Dissertations / Theses on the topic 'Neutron diffraction technique'

Il est désormais possible, en utilisant le modèle de densité électronique résolue en spin (CRM2), de combiner les diffractions des rayons X et des neutrons (polarisés) pour déterminer les distributions électroniques de charge et de spin de matériaux magnétiques cristallins. Cette méthode permet la mise en évidence des chemins d’interactions rendant compte de l’ordre magnétique. Le modèle résolu en spin a été appliqué aux complexes de coordination avec un métal de transition portant la majorité du moment magnétique, il a été ensuite utilisé pour étudier les radicaux purs organiques contenant des électrons non appariés délocalisés sur un groupement chimique et les matériaux inorganiques. Dans le radical Nit(SMe)Ph, la modélisation des densités de charge et de spin a permis, en accord avec les résultats antérieurs, de montrer que le spin est délocalisé sur le groupe O-N-C-N-O (fonction nitronyle nitroxyde). Elle a également permis de montrer l’implication des liaisons hydrogène dans les interactions magnétiques ferromagnétique observé en dessous de 0.6K. Cette étude a mis en évidence une répartition dissymétrique de la population de spin sur les deux groupes N—O dont seuls les calculs CASSCF permettent de reproduire l’amplitude. Cette dissymétrie proviendrait d’une combinaison d’effets moléculaires et cristallins. Dans le radical p-O2NC6F4CNSSN de la famille des dithiadiazolyles, la modélisation par affinement joint montre que la majorité du spin est porté par le groupement –CNSSN en accord avec les travaux antérieurs. Grace aux propriétés topologiques de la densité de charge, des interactions halogène, chalcogène et π ont été mis en évidence. Certaines de ces interactions favorisent des couplages magnétiques, notamment les contacts S…N2 entre molécules voisines pouvant contribuer à l’ordre ferromagnétique observé à très basse température (1.3K). Quant au matériau inorganique, YTiO3, les densités de charge en phases paramagnétique et ferromagnétique ont été déterminées ainsi que la densité de spin dans la phase ferromagnétique. Les résultats de cette étude montrent que les orbitales d les plus peuplées en électrons de l’atome de Ti sont dxz et dyz.. L’ordre orbital présent dans ce matériau est observé à 100 et à 20 K suggérant que l’ordre orbitalaire est lié à la distorsion des octaèdres. La fonction d’onde de l’électron non apparié est une combinaison linéaire de ces orbitales t2g
X-ray and neutron diffraction methods can be combined to determine simultaneously electron charge and spin densities in crystals based on spin resolved electron density model developed at CRM2. This method enables to carry out the study of interaction paths leading to the observed ferromagnetic order. First applications of this model were to coordination complexes, where the unpaired electron is mainly located on the transition metal, then generalized to explore organic radicals and to inorganic materials. In radical Nit(SMe)Ph, the modeling of the experimental charge and spin densities showed localization of spin density on O-N-C-N-O group (nitronyl -nitroxyde function), in agreement with previous works. It is also evidenced the involvement of the hydrogen bonds in the magnetic interactions leading to the ferromagnetic transition at very low temperature (0.6K). This study revealed dissymmetrical spin population of the two N-O groups that only CASSCF-type calculations can reproduce in amplitude (not DFT). This dissymmetry originates from both molecular and crystal effects. In radical p-O2NC6F4CNSSN belonging to the family of dithiadiazolyl, the joint refinement showed that the majority of the spin is distributed on -CNSSN group in agreement with the previous works. From topological properties of the charge density, halogen, chalcogen and π interactions have been highlighted. The most important magnetic interactions are observed through the network formed by contacts S ... N2 between neighboring molecules leading to the ferromagnetic order below 1.23K. Concerning the inorganic material, YTiO3, the charge densities in both paramagnetic and ferromagnetic phases and spin density were modelled. The results show that the most populated d orbitals of Ti atom are dxz and dyz. The orbital ordering evidenced in this material is observed at 100 and 20 K due to the orthorhombic distorsion. The wave function of the unpaired electron is a linear combination of these particularly populated t2g orbitals

Cette thèse porte sur l'utilisation de plusieurs techniques de diffusion de neutrons polarisés pour la conduite d'expériences de diffraction et de spectroscopie inélastique à haute résolution. Nous décrivons de façon exhaustive l'option à écho de spin neutronique résonant ZETA, installée sur le spectromètre triple axe thermique CRG IN22 à l'Institut Laue Langevin. Grâce à elle, nous étudions la structure nucléaire et la dynamique de spin de plusieurs systèmes modèles. Dans un premier temps, nous nous intéressons à la série BaM2(XO4)2 (M = Co, Ni; X = As, P) dont les membres sont de bons exemples de systèmes magnétiques quasi-bidimensionnels. L'effet de la mise en ordre magnétique sur leurs paramètres de maille est révélé par diffraction de Larmor. De plus, nous montrons que l'évolution thermique de la durée de vie du mode de magnon optique dans BaNi2(PO4)2 est fortement affecté par la présence de défauts dans sa structure. Ensuite, nous abordons le composé à chaînes et échelles de spin 1/2 Sr14Cu24O41. Nous nous focalisons d'abord sur l'étude du pic inélastique associé au gap de spin des échelles et présentons une méthode capable de montrer de façon directe la dégénérescence de la transition concernée. Ensuite, nous évaluons sa largeur énergétique intrinsèque et observons l'effet des différentes mises en ordre de charge sur la structure cristallographique du matériau. Finalement, nous adaptons l'instrumentation disponible pour mener des expériences de réflectométrie résolues en temps, par le biais de la méthode MIEZE, sur une multicouche magnétique pouvant posséder des propriétés intéressante pour des applications en spintronique
This thesis is mainly concerned with the use of several polarized neutron scattering techniques for carrying high resolution diffraction and inelastic spectroscopy experiments. We describe exhaustively our neutron resonant spin-echo option ZETA, installed on the thermal triple-axis spectrometer CRG IN22 at Institut Laue Langevin. Through it, we study the nuclear structure and spin dynamics of several model systems. First, we are interested in the BaM2(XO4)2 (M = Co, Ni; X = As, P)-family which members are good prototypes of quasi-2D magnetic systems. The effect of magnetic ordering on lattice constants is revealed thanks to Larmor diffraction. Moreover, we show that the thermal evolution of optic magnon lifetime in BaNi2(PO4)2 is strongly affected by the presence of defects in its structure. Then, we address the spin-chain and -ladder compound Sr14Cu24O41. We first focus on the study of the inelastic peak associated with the spin gap in the ladders spectrum and introduce a method capable of showing directly the degeneracy of the associated spin transition. We also evaluate its intrinsic linewidth and observe the effect of different charge ordering process on the material crystallographic structure. Ultimately, we adapt our instrumentation to perform time-resolved reflectometry experiments on a magnetic multilayer which can possess interesting properties for spintronics applications, through the so-called MIEZE technique

La fabrication de prothèses dentaires à base de titane a connu un réel essor ces dernières années. Cependant, la production de ces produits reste assez coûteuse, et le choix de producteurs est encore restreint. Les partenaires du projet de recherche Européen Den-ticast® ont identifié un fort potentiel pour la création d'une machine innovante, capable de produire ces pièces à un coût réduit et à un niveau de qualité élevé. Le projet est axé sur le domaine de la production de pièces de métal pour l'usage dentaire, avec comme objectif, le développement d'un nouveau système polyvalent de coulée des alliages, qui doit permettre de couler l'ensemble des alliages dentaires actuellement commercialisés (NiCr, CoCr), mais aussi le titane et ses alliages. Le prototype Denticast® associe, pour la première fois, la fusion par induction et l'injection par centrifugation à haute vitesse, sous vide secondaire. Entièrement programmable, cette machine doit pouvoir évoluer en fonction du développement de nouveaux alliages sur le marché dentaire.Ce projet réunit des partenaires européens de 3 pays différents (France, Allemagne, Italie) et 3 secteurs d'activité : industriel, académique et odontologique, de sorte que chacun ap-porte un aspect complémentaire au projet. Il comporte 3 phases principales : une phase d'étude, une phase de conception et une phase d'évaluation du prototype.Nos résultats montrent que Denticast® est capable de produire des pièces à usage dentaire de qualité, à grains fins et homogènes, avec un niveau de contrainte résiduelle relativement bas, et une fraction volumique de porosité faible. Les caractéristiques mécaniques sont globalement supérieures ou équivalentes aux systèmes commerciaux du marché
Although the manufacture of titanium dental prostheses has experienced a real rise in the last years, the production of those products remains quite expensive, and the choice of pro-ducers is still limited. The partners of the European research project Denticast® have identi-fied a high potential for the creation of an innovative machine that can produce those dental parts at low cost and high quality level. The aim of this research is the development of a new, innovative and versatile system of casting alloys, which can cast all dental alloys (NiCr, CoCr) as well as titanium and its alloys. The prototype Denticast® associates for the first time the melting by induction and the injection by centrifugation with high speed under vacuum. Totally preset, this machine should be able to evolve according to the devel-opment of new dental materials.The project combines European partners from 3 different countries (France, Germany and Italy) and three sectors: industrial, academic and dental, so that each of them contributes to the project. It presents three main phases: a study phase, a phase of design and the evalua-tion phase of the prototype.Our results show that Denticast® is able to produce quality parts for dental use with a ho-mogeneous and fine grain, with a low level of residual stress and a relatively low volume of fraction porosity. In most cases, the mechanical characteristics are equal or even greater than other systems on the market at present

The structures of lithium and lead tellurite glasses (Li2O-TeO2 and PbO-TeO2) are studied using the combinations of neutron diffraction, isotope substitution neutron diffraction, and synchrotron X-ray diffraction. Additional complementary methods such as density measurement, thermal analysis and Raman spectroscopy show that the tellurite networks in lithium and lead tellurite glasses exhibit similar behaviour as a function of composition. From the diffraction data, real-space interatomic information on the glasses was extracted. The local environments of Te remain largely unchanged in both glasses if the second content is less than 15 mol%, as reported earlier for K2O-TeO2. For Li2O or PbO contents greater than 15 mol%, however, the average Te-O coordination number changes with composition and differently for the two oxides. A TeO2 Model, which has been successfully applied to K2O-TeO2 glasses, is extended to Li+ and Pb2+. By comparing the total correlation functions of the glasses to relevant crystal phases, the short-range parameters of the crystals can be used to optimise the model for Li+ and Pb2+ and explain the value of the average coordination number of Te. The environments of Li+ and Pb2+ were extracted using isotope substitution neutron diffraction (Li) and complementary neutron–X-ray diffraction (Pb). In the glasses studied (10, 15, 20, 25 and 30 mol% Li2O and 10, 12.5, 15, 17.5 and 20 mol% PbO), both Li+ and Pb2+ behave as modifiers with the average nLiO = 4 – 5 and nPbO = 8 with the distances rLiO and rPbO comparable to crystal phases of similar composition. The structures of lithium and potassium borogermanate glasses are studied using the combinations of neutron diffraction, isotope substitution neutron diffraction, and 11B MAS NMR. From the complementary methods such as density measurement, and Raman spectroscopy, changes are seen to occur in both borate and germanate networks. From 11B NMR, the average B-O coordination number, nBO, in lithium borogermanate glasses is different from nBO in potassium borogermanate glasses of the same stoichiometry and resembles the behaviour of Li+ and K+ in in borosilicate glasses, as described by the Zhong’s lithium borosilicate model and Dell and Bray’s sodium borosilicate model. From neutron diffraction data (null isotope neutron diffraction for lithium borogermanate), the average Ge-O coordination number nGeO is extracted and, like nBO, nGeO in lithium borogermanate is different from potassium borogermanate. In the former, nGeO increases as a function of Li2O, whilst in the latter, nGeO shows a maximum at about 20% K2O. For Li+, the average Li-O coordination number nLiO can be obtained using the difference technique (using diffraction data from samples made with natural and null-scattering lithium isotopes). For the limited samples examined, nLiO was found to have a value of 4 to 5 with two distinct Li-O distances which can be assigned to Li-OB and Li-OGe distances.

Neutron diffraction is an extremely powerful technique in condensed matter research; it can be used to measure crystallographic structures, including some of those undeterminable using X-rays. It is also perhaps the most powerful technique for determining magnetic structures, and for probing the strength of magnetic interactions, revealing information beyond that extractable from a magnetometer. High pressure is used by many condensed matter researchers as an additional thermodynamic variable, or tool to perturb otherwise stable systems, and has been used with neutron diffraction for many years. When coupled with low temperatures, this has led to the discovery of an enormous range of non-ambient phases of matter, with a range of exotic properties, some of which are discussed in this thesis. Pressure has a very strong effect on the magnetic properties of a material, with many of the most unusual magnetic phases existing only at extremely low temperatures, or pressures which can only be reached on very small samples. The main topic for this thesis is the study, development, and implementation of new techniques to combine low temperatures, high pressures, and neutron diffraction measurements from micro sized samples. A new pressure cell has been designed, tested, and commissioned with neutron beam time on the WISH diffractometer at the ISIS neutron facility. The cell is compact, with a total mass of approximately 5 kg, and is capable of generating large loads in excess of 4.5 tonnes force. Depending on the sample size used with the cell, the opposed anvil system is capable of generating a range of different pressures beyond what is widely available for low temperature neutron diffraction measurements. To save wasted experimental time in cooling and warming the device, the cell is capable of varying the applied load continuously down to 5 K, whilst the sample pressure can also be measured in-situ using a compact spectrometer system. Obtaining refineable neutron diffraction data from the small samples (< 1mm3) possible in an opposed anvil pressure cell is challenging due to extremely low ratios of signal-to-background when compared with large volume pressure cells. Finite element analysis (FEA) was performed to minimise the mass of the cell, whilst also minimising the amount of supporting material in the beam. Despite this, the signal from the sample is typically very weak; to overcome this, a novel 3D printed device has been designed and tested to collimate extremely small samples, removing much of the background signal from the surrounding material. It has enabled neutron data to be collected from samples an order of magnitude smaller than previously measurable in the cell. To maximise the pressures achievable in the pressure cell, for a given sample volume, an extended FEA study was performed to understand the evolutions of stresses in the cell, and understand the limitations of using sapphire as an anvil material. To complement this work, a compact piston cylinder cell has also been designed for a combination of different measurements. One of the key challenges in high pressure research is in knowing, or ensuring, that the conditions the sample is under are approximately the same for a variety of different measurements. Since different instruments, and techniques, may not allow for the same apparatus to be used between them, this is not always possible. A compact clamped piston cylinder cell has been designed, suitable for in-situ electrical measurements, with additional potential for simultaneous neutron diffraction measurements. The device is demonstrated through an ultrasonic characterisation of the compound UGe2. In addition to the information obtainable from neutron diffraction, much can be learnt from studying the transport properties of a material. This information can be used alongside neutron data to provide a full understanding of how a material behaves. One technique of interest measures how the electrical properties of a material changes under applied magnetic field. This is difficult to achieve under pressure due to the often anisotropic construction of the pressure cell affecting the magnetic field on the sample in different orientations, and the challenge in getting wires to the sample under pressure. This thesis presents the design, and preliminary testing, of an ultra compact high symmetry piston cylinder cell designed to be taken to sub-Kelvin temperatures and rotationally oriented in applied magnetic field. The spherical construction of the cell means that the field on the sample position is, to a very close approximation, identical in all orientations. Finally, this thesis presents a study of the binary alloy Pd3Fe under pressure. Pd3Fe was recently reported to undergo a large-volume collapse under high pressure at room temperature, resulting in near zero thermal expansion]. There are several competing theories on the mechanism behind this process. To investigate further, a series of single crystal Pd3Fe samples were grown, cut, prepared, and extensively analysed. The results of this study suggest that the cause for the large volume collapse may not be magnetic in nature, as previously expected.

We envisage a fundamental study of the physical mechanisms (dislocation slip versus deformation twinning) involved in plastic deformation of hexagonal close-packed (HCP) metals like titanium and magnesium. A novel combination of X-ray imaging and diffraction techniques, termed X-ray diffraction contrast tomography (DCT), will be used to investigate details of the deformation process in the bulk of polycrystalline specimen. DCT provides access to the position, 3D shape, (average) orientation and elastic strain tensor of grains in polycrystalline sample volumes containing up to 1000 grains and more. Ultimately, an extension of the X-ray DCT technique is associated with a section topography methodology on the same instrument. This combination enables the measurement of local orientation and elastic strain tensors inside selected bulk grains. A very preliminary study of this approach is carried out on a magnesium alloy, underlying the current limitations and possible improvements of such approach. In this thesis, the data acquisition and analysis procedures required for this type of combined characterisation approach have been developed. The work is supported by the use of neutron diffraction, for an in-situ loading experiments, and two-dimensional electron backscatter diffraction (EBSD), for the initial microstructure of the materials and cross-validation of the results obtained with the X-ray DCT technique.

Des études ont démontré que les contraintes résiduelles jouent un rôle important dans la distorsion des composantes usinées. Ce phénomène engendre plusieurs problèmes dans le domaine de l'aéronautique aux niveaux de l'assemblage et du taux de rebuts. Il est donc essentiel de mieux comprendre ce phénomène afin de trouver éventuellement des solutions pour minimiser les impacts. Ce projet d'étude propose une approche expérimentale afin de valider l'influence des contraintes résiduelles présentes dans le matériau bmt avant l'usinage d'une composante. Il existe maintenant un aluminium dont le procédé de mise en forme a été contrôlé afin de minimiser les contraintes résiduelles. Ce type de matériau a donc permis d'effectuer une étude comparative de l'influence des contraintes présentes avant l'usinage. L'utilisation d'une méthode de mesure non-destmctive de contraintes par faisceaux de neutrons et le mesurage des déformations géométriques par balayage laser sont des méthodes assez nouvelles qui ont également permis de réaliser ce projet. Les résultats obtenus montrent que le matériau dont les contraintes initiales sont minimales est en mesure de pallier au problème de la distorsion. Ce qui prouve que les contraintes résiduelles présentes dans le matériau bmt sont en partie responsables de la distorsion. Toutes les pièces usinées dans le matériau standard ont subi des déformations tandis que les pièces usinées dans le matériau avec procédé contrôlé ont subi très peu de déformations. Au niveau des causes possibles, il a été observé que la distribution des contraintes, leurs signes, ainsi que leurs intensités peuvent être à l'origine des déformations.

Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xxvi, 255 p.; also includes graphics. Includes abstract and vita. Advisor: Patrick M. Woodward, Dept. of Chemistry. Includes bibliographical references (p. 221-228).

Le besoin de reculer les possibilités d'implantation de racines artficielles dans des os de faible qualité et de diminuer les temps de procédures cliniques revalorise l'intérêt pour les revêtements bioactifs un temps dénigrés. L'utilisation des propriétés biomécaniques très supèrieurs de l'hydroxyapatite de taille nanométrique est une voie de recherche en plein essor pour revêtir les implants. La première partie de notre travail développe la mise au point d'un procédé de revêtement de pièces en Ti-6A1-4V à partir de poudre d'hydroxyapatite de taille nanométrique par torche à plasma. Le succès de la reconstruction osseuse autour des implants dentaires dépend directement de la distribution des orientations des cristaux d'hydroxyapatite de l'os reconstitué. La distribution des cristaux d'hydroxyapatite doit y conserver l'orientation préférentielle de l'os d'origine pour qu'il n'y ait aucune instabilité ou perturbation mécanique qui augmente le risque de rejet du biomateriaux par le corps. La seconde partie de notre étude à analyser d'un point de vue biomécanique la reconstruction osseuse obtenue à proximité de l'interface implantaire grâce à la diffraction neutronique et à la diffraction au synchrotron sur des échantillons revêtus selon notre protocole et implantés trois mois chez le mouton. Notre technique d'analyse originale, la pertinence du développement de revêtements d'hydroxyapatite élaborés à partir de poudre de taille nonamétrique et leur protocole de fabrication sont enfin discutés.

In-situ time-resolved synchrotron X-ray and neutron powder diffraction techniques have been applied to the study of solid state structural transitions within the organic polymorphic molecular systems of lactose, trehalose and theophylline. Diffraction techniques offer an unequalled method of polymorph identification and quantification, and have repeatedly demonstrated throughout this work that they can be utilised to follow and kinetically evaluate structural transitions in real time. The study of lactose crystallisation provides further proof of the transient ( lo::1/3) mixed crystal polymorph as the initial crystallisation product, which is then followed by the typical beta lactose and alpha lactose monohydrate phases. The formation of the (lo:: l,B) mixed crystal form has been mapped and kinetically analysed; the complex multi-step crystallisation behaviour is likely to result from the high degree of polymorphism which is displayed within the lactose system. The dehydration studies of the three systems show that dehydration kinetics can vary as a function of processing conditions and environments. Evidence of a previously undocumeuted theophylline polymorph has been observed which is accessible via the seeded dehydration of theophylline monohydrate with anhydrous theophylline form II. The best production of beta lactose from the 1-biannual dehydration of alpha lactose monohydrate to date is documented and is attained from dehydration within a hydrophobic cocoa butter environment; this transition is mediated via a crystalline phase whose identity is uncertain, yet displays a unique Bragg peak at rv 12.87° 20. Neutron diffraction techniques reveal that the water content and crystalline weight fraction of trehalose dihydrate are decoupled quantities, and the dihydrate lattice can sustain substantial water loss. These observations provide supporting evidence of a transiently stable, partially hydrated state of trehalose. In addition, the applicability of the Dl9 single-crystal diffraction beamline at the Institut Laue-Langevin in the study of hydrated powder samples is reported, demonstrating the versatility of the instrument with the capability of performing dynamic studies with a time-resolution of 15 s.

The majority of structural studies on DNA have been carried out using fibre diffraction, while studies of its dynamics and thermal behaviour have been mainly performed in solution. When the DNA double helix is heated, it exhibits local separation of the two strands that grow in size with temperature and lead to their complete separation. This work has investigated various aspects of this phenomenon. The experiments reported in this thesis were carried out on films of oriented fibres of DNA prepared with the Wet Spinning Apparatus. Thus, sample preparation and characterisation are essential parts of the research. The structures of two forms of DNA, A and B, have been explored as a function of relative humidity at fixed ionic conditions. A method to eliminate traces of ever-present B-form contamination in A-form samples was established. The high orientation of the DNA molecules within the samples allowed us to investigate dynamical fluctuations and the melting transition of DNA using neutron scattering, which can provide the spatial information crucial to understand a phase transition, probing the static correlation length along the molecule as a function of temperature. The transition has been investigated for A and B-forms in order to understand its dependence on molecular configuration.Furthermore, after the first melting, denatured DNA films show typical glass behaviour. Their thermal relaxation has been explored using calorimetry.Neutron and X-ray inelastic scattering (INS and IXS) were used in the past to measure longitudinal phonons in fibre DNA, and the results shown disagreement. Recent INS measurements supported with phonon simulations have been crucial to understand the different dispersion curves reported to date. Experiments using INS and IXS have been carried out to continue with this investigation. Attempts to observe the transverse fluctuations associated to the thermal denaturing of DNA, never experimentally investigated before, have been made.

Ce travail porte sur l'etude des composites a matrice metallique (cmm) par la technique de la diffraction des neutrons et plus particulierement sur l'analyse du comportement elastoplastique de tels materiaux. Pour cela, nous avons tout d'abord evalue les contraintes macroscopiques dans un cmm a base aluminium renforce avec 17% en volume de particules de carbures de silicium. L'un des deux echantillons analyses a subi une flexion 4 points ; les mesures ont ete realisees apres flexion. La difference des coefficients thermique de dilatation impose que la matrice soit en tension tandis que le renfort en compression dans l'echantillon n'ayant subi aucune deformation plastique. Pour l'echantillon deforme, la reponse du composite est regit par la loi de la resistance des materiaux appliquee a une barre flechie. Ces contraintes macroscopiques sont en fait la somme de plusieurs contraintes de differentes origines (elastique, thermique, plastique) : en evaluant la contribution elastique par le modele d'eshelby, nous avons determine les contraintes microscopiques : pour l'echantillon non deforme, elles sont constantes et equivalentes dans les trois directions principales sur toute la largeur de la barre. Pour la barre ayant ete deforme, on observe une relaxation des contraintes thermiques dans la region proche de la surface. Ce resultat est confirme par la mesure par diffraction de neutrons sur des echantillons de traction/compression. On a par ailleurs observe l'influence des traitements thermique et de mise en forme sur ces cmm : la cission critique (etabli par un modele autocoherent) depend uniquement du mode de refroidissement de l'echantillon. Enfin, une etude a ete realisee sur des cmm a base titane pour la snecma sur des inserts utilises dans les compresseurs des moteurs d'avions. L'evolution des contraintes entre la jante et l'alesage est confirme par une modelisation aux elements finis et constitue par ailleurs les premiers resultats experimentaux dans ce domaine.

L'adoption d'un cycle énergétique propre et sans émissions utilisant l'hydrogène comme vecteur d'énergie pourrait être la solution afin de limiter les effets néfastes de la crise énergétique et du réchauffement climatique sur la planète. Ainsi, le manque de dispositifs efficaces de stockage d'hydrogène a stimulé la recherche de nouveaux systèmes. Dans ce manuscrit, la déshydrogénation du complexe bis-dihydrogéno-ruthénium sans additifs au centre de ruthénium a été rapportée au chapitre II. Le complexe dimérique inhabituel et rare portant deux ponts phosphido a été consulté par thermolyse du complexe bis (dihydrogène) RuH2(H2)2(PCyp3)2. Le complexe a été caractérisé par RMN, IR, UV-visible, rayons X, structure neutronique et calculs DFT. Étonnamment, le complexe présente une absorption et une libération réversibles de H2 à la température ambiante en solution ainsi qu'à l'état solide. Il s'agit d'un critère majeur pour la conception d'un matériau de stockage d'hydrogène solide. L'activation de la liaison H-H a fait l'objet d'une étude détaillée au chapitre III. Plusieurs nouveaux complexes de ruthénium portant des ligands de coordination fac, 1,3,5-triaminocyclohexane (tach) et 1,4,7-triazacyclononane (tacn) et différents anions ont été préparés. Une enquête DFT a été déployée tout au long de ces études pour un examen de niveau fin de l'activation des liaisons H-H. Un objectif intéressant dans le contexte du stockage de l'hydrogène est de combiner l'hydrure de magnésium, le MgH2 ou les MOF à des complexes organométalliques. Tel est l'objet du quatrième chapitre. Le dopage de l'hydrure de magnésium avec des précurseurs de ruthénium ou de nickel montre des résultats prometteurs
Adopting clean and emission- free energy cycle using hydrogen as an energy carrier could be the solution in order to curb the ill effects of energy crisis and global warming on the planet. Thus, the lack of efficient hydrogen storage devices has stimulated the search of new systems. In this manuscript, the dehydrogenation of the bis-dihydrogen ruthenium complex without additives at the ruthenium center has been reported in Chapter II. The unusual and rare dimeric complex bearing two phosphido bridges was accessed from thermolysis of the bis(dihydrogen) complex RuH2(H2)2(PCyp3)2. The complex was characterized by NMR, IR, UV-Visible, X-ray, neutron structure and DFT calculations. Surprisingly, the complex shows a reversible up take and release of H2 at room temperature in solution as well as in the solid state. This is one major criteria for designing a solid hydrogen storage material. The activation of the H-H bond has been subjected to a detailed study in Chapter III. Several novel ruthenium complexes bearing fac-coordinating ligands, 1,3,5-triaminocyclohexane (tach) and 1,4,7-triazacyclononane (tacn) and different anions have been prepared. DFT investigation has been deployed throughout these studies for a fine-level examination of H-H bond activation. An attractive goal in the context of hydrogen storage is to combine magnesium hydride, MgH2 or MOFs to organometallic complexes. This is the purpose of the fourth chapter. Doping magnesium hydride with ruthenium or nickel precursors shows promising results

Ce travail porte sur la synthèse, la mise en forme et la caractérisation desolutions solides de type tysonite RE1-xMxF3-x (RE = La, Sm, Ce et M = Ba, Ca, Sr). Dans unpremier temps, une démarche d’étude rigoureuse est mise en place pour la solution solide ditede référence, La1-xBaxF3-x. Les synthèses menées à l’état solide aboutissent à une maîtrise dela composition chimique et à l'établissement de lois de variations des paramètres structuraux.Une meilleure compréhension de l’influence de la structure sur la mobilité des ions F- estégalement acquise. L’influence du frittage dans l’obtention de bonnes valeurs de conductivitéionique est également à souligner. Dans un second temps, les effets de la nanostructurationpar mécanobroyage sur les propriétés de conductivité sont évalués. L’utilisation de laméthodologie des plans d’expériences mène à la mise au point des réglages optimums debroyage. Il apparaît alors que la synthèse des électrolytes peut être accélérée et mise àl’échelle tout en gardant des valeurs optimales de conductivité. Enfin, la démarche déterminéeest appliquée à d'autres solutions solides de type tysonite et à la recherche du conducteurionique le plus performant. Si les composés issus de la substitution Ce/Sr ou encore Sm/Casemblent les plus prometteurs, la plus grande stabilité chimique de la solution solide La1-xSrxF3-x est le compromis idéal pour l'utiliser comme électrolyte solide lors des mesuresélectrochimiques des batteries
This work deals with the synthesis, shaping and characterization of RE1-xMxF3-x (RE = La, Sm, Ce et M = Ba, Ca, Sr) tysonite-type solid solutions. In a first part, onemeticulous approach has been set up for La1-xBaxF3-x solid solution, chosen as a reference.The solid-state synthesis of these materials led to a better knowledge of their chemicalcomposition (Vegard’s laws) and of the structure-ionic mobility correlations. The impact ofthe sintering process on the ionic conductivity is also highlighted. In a second part, the effectsof the nanostructuration conducted by ball-milling of the microcrystalline samples areevaluated. The use of the Design of Experiments methodology led to identify the optimummilling conditions. It appears that the synthesis of electrolytes can be sped- and scaled-up,while keeping high ionic conductivity properties. At last, this approach is applied on othertysonite-type solid solutions, to look for the best electrolyte. The Ce/Sr and Sm/Casubstitutions generate very promising ionic conductors but not really (electro)chemicallystable compounds. A compromise has been found with the choice of the La1-xSrxF3-x solidsolution as the FIB electrolyte for the electrochemical performances tests, regarding its higherchemical stability

The novel approaches in modelling and experimental investigations on welding integrity for single and multi-pass high strength low alloy steel (HSLA) welds is presented here. High level of welding stresses (mainly tensile mode) are generated during the construction of pipelines which are due to non-uniform temperature distribution and cooling rates as well as using clamps during welding and mechanical handling loads which occur during lifting the front end of pipeline to place it on supports. Existing of such high tensile stresses combined with hydrogen rich cellulosic electrodes used by Australian pipeline industry has increased the risk of Hydrogen assisted cold cracking (HACC) in the weld metal, in particular root pass of girth welding, which clearly has detrimental effect on weld integrity and its performance in service. The prediction and measurement of this welding stresses in pipeline construction was limited to a few studies. The current project was therefore started with emphasis on the effect of welding stresses on HACC susceptibility of the root pass of pipeline girth welding using Welding Institute of Canada (WIC) weldability test. 3D finite element models are developed and validated against neutron diffraction measurements to investigate the effects of various welding process parameters and regimes on residual stresses for the root pass of the WIC test. Chapter 4 presents the experimentally validated numerical simulation results of the root pass of the WIC test. However after initial modelling and experimental measurements the project was extended toward measurement of residual stresses (using neutron diffraction) for multi-pass welding in HSLA welds coupled with microstructural characterization and mechanical property studies with the view of full applicability for pipeline/ pressure vessel applications. It was found that welding parameters have significant effects on the residual stress-microstructural-mechanical property interrelationships of multipass HSLA welds. Therefore a set of welded specimens was prepared to investigate such interrelationships for the following welding parameters: Heat input effects (variable travel speed); The alterations in welding direction (welding sequence); The effects of welding process (combination of modified short arc and fluxed core arc welding versus shielded metal arc welding) It was found that increasing the heat input (reduction in welding speed) is beneficial in reduction of residual stresses. This could be correlated with the formation of microstructural constituent of mainly polygonal ferrite in the weld metal and HAZ of high heat input welds. Furthermore, there was no significant effect on the magnitude of the residual stresses, microstructural characteristics and mechanical properties when the weld deposition direction was changed. The findings also indicated using SMAW lead to significant reduction in residual stresses in comparison with the combination of MSAW+FCAW processes. The results of such investigations are presented in chapters 5-7. After identifying such interrelationship effects, this research study develops further to investigate the effects of mitigation techniques on relaxation of residual stresses/strains in weldments. In-situ neutron diffraction studies was conducted, coupled with in-depth microstructural/mechanical property studies, in which the rate of relaxation, holding time effects and the underlying mechanism behind stress relaxation for HSLA steel welds was investigated. One of the core finding of this investigation is the insignificant effects of holding time on stress/strain relaxations of HSLA welds. It was also found that strain relaxation in the initial stage of heating (temperatures up to about 360-370 ºC) is due to reduced yield strength with increasing temperature, while for the higher temperatures (370-600 ºC) strain relaxation is due to development of creep strain. Microstructural studies also indicate existing of sub-grains in the PWHT specimen, which is due to dislocation climb, pointing out to creep (creep strain development) as the driving mechanism behind stress relaxation during PWHT. The results are presented in chapter 8 of the thesis. Such findings will also be fully elaborated in the up-coming publications. Future work will be investigating the effects of plate thickness and the type of material on strain relaxation behaviour for various weld joints to establish a “time-temperature-rate of relaxation-thickness-holding time-material type” envelope. Such findings could offer the prospect of more economic heat treatment standards that combine cost savings with optimised mechanical properties and residual stress states.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2017