueuse de 0,25 mol.L⁻¹ de H₂SO₄. Nous obtenons ainsi les nanodépôts catalytiques après une calcination à des températures comprises entre 500 et 700°C sous O₂. Les techniques de BET, ATG-ATD, MET, DRIFT, analyse élémentaire et DRX sont déployées pour caractériser ces catalyseurs. Les cinétiques du processus d’estérification et de transestérification ont été étudiées en fonction des conditions de la préparartion des catalyseurs nanostructurés. Les nanodépôts catalytiques acides de ZrO₂-SO₄²⁻ possèdent une activité catalytique 50 fois plus élevée que celle des nanopoudres dans la réaction d’estérification de l’acide palmitique dans le méthanol à 65°C. Les nanodépôts calcinés à 580°C ont la meilleure stabilité vis à vis des essais de recyclage. L’activité catalytique des nanodépôts est aussi valable avec d’autres charges dont la composition est similaire à celle des huiles non-comestibles puis celle des déchets grasIn this work, we have realized novel nanoparticulate catalysts ZrO₂-SO₄²⁻ for biofuel production. We have studied nucleation-growth kinetics of zirconium-oxo-alkoxy (ZOA) nanoparticles in the sol-gel process. The monodispersed nanoparticles of 3.6 nm diameter were realised in a sol-gel reactor with rapid (turbulent) micro-mixing of liquid solutions containing ZNP and H₂O in 1-propanol at 20°C. The nanocoatings were realised of stable colloids of ZOA nanoparticles on silica beads along with common powders obtained after precipitation of unstable colloids. The acid ZrO₂-SO₄²⁻" catalysts were prepared after drying at 80°C, wet impregnation in 0.25 mol.L⁻¹ aqueous solution of sulfuric acid and subsequent thermal treatment between 500 and 700°C and studied with BET, DTA-DSC, TEM, DRIFT, elemental analysis, DRX and other methods. The catalyst nanocoatings calcinated at 580°C showed strong activity in esterification reaction of palmitic acid in methanol at 65°C, which is about 50 times higher than that of nanopowders, and also possesses the highest stability towards recycling. Tha catalytic performance of catalytic nanocoatings was also confirmed on unedible and waste oils
5
Chandler, Mei Qiang. "Multiscale modeling of hydrogen-enhanced void nucleation." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-03192007-103416.
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Landron, Caroline. "Ductile damage characterization in Dual-Phase steels using X-ray tomography." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00738820.
Повний текст джерелаАнотація:
Dans le cadre du développement de nuances d'aciers toujours plus performantes en termes de résistance à l'effort et à l'endommagement, les aciers Dual-Phase (DP) présentent un bon compromis résistance/ductilité. Cependant, il est nécessaire de disposer de meilleures connaissances concernant les mécanismes menant à la rupture de tels aciers. Les mécanismes d'endommagement ont ainsi été étudiés dans cette thèse à l'aide de la tomographie aux rayons X. Des essais de traction in-situ ont été réalisés sur plusieurs nuances d'aciers DP, un acier ferritique et un acier martensitique afin de caractériser chaque étape de l'endommagement ductile. Des observations qualitatives et des données quantitatives concernant la germination de l'endommagement, la croissance des cavités et la coalescence ont été recueillies lors de ces essais. Ces données quantitatives ont ensuite été utilisées pour le développement et/ou la validation de modèles d'endommagement. Une prédiction de la cinétique de germination a ainsi été proposée et la version du modèle de croissance de cavités de Rice et Tracey corrigée par Huang et prenant mieux en compte l'effet de la triaxialité a été validée expérimentalement. L'étape de coalescence des cavités menant à la rupture des matériaux a pour la première fois été caractérisée de façon quantitative dans un matériau industriel et des critères de coalescence ont été appliqués localement sur les couples de cavités présentes dans le matériau. L'utilisation de ces modèles analytiques a permis une meilleure compréhension des propriétés agissant sur les phénomènes mis en jeu. L'effet de la part cinématique de l'écrouissage sur la germination et la croissance de l'endommagement a notamment été souligné et validé par des essais de chargements complexes.
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Gautier, Maxime. "Etude de la formation de nanoparticules de carbone au cours de la décomposition thermique d'hydrocarbures : application à la coproduction de noir de carbone et d'hydrogène par craquage thermique du méthane par voie plasma." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM061/document.
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Cette thèse s’inscrit dans le cadre du développement d’un procédé de décarbonation directe du méthane par voie plasma pour la coproduction de noir de carbone et d’hydrogène. Ce procédé est particulièrement intéressant dans la contexte d'un mix électrique faiblement carboné en offrant une solution pour diminuer drastiquement les émissions des procédés actuels de production de noir de carbone et d’hydrogène qui comptent parmi les procédés actuels les plus polluants en termes d'émissions de CO2. A court terme, la viabilité économique de ce procédé passe par la valorisation simultanée de ces deux produits : noir de carbone et hydrogène. À plus long terme, il pourrait représenter une réelle alternative à la capture et le stockage du CO2.Cette étude a pour but de proposer des méthodes numériques fiables et robustes afin de mieux comprendre, contrôler, voire optimiser les caractéristiques morphologiques des noirs de carbone issus de ce procédé, caractéristiques qui jouent un rôle primordial sur la qualité et les applications des noirs de carbone. Elle traite ainsi de l’évolution de systèmes carbonés en partant du combustible sous sa forme moléculaire jusqu’à la formation de nanoparticules puis de microstructures solides et aborde les phénomènes de nucléation, de croissance chimique, de croissance par coagulation, de maturation et d’agrégation.Des outils et des méthodes numériques ont ainsi pu être développés afin de simuler la formation de particules solides au sein d’un écoulement fluide. Ceux-ci purent être implémentés avec succès à un code CFD. Enfin des simulations numériques du procédé en question ont été réalisées en intégrant les phénomènes de transferts thermiques et de turbulence spécifiques aux plasmas thermiquesThis thesis takes part of the development of a direct decarbonation process of methane by plasma to produce both carbon black and hydrogen. This process is particularly interesting in an electrical mix context with low carbon emission. It proffers a solution to reduce drastically CO2 emissions rejected by the current carbon black and hydrogen ways of production, which are ones of the most polluting industrial processes.This study aims to develop reliable and robust numerical methods for a better understanding and a greater control of the morphologic features of the carbon black generated. These features play a key role in the quality and applications of the carbon black produced. This research retraces the evolution of the carbon structure from the molecules of the fuel to the formation of nanoparticles and solid microstructures. It tackles different phenomenon such as: nucleation, chemical growth, coagulation, maturity and aggregation.Numerical tools and methods were developed thereby and enable to simulate carbon particle formation. They were successfully implemented in a commercial CFD software. Eventually numerical simulation of the plasma process were performed, integrating heat transfers and turbulence
8
Shabrov, Maxim N. "Micromechanical modeling of void nucleation in two phase materials /." View online version; access limited to Brown University users, 2005. http://wwwlib.umi.com/dissertations/fullcit/3174672.
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9
Lieberman, Evan. "Simulation of Void Nucleation in Single-Phase Copper Polycrystals." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/707.
Повний текст джерелаАнотація:
A systematic investigation is presented into the microstructural and micromechanical influences on ductile damage nucleation with an emphasis on grain boundaries in polycrystals. Microstructures obtained from experiments on copper polycrystals are characterized using Electron Backscatter Diffraction (EBSD) and near-field High-Energy Diffraction Microscopy (nf-HEDM) and the occurrence of damage is compared with micromechanical values obtained using an elasto-viscoplastic model based on the Fast- Fourier Transform (EVPFFT). The model produces full-field solutions for the stress and strain in voxelized polycrystalline microstructures. In order to resolve the fields onto interfaces, local Cartesian moments of the polycrystalline grain structure are used to extract the normals of grain boundaries and the tangents of triple junctions directly from the voxelized microstructure. Thus projecting the stress yields a parameter with potential significance, i.e. the grain boundary surface tractions. We identify “traction hotspots”, i.e. regions with tractions that are significantly above the mean, for the case of uniaxial tension. These show correlations with the angle between the grain boundary normal and the loading axis, a trend that some experiments also show when boundaries that nucleated voids are analyzed using EBSD, though differences present between the simulation and experiment hint that further criteria are needed. Nf-HEDM was used to record microstructure images of a polycrystalline sample before and after it undergoes damage. The damage locations in the post-shocked image are mapped onto the pre-shocked image, allowing stress and strain values from the EVPFFT model in the regions that eventually nucleated damage to be correlated with the locations of the void. The unexpected result was that differences in plastic work across boundaries correlated with voids, whereas vi quantities such as triaxiality and normal forces across boundaries did not.
10
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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11
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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12
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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13
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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14
Pushkareva, Marina. "Study of Void Growth in Commercially Pure Titanium." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35667.
Повний текст джерелаАнотація:
The ductile fracture process, which consists of the nucleation, growth and coalescence of microvoids, was extensively studied for materials deforming homogeneously. For materials with a non-homogeneous deformation behavior, such as those having hexagonal closed packed (HCP) crystal structure, experimental and numerical data is lacking. Therefore, the fracture properties of materials with such HCP structure, like titanium (used in aerospace and biomedical applications), zirconium (nuclear industry) and magnesium (manufacturing industry) are not well understood. The main research objective of this Ph.D. thesis is to better understand the mechanisms governing fracture in commercially pure (CP) titanium. In particular, the effect of grain orientation on void growth is investigated. The fracture process of CP titanium was visualized in model materials containing artificial holes. These model materials were fabricated using a femtosecond laser coupled with a diffusion bonding technique to obtain voids in the interior of titanium samples. Diffusion bonding was carried out either above or below the phase transformation temperature resulting in different microstructures. Changes in void dimensions during in-situ straining were recorded in three dimensions using x-ray computed tomography. Void growth obtained experimentally was compared with the Rice and Tracey model which predicted well the average void growth. However, a large scatter in void growth was observed experimentally and was explained in terms of differences in grain orientation which was confirmed by crystal plasticity simulations. It was also shown that grain orientation has a stronger effect on void growth than intervoid spacing and material strength. Intervoid spacing, however, appears to control whether the intervoid ligament failure is ductile or brittle. While this study showed a good agreement between experiments and simulations on average, there is no direct void growth comparison for particular grain orientations. In a follow-up study, an experimental approach was developed to directly relate the growth of a void to its underlying grain orientation. This is achieved by first annealing CP titanium samples below the α-β phase transformation temperature, then performing electron backscatter diffraction iii (EBSD) and finally diffusion bonding the samples together. Samples were then tested in x-ray tomography. This study showed the importance of the local state of strain on void growth. Crystal plasticity simulations that take into account the particular grain orientation and the local state of strain were found to predict well experimental void growth. Crystal plasticity simulations confirmed that the orientation of the voidcontaining grain is more important than the orientation of surrounding grains and more important than the volume fraction of voids, in order to determine void growth. This thesis on the growth and coalescence of voids is important to validate and improve the predictions of ductile fracture models and to design new materials with improved fracture properties.
15
Stieß, Michael. "Studies on microtubule nucleation during axon growth." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-123575.
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16
Monette, Liza. "Numerical simulations of nucleation and growth phenomena." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64053.
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O'Neill, K. P. "Island nucleation and growth during submonolayer deposition." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18117.
Повний текст джерелаАнотація:
In this thesis, we develop a number of theoretical approaches that can be used to investigate the nucleation and growth of islands in submonolayer deposition. In particular, we consider initially a rate-equation approach in which we propose a system of differential equations as a mean-field model of the submonolayer deposition of monomers onto a surface. A key feature of these equations is that they depend explicitly on a parameter known as the critical island size. We use rigorous and novel mathematical techniques to obtain results on the asymptotic behaviour of the point island size distribution. A fragmentation theory approach is also used in a one-dimensional model to obtain information on the asymptotic behaviour of the distribution of gaps between islands, the latter being represented by points on a line. This then leads to corresponding results for the capture zone distribution (CZD) associated with the islands. The CZD asymptotic forms that we obtain will be seen to differ from those of the Generalised Wigner Surmise (GWS) which has recently been proposed for island nucleation and growth models. The results predicted by our fragmentation approach and by the GWS are compared to kinetic Monte Carlo simulation data, and although this highlights both strengths and deficiencies in each approach, it also provides evidence that the fragmentation approach is more satisfactory than the GWS. ii We conclude by presenting a model for the nucleation of point islands in one dimension that leads to distributional fixed point equations. This approach develops a new retrospective view of how the inter-island gaps and capture zones have developed from the fragmentation of larger entities. Solutions of these equations are compared to the simulation data, and to theoretical models based on more traditional fragmentation theory approaches. These comparisons confirm the competitive performance of the distributional fixed point equations.
18
Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe, and Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193483.
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe, and Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals." Diffusion fundamentals 6 (2007) 28, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14203.
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20
Srivastava, Ankit. "Void Growth and Collapse in a Creeping Single Crystal." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc84281/.
Повний текст джерелаАнотація:
Aircraft engine components can be subjected to a large number of thermo-mechanical loading cycles and to long dwell times at high temperatures. In particular, the understanding of creep in single crystal superalloy turbine blades is of importance for designing more reliable and fuel efficient aircraft engines. Creep tests on single crystal superalloy specimens have shown greater creep strain rates for thinner specimens than predicted by current theories. Therefore, it is necessary to develop a more predictive description of creep processes in these materials for them to be used effectively. Experimental observations have shown that the crystals have an initial porosity and that the progressive growth of these voids plays a major role in limiting creep life. In order to understand void growth under creep in single crystals, we have analyzed the creep response of three dimensional unit cells with a single spherical void under different types of isothermal creep loading. The growth behavior of the void is simulated using a three dimensional rate dependent crystal plasticity constitutive relation in a quasi-static finite element analysis. The aim of the present work is to analyze the effect of stress traixiality and Lode parameter on void growth under both constant true stress and constant engineering stress isothermal creep loading.
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Innocenti, Malini Riccardo. "Simulation of the nucleation and growth of biominerals." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13253/.
Повний текст джерелаАнотація:
Nature appears to always be a step ahead. Through millions of years of evolution it has developed an incredible array of tools and machinery for a multitude of different applications. Biomineralization is one of those processes. It leads to the formation of a material with functions that include lenses, exoskeletons, grinding tools, mineral reservoirs and shells. All of these materials, are tailor-made for their applications by a complex interplay between the mineral phase and the organic matter. Understanding the fundamental mechanisms leading to the formation of these functional materials would lead to the development of new manufacturing methods to control matter at the nm scale. Nucleation is a process that is still not well understood. Recent investigation suggests the existence of (meta)stable complexes prior to the precipitation of a wide number of mineral systems. Due to the current resolution limit, it is not possible to directly observe the molecular mechanisms involved. In this thesis, Molecular Dynamics simulations have been used to probe the association of calcium phosphate ionic complexes and their aggregation in solution. To obtain the free energy of the reactions, Umbrella Sampling was used. The results partially confirm the experimental observations showing that the [Ca(HPO4)3]4- is stable and can exist in solution. In addition, the aggregation of both the [Ca(HPO4)3]4- and [Ca(HPO4)2]2- complexes were analysed allowing for a step-by-step understanding of one of the potential pathways prior to the nucleation of calcium phosphate minerals. As living organisms have been observed to initially precipitate an amorphous phase prior to the development of crystalline minerals it is important to understand its properties. Hydrous amorphous calcium carbonate is usually the precursor of both calcite and aragonite. As multiple short range structures have been observed for this phase, it is important to sample comprehensively the ensemble of configurations. By studying four models of hydrous ACC obtained in different ways, the structure and role of the water molecules within the structure were analysed. All the structures match experimentally obtained data. Formation of continuous, or percolating, channels was found to be metastable compared to more homogeneous distributions. Additionally the diffusion coefficient of the ions were extremely small suggesting that large scale reorganisation would require a large driving force. Biomolecules, including proteins, proteoglycans, glycosoamminoglycans, amino acids and peptides have the ability to dramatically alter the nucleation and growth process of biominerals. Often they induce the formation of minerals with non-equilibrium geometries. Here the effect of small organic molecules on the association of ions in solution and on the surface of an amorphous intermediate were investigated using Molecular Dynamics. The results show that organic molecules can stabilise ionic complexes, and can have an important effect on the water dynamics associated with ions.
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O'Reilly, Keyna A. Q. "The nucleation and growth of transition metal aluminides." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306035.
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Haezebrouck, Dennis Michael. "Nucleation and growth of a single martensitic particle." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14839.
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Liashenko, O., and A. Gusak. "Heterogeneous nucleation and depletion effect in nanowire growth." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20626.
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Mozaffari, Saeed. "Modeling the Nucleation and Growth of Colloidal Nanoparticles." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104448.
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Controlling the size and size distribution of colloidal nanoparticles have gained extraordinary attention as their physical and chemical properties are strongly affected by size. Ligands are widely used to control the size and size distribution of nanoparticles; however, their exact roles in controlling the nanoparticle size distribution and the way they affect the nucleation and growth kinetics are poorly understood. Therefore, understanding the nucleation and growth mechanisms and developing theoretical/modeling framework will pave the way towards controlled synthesis of colloidal nanoparticles with desired sizes and polydispersity.
This dissertation focuses on identifying the possible roles of ligands and size on the kinetics of nanoparticle formation and growth using in-situ characterization tools such as small-angle X-ray scattering (SAXS) and kinetic modeling. The presented work further focuses on developing kinetic models to capture the main nucleation and growth reactions and examines how ligand-metal interactions could potentially alter the rate of nucleation and growth rates, and consequently the nanoparticle size distribution. Additionally, this work highlights the importance of using multi-observables including the concentration of nanoparticles, size and/or precursor consumption, and polydispersity to differentiate between different nucleation and growth models and extract accurate information on the rates of nanoparticle nucleation and growth. Specifically, during the formation and growth of colloidal nanoparticles, complex reactions are occurring and as such nucleation and growth can take place through various reaction pathways. Therefore, sensitivity analysis was applied to effectively compare different nucleation and growth models and identify the most important reactions and obtain a reduced model (e.g. a minimalistic model) required for efficient data analysis. In the following chapters, a more sophisticated modeling approach is presented (population balance model) capable of capturing the average-properties of nanoparticle size distribution. PBM allows us to predict the growth rate of nanoparticles of different sizes, the ligand surface coverage for each individual size, and the parameters involved in altering the size distribution. Additionally, thermodynamic calculations of nanoparticle growth and ligand-metal binding as a function of size and ligand surface coverage were conducted to further shed light on the kinetics of nanoparticle formation and growth. The combination of kinetic modeling, in-situ SAXS and thermodynamic calculations can significantly advance the understanding of nucleation and growth mechanisms and guide toward controlling size and polydispersity.Doctor of Philosophy
The synthesis of colloidal metal nanoparticles with superior control over size and size distribution, and has attracted much attention given the wide applications of these nanomaterials in the fields of catalysis, photonics, and electronics. Obtaining nanoparticles with desired sizes and polydispersity is vital for enhancing the consistency and performance for specific applications (e.g., catalytic converters for automotive emission). Ligands are often employed to prevent agglomeration and also control the nanoparticle size and size distribution. Ligands can affect the precursor reactivity and therefore the reduction/nucleation by binding with the metal precursor. Nucleation refers to the assimilation of few atoms to form initial nuclei acting as templates for nanoparticle growth. Additionally, ligands can bind with the nanoparticle surface sites and change the rate of surface growth and therefore the final nanoparticle size. Despite strong effects of ligands in the colloidal nanoparticle synthesis, their exact role in the nucleation and growth kinetics is yet to be identified. Additionally, nucleation and growth models capable of unraveling the underlying mechanisms of nucleation and growth in the presence of ligands are still lacking in the literature. Therefore, obtaining nanoparticles with desired sizes and polydispersity mostly relies on trial-and-error approach making the synthesis costly and inefficient. As such, developing models capable of predicting suitable synthesis conditions is contingent upon understanding the chemistry and mechanism involved during nanoparticles formation. Therefore, in this study, novel kinetic models were developed to capture the nucleation and growth kinetics of colloidal metal nanoparticles under different synthetic conditions (different types of solvents, different concentrations of ligand and metal). In-situ SAXS was further employed to measure the average diameter, concentration of nanoparticles, and polydispersity during the synthesis and extract the nucleation and growth rates (evolution of concentration of nanoparticles and size). First, an average-property model was developed to account for ligand-metal bindings and capture the size and concentration of nanoparticles during the synthesis. Then, a more complex modeling approach; PBM, accompanied by the thermodynamic calculations of surface growth and ligand-nanoparticle binding enthalpies was implemented to capture the size distribution. As it will be shown later, the determination of the underlying mechanisms resulted in a highly predictive kinetic model capable of predicting the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can serve as a powerful tool to synthesize nanoparticles with specific sizes and polydispersity.
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Knelangen, Matthias. "Nucleation and growth of group III-nitride nanowires." Doctoral thesis, Humboldt-Universität zu Berlin, 2013. http://dx.doi.org/10.18452/16855.
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Diese Arbeit beschreibt das MBE-Wachstum und die Charakterisierung von Gruppe-III-Nitrid-Nanostrukturen. Die Arbeit beginnt mit dem katalysatorfreien Wachstum von GaN-Nanowires (NW) auf Si(111) mittels MBE. Es wird gezeigt, dass GaN NW als sph\"arische Inseln nukleieren und im weiteren Wachstum in eine NW-Geometrie übergehen. Die amorphe Zwischenschicht führt zum Verlust der epitaktischen Ausrichtung und somit zu gekippten Säulen und Koaleszenz. Diese Koaleszenz führt zur Enstehung von Versetzungen und Stapelfehlern in den Nanosäulen, welche einen starken Einfluss auf die optischen Eigenschaften haben: Während Versetzungen die Säulen optisch passivieren, haben Stapelfehler charakteristische Emissionen. Durch Kombination von Elektronenmikroskopie und Cathodolumineszenz wird die charateristische Wellenlänge eines Stapelfehlers gemessen. Epitaktisches Wachstum von GaN auf Si(111) kann durch die Verwendung einer AlN-Pufferschicht erreicht werden. Die Nukleation von GaN auf AlN/Si geschieht als linsenförmige Inseln. Im weiteren Verlauf des Wachstums erfolgen mehrere charakteristische Formübergänge, bei denen Facetten gebildet werden, um die Verspannung durch Gitterfehlanpassung elastisch zu relaxieren. Bei einer kritischen Inselgröße (und damit bei einem kritischen Spannungszustand) tritt eine platische Relaxation ein und es wird eine Versetzung an der AlN/GaN-Grenzfläche gebildet. Daraufhin tritt ein Übergang zur NW-Geometrie ein. Der dritte Teil dieser Arbeit beschreibt das Wachstum von (In,Ga)N/GaN NW Heterostrukturen. Mit MBE werden GaN NW mit zwei (In,Ga)N-Einschlüssen gewachsen. Die chemische Zusammensetzung wird mittels einer Kombination von hochauflösender Röntgenbeugung und einer Gitterverzerrungsanalyse von hochaufgelösten transmissionselektronenmikroskopischen Aufnahmen bestimmt. Die Strukturanalyse zeigt, dass die (In,Ga)N-Einschlüsse vollkommen in die GaN-Matrix eingebettet sind, und dass keine plastische Relaxation stattfindet.This work covers the MBE growth and characterization of group III-nitride nanostructures. The work begins with the catalyst-free growth of GaN nanowires (NWs) on Si(111) by plasma-assisted MBE. The importance of substrate preparation and the formation of an amorphous SiN interlayer are described. GaN NWs are shown to nucleate as spherical islands and to furhter undergo a shape transition towards the NW geometry. The amorphous interlayer leads to a loss in epitaxial alignment and thus to NW tilt and coalescence. Coalescence leads to the formation of dislocations and stacking faults (SFs) in the NWs which greatly affect their optical properties. Dislocations are shown to have a detrimental effect on the optical quality, whereas SFs are shown to have a characteristic emission wavelength. Epitaxial growth of GaN on Si(111) can be achieved by using an AlN buffer layer. The nucleation and growth GaN NWs on AlN-buffered Si(111) is shown to happen via the pseudomorphical nucleation of spherical islands. As these islands grow, they undergo several characteristical shape changes, with the formation of facets in order to elastically relieve the lattice-mismatch induced strain. At a critical island size (and thus strain level), plastic relaxation happens by the formation of a misfit dislocation at the AlN/GaN interface. A subsequent transition to the NW geometry is observed, driven by the anisotropy of surface energies. The third part of this work covers the growth of (In,Ga)N/GaN NW heterostructures. GaN NWs with two stacked (In,Ga)N insertions are grown by MBE. The chemical composition is assessed by combining synchrotron-based HRXRD and a geometrical phase analysis of HRTEM micrographs. The structural analysis reveals that the (In,Ga)N insertions are embedded in the GaN matrix and that no plastic relaxation happens. The In content is shown to vary within a single insertion: The top region is more In rich due to In segretation during growth.
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JAYASEELAN, VIDHYA SAGAR. "Diamond Heteroepitaxy by Bias Enhanced Nucleation." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1202537092.
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Chan, Chit-yiu. "Nucleation and growth of cubic boron nitride thin films /." access full-text access abstract and table of contents, 2005. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ap-b19887693a.pdf.
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Thesis (Ph.D.)--City University of Hong Kong, 2005."Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references (leaves 147-154)
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Schöll, Jochen. "Nucleation, growth, and solid phase transformations during precipitation processes /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16779.
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Runevall, Odd. "Helium Filled Bubbles in Solids : Nucleation, Growth and Swelling." Doctoral thesis, KTH, Reaktorfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-90960.
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When nuclear fuel, fabricated for the purpose of transmuting spent fuel is irradiated, significant amounts of He is produced from alpha particles mainly emitted when 242Cm decays into 238Pu. From irradiation experiments it is known that the presence of He in the solids alters the swelling behaviour of the material. The thesis presents the theoretical background from which nucleation models of He bubbles can be formulated. Such models are presented for He in metals, and the case of He in Mo is studied as an example. MgO, which together with Mo is suggested as a matrix material in transmutation fuel is also studied and the stability of He containing bubbles in this material is discussed. By calculating parameters for a rate theory model derived from atomistic modelling, it is shown that He can stabilise vacancy clusters and cause cluster growth at temperatures and irradiation doses where nucleation and growth would not otherwise occur. At the initial stages of nucleation He can stabilise small bubbles while larger bubbles are unstable. This results in an incubation time of swelling, which implies that He does not always cause increased swelling, but can at certain irradiation conditions slow down the growth of large vacancy clusters and thereby delay swell\-ing beyond the time of the irradiation. When comparing the behaviour of bubble nucleation in Mo and MgO, it is found that He has a significant impact even at very low concentrations in Mo. In contrast, the concentration of He has to be considerably higher in MgO to affect the swelling behaviour. For an inert matrix fuel, designed for transmutation purposes, this implies that the Mo matrix will have a tendency to swell considerably at rather high temperatures due to He stabilised vacancy clusters. If operated at lower temperatures, the swelling could instead be reduced due to the incubation time. In a MgO matrix, the swelling behaviour will instead depend largely on the production rate of He. For a low production rate, the material will have a swelling behaviour similar to the one seen when He is not present in the material. A high production rate implies that He will remain in vacancy clusters, thereby stabilising the clusters and enhancing the growth and swelling.
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Hawtin, Robert William. "Molecular Simulation of Clathrate Hydrate Nucleation, Growth and Inhibition." Thesis, University of Warwick, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487912.
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Gas hydrates are solid crystalline mixtures of water and small gas molecules, such as those found in natural gas. They are stable at temperatures and pressures commonly found on the seafloor and in sub-sea pipelines for the transportation of natural gas. It is the propensity of gas hydrates to cause blockages in pipelines that necessitates the addition of inhibitors to prevent hydrate formation. Recent work has focused on developing 'low dosage hydrate inhibitors', LDHls, which act to delay nucleation or prevent growth while present at low concentrations, but identifying new chemicals to provide more active LDHls has been hindered by the absence of a clear molecularlevel understanding of their activity. Molecular Dynamics simulations designed to shed light on the molecular-level processes of gas hydrate nucleation and inhibition are presented in this thesis. Nucleation of a model methane hydrate has been simulated with and without the presence of known LDHls. Nucleation in the absence of any additives has been investigated by a range of methods, including 'local phase assignment'. Hydrate has been shown to form a dynamic cage structure with elements of hydrate structures I and II. It is proposed that the stable bulk hydrate structure arises out of this dynamic structure. Crystal growth has been calculated to be favourable for clusters in excess of 200 hydrate-like water molecules in size, thus providing an estimate for the critical cluster size in these systems. In a system including the kinetic inhibitor polydimethylaminoethylmethacrylate (PDMAEMA) hydrate growth from a seed crystal of 225 water molecules was accelerated compared to the uninhibited system. Repeated simulations and statistical analysis showed the magnitude of the promotion effect to be greater with increased levels of PDMAEMA immersion. Binding of the PDMAEMA to the surface of the hydrate was seen, which is in agreement with current theories of inhibitor activity. The simulations and protocol have also been extended in systems containing other kinetic inhibitors.
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Fontenot, Kevin. "Nucleation and growth in mini/macro emulsion polymerization systems." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/10922.
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Hassan, S. A. "Particle nucleation and growth in emulsion polymerisation of styrene." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377034.
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Whitfield, Michael David. "Nucleation, growth and acoustic properties of thin film diamond." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368194.
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Gomez, Said Hamad. "Computational study of the nucleation and growth of ZnS." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445565/.
Повний текст джерелаАнотація:
Several computational techniques have been employed to perform an extensive theoretical study of different aspects of ZnS nucleation and growth. First, we use Density Functional Theory and ineratomic potential based calculations to calculate the surface energies for the most common surfaces in the two crystalline phases of ZnS wurzite and sphalerite. This study allows us to calculate the crystal morphologies for both phases, which agree with those observed experimentally. The predicted morphologies correspond to those that crystallites of micrometer sizes would adopt, but in order to understand the nucleation processes we need models for nanoclusters. We therefore use a global minimization technique (simulate annealing), with which we obtain the most stable configuration in vacuum for (ZnS)n clusters, n=10-47, 50, 60, 70 and 80. These clusters are classified into two groups. Clusters with n=10-47, denoted bubble clusters, are hollow structures in which all the atoms are three coordinated. Such structures contrast with the expectation of bulk-like structures in which most of the atoms are four coordinated. Larger (ZnS)n clusters (n=50, 60, 70 and 80) adopt what we have denoted double bubble structures, in which one big bubble encloses a smaller one. The two bubbles are bonded through covalent bonds, therefore creating a network of four coordinated atoms. Density Functional Theory as well as interatomic potential based calculations are employed to calculate the properties of these particles. The thesis concludes with a molecular dynamics study of the nucleation of ZnS in water solution, which reveals that bubble clusters are also formed in the presence of water, and gives insight into the detailed mechanisms of their formation.
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Nitsche, Heiko. "Kinetics of crystallization in amorphous alloys nucleation and growth /." [S.l. : s.n.], 2005. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11947826.
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Lee, Sangil. "Fundamental study of underfill void formation in flip chip assembly." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29755.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Baldwin, Daniel; Committee Member: Colton, Jonathan; Committee Member: Ghiaasiaan, Mostafa; Committee Member: Moon, Jack; Committee Member: Tummala, Rao. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Park, Yensil. "Heterogeneous Nucleation in a Supersonic Nozzle." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1545323828317256.
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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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Pang, Ka-yan. "Nucleation and growth of GaN islands by molecular-beam epitaxy." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36776543.
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Stinson, O'Gorman Dean Edward. "Theory and large-scale numerical simulations of nucleation and growth." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ29792.pdf.
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Mori, Brian Katsuo. "Studies of bubble growth and departure from artificial nucleation sites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0009/NQ35258.pdf.
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Li, Qinghua. "Colloidal zeolites : from nucleation to zoned films by seeded growth /." Luleå, 2002. http://epubl.luth.se/1402-1544/2002/04/index.html.
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Hounslow, Michael John. "A discretized population balance for simultaneous nucleation, growth and aggregation /." Title page, summary and table of contents only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phh839.pdf.
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Shin, Jong Ho. "Role of nucleation and growth in two-phase microstructure formation." [Ames, Iowa : Iowa State University], 2007.
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Stinson, O'Gorman Dean. "Theory and large-scale numerical simulations of nucleation and growth." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27417.
Повний текст джерелаАнотація:
In this work we have re-examined the classical problem of nucleation and growth. We present a new model that combines steady-state homogeneous nucleation theory with the classical Lifshitz-Slyozov mechanism of growth. This model considers the substantial correlations between droplets and naturally incorporates the crossover from the early-stage, nucleation dominated regime to the scaling, late-stage, coarsening regime within a single framework, without ad-hoc assumptions. This is achieved by the development of a set of self-consistent interface equations which describe the decay of metastable states. The model is implemented numerically and some interesting dynamical behaviour is observed, including the reproduction of the expected late-time scaling and power-law growth laws for the key mean-field variables.
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Pang, Ka-yan, and 彭嘉欣. "Nucleation and growth of GaN islands by molecular-beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36776543.
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Van, Dyke Alexander Scott. "Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces." Thesis, Kansas State University, 2015. http://hdl.handle.net/2097/19105.
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Master of ScienceDepartment of Mechanical and Nuclear Engineering
Amy R. Betz
The purpose of this research was to test if biphilic surfaces mitigate frost and ice formation. Frost, which forms when humid air comes into contact with a surface that is below the dew point and freezing temperature of water, hinders engineering systems such as aeronautics, refrigeration systems, and wind turbines. Most previous research has investigated increasingly superhydrophobic materials to delay frost formation; however, these materials are dependent on fluctuating operating conditions and surface roughness. Therefore, the hypothesis for this research was that a biphilic surface would slow the frost formation process and create a less dense frost layer, and water vapor would preferentially condense on hydrophilic areas, thus controlling where nucleation initially occurs. Preferential nucleation can control the size, shape, and location of frost nucleation. To fabricate biphilic surfaces, a hydrophobic material was coated on a silicon wafer, and a pattern of hydrophobic material was removed using photolithography to reveal hydrophilic silicon-oxide. Circles were patterned at various pitches and diameters. The heat sink was comprised of two parts: a solid bottom half and a finned upper half. Half of the heat sink was placed inside a polyethylene base for insulation. Tests were conducted in quiescent air at room temperature, 22 °C, and two relative humidities, 30% and 60%. Substrate temperatures were held constant throughout all tests. All tests showed a trend that biphilic surfaces suppress freezing temperature more effectively than plain hydrophilic or hydrophobic surfaces; however, no difference between pattern orientation or size was noticed for maximum freezing temperature. However, the biphilic patterns did affect other aspects such as time to freezing and volume of water on the surface. These effects are from the patterns altering the nucleation and coalescence behavior of condensation.
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Canestrari, Nicolò. "Nucleation and growth of iron nanoparticles by gas phase condensation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24849/.
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We aim at better understanding how nucleation occurs in a gas condensation chamber, discussing in particular the formation of iron nanoparticles in Argon atmosphere and Helium atmosphere, and the use of the method of moments to study their growth.
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Ocansey, Paul Morgan-Narteh. "Nucleation and early growth during solidification of aluminum-copper alloys." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187082.
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Using a relatively simple experimental setup, thermal history, microstructural evolution, nucleation, and early growth during solidification of aluminum-copper alloys are investigated. In particular, nucleation rates are measured, and contact angles calculated using the classical heterogeneous nucleation theory. Also, growth velocities of the dendrites are measured and compared with those predicted using kinetic models in order to elucidate which model is controlling during recalescence or early growth. Two groups of aluminum alloys with 5.1, 6.6, 15.6, and 30 wt% Cu are studied. One group is uninoculated and the other is grain refined with Ti-B-Al, Ti-B, and Ti-C-Al master alloys. In alloys that exhibit recalescence of primary solid, solidification occurs at a temperature, approximately 0.4 °C or less before the minimum in the curve is reached. Grain refined alloys exhibit dendrites which are equiaxed in morphology and appear as clusters in a matrix of quenched liquid. Uninoculated alloys, however, contain somewhat columnar dendrites. Nucleation rates are composition sensitive and range from 4.8 x 10¹³ m³/s to 1.6 x 10\sp¹⁵ m³/s in uninoculated alloys; with an increase in copper content there is an increase in nucleation rate. In grain refined alloys, the same metric measures from 4.4 x 10¹⁶ m³/s to 1.4 x 10¹⁹ m³/s. The calculated contact angles are consistently smaller in the grain refined alloys when compared with their uninoculated counterparts and are rather sensitive to small changes in the measured undercooling. For example, if the undercooling with respect to the liquidus temperature is known to within ± 1°, the calculated contact angle changes by ± 0.8°. Experimental growth rates in grain refined alloys are less than in uninoculated alloys, because the undercoolings during the early stages of growth are less. While growth rate in uninoculated alloys typically range from 2.2 x 10⁻⁴ m/s in the most concentrated alloy to 1.8 x 10⁻³ m/s in the most dilute alloy, the same metric in grain refined alloys ranges from 7.8 x 10⁻⁵ m/s to 1.7 x 10⁻⁴ m/s. Experimental growth rates compare favorably to dendrite growth models of Ivantsov, and Lipton-Glicksman-Kurz. Consequently, during recalescence and/or early growth, the growth velocity of primary solid is controlled by solute diffusion processes and not by interface kinetics.