Le principal objectif de cette étude est d'acquérir des données de base sur la dissolution de composés (U,Pu)O2 en appui à la compréhension des phénomènes intervenant lors des étapes de dissolution des combustibles MOX des filières de réacteurs à eaux légères et à neutrons rapides sodium. Les études antérieures, en particulier sur des combustibles MOX non irradiés, ont mis en évidence la complexité d'une compréhension des mécanismes de dissolution par une approche directe. En effet, la dissolution dépend d'un grand nombre de paramètres, qui sont principalement les conditions chimiques d'attaque (acidité, température, ...), mais surtout les caractéristiques physico-chimiques de la pastille considérée (teneur en plutonium, homogénéité de la teneur en plutonium, microstructure, géométrie, ...), la majorité d'entre elles étant fortement dépendantes du procédé de fabrication utilisé. Pour éviter l'obtention de réponses moyennées du fait de la présence d'une hétérogénéité de la répartition en Pu au sein des pastilles, on se propose de réaliser une étude sur des poudres de composés monophasés de stœchiométrie parfaitement définie (U et Pu) et de morphologie parfaitement déterminée. Une approche par étapes a permis de déterminer les différents paramètres clé déterminant les cinétiques de dissolution de ces oxydes d’actinides (surface spécifique, taille des cristallites, teneur en Pu, activité des ions nitrate, température de dissolution, énergie d’activation).Une loi cinétique globale permettant de décrire les cinétiques de dissolution des oxydes U1-xPuxO2 a été établie à partir de 45 essais différents (avec 0≤x≤1). Elle décrit les cinétiques de dissolution obtenues à toutes teneurs en plutonium et morphologies de l’oxyde, dans des gammes de températures variant de 50 à 95°C et des intervalles d’acidités variant de 1,5 à 8,5 mol/L. Le modèle ainsi créé décrit assez précisément la cinétique de dissolution de n’importe quel oxyde U1-xPuxO2 alors qu’il existe plus de cinq ordres de grandeurs d’écart entre les cinétiques de dissolution de l’UO2 et du PuO2. Des essais complémentaires sur des composés monophasés ont été menés validant le caractère prédictif du modèle. / The main objective of this study is to acquire data on the dissolution of (U, Pu)O2 compounds to support the understanding of the phenomena occurring during the dissolution steps of MOX fuels irradiated in light water or sodium fast reactors. Previous studies, in particular on unirradiated MOX fuel, have highlighted the complexity of understanding the dissolution mechanisms through a direct approach. Indeed, the dissolution depends on a large number of parameters, which are mainly chemical dissolution parameters (acidity, temperature…). But it also depends on the physico-chemical characteristics of the fuel pellets (plutonium content, homogeneity of the plutonium content, microstructure, geometry...), a majority of which being highly dependent on the manufacturing process used. To avoid getting averaged responses due to the presence of heterogeneity in the Pu distribution in pellets, it is proposed to carry out a study on single-phase compounds in the shape of powders characterized by a well-defined stoichiometry (U and Pu) and a perfectly determined morphology. A step approach allowed the determination of the key parameters controlling the dissolution kinetics of these actinide oxides (specific surface area, crystal size, Pu content, activity of nitrate ions, dissolution temperature).A global kinetics law describing the dissolution kinetics of U1-xPuxO2 oxides was established from 45 dissolution tests (with 0≤x≤1, [HNO3] and temperature ranging from 1.5 to 8.5M and from 50 to 95°C respectively). Despite the 5 orders of magnitude between dissolution kinetics of UO2 and PuO2, the model shows a good precision. Additional dissolution tests were conducted on different single-phase oxide powders to validate the predictive quality of this model.

The electric vehicle itself today outlives its battery, necessitating battery replacement. Lithium titanium oxide (LTO) has, in this context, been suggested as a new anode material in heavy electric vehicle applications due to intrinsic properties regarding safety, lifetime and availability. The work presented here is focused on the LTO electrode/electrolyte interface. Photoelectron spectroscopy (PES) has been applied to determine how and if the usage of LTO could prevent extensive anode-side electrolyte decomposition and build-up of a surface layer. The presence of a solid electrolyte interphase (SEI) comprising LiF, carbonates and ether compounds was found in half-cells utilizing a standard ethylene:diethylcarbonate electrolyte with 1 M LiPF6. Via testing of symmetrical LTO-LTO cells, the stability of the formed SEI was put in to question. Moreover, the traditional polyvinylidene difluoride (PVdF) binder was replaced by more environmentally benign carboxylmethyl cellulose (CMC) and polyacrilic acid (PAA) binders in LTO electrodes, and it was found that CMC helped to form a more stable surface-layer that proved beneficial for long term cycling. Following the half-cell studies, full-cells were investigated to observe how different cathodes influence the SEI of LTO. The SEI in full-cells displayed characteristics similar to the half-cells, however, when utilizing a high voltage LiNi0.5Mn1.5O4 cathode, more electrolyte decomposition could be observed. Increasing the operational temperature of this battery cell generated even more degradation products on the LTO electrodes. Mn was also found on the anode when using Mn-based cathodes, however, it was found in its ionic state and did not significantly affect the composition or behavior of the observed SEI layer. Furthermore, by exchanging the electrolyte solvent for propylene carbonate, the thickness of the SEI increased, and by replacing the LiPF6 salt for LiBF4 the stability of the SEI improved. Thus is it demonstrated that such a passivation can be beneficial for the long-term surface stability of the electrode. These findings can therefore help prolong the lifetime of LTO-based battery chemistries.

One-dimensional (1D) nanostructures (NSs) of Zinc Oxide (ZnO) such as nanorods (NRs) have recently attracted considerable research attention due to their potential for the development of optoelectronic devices such as ultraviolet (UV) photodetectors and light-emitting diodes (LEDs). The potential of ZnO NRs in all these applications, however, would require synthesis of high crystal quality ZnO NRs with precise control over the optical and electronic properties. It is known that the optical and electronic properties of ZnO NRs are mostly influenced by the presence of native (intrinsic) and impurities (extrinsic) defects. Therefore, understanding the nature of these intrinsic and extrinsic defects and their spatial distribution is critical for optimizing the optical and electronic properties of ZnO NRs. However, identifying the origin of such defects is a complicated matter, especially for NSs, where the information on anisotropy is usually lost due to the lack of coherent orientation. Thus, the aim of this thesis is towards the optimization of the lowtemperature solution-based synthesis of ZnO NRs for device applications. In this connection, we first started with investigating the effect of the precursor solution stirring durations on the deep level defects concentration and their spatial distribution along the ZnO NRs. Then, by choosing the optimal stirring time, we studied the influence of ZnO seeding layer precursor’s types, and its molar ratios on the density of interface defects. The findings of these investigations were used to demonstrate ZnO NRs-based heterojunction LEDs. The ability to tune the point defects along the NRs enabled us further to incorporate cobalt (Co) ions into the ZnO NRs crystal lattice, where these ions could occupy the vacancies or interstitial defects through substitutional or interstitial doping. Following this, high crystal quality vertically welloriented ZnO NRs have been demonstrated by incorporating a small amount of Co into the ZnO crystal lattice. Finally, the influence of Co ions incorporation on the reduction of core-defects (CDs) in ZnO NRs was systematically examined using electron paramagnetic resonance (EPR).

Carbonaceous materials, especially in micro and nanoscale, are useful in optical, energy storage, electronic, and biomedical devices or technologies. Techniques have been developed for preparation and modification of the carbonaceous materials, while it is still challenging to tailor the properties of carbonaceous materials effectively and economically. Laser is a powerful tool in academic and industrial laboratories, which also plays important roles in the preparation and modification of high-performance carbonaceous nanomaterials. In this study low-cost hydrothermal synthesis, high-temperature annealing, and Laser ablation (LAL) methods are developed to prepare functionalized carbon nanomaterials and modify their electrochemical and optical properties. Sub-micro hollow carbon spheres are synthesized via hydrothermal carbonization and high-temperature activation without any templates. Good capacitive properties are obtained after activation. The electrochemical properties of the activated carbon spheres depend on the media of the activation. The capacitance of the activated carbon spheres significantly increases with the addition of water as an activation agent. Carbon dots (CDs) are synthesized via a facile and economic hydrothermal (HTC) process using both small-molecule sugar (Xylose) and ground soybean residuals as precursors. The photoluminescence (PL) properties of the as-prepared and further-treated CDs are systematically studied. For the xylose-synthesized CDs, the initial green PL emission disappears after high-temperature treatment at 850 ℃ for 2 h. With further LAL treatment in NH4OH solutions, the PL emission is re-acquired, and a blue shift in emission is observed. Thus, the LAL is found to be an effective method to modify the CDs and their PL properties. For the nitrogen-doped soybean waste-derived carbon particles, they show strong blue emissions, which essentially disappear after 850 ℃ annealing for 2 hours in an argon flow. Then, PL appears again after laser ablation in a 10% NH4OH solution. The conversion from the blue emission to no emission and then back to blue emission again implies the effect of the functional groups on the PL properties of the CDs.

Lithium-ion batteries are of great importance for today's society. The state-of-the-art batteries that are used today use a fluorinated electrolyte that contains the salt LiPF6 and acts as both a safety hazard and an environmental issue due to its ability to form the toxic gas hydrogen fluoride (HF). This project aims to find a fluorine-free electrolyte that can be used in silicon-based lithium-ion batteries to make them more environmentally friendly without detriment to the electrochemical performance. To do so, an additive that may form a solid electrolyte interphase (SEI) stable enough to allow a fluorine-free electrolyte to replace the ones used today is sought for. The salt of interest is lithium  bis(oxalato)borate (LiBOB). Based on previous research electrolytes using LiBOB in either the solvent γ-Butyrolactone (GBL) or a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are examined. The additives used are vinylene carbonate (VC) and 1,3,2-dioxathiolane 2,2-dioxide (DTD). Techniques used are cyclic voltammetry, linear sweep voltammetry, galvanostatic charge and discharge, X-ray photoelectron spectroscopy and scanning electron microscopy.  The cells using GBL as solvent have cycled very poorly during this project while LiBOB in EC:EMC + VC shows the most promising results, with highest capacity retention and less amount of degraded LiBOB during the first charge. It is also to be noted that both EC:EMC based electrolytes provide the formation of a passivating solid electrolyte interface (SEI) and are of interest for further investigation based on the results obtained during this project.

There are many interesting applications of proton conducting oxides, such as electrolytes in fuel cells, hydrogen sensors and catalytic membranes for hydrogenation or dehydrogenation of organic compounds. Previous work explored doping BaTiO3 with the Rare Earth Element (REE) Sc to introduce oxygen vacancies in the structure, making it a Proton Conductor (PC). PC oxides are often perovskite materials, ABX3, wherethe A- or B-site are doped in such a way that less oxygen can be contained, creating oxygen vacancies. When these materials are then hydrated so that water molecules occupy the vacancies, hydrogen is essentially added to the system in the form of protons. This study expanded on those results, exploring possible dopants that are non-REEs, theoretically improving availability and cost. Fe and Al were chosen as B-site dopants and Sr was included as an alternative to Ba as the A-site cation, compensating for the smaller size of the Fe- and Al atoms compared to Ti. Solid state synthesis was used to manufacture the different compounds and then X-Ray Diffraction (XRD), ThermoGravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) were used inorder to investigate their properties. The main focus was to explore ift he materials could be synthesised using this method, their structures and how they reacted to hydration. All Al doped samples could not be made phase pure with the synthesis parameters used. BaTi0.5Fe0.5Oy was stabilised by the inclusion of Ti, as it did not decompose during hydration, unlike pure BaFeOx. Significant hydration was achieved in a wet nitrogen atmosphere at 185°C, but its structure type was hexagonal, which is known to be unfavourable for proton conduction. SrTi0.5Fe0.5Oy had a cubic structure which is a beneficial structural trait for proton conduction, but negligible hydration was observed by TGA. A small increase in cell volume indicates that it might still have taken up some water, but the methods used for hydration were not optimal for this material. The oxygen content of the materials was not determined in this project and methods such as Mössbauer spectroscopy and iodometric titration should be included in any related future studies.

This thesis explores how to use the dry nanoporous structure of cellulosic fibres in new types of composite materials. A large effort was also given on how to correctly characterize the structure of fibres where the wet structure has been preserved also in the dry state. Delignified wood fibres have an open fibrillar structure in their water-swollen state. In the present work, this open fibrillar structure was preserved in the dry state by performing a liquid exchange procedure and the samples were thereafter carefully dried with Ar(g). The samples of never-dried TEMPO-oxidized dissolving pulp had a specific surface area of 130 m2/g in the dry state, as measured using the Brunauer, Emmet, and Teller (BET) Nitrogen gas adsorption method. This open structure was also revealed using field emission scanning electron microscopy (FE-SEM). The water-swollen and dry open structures were thoroughly characterized for various pulps. A new method for determining the pore size of water-swollen delignified cellulosic fibres is presented. By combining the results from solid state nuclear magnetic resonance NMR, measuring the specific surface area [m2/g] in the water-swollen state, with fibre saturation point (FSP), measuring the pore volume of fibres in water-swollen state [mass water/mass fibre], the average pore size can be determined without the need of assuming a certain pore geometry. The dry nanoporous structure was then used as a scaffold for in-situ polymerization, to demonstrate how the properties of the fibrils in the fibre wall can be exploited without the need to disintegrate the fibre wall. Both poly(methylmethacrylate) (PMMA) and poly(butylacrylate) (PBA) were successfully used as the polymeric matrix, and both nanocomposites (i.e., fibre/PMMA and fibre/PBA) had a fibre content of approximately 20 w%. The structure of the composites was characterized using SEM and Atomic Force Microscopy (AFM) operated in the phase imaging mode. The AFM results indicate that the cellulose aggregates and polymeric matrix were successfully mixed on a nanoscale, creating a nanocomposite of interpenetrating polymer molecules and cellulose fibrils, rather than a microcomposite, when using microscopic cellulose fibres. The water absorption capacity of the nanocomposites was reduced significantly, indicating that almost all nanopores in the fibre wall were successfully filled with matrix polymer. The mechanical properties were investigated, showing the importance of nanosized reinforcement compared to fibres of micrometer size. / <p>QC 20121011</p>

Fibers are classified into two groups; natural fibers and man-made fibers (MMF). There are three kinds of MMF: those made by transformation of natural polymers, those made from synthetic polymers and those made from inorganic material. Chitosan is classified as a biobased polymer and can be spun into man-made fibers. Due to its various functions, including anti-microbial, biocompatibility, biodegradability, metal-chelating, metal ions-coupling properties and general high molecular affinity, much attention has been paid recently to include chitosan into various concepts. The overall aim of this master thesis was to investigate the possibilities to make an antibacterial paper. Because chitosan contain primary amino groups that are cationic under mildly acidic conditions, it has antibacterial properties. Lab scale spinning of chitosan filaments was attempted in order to produce chitosan staple fibers that could be mixed with pulp fibers to make paper with antibacterial properties. Spinning methods used for a particular polymer is determined by the characteristics of the polymer. In the development of chitosan spinning at laboratory scale three different spinning methods were tested. A successful filament was produced by dry wet spinning. The filament was superior to the others in terms of dope composition and weight ratio of chitosan/acetic acid for protonation of the amino groups. Furthermore, the addition of glycerol improved the swelling of the chitosan hydrogel (or dope). Moreover, the condition of the coagulation step resulted in a good solidified filament with satisfactory elasticity and strength to be able to be taken up by a drawing cylinder. However, too small amounts of chitosan were produced in the development of chitosan spinning at lab scale and for production of antibacterial paper of chitosan. A second option was melt spinning of polylactide (PLA) filaments containing various amounts of chitosan. In this case PLA act as a carrier of chitosan into the paper sheet. Continuous filaments were spun in a sufficient amount. The antibacterial activity of PLA/chitosan fibers on E. coli bacteria was tested both on PLA/chitosan fibers as well as on suspensions. Under nutrient free conditions weak antibacterial effects was observed both for fibers and suspensions. However, in a more nutrient rich environment no effect was observed. This suggests that the produced fibers only had a weak antibacterial activity. To my knowledge the use of PLA in fiber form to carry chitosan into paper has not been attempted previously although different approaches to use chitosan as e.g. wound dressing is well described. In conclusion, there is a possibility to produce man made biodegradable fibers using chitosan and PLA that potentially could be added to paper. This paper might exert antibacterial properties that could have an interest to the market, e.g. for cleaning, in hospitals, and in the food industry.

Nanoparticles are used as electrocatalysts due to their large surface area-to-volume ratios. Most studies of nanoparticle electrocatalysis are performed on collections of particles on a support, which represent ensemble average behavior influenced by spatial distribution of the nanoparticles. Therefore, recent emphasis has been placed on analyzing electrocatalytic behavior of single particles. The focus here is to develop carbon ultramicro- and nanoelectrode platforms for studying the electrocatalytic properties of single metal nanoparticles. Ultramicroelectrodes were prepared using chemical vapor deposition of carbon in pulled quartz capillaries. Electrode diameters were determined by cyclic voltammetry. Electrodes were modified using a soft nitriding technique to enable immobilization of platinum nanoparticles through reduction of H2PtCl6 using NaBH4. Cyclic voltammetry was used to determine the presence of platinum particles through characteristic peaks associated with Pt oxide formation and reduction. Ultimately, these electrodes could be used to analyze single uncapped nanoparticles to understand the electrochemical properties of single nanoparticles.

Kinetics investigations of the thermal Cope rearrangement of meso-and d1-3,4-diphenylhexa-1,5-dienes were undertaken in order to gain information about the transition states for these reactions by determining the appropriate enthalpies and entropies of activation. Of particular interest were the activation parameters for the meso compounds' rearrangement as it represents the only known example in which both four-and six-centered transition states are of comparable energy. Kinetics of the dl isomers' rearrangement in the temperature range 90-110⁰were determined using 5 X 10¯⁵M solutions of the olefin in heptane contained within sealed Pyrex ampules. Extents of reaction were determined from UV absorbance measurements at 256 nm. Product instability, becoming pronounced after 85-90% reaction, was observed. Two rate constants were calculated covering 0-85% and 0-98% reaction respectively, from each set of data. Evaluations of enthalpies of activation from the two sets of rate constants gave, respectively, 23.8 and 23.9 kcal/mole, indicating that inclusion of the increasingly erratic kinetics data collected after 85% reaction had little effect upon this activation parameter. The corresponding entropies of activation at 100⁰were -12.9 and -12.6 eu. Both activation parameters are consistent with those for other Cope rearrangements indicating that the thermal isomerization of dl-3,4-diphenylhexa-1,5-diene in the temperature range 90-110⁰is normal in every respect. Kinetics studies of the more interesting meso-diene were precluded by the failure to locate means of controlling product decomposition, which would be expected to become more severe at the higher temperature required (140-160⁰). Additionally, alumina-catalyzed isomerizations first observed accidently for the d1-diene, and subsequently verified for both meso--and d1-olefins, were examined. In contact with 100 times its weight of very active alumina at room temperature the d1 isomer was found to undergo conversion in the extent of 40% during a two-hour period to trans, trans-1,6-diphenylhexa-1,5-diene.meso--3,4-Diphenylhexa-1 ,5-diene underwent structural reorganization more slowly; after 70 hours over alumina a 15% conversion to a 9:1 mixture of cis-trans and trans,trans-1,6-diphenylhexa-1,5-dienes was noted. The stereo specificities observed for these unusual catalyzed rearrangements parallel those of their thermally-induced counterparts. Modifications in the syntheses of meso- and d1-1, 6--dibromo-3,4-diphenylhexanes, and meso--and dl-3,4-diphenylhexa-1,5-dienes, are also presented.