Dissertations / Theses on the topic 'Allotrop'

Schwerpunkte der Arbeit waren die Synthese und in-situ Charakterisierung metastabiler Modifikationen der Elemente Silicium und Germanium, sowie die Darstellung binärer Silicide und Germanide der Erdalkali- und Seltenerdmetalle unter Druck (bis 20 GPa) und bei hoher Temperatur (bis 2200 K). Dabei konnten die Phasenbeziehungen von Allotropen des Germaniums näher beleuchtet werden und es gelang, eine neue Germaniummodifikation, Ge(hR8), in-situ strukturell zu charakterisieren. Die neu dargestellten metastabilen binären Silicide und Germanide unterteilen sich strukturell in solche, die clathratartige Tetrel-Netzwerke mit einer Koordinationszahl von drei und vier enthalten und in jene, bei denen die Anzahl benachbarter Tetrelatome vier übersteigt. So konnten beispielsweise Netzwerke dargestellt werden, die acht homonukleare Silicium oder Germanium Kontakte im Netzwerk aufweisen. Neben der strukturellen Charakterisierung standen die Bestimmungen der elektrischen Leitfähigkeit und des Magnetismus, sowie die Ermittlung der thermischen Eigenschaften im Focus der Arbeit
Key aspects of the present work were the synthesis and in-situ characterization of metastable modifications of elemental silicon and germanium as well as the preparation of binary silicides and germanides of the alkaline earth and rare earth metals under pressure (up to 20 GPa) and at elevated temperatures (up to 2200 K). In that process the phase relations of germanium allotropes could be examined more closely and led to the preparation of a new germanium modification, Ge(hR8), which could be structurally characterized by in-situ experiments. The prepared silicides and germanides can be structurally separated in those containing clathrate-like networks with a coordination number of three and four and those which contain more neighbors in the network than four e.g., eight homonuclear silicon or germanium contacts in the network of CeSi5 and CeGe5. Beside the structural characterization the determination of the electrical resistivity and the magnetical properties as well as the analysis of the thermal behavior were in focus of the work

Schwerpunkte der Arbeit waren die Synthese und in-situ Charakterisierung metastabiler Modifikationen der Elemente Silicium und Germanium, sowie die Darstellung binärer Silicide und Germanide der Erdalkali- und Seltenerdmetalle unter Druck (bis 20 GPa) und bei hoher Temperatur (bis 2200 K). Dabei konnten die Phasenbeziehungen von Allotropen des Germaniums näher beleuchtet werden und es gelang, eine neue Germaniummodifikation, Ge(hR8), in-situ strukturell zu charakterisieren. Die neu dargestellten metastabilen binären Silicide und Germanide unterteilen sich strukturell in solche, die clathratartige Tetrel-Netzwerke mit einer Koordinationszahl von drei und vier enthalten und in jene, bei denen die Anzahl benachbarter Tetrelatome vier übersteigt. So konnten beispielsweise Netzwerke dargestellt werden, die acht homonukleare Silicium oder Germanium Kontakte im Netzwerk aufweisen. Neben der strukturellen Charakterisierung standen die Bestimmungen der elektrischen Leitfähigkeit und des Magnetismus, sowie die Ermittlung der thermischen Eigenschaften im Focus der Arbeit.
Key aspects of the present work were the synthesis and in-situ characterization of metastable modifications of elemental silicon and germanium as well as the preparation of binary silicides and germanides of the alkaline earth and rare earth metals under pressure (up to 20 GPa) and at elevated temperatures (up to 2200 K). In that process the phase relations of germanium allotropes could be examined more closely and led to the preparation of a new germanium modification, Ge(hR8), which could be structurally characterized by in-situ experiments. The prepared silicides and germanides can be structurally separated in those containing clathrate-like networks with a coordination number of three and four and those which contain more neighbors in the network than four e.g., eight homonuclear silicon or germanium contacts in the network of CeSi5 and CeGe5. Beside the structural characterization the determination of the electrical resistivity and the magnetical properties as well as the analysis of the thermal behavior were in focus of the work.

The synthesis of the sulfur homocycles S6, S9, S10, S12 and S20, which belong to the group of sulfur allotropes, has been achieved based on existing procedures. Polymeric sulfur Smu was also prepared.
The parameters of a small scale model reaction between 2,3-diphenyl-1,3-butadiene and S10 were optimized. Products were identified and 1H-NMR yields were calculated by comparison with an internal standard. The experimental parameters of this model served as a base for further reactions of S 10 with a variety of simple or conjugated olefins. The products of these reactions were fully isolated and characterized using standard spectroscopic techniques. The structures of a new bis-sulfurated compound having a norbornane framework and of the product obtained from the dimerization of norborn-5-ene-2,3-dithiol were also confirmed by single crystal X-ray crystallography.
The sulfur homocycles S9, S12 and S20 were also found to react with norbornene and two different 1,3-dienes. Products were identified and 1H-NMR yields for these small scale reactions were calculated by internal standard comparison. Differences and similarities with the products obtained with S10 are discussed. Sulfuration efficiencies of the different allotropes towards selected substrates are also compared.
A mechanistic study was carried out. The implication of sulfur radicals in the thermal decomposition of S10 has been suggested. Reaction mechanisms accounting for the formation of the different products observed are proposed.

In the first section of the thesis graphitic carbon nitride was for the first time synthesised using the high-temperature condensation of dicyandiamide (DCDA) – a simple molecular precursor – in a eutectic salt melt of lithium chloride and potassium chloride. The extent of condensation, namely next to complete conversion of all reactive end groups, was verified by elemental microanalysis and vibrational spectroscopy. TEM- and SEM-measurements gave detailed insight into the well-defined morphology of these organic crystals, which are not based on 0D or 1D constituents like known molecular or short-chain polymeric crystals but on the packing motif of extended 2D frameworks. The proposed crystal structure of this g-C3N4 species was derived in analogy to graphite by means of extensive powder XRD studies, indexing and refinement. It is based on sheets of hexagonally arranged s-heptazine (C6N7) units that are held together by covalent bonds between C and N atoms. These sheets stack in a graphitic, staggered fashion adopting an AB-motif, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. This study was contrasted with one of many popular – yet unsuccessful – approaches in the last 30 years of scientific literature to perform the condensation of an extended carbon nitride species through synthesis in the bulk. The second section expands the repertoire of available salt melts introducing the lithium bromide and potassium bromide eutectic as an excellent medium to obtain a new phase of graphitic carbon nitride. The combination of SEM, TEM, PXRD and electron diffraction reveals that the new graphitic carbon nitride phase stacks in an ABA’ motif forming unprecedentedly large crystals. This section seizes the notion of the preceding chapter, that condensation in a eutectic salt melt is the key to obtain a high degree of conversion mainly through a solvatory effect. At the close of this chapter ionothermal synthesis is seen established as a powerful tool to overcome the inherent kinetic problems of solid state reactions such as incomplete polymerisation and condensation in the bulk especially when the temperature requirement of the reaction in question falls into the proverbial “no man’s land” of classical solvents, i.e. above 250 to 300 °C. The following section puts the claim to the test, that the crystalline carbon nitrides obtained from a salt melt are indeed graphitic. A typical property of graphite – namely the accessibility of its interplanar space for guest molecules – is transferred to the graphitic carbon nitride system. Metallic potassium and graphitic carbon nitride are converted to give the potassium intercalation compound, K(C6N8)3 designated according to its stoichiometry and proposed crystal structure. Reaction of the intercalate with aqueous solvents triggers the exfoliation of the graphitic carbon nitride material and – for the first time – enables the access of singular (or multiple) carbon nitride sheets analogous to graphene as seen in the formation of sheets, bundles and scrolls of carbon nitride in TEM imaging. The thus exfoliated sheets form a stable, strongly fluorescent solution in aqueous media, which shows no sign in UV/Vis spectroscopy that the aromaticity of individual sheets was subject to degradation. The final section expands on the mechanism underlying the formation of graphitic carbon nitride by literally expanding the distance between the covalently linked heptazine units which constitute these materials. A close examination of all proposed reaction mechanisms to-date in the light of exhaustive DSC/MS experiments highlights the possibility that the heptazine unit can be formed from smaller molecules, even if some of the designated leaving groups (such as ammonia) are substituted by an element, R, which later on remains linked to the nascent heptazine. Furthermore, it is suggested that the key functional groups in the process are the triazine- (Tz) and the carbonitrile- (CN) group. On the basis of these assumptions, molecular precursors are tailored which encompass all necessary functional groups to form a central heptazine unit of threefold, planar symmetry and then still retain outward functionalities for self-propagated condensation in all three directions. Two model systems based on a para-aryl (ArCNTz) and para-biphenyl (BiPhCNTz) precursors are devised via a facile synthetic procedure and then condensed in an ionothermal process to yield the heptazine based frameworks, HBF-1 and HBF-2. Due to the structural motifs of their molecular precursors, individual sheets of HBF-1 and HBF-2 span cavities of 14.2 Å and 23.0 Å respectively which makes both materials attractive as potential organic zeolites. Crystallographic analysis confirms the formation of ABA’ layered, graphitic systems, and the extent of condensation is confirmed as next-to-perfect by elemental analysis and vibrational spectroscopy.
Die vorliegende Arbeit befasst sich mit der Synthese und Charakterisierung neuer Allotropen und Nanostrukturen von Karbonitriden und berührt einige ihrer möglichen Anwendungen. Alle gezeigten, ausgedehnten, kovalent verbundenen Karbonitridgerüste wurden in einem ionothermalen Syntheseprozess – einer Hochtemperaturbehandlung in einem eutektischen Salzgemisch als ungewöhnlichem Lösungsmittel – aus einfachen Präkursormolkülen erzeugt. Der Kondensationsmechanismus folgt einer temperaturinduzierten Deaminierung und Bildung einer ausgedehnten, aromatischen Einheit; des dreifach substituierten Heptazines. Die Dissertation folgt vier übergreifenden Themen, beginnend mit der Einleitung in Karbonitridsysteme und der Suche nach einem Material, welches einzig aus Kohlenstoff und Stickstoff aufgebaut ist – einer Suche, die 1834 mit den Beobachtungen Justus von Liebigs „über einige Stickstoffverbindungen“ begann. Der erste Abschnitt zeigt die erfolgreiche Synthese von graphitischem Karbonitrid (g-C3N4); einer Spezies, welche auf Schichten hexagonal angeordneter s-Heptazineinheiten beruht, die durch kovalente Bindungen zwischen C- und N-Atomen zusammengehalten werden, und welche in einer graphitischen, verschobenen Art und Weise gestapelt sind. Der zweite Abschnitt berührt die Vielfalt von Salzschmelzensystemen, die für die Ionothermalsynthese geeignet sind und zeigt auf, dass die bloße Veränderung der Salzschmelze eine andere Kristallphase des graphitischen Karbonitrides ergibt – das g-C3N4-mod2. Im dritten Abschnitt wird vom Graphit bekannte Interkallationschemie auf das g-C3N4 angewendet, um eine Kalliuminterkallationsverbindung des graphitischen Karbonitirdes zu erhalten (K(C6N8)3). Diese Verbindung kann in Analogie zum graphitischen System leicht exfoliiert werden, um Bündel von Karbonitridnanoschichten zu erhalten, und weist darüberhinaus interessante optische Eigenschaften auf. Der vierte und letzte Abschnitt handelt von der Einführung von Aryl- und Biphenylbrücken in das Karbonitridmaterial durch rationale Synthese der Präkursormoleküle. Diese ergeben die heptazinbasierten Frameworks, HBF-1 und HBF-2 – zwei kovalente, organische Gerüste.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages [81]-[85]).
This thesis reviews the progress leading to the modem picture of 2-dimensional carbon materials, while providing new contributions into the mechanics and failure of the graph-yne family of materials. A first original contribution involves a discussion of material failure across the graphyne family and discussion of a proposed spring abstraction for these materials under mechanical loading. A second contribution is the contrast of these behaviors with graphene and the implications for proposed applications. We apply the mathematical framework of category theory to articulate the precise relation between structure and mechanics of a microscopic system in a macroscopic model domain, by maintaining the chosen molecular properties across a multitude of length scales, from the nanoscale to the continuum scale. The process demonstrates how it becomes possible to 'protoype a model', as category theory enables us to maintain certain information across disparate fields of study, distinct scales, or physical realizations of an abstract system. This method can be thought of as a prototyped model in which a behavior is brought to a different realization as a case study, we use largescale multi-material printing to examine the scaling of the Young's modulus of a particular family 2-D carbon allotropes at the macroscale and validate the printed model using experimental testing. The resulting hand-held materials can be examined more readily and yield insights beyond those available in purely digital representations which is shown through a twisting analysis.
by Dieter B. Brommer.
S.M.

The research reported in this manuscript concerns the structural characterization of graphene membranes and single-walled carbon nanotubes (SWCNTs). The experimental investigation was performed using a wide range of transmission electron microscopy (TEM) techniques, from conventional imaging and diffraction, to advanced interferometric methods, like electron holography and Geometric Phase Analysis (GPA), using a low-voltage optical set-up, to reduce radiation damage in the samples. Electron holography was used to successfully measure the mean electrostatic potential of an isolated SWCNT and that of a mono-atomically thin graphene crystal. The high accuracy achieved in the phase determination, made it possible to measure, for the first time, the valence-charge redistribution induced by the lattice curvature in an individual SWCNT. A novel methodology for the 3D reconstruction of the waviness of a 2D crystal membrane has been developed. Unlike other available TEM reconstruction techniques, like tomography, this new one requires processing of just a single HREM micrograph. The modulations of the inter-planar distances in the HREM image are measured using Geometric Phase Analysis, and used to recover the waviness of the crystal. The method was applied to the case of a folded FGC, and a height variation of 0.8 nm of the surface was successfully determined with nanometric lateral resolution. The adhesion of SWCNTs to the surface of graphene was studied, mixing shortened SWCNTs of different chiralities and FGC membranes. The spontaneous atomic match of the two lattices was directly imaged using HREM, and we found that graphene membranes act as tangential nano-sieves, preferentially grafting achiral tubes to their surface.

Diffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding. Due to diffusional interactions that can occur between these two components, a third is sometimes added between the fuel and cladding to serve as a diffusion barrier layer. Fe, Mo, and Zr can act as either cladding or barrier layer constituents and both Mo and Zr also serve as alloying additions in uranium based metallic fuels. Therefore, a fundamental understanding of the diffusional interactions in these systems is critical in predicting the performance and lifetime of these fuels. In order to study this diffusion behavior, a series of solid-to-solid diffusion couples were assembled between Fe, Mo, and Zr. These couples were then diffusion annealed isothermally for various predetermined times over a range of temperatures, including some both above and below the allotropic transformation temperatures for Fe and Zr. Following the diffusion anneal, the couples were water quenched, cross-sectioned, and prepared for microstructural and compositional characterization. A combination of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to obtain micrographs showing the microstructure and to collect compositional data for identifying intermediate phases and determining concentration profiles across the interdiffusion zone. Based on this characterization, the phases that developed in the diffusion zones were identified. In the Mo-Zr system, a large Zr solid solution layer developed in the couples annealed at and above 850[degrees]C and a thin (~1-2 [micro]m) layer of Mo2Zr formed in all couples. Growth constants and concentration dependent interdiffusion coefficients were calculated for the Mo2Zr and Zr solid solution phases, respectively. In the Fe-Mo system, both the [lambda]-Fe2Mo and [micro]-Fe7Mo6 phases were observed in couples annealed at 900[degrees]C and below while [micro]-Fe7Mo6 and [alpha]-Fe solid solution layers were observed in couples annealed above 900[degrees]C. The relevant growth constants and activation energies for growth were calculated. In the Fe-Zr system, the couple annealed at 750[degrees]C developed an FeZr2 and an FeZr3 layer while the couple annealed at 850[degrees]C developed an Fe2Zr and Fe23Zr6 layer in the diffusion zone. The results of this analysis were then compared to available information from literature and the corresponding binary phase diagrams for each system. The results are discussed with respect to the effects of the allotropic transformations of Fe and Zr on the interdiffusion behavior in these systems.
ID: 031001410; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Yongho Sohn.; Title from PDF title page (viewed June 13, 2013).; Thesis (M.S.M.S.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 84-89).
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering; Accelerated BS to MS

Différentes approches ont été utilisées pour évaluer les effets de deux formes de nanoparticules de carbone (NPC), nanotubes et graphène, afin de comprendre les mécanismes de la réponse générée par la diatomée benthique d'eau douce Nitzschia palea. Les effets à l'échelle de la communauté ont démontré un impact temporaire sur la croissance du biofilm et une accumulation des NPC dans la matrice extracellulaire. L'application d'une étude transcriptomique a mis en évidence l'importance de l'interaction physique, à l'origine d'altération du frustule, dans la mise en place de cette réponse extracellulaire se traduisant par une surproduction des substances exo-polymériques (EPS). Cette approche a également révélé l'impact des NPC sur l'activité photosynthétique des diatomées et une modification du métabolisme énergétique, suggérant une allocation énergétique en faveur de la production d'EPS. L'étude du protéome extracellulaire a permis d'avoir un premier aperçu de la composition de la matrice extracellulaire, principalement constituée de protéines à caractère hydrophobe. Lors de l'exposition aux NPC, les diatomées semblent produire un système adhésif complexe permettant de renforcer la matrice extracellulaire et d'augmenter la stabilité du biofilm tout en piégeant les NPC. L'exposition des diatomées face au deux formes de NPC induit une réponse présentant une forte similitude notamment pour les plus fortes concentrations testées
Different approaches were used to assess the effect of two forms of carbon-based nanoparticles (CNP) nanotubes and graphene, in order to determine the mechanism of the response generated by the benthic freshwater diatom Nitzschia palea. The effect at the cellular community scale demonstrated a temporary impact on biofilm growth and an accumulation of NPC in the extracellular matrix. The use of transcriptomic study evidenced the role of the physic interaction, causing alteration of the frustule, in the extracellular response leading to an overexcretion of exopolymeric substances (EPS). This approach also revealed the impact of NPC on the photosynthetic activity of diatoms and a modification of the energetic metabolism suggesting an energetic allocation for the EPS production. The study of the extracellular proteome allowed to have a first insight of the extracellular matrix composition, in majority composed of hydrophobic-like proteins. In NPC exposure, diatoms seemed to produce an adhesive system allowing to strengthen the extracellular matrix and increase the biofilm stability while trapping NPC. The exposition of diatoms to the two NPC forms induce a response greatly similar for the highest tested concentration

Graphene is a two-dimensional system consisting of a single planar layer of carbon atoms with hexagonal arrangement. Various approaches have been proposed to control its physical and electronic properties. When appropriately cut, rolled, and bonded, graphene generates single-walled carbon nanotubes of varying diameters. Graphite intercalation compounds are materials formed by inserting molecular layers of compounds between stacked sheets of graphene. We have studied the physical and electronic responses of two graphene layers intercalated with FeCl3 and of metallic, semi-metallic and semiconducting nanotubes when normally biased using electric fields of various magnitudes. By means of first-principles density functional calculations, our results indicate that the band structures of the aforementioned graphene structures are modified upon application of a bias voltage. In the case of nanotubes, electric biasing allows tuning of the band gap leading to a transition from semiconducting to metallic state, or vice versa. In the case of the FeCl3 intercalant compounds, electric biasing results in shifting of the Dirac point.

Ce travail de thèse a pour objectif d’étudier la possibilité d’immobilisation de nanoparticules de TiO₂ dans différentes classes de substrats d’alumine monolithique poreuse et d’inspecter leurs activités en photocatalyse. Les monolithes d’alumine sont obtenus par oxydation à l’air atmosphérique et à la température ambiante, d’une surface d’aluminium amalgamée. Après élaboration et consolidation par traitement chimique et/ou thermique, différents substrats sont obtenus, qui différent par leurs propriétés allotropiques, microstructurales, et leur surface spécifique. L’élaboration du photocatalyseur est réalisée selon un procédé sol-gel à partir du précurseur, tétraisopropoxyde de titane (TTIP) dans un réacteur sol-gel à micromélange rapide. L’immobilisation d’oxo-nanoparticules de TiO₂ est réalisée dans le même réacteur par imprégnation des monolithes d’alumine. Des traitements thermiques ultérieurs permettent d’obtenir des nanoparticules de dioxyde de titane en phase anatase. Les caractéristiques structurales des nanodépôts ont été quantifiées par diffraction des rayons X, adsorption de N₂, microscopie électronique à balayage et à transmission. La décomposition photocatalytique d’un polluant modèle (l’éthylène) a été effectuée dans un réacteur tubulaire à lit fixe. Des études sur l’influence de la température de traitement des dépôts sur la taille et la variété allotropique du TiO₂ immobilisé sur les différents types de supports sont détaillées dans ce travail. La répercussion des propriétés structurales et cristallochimiques sur l’activité photocatalytique est discutée mettant en évidence le rôle du substrat alumineux dans la stabilisation de la phase de TiO₂ la plus active en photocatalyse : la phase anatase
This PhD work aims to explore the possibility of immobilization of TiO₂nanoparticles in different classes of ultraporous monolithic alumina and inspect their photocatalytic activities. The alumina monoliths are obtained by oxidation of alumina with atmospheric air and at room temperature. After development and consolidation by chemical and / or thermal treatments different substrates are obtained which differby their allotropic properties, microstructure and specific area. The preparation of photocatalyst is made according to a sol-gel process from the precursor: titanium tetra-isopropoxyde (TTIP). It is performed by a sol-gel reactor with rapid micromixing and in-situ particules granulometry contol. Immobilization of oxo-TiO₂ nanoparticles is carried out in the same reactor by impregnating alumina monoliths. Subsequent heat treatments lead to anatase nanoparticles of titanium dioxide. The structural characteristics of nanocoatings were studied by X-ray diffraction, N₂ adsorption, scanning and transmission electron microscopy. The photocatalytic decomposition of a model pollutant (ethylene) was carried out in a fixed bed tubular reactor. Studies of influence of processing temperature on size and allotropic form of TiO₂ immobilized on different types of substrates are detailed in this work. The impact of structural and allotropic properties on the photocatalytic activity is discussed, highlighting the role of the alumina substrates in the stabilization of the most active TiO₂ polymorph in photocatalysis: anatase

In the literature, a number of syntheses of carbon materials under extreme condition exhibit the presence of a carbon phase, called n-diamond, whose crystal structure remains unclear. Several crystallographic arrangements have been proposed, which are critically assessed in this work with regards to dynamical stability. It is shown that tetragonal carbon (glitter) is the only structure that satisfies this criterion. Glitter is a metallic 3-, 4-connected allotrope containing 1,4-cyclohexadieneoid units, giving a high energy meta- stable phase. Applying a fully first principles approach, which couples den- sity functional theory (DFT) calculations and Ising-like parameterisation, the possibility of stabilising the structure with nitrogen, boron and silicon substitutions has been investigated, finding that there are arrangements with negative formation energy. These novel arrangements have been tested for vibrational stability, whereby it has been proven that they are dynamically stable. Moreover a bandgap opens, leading to semiconductor bulk materials based on Si, C, B and N. Graphene, a carbon allotrope having the so-called chicken-net structure, is a zero-bandgap semiconductor, which make it promising for nano-electronic applications. However tuning and modifying the bandgap would expand the range of possible applications, in particular for post-silicon transistors. The effect of B substitutions in the graphene lattice has been studied, in terms of stability and electronic structure. The doping at low B concentration has been studied with a direct DFT approach while the effect at higher concentration has been studied with the above-mentioned coupled approach. Novel arrangements, that have semiconductor behaviour, have been proven to be dynamically stable at 0 K. The effect of a second B-C layer has also been investigated, finding that is effective on bandgap tuning.

The master thesis deals with DSC measurments a calculation of kinetic parameters. In the theoretical part, iron alotropy is briefly described, followed by a description of the DSC analysis itself. The thesis also includes division and derivation of isoconversional methods for calculating the activation energy. In the experimental part, a series of measurments is perfomed on pure iron prepared by Cold Spray method. In the paper the influence of deformation on the Curie temperature of the magnetic transformation in -Fe and transformation > is investigated. The activation energy is calculated for transformation > for different degrees of deformation. The degree of deformation is monitored by channeling contrast.

Die Vorhersage und Identifizierung von stabilen und metastabilen Stoffen ist ein wichtiges Instrument zur Bildung neuer Werkstoffe. Vor diesem Hintergrund gewinnen Konzepte einer rationalen Synthese zunehmend an Bedeutung: Die Berechnung der elektrochemischen Spannungsreihe für Festkörper und flüchtiger Phasen ermöglicht eine einfache Vorhersage der Reaktionswege. Unter Verwendung der elektrochemischen Spannungsreihe der Systeme As / P / O und As / P / X (X = F, Cl, Br, I) kann die Bildung von Elementallotropen über die Oxid- und Halogenidverbindungen in thermitischen Reaktionen abgeleitet werden. Die Analyse der Phasenbildung wird mit einer In-situ-Methode zur Überwachung von Gasphasenreaktionen gewonnen. Im Verlauf der Phasenformationen - zur Erreichung des Fest-Gas-Gleichgewichtes - können charakteristische Effekte beobachtet werden
The prediction and identification of stable and metastable substances is an important tool to achieve new materials. With this objective in mind, concepts of a rational synthesis are gaining increasing importance: calculation of electromotive series of solids allows easy prediction of reaction pathways. Using the electromotive series of systems As/P/O and As/P/X (X = F, Cl, Br, I) the formation of element allotropes via the oxide and halide compounds in thermite type reactions can be deduced. The analysis of phase formation is acquired with an in situ method for monitoring gas-phase reactions. In the course of phase formations - attaining the solid-gas equilibrium state - characteristic effects can be observed

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.
Includes bibliographical references (p. 95-104).
The structural, dynamical, and thermodynamic properties of different carbon allotropes are computed using a combination of ab-initio methods: density-functional theory for total-energy calculations and density-functional perturbation theory for lattice dynamics. For diamond, graphite, graphene, and armchair or zigzag single-walled nanotubes we first calculate the ground-state properties: lattice parameters, elastic constants and phonon dispersions and density of states. Very good agreement with available experimental data is found for all these, with the exception of the c/a ratio in graphite and the associated elastic constants and phonon dispersions. Agreement with experiments is recovered once the experimental c/a is chosen for the calculations. Results for carbon nanotubes confirm and expand available, but scarce, experimental data. The vibrational free energy and the thermal expansion, the temperature dependence of the elastic moduli and the specific heat are calculated using the quasi-harmonic approximation. Graphite shows a distinctive in-plane negative thermal-expansion coefficient that reaches its lowest value around room temperature, in very good agreement with experiments. The predicted value for the thermal-contraction coefficient of narrow single-walled nanotubes is half that of graphite, while for graphene it is found to be three times as large.
(cont.) In the case of graphene and graphite, the ZA bending acoustic modes are shown to be responsible for the contraction, in a direct manifestation of the membrane effect predicted by I. M. Lifshitz over fifty years ago. Stacking directly hinders the ZA modes, explaining the large numerical difference between the thermal-contraction coefficients in graphite and graphene, notwithstanding their common physical origin. For the narrow nanotubes studied, both the TA bending and the "pinch" modes play a dominant role. For larger single-walled nanotubes, it is postulated that the radial breathing mode will have the! most significant effect on the thermal contraction, ultimately reaching the graphene limit as the diameter is increased.
by Nicolas Mounet.
S.M.

La prédiction de l’état mécanique de structures en acier soumises à des chargements thermiques ne peut se faire sans modélisation du phénomène de changement de phase allotropique. En effet, le changement de phase induit, pour les aciers, un mécanisme appelé plasticité de transformation conduisant à une déformation irréversible pour des chargements inférieurs à la limite élastique des phases. De nombreux modèles analytiques ont proposé une approche homogénéisée pour la prédiction de l’état mécanique. Mais, pour des chargements complexes, ces modèles se révèlent inadéquates. Prenant acte de ces lacunes, nous présentons une modélisation plus proche de sa description heuristique. L’échelle mésoscopique retenue pour ce travail est de l’ordre de la taille de grain. A cette échelle, nous considérons le comportement de chaque phase comme homogène au sens de la mécanique des milieux continus, par contre, le front de changement de phase est modélisé explicitement. Cette approche mésoscopique du phénomène s’est faite expérimentalement et numériquement. Expérimentalement, nous avons mis au point et utilisé une manipulation permettant la traction et le chauffage sous vide partiel d’une éprouvette. L’acquisition de la surface de l’échantillon pendant la transformation martensitique a conduit, sous certaines hypothèses et grâce à la corrélation numérique d’image, à l’identification partielle des zones affectées localement par la transformation. Numériquement, l’utilisation de la méthode des éléments finis étendus appliquée à des champs de déplacement faiblement discontinus. L’utilisation de cette méthode nécessite la modélisation du support de discontinuité -le front. Pour cela, en s’aidant de la méthode level set, nous avons créé des schémas numériques éléments finis permettant la représentation du support et sa propagation. En sus, nous nous sommes intéressés au calcul des forces motrices définies sur le front à partir du tenseur d’Eshelby et représentatives de sa vitesse locale
The prediction of the mechanical state of steel structures submit to thermo-mechanical loading must take into account consequences of allotropic phase change. Indeed, phase change induce, at least for steels, a mechanism of TRansformation Induced Plasticity (TRIP) leading to irreversible deformation even for loading less than elastic yield limit. Homogeneized analytical models generally fail to achieve a correct prediction for complex loading. In order to overcome these difficulties, we present a model achieving a sharper description of the phenomenon. The mesoscopic working scale we adopt here is the grain scale size. Hence, we consider that the behaviour of each phase is homogenous in the sense of continuous media mechanic, whereas the front is explicitly described. We work both experimentally and numerically. Experimentally, we designed a test facility enabling thermo mechanical loading of the sample under partial vacuum. Acquisition of sample surface while martensitic transformation is happening leads, under some hypothesis and thanks to Digital Image Correlation, to the partial identification of area affected by transformation. Numerically, the eXtended Finite ElementMethod is applied for weakly discontinuous displacement fields. Used of this method needs to numerically track the transformation front -discontinuity support. In that goal, based on level set method, we develop FEM numerical scheme enabling recognition and propagation of discontinuity support. Finally, this work is complete by an approach of driving forces introduced through Eshelbian mechanics which are dual of front velocity. Keywords : allotropic phase change, TRansformation Induced Plasticity, eXtended Finite Element Method (X-FEM), Level set method

Les propriétés mécaniques des alliages de fer sont largement conditionnées par leur microstructure et la population de défauts locaux qu’elle contient. Comme il s'agit d'un moment de forte interaction entre ces deux éléments, l'étude des transformations α-γ et γ-α du fer mérite une attention particulière. Outre le passage d'une structure cristalline cubique centrée à une structure cubique faces centrées – donc de compacités différentes –,elles sont associées à une réduction des paramètres de maille. Le changement de volume correspondant est responsable de déformations mécaniques locales autour des sites de germination. La technique de corrélation d'images numériques(CIN) s'est montrée fiable pour ce qui est de calculer des champs cinématiques à l'échelle de quelques grains. Dans ce travail, elle est adaptée à la capture de localisations de la déformation pendant les transformations allotropiques. Un banc expérimental est conçu pour obtenir des images haute résolution avec un contrôle fin des sollicitations thermiques. Des essais de validation sont d'abord effectués sur du fer industriel. Puis des échantillons de fer haute pureté sont ensuite soumis à des cycles de transformation α-γ-α et les champs de déformation correspondant sont calculés par CIN. Associés à l'acquisition des orientations initiales et finales, ils sont utilisés pour valider les mécanismes de transformation proposés dans la littérature. En parallèle, un modèle, écrit en petites déformations, est construit en incorporant des composants liés à la transformation dans une fonctionnelle dont les conditions de stationnarité sont équivalentes au problème thermomécanique à résoudre. Les incréments des variables internes, incluant glissements plastiques et fractions volumique transformées, sont obtenus en minimisant cette fonctionnelle
Mechanical properties of iron-based alloys are largely conditioned by their microstructure and the population of local defects inside this microstructure. As it is a moment of massive interplay between these two elements, the study of the α-γ and γ-α transformations in iron is of particular interest. Besides a change from a body-centered cubic to a face-centered cubic crystal structure – and thus a change in compacity –, they lead to a lattice parameter reduction. The corresponding change in volume is responsible for local mechanical deformations around transformation sites. Digital Image Correlation (DIC) technique has been proven reliable to compute kinematic fields at the scale of a few grains. In the present work, an adaptation of this technique to the observation of strain localizations induced by the formation of a new phase is proposed. A home-made device is designed to obtain high resolution images and to control heating and cooling. Tests are first conducted on industrial iron to assess the viability of the procedure. High-purity iron samples are then submitted to α-γ-α transformation cycles and the associated strain fields are computed. In combination with the acquisition of initial and final orientations they are used to validate transformation mechanisms proposed in the literature. In parallel, a model, written under the small strain format, is built by incorporating transformation related components into a power functional whose stationarity conditions are equivalent to the thermomechanical problem. In accordance with variational principles, the evolution of internal variables,including plastic slip increments and fraction of the material locally transformed, are computed through the minimization of the functional

Recent carbon allotropes such as carbon nanotubes (CNTs), fullerenes (C60s) and graphene have attracted great interests in both science and engineering due to their unique properties such as excellent electrical and mechanical properties as well as its vast surface area, and have led to many commercial applications. Especially, CNTs have been considered to be one of the promising candidates in the Li ion battery system because of its outstanding properties. However, the experimental results in the pristine CNT system have shown just slight improvement than original graphitic carbon material, which has been attributed to the weak adsorption of Li on CNTs. In this study, we investigated two types of CNT-C60 hybrid system consisting of CNTs and C60s to improve Li adsorption capabilities and predict its performance through quantum mechanical (QM) computations. First, we investigated adsorption energy of lithium (Li) on dilute CNT-C60 hybrid and CNT-C60 nanobud system as well as various electronic properties such as band structure, density of states (DOS), molecular orbital and charge distribution. Then, we expanded our interest to the more realistic condensed structure of CNT-C60 hybrid and nanobud system to examine actual electrochemical characteristics. The study of the condensed structure has been expanded to the very unique CNT-C60 nano-network system and examined mechanical strength as well as electronic properties. Finally, Li adsorption on other carbon allotropes system such as graphene-C60 hybrid and graphene-C60 bud system was investigated in order to provide fundamental understanding of electronic interaction between carbon allotrope and effect of Li adsorption.

L'écotoxicité de différentes nanoparticules de carbone (NPC) a été évaluée chez des organismes aquatiques, en particulier chez Xenopus laevis. Il a été montré que la surface des NPC est le paramètre le plus pertinent pour décrire l'inhibition de croissance chez le xénope, indépendamment de leur forme allotropique et de leur état de dispersion. L'induction des micronoyaux a aussi été étudiée chez le xénope, et l'oxyde de graphène (GO) s'est révélé génotoxique à faible dose, résultat corroboré par l'étude de l'expression des gènes. Les mécanismes de toxicité impliqués seraient notamment liés aux fonctions oxygénées de la particule. De plus, le GO a aussi entrainé de la génotoxicité chez Pleurodeles waltl. et de la tératogénicité, des retards de développement et de l'inhibition de croissance chez Chironomus riparius. La mise en interaction de ces organismes au sein d'un mésocosme a également conduit à l'observation de génotoxicité chez le pleurodèle en présence de GO
The ecotoxicity of different carbon-based nanoparticles (CNPs) was assessed in freshwater organisms, especially in Xenopus laevis. The surface of the CNPs was shown to be the more relevant parameter to describe the growth inhibition in Xenopus, regardless of their allotropic form and their state of dispersion. Micronucleus induction was also studied in Xenopus and graphene oxide (GO) was found genotoxic at low dose. This result was in compliance with the study of genes expression. The involved toxicity mechanisms would be related to the oxidized functions of the CNP. Moreover, GO was also found responsible for genotoxicity in Pleurodeles waltl. and for teratogenicity, development delay and growth inhibition in Chironomus riparius. These organisms have finally been put together in a mesocosm, which has also led to genotoxicity in Pleurodeles in the presence of GO

Delottococcus aberiae (Hemiptera: Pseudococcidae) es un pseudocóccido invasor originario del África subsahariana que fue detectado causando graves daños en cítricos del este de España en el año 2009. Debido al desconocimiento existente sobre esta especie, la gestión de D. aberiae se ha llevado a cabo mediante el uso de tratamientos químicos autorizados contra este tipo de insectos. Sin embargo, la última Directiva Europea (2009/128/EC) sobre el uso sostenible de productos fitosanitarios estipula que la aplicación de plaguicidas en el ámbito agrícola debe reducirse, promoviendo estrategias de manejo más sostenibles como es la aplicación del control biológico de plagas. Además, cuando una especie invasora llega por primera vez a un territorio es necesario estudiar su biología, comportamiento, daños causados y posibilidades de control. En esta tesis se presentan por primera vez estos estudios de biología y comportamiento de la plaga así como un análisis de los daños producidos por D. aberiae. También se han realizado estudios con el objetivo de implementar la aplicación de un programa de control biológico clásico sobre esta especie en cítricos en España. Para analizar la biología y comportamiento de D. aberiae se han muestreado durante tres años varias parcelas de cítricos con poblaciones de D. aberiae en la Comunidad Valenciana. En estas parcelas se han recogido muestras y contabilizado todos los pseudocóccidos presentes, su estadío de desarrollo y el estrato y órgano del árbol donde se encontraban. El periodo de daños al fruto fue estudiado en semicampo y campo mediante la infestación artificial con D. aberiae de frutos de distintos tamaños de diámetro. Por último se estudió el comportamiento y las posibilidades de control biológico de D. aberiae muestreando diversas parcelas de cítricos en su zona de origen (Sudáfrica). Los resultados mostraron que la abundancia de las poblaciones de D. aberiae en cítricos es elevada en primavera y verano, reduciéndose a niveles mucho más bajos en otoño e invierno. Además el insecto completa varias generaciones a lo largo del año, estando dos de ellas muy claramente definidas y siendo las que dan lugar a elevadas poblaciones de la plaga. En cuanto a su distribución, D. aberiae se instaló principalmente en la copa del árbol y se observaron migraciones entre los distintos órganos, mostrando una clara preferencia por el fruto en desarrollo. Entre febrero y septiembre parte de las poblaciones de D. aberiae se encontraron en tronco y suelo, existiendo movimientos de subida y de bajada a la copa en función de la fenología de la planta y las condiciones climáticas. La comparativa entre técnicas de muestreo reveló que las trampas de cartón corrugado proporcionan una medida cuantitativa de la abundancia de D. aberiae en las parcelas. Por su parte, las trampas pegajosas, provistas de hembras de D. aberiae, fueron capaces de detectar los principales vuelos de machos. Por otro lado, D. aberiae causó daños directos al fruto (deformación y/o reducción de tamaño) al alimentarse del ovario de la flor o de los primeros estados de desarrollo de éste. Estos daños son posiblemente debidos a su interferencia con el proceso de división celular. Por último, en Sudáfrica, lugar de origen de la plaga, los mayores niveles poblaciones de D. aberiae se encontraron en verano y la tasa de parasitismo fue máxima en otoño. Entre el complejo de enemigos naturales de D. aberiae encontrados destacaron dos especies, Anagyrus sp. nov. 1 (Hymenoptera: Encyrtidae) y Allotropa sp. nov. (Hymenoptera: Platygastridae). Ambos parasitoides podrían tener un papel importante en un programa de control biológico contra D. aberiae en España. Por ahora, Anagyrus sp. nov. 1 parece el mejor candidato por sus mayores tasas de parasitismo en Sudáfrica.
Delottococcus aberiae (Hemiptera: Pseudococcidae) is an invasive mealybug native to sub-Saharan Africa that was detected causing significant damage to citrus fruits in eastern Spain in 2009. Due to the lack of knowledge about this species, the management of D. aberiae has been carried out by the application of authorized insecticides against mealybugs. However, the latest European Directive (2009/128 / EC) on the sustainable use of pesticides stipulates that chemical treatments in agroecosystems must be reduced, promoting more sustainable management strategies such as the application of biological control methodologies. In addition, when an invasive species arrives for the first time in a territory it is necessary to study its biology, behavior, damage caused and control possibilities. This thesis presents for the first time these studies of biology and behavior of the pest as well as a characterization of the damage produced by D. aberiae. The possibilities of implementing a classical biological control program against this species in citrus in Spain have also been studied. To analyze the biology and behavior of D. aberiae, several citrus orchards infested with the mealybug have been sampled for three years in the Valencian Community (eastern Spain). Samples have been collected periodically and the number of mealybugs, their developmental stage as well as the infested stratum and organ where they were present have being recorded. The period of damage to the fruit was studied in semi-field and field conditions by the artificial infestation with D. aberiae of fruits of different diameter. Finally, the behavior and possibilities of biological control of D. aberiae were studied by sampling several citrus orchards in the native area of the mealybug (South Africa). Results showed that the density of D. aberiae populations in citrus orchards is high in spring and summer, decreasing to lower levels in autumn and winter. In addition, the insect completes several generations throughout the year and two of them are clearly defined and result in high population levels. Regarding its distribution, D. aberiae was mostly installed in the canopy of the tree and migrations were observed between different organs, showing a clear preference for the developing fruit. From February to September some mealybugs were found in the trunk and soil, moving upwards or downwards depending on the phenology of the plant and the climatic conditions. The comparison between sampling techniques revealed that corrugated cardboard band traps provide a quantitative measurement of D. aberiae density in the orchards. On the other hand, sticky traps, baited with D. aberiae females were able to detect the main male flight periods. D. aberiae caused direct damage to the fruit (deformation and/or reduction in size) by feeding on the ovary of the flower or on small fruits in development. These damages are probably due to their interference with the process of cell division. Finally, in South Africa, native area of the pest, the highest density levels of D. aberiae were found in summer and the highest parasitism rates occurred in autumn. Among the complex of D. aberiae natural enemies, the two most abundant species were Anagyrus sp. nov. 1 (Hymenoptera: Encyrtidae) and Allotropa sp. nov. (Hymenoptera: Platygastridae). Both parasitoids could play an important role in a biological control program against D. aberiae in Spain. For now, Anagyrus sp. nov. 1 seems the best candidate because of its higher rates of parasitism in South Africa.
Delottococcus aberiae (Hemiptera: Pseudococcidae) és un pseudocòccid invasor originari de l'Àfrica subsahariana que va ser detectat causant greus danys en cítrics de l'est d'Espanya l'any 2009. A causa del desconeixement existent sobre aquesta espècie, la gestió de D. aberiae s'ha dut a terme mitjançant l'ús de tractaments químics autoritzats contra aquest tipus d'insectes. No obstant això, l'última Directiva Europea (2009/128/EC) sobre l'ús sostenible de productes fitosanitaris estipula que l'aplicació de plaguicides en l'àmbit agrícola ha de reduir-se, promovent estratègies de maneig més sostenibles com és l'aplicació del control biològic de plagues. A més, quan una espècie invasora arriba per primera vegada a un territori és necessari estudiar la seua biologia, comportament, danys causats i possibilitats de control. En aquesta tesi es presenten per primera vegada els estudis de biologia i comportament de la plaga així com una anàlisi dels danys produïts per D. aberiae. També s'han realitzat estudis amb l'objectiu d'implementar l'aplicació d'un programa de control biològic clàssic sobre aquesta espècie en cítrics a Espanya. Per a analitzar la biologia i comportament de D. aberiae s'han mostrejat durant tres anys diverses parcel·les de cítrics amb poblacions de D. aberiae a la Comunitat Valenciana. En aquestes parcel·les s'han recollit mostres i comptabilitzat tots els pseudocòccids presents, el seu estadi de desenvolupament i l'estrat i òrgan de l'arbre on es trobaven. El període de danys al fruit va ser estudiat en semicamp i camp mitjançant la infestació artificial amb D. aberiae de fruits de diferents mides de diàmetre. Finalment es va estudiar el comportament i les possibilitats de control biològic de D. aberiae mostrejant diverses parcel·les de cítrics en la seua zona d'origen (Sud-àfrica). Els resultats van mostrar que l'abundància de les poblacions de D. aberiae en cítrics és elevada a la primavera i estiu, reduint-se a nivells molt més baixos a la tardor i hivern. A més l'insecte completa diverses generacions al llarg de l'any, estant dos d'elles molt clarament definides i sent les que donen lloc a elevades poblacions de la plaga. Quant a la seua distribució, D. aberiae es va instal·lar principalment en la copa de l'arbre i es van observar migracions entre els diferents òrgans, mostrant una clara preferència pel fruit en desenvolupament. Entre febrer i setembre part de les poblacions de D. aberiae es van trobar en tronc i sòl, existint moviments de pujada i de baixada a la copa en funció de la fenología de la planta i les condicions climàtiques. La comparativa entre tècniques de mostreig va revelar que les trampes de cartró corrugat proporcionen una mesura quantitativa de l'abundància de D. aberiae en les parcel·les. Per la seua banda, les trampes apegaloses proveïdes de femelles de D. aberiae van aconseguir detectar els principals vols de mascles. D'altra banda, D. aberiae va causar danys directes al fruit (deformació i/o reducció de mida) en l'alimentar-se de l'ovari de la flor o dels primers estats de desenvolupament d'aquest. Aquest danys són possiblement deguts a la seua interferència amb el procés de divisió cel·lular. Finalment, a Sud-àfrica, lloc d'origen de la plaga, els majors nivells poblacionals de D. aberiae es van trobar a l'estiu i la taxa de parasitisme va ser màxima a la tardor. Entre el complex d'enemics naturals de D. aberiae trobats van destacar dues espècies, Anagyrus sp. nov. 1 (Hymenoptera: Encyrtidae) i Allotropa sp. nov. (Hymenoptera: Platygastridae). Tots dos parasitoides podrien tindre un paper important en un programa de control biològic contra D. aberiae a Espanya. Per ara, Anagyrus sp. nov. 1 sembla el millor candidat per les seues majors taxes de parasitisme a Sud-àfrica.
Martínez Blay, V. (2018). Biology and management, by application of classical biological control, of the invasive mealybug Delotoccoccus aberiae (Hemiptera:Pseudococcidae) in citrus orchards in Spain [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/106363
TESIS

Pour l'elaboration de films granulaires co-ag, une solution electrolytique a ete developpee contenant a la fois des ions argent et cobalt. Sa mise au point a necessite une etude approfondie tant chimique qu'electrochimique. Les cinetiques de reduction electrochimiques de l'argent et du cobalt ont ete analysees grace a des mesures electrogravimetriques in-situ. Les recherches menees sur l'electrocristallisation du cobalt sur l'argent ont permis d'identifier une germination progressive tridimensionnelle du cobalt. L'analyse structurale par diffraction de rayons x des echantillons indique la forte texture des depots d'argent et de cobalt. Par ailleurs, des mesures de resonance magnetique nucleaire prouvent la presence des deux phases allotropiques du cobalt : cfc et hcp. Les mesures magnetiques ont mis en evidence le caractere superparamagnetique de nos echantillons a faible concentration en cobalt et un comportement ferromagnetique aux plus fortes concentrations. Des mesures de transport ont permis d'observer des courbes de magnetoresistance tres pointues avec des champs de saturation inferieurs a 10 koe et une sensibilite maximale de 2%koe a ete determinee. Enfin, les etapes de recuits effectuees sur l'alliage co 1 7ag 8 3 montrent une deterioration de la magnetoresistance a temperature de recuit croissante.

碩士
國立交通大學
建築研究所
91
This thesis is a kind of portfolio composed by 3 parts and 6 design projects，which emphasizes on representing the design process of spatial issues. Not only parts but also each project have 3 study phases including 1>spatial study 2> systematic system 3> shifting study, such as follows : this part exercises the design of spatiotemporal fields on site through the viewpoints of topology to study the Complex Fractions. develop an urban context system and realize a looping fabric in mutations of urban structure, to study the Complex Systematic Fabric. spatial or social mechanisms shift from the differences of fields.This part emphasizes on studying the interaction between spaces and cross- field mechanisms in the next coming era, the complex Polysemous Shifts.

Thesis (M.Arch.)--State University of New York at Buffalo, 2008.
Title from PDF title page (viewed on Jan. 15, 2009) Available through UMI ProQuest Digital Dissertations. Thesis adviser: Khan, Omar Includes bibliographical references.

The focus of the present research is to find the relative thermodynamic stability of ?-boron and ?-boron via heat capacity measurements. Efforts to synthesize ?-boron through the application of vapour-liquid-solid theory resulted in the discovery of a new chemical vapour deposition approach. The heat capacities of both synthesized ?-boron and commercial (99.5%) ?-boron were determined using relaxation calorimetry over the temperature range 0.2 K to 400 K. These data, in combination with literature information, allowed the calculation of the Gibbs energy of the ?-boron to ?-boron transition from 0 K to 1985 K. It was found that the transition from ?-boron to ?-boron was thermodynamically favourable at all temperatures up to 1985 K with a value of ?Gt(T = 300 K) = -10 kJ mol-1 ± 1 kJ mol-1 and ?Gt(T = 1985 K) = -15 kJ mol-1 ± 1 kJ mol-1.

碩士
國立成功大學
建築學系
104
Origami as topic, investigate the action origami object “Fortune teller”. From the crease pattern derived 3 forms: kite, main center and the new crease pattern of change the crease definition, deemed 3 different units. Next, the 3 units and original object began forming in the same sequence and observe the morphological changes. 　Units are organized in the same sequence instead derived distinct forms, and all the forms constituted by same element: isosceles right triangle. Namely same elements different quantity and different structure, obtain different form, the concept like Allotropes, and named the method: 1.1.2-L from the degree of the element. 1.1.2-L has 4 series in, each series developing one design; each design has its own moving mechanism, during the movement form showed the morphological change.

abstract: New forms of carbon are being discovered at a rapid rate and prove to be on the frontier of cutting edge technology. Carbon possesses three energetically competitive forms of orbital hybridization, leading to exceptional blends of properties unseen in other materials. Fascinating properties found among carbon allotropes, such as, fullerenes, carbon nanotubes, and graphene have led to new and exciting advancement, with recent applications in defense, energy storage, construction, and electronics. Various combinations of extreme strength, high electrical and thermal conductivity, flexibility, and light weight have led to new durable and flexible display screens, optoelectronics, quantum computing, and strength enhancer coating. The quest for new carbon allotropes and future application persists. Despite the advances in carbon-based technology, researchers have been limited to sp3 and sp2 hybridizations. While sp3 and sp2 hybridizations of carbon are well established and understood, the simplest sp1 hybridized carbon allotrope, carbyne, has been impossible to synthesize and remains elusive. This dissertation presents recent results in characterizing a new sp1 carbon material produced from using pulsed laser ablation in liquid (PLAL) to ablate a gold surface that is immersed in a carbon rich liquid. The PLAL technique provides access to extremely non-thermal environmental conditions where unexplored chemical reactions occur and can be explored to access the production of new materials. A combination of experimental and theoretical results suggests gold clusters can act as stabilizing agents as they react and adsorb onto the surface of one dimensional carbon chains to form a new class of materials termed “pseudocarbynes”. Data from several characterization techniques, including Raman spectroscopy, UV/VIS spectroscopy, and transmission electron microscopy (TEM), provide evidence for the existence of pseudocarbyne. This completely new material may possess outstanding properties, a trend seen among carbon allotropes, that can further scientific advancements.
Dissertation/Thesis
Masters Thesis Chemical Engineering 2018

Die Vorhersage und Identifizierung von stabilen und metastabilen Stoffen ist ein wichtiges Instrument zur Bildung neuer Werkstoffe. Vor diesem Hintergrund gewinnen Konzepte einer rationalen Synthese zunehmend an Bedeutung: Die Berechnung der elektrochemischen Spannungsreihe für Festkörper und flüchtiger Phasen ermöglicht eine einfache Vorhersage der Reaktionswege. Unter Verwendung der elektrochemischen Spannungsreihe der Systeme As / P / O und As / P / X (X = F, Cl, Br, I) kann die Bildung von Elementallotropen über die Oxid- und Halogenidverbindungen in thermitischen Reaktionen abgeleitet werden. Die Analyse der Phasenbildung wird mit einer In-situ-Methode zur Überwachung von Gasphasenreaktionen gewonnen. Im Verlauf der Phasenformationen - zur Erreichung des Fest-Gas-Gleichgewichtes - können charakteristische Effekte beobachtet werden.
The prediction and identification of stable and metastable substances is an important tool to achieve new materials. With this objective in mind, concepts of a rational synthesis are gaining increasing importance: calculation of electromotive series of solids allows easy prediction of reaction pathways. Using the electromotive series of systems As/P/O and As/P/X (X = F, Cl, Br, I) the formation of element allotropes via the oxide and halide compounds in thermite type reactions can be deduced. The analysis of phase formation is acquired with an in situ method for monitoring gas-phase reactions. In the course of phase formations - attaining the solid-gas equilibrium state - characteristic effects can be observed.

碩士
國立成功大學
材料科學及工程學系
102
The phase behavior of a binary eutectic system of poly(9,9-di-n-octyl-2,7- fluorene) (PFO) and hexamethylbenzene (HMB) has been explored. During cooling from homogeneous molten state, a smectic phase of PFO developed epitaxially on HMB substrate. Upon further annealing at 120 °C, epitaxial organization results in the growth of β crystal. In order to decipher the route of molecular organization, this research advanced to elucidate involved epitaxial interactions through simulation and experimental approaches. Instead of the conventional packing tendency of fluorene backbones, the settlement of side chains within underneath lattice grooves of HMB contact plane emerged as an unexpected dominant epitaxial relationship. After adding 1 wt % of carbon nanotubes into this HMB/PFO binary system, the extent of coplanar conformation of backbone is reduced by involved interactions. As a result, the re-absorption of emitted blue light is lessened, leading to stronger blue emission. Furthermore, during the phase transition route of comb-like PFO, mixed nanotubes can be segregated into amorphous regions, resulting in oriented arrays of nanotube bundles within thin film. Not only the parallel orientation, the segregation distance between nanotube bundles can be adjusted also by the crystallization rate of PFO, which helps to enhance the use of carbon nanotube within polymeric thin film.

Measurement of all the mechanical properties of carbon nanotubes is extremely difficult because of its small size. In the present work, all the five transverse isotropic properties of single wall carbon nanotubes (SWCNTs) and double wall carbon nanotubes are estimated through molecular structural mechanics for different chirality, length and assumed thickness. Armchair, zigzag & chiral SWCNTs and polychiral DWCNTs are considered for the analysis. Longitudinal and lateral Young’s modulus; longitudinal and lateral Poisson’s ratio and shear modulus are estimated for 1080 SWCNTs and 1170 polychiral DWCNTs. Effect of temperature on all the properties of SWCNT are investigated. Modal characterization of SWCNT is carried out in base fixed condition and different mode shapes viz. axial, torsion and bending mode shapes are identified based on the effective mass. Once the transverse isotropic properties of SWCNTs are estimated, these are used to estimate the transverse isotropic properties of nanocomposites embedded with SWCNT agglomerates. During the manufacturing of nanocomposite, SWCNT agglomerates are formed due to sticking of number of SWCNTs. Parametric studies are carried out to see the effect of SWCNT length on the properties of nanocomposite. Empirical formulae for all the transverse isotropic properties of SWCNT at room temperature and elevated temperature; frequency of SWCNT are derived. Empirical formulae for polychiral DWCNT transverse isotropic properties are estimated. Input for these empirical formulae are the length, chirality and assumed thickness. Empirical formulae were also derived for nanocomposite embedded with different number of SWCNTs having different chirality. The derived empirical formulae were validated with available analytical and experimental results for some sample cases.

This thesis consists of two independent papers:

PAPER I:

The spectral reflectance of elemental sulfur is examined in a set of laboratory experiments to determine the factors that affect the transformation rate of monoclinic (β) sulfur and various other sulfur allotropes into orthorhombic (α) sulfur. The laboratory data have implications for the spectral variation and physical behavior of freshly solidified sulfur, if any exists, on Jupiter's satellite Io. Depending on its thermal history, molten sulfur on Io would initially solidify into a glassy solid or a monoclinic crystalline lattice; these forms might contain polymeric sulfur molecules as well as the more abundant S₈ molecules. If freshly frozen sulfur on Io could lose heat rapidly and approach ambient dayside Io temperatures within several hours, then some of the metastable sulfur allotropes could be maintained on Io virtually indefinitely. Small droplets of sulfur ejected during plume eruptions might cool quickly enough to preserve these allotropes, but sulfur in large volcanic flows or lakes would probably remain warm long enough for phase transformations to proceed at a visible rate.

PAPER II:

Photodissociation of methane at high levels in Neptune's atmosphere leads to the production of more complex hydrocarbon species such as ethane, acetylene, methylacetylene, propane, diacetylene, ethylacetylene, and butane. These gases diffuse to the lower stratosphere where temperatures are low enough to allow all seven of the aforementioned species to condense. Particle formation may not occur readily, however, as the vapor species become supersaturated. We present a theoretical analysis of particle formation mechanisms at conditions relevant to Neptune's troposphere and stratosphere and show that hydrocarbon nucleation is very inefficient under Neptunian conditions: saturation ratios much greater than unity are required for aerosol formation by either heterogeneous, ion-induced, or homogeneous nucleation. Thus, stratospheric hazes may form far below their saturation levels. We compare nucleation models with detailed atmospheric photochemical models in order to place realistic constraints on the altitude levels at which we expect hydrocarbon hazes or clouds to form on Neptune.

Carbon nanomaterials, such as carbon nanotubes and graphene, have attracted significant interest over the past several years due to their outstanding and unusual combination of physical properties. These properties can be modified in a controllable way by chemical functionalization in order to enable specific technological applications. One example is hydrogenation, achieved by the exposure of these materials to a source of atomic hydrogen. This process has been considered for hydrogen storage purposes and for the control of the band gap of these materials for applications in carbon-based electronics. Hydrogen atoms are chemisorbed onto the surface of these materials, introducing sp3-hybridized C-C bonds in a structure originally formed by delocalized sp2 C-C bonding. This bonding transition causes severe structural and morphological changes to the graphene layers/walls. Also, it has been demonstrated that the exposure of multi-walled carbon nanotubes (MWCNTs) to a H2 plasma leads to the formation of diamond nanocrystals embedded within the nanotube walls. This thesis presents a computational analysis of the effects of hydrogen chemisorption on the structure and morphology of graphene and single-walled carbon nanotubes (SWCNTs), as well as of the different nanostructures that can be generated upon formation of inter-shell and inter-layer sp 3 C-C bonds in MWCNTs and few-layer graphene (FLG), respectively. The analysis is based on a synergistic combination of atomic-scale modeling tools, including first-principles density functional theory (DFT) calculations and classical molecular-dynamics (MD) and Monte Carlo (MC) simulations. The results demonstrate that SWCNTs and graphene swell upon hydrogenation and provide interpretations to experiments reported in the literature; this swelling depends strongly on the hydrogen surface coverage. A MC/MD-based compositional relaxation procedure generates configurations whose arrangements of H atoms are in excellent agreement with experimental observations. Detailed structural analysis of the hydrogenated surfaces is carried out, providing information which cannot be extracted easily from conventional experimental techniques. The findings of the analysis are used to explain the limitations on the maximum H storage capacity of SWCNT bundles upon their exposure to an atomic H flux. Furthermore, it is demonstrated that the structures resulting from formation of inter-shell or inter-layer C-C bonds are stable and provide seeds for the nucleation of crystalline carbon phases embedded into the shells and layers of the MWCNT and FLG structures, respectively. The key parameter that determines the type and size of the generated nanocrystals is the chiral-angle difference between adjacent layers/walls in the original structure. A novel type of carbon structure, consisting of fullerene-like caged configurations embedded within adjacent graphene layers, has been discovered for the case where the graphene layers are rotated with respect to each other; interestingly, one class of these structures retains the unique and desired electronic properties of single-layer graphene.

The major directions of this dissertation involve (1) the syntheses and characterization of molecular polygons incorporating sp1hybridized carbon linkers and L2Pt corners (L2 = cis-1,3-diphosphine), (2) the development of protected carbon chain complexes featuring fluorous phosphine ligands and (3) click reactions of metal terminal polyynyl complexes and further metallations of the resulting triazole rings. A brief overview is provided in Chapter I. Chapter II details the syntheses of molecular squares containing bidendate diphosphine ligands of the formula R2C(CH2PPh2)2 where R = Me, Et, n-Bu, n-Dec, Bn, and p-tolCH2 (general designation dppp*), in which the R2 groups are intended to circumvent the solubility issues encountered by others. Their syntheses involve double substitutions of the dimesylate compounds R2C(CH2OMs)2 using KPPh2. Building blocks of the formulae (dppp*)PtCl2 and (dppp*)Pt((C≡C)2H)2 are synthesized and characterized, including one crystal structure of the latter. The target complexes are accessed by reactions of (dppp*)PtCl2 with (dppp*)Pt((C≡C)2H)2 under Sonogashira type conditions. Six new squares of the formula [(R2C(CH2PPh2)2)Pt(C≡C)2]4 are characterized including two crystal structures. Further topics include approaches to higher homologues and cyclocarbon synthesis. Chapter III focuses on carbon chain complexes bearing fluorous phosphine ligands of the formula P((CH2)mRfn)3 (Rfn = (CF2)n-1CF3; m/n = 2/8, 3/8, and 3/10). Precursors of the formula trans-(C6F5)((Rfn(CH2)m)3P)2PtCl are synthesized and characterized, including one crystal structure, which reveals phase separation of the fluorous and non-fluorous domains. Reactions with butadiyne give trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C≡C)2H. Oxidative homocouplings afford the target complexes trans,trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C≡C)4(C6F5)(P((CH2)mRfn)3)2Pt. Cyclic voltammetry indicates irreversible oxidations of the title compounds, in contrast to partially reversible oxidations of non-fluorous analogues. Chapter IV focuses on multimetallic complexes achieved by click reactions in metal coordination spheres. The copper catalyzed click reaction between trans-(C6F5)(p-tol3P)2Pt(C≡C)2H (1) and (η5-C5H4N3)Re(CO)3 affords the bimetallic 1,2,3-triazole trans-C6F5)(p1tol3P)2PtC≡CC=CHN((η51C5H4)Re(CO)3)N=N. Further reactions with Re(CO)5OTf and Re(CO)5Br give trimetallated adducts, which represent the first species of this type. An alternative route to a trimetallic complex involves the twofold cycloaddition of the diazide (η5-C5H4N3)2Fe and 1, giving (η5-C5H4NN=N-C(trans-(C≡C)Pt(Pp-tol3)2(C6F5)=CH)2Fe. The crystal structures of the di and trimetallic complexes are compared, but attempts to achieve a fourth metallation involving the =CH groups are unsuccessful. However, when the triazolium salt [trans-(C6F5)(p-tol3P)2PtC≡CC=CHN(CH2C6H5)N=N(Me)]+ I– is treated with Ag2O and [Rh(COD)Cl]2, a =CRh adduct is obtained. The success of =CH metallation is correlated to the 1H NMR chemical shift, indicative of an electronic effect.