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The present thesis work is focused on the low-temperature transformation of food industry wastes like mussel shells into nanocrystalline ions-substituted hydroxyapatite powder, having similarities with natural bone apatite, on the consolidation of such powder by cold sintering, and on the physicochemical characterization of the raw materials, synthesised powders and sintered pellets. Nonetheless the evaluation of the mechanical and biological properties was carried out to address cold sintered bodies to possible scaffolds for bone tissue engineering applications. Mussel shells, like other biogenic source of calcium carbonate/phosphate, have the attractive of being a “zero”-cost raw material because they are a waste, but also of having trace elements (Mg, Na, Sr, etc.) which, if found in a bioceramic, have a positive effect on the biological properties. Therefore, mussel shell-derived hydroxyapatite could resemble the mineralized bone tissue, being natural apatite nanometric, ion substituted and with low crystalline tenor. In the first part of the manuscript, two production methods were explored: mechanochemistry and dissolution-precipitation synthesis. Mechanochemistry was carried out at room temperature by directly mixing crushed mussel shells with phosphoric acid in a ball mill. Nanocrystalline multi-ions substituted hydroxyapatite was produced after 4 h of milling and drying at 150°C. Conversely, dissolution-precipitation synthesis was carried out in two steps: the dissolution of crushed mussel shells by adding phosphoric and chloric acid occurred at room temperature, whereas the precipitation of calcium phosphates induced by soda solution, occurred at 45°C. Dissolution-precipitation was further implemented to produce a homogeneous composite material in a single-step by introducing chitosan (in a 2/5/10 wt%) during the dissolution step. The idea was to produce a composite material able to mimic the natural bone tissue composition. In the second part of the manuscript, cold sintering was investigated for the consolidation of the synthesised hydroxyapatite and hydroxyapatite-based composites at a maximum temperature of 200 °C to avoid phase transformation, limit grain growth and preserve the osteoconduction of the bioceramic materials. The effect of the main process parameters such as solvent amount, pressure, temperature and holding time was discussed. Pressure-solution creep and plastic deformation were pointed out as the fundamental consolidation mechanisms in cold sintering, the pressure playing the major role. With a synergistic combination of pressure (600 MPa), temperature (200°C) and liquid phase (20 wt%) it was possible to consolidate hydroxyapatite above 80% relative density in only 15 min. Furthermore, pressure and temperature act a complementary agent during cold sintering. In fact, it was possible to consolidate nanometric HAp and HAp/chitosan composites above 90% relative density by increasing the applied pressure up to 1.5 GPa at room temperature. The mechanical properties of cold sintered pellets were investigated, and resulted in a flexural bending strength and Vickers microhardness, respectively, of 45 MPa and 1.1 GPa for pure hydroxyapatite and of 55 MPa and 0.8 GPa for HAp/chitosan composite. In the frame of bone tissue engineering applications, cold sintered bodies were also preliminarily tested in vitro to establish their bioactivity, their cellular viability through cytotoxicity assessment, and the ability to sustain cells adhesion, osteogenic differentiation. And extracellular matrix mineralization.

La richesse en Th et en U de la monazite en fait un excellent géochronomètre pour dater les roches magmatiques et métamorphiques de la croûte terrestre. Peu sensible à la diffusion du Pb dans sa structure cristalline, elle peut enregistrer des évènements géologiques de haute température sans risque de remise à zéro de son géochronomètre. Réservoir principal des actinides et des lanthanides, elle participe à de nombreuses réactions minéralogiques, faisant aussi d’elle un très bon traceur pétrogénétique. Coupler sa chimie à son isotopie permet donc d’interpréter précisément la nature des processus géologiques dont elle enregistre l'âge. L’étude de trois objets géologiques distincts a permis de montrer que la monazite est très sensible aux interactions avec les fluides. Ils vont induire sa dissolution partielle ou totale, suivie de la recristallisation de nouveaux grains. De multiples paramètres vont influencer son comportement face au fluide. Ainsi, à basse température (350°C - 450°C) dans un microgranite, un fluide riche en fluor et carbonates va favoriser la dissolution-précipitation de la monazite, alors qu’un fluide riche en éléments alcalins n’aura aucun effet sur elle. Par contre, à plus haute température (> 600°C) dans des roches métapélitiques, ce même fluide va induire sa dissolution-précipitation. En fonction de la mobilité du Pb, du Th et de l’U, le mécanisme de dissolution-précipitation peut avoir différents impacts sur le géochronomètre : ainsi, l'âge des grains recristallisés peut soit correspondre à l’âge du grain initial, soit dater l’interaction avec le fluide, soit n’avoir aucune signification géologique. Les systèmes isotopiques U-Pb et Th-Pb peuvent également être affectés par l’incorporation de Pb commun dans la monazite lors de sa cristallisation (jusqu’à plusieurs centaines de ppm), ce qui va artificiellement vieillir les âges enregistrés. L'ensemble de ces observations montre que l'âge enregistré par la monazite s'interprète au cas par cas. Dans l’avenir, l’optimisation de l’utilisation de la monazite comme géochronomètre doit passer par (1) une amélioration des techniques d’analyses (augmentation de la résolution spatiale pour résoudre des problèmes géologiques à l’échelle nanométrique, standardisation avec des monazites homogènes) et (2) un couplage de différents types d’analyses (chimie, datation, isotopes de l’oxygène). Ceci devrait permettre d’interpréter aux mieux les âges qu’elle enregistre. / Monazite is regarded as a robust geochronometer in magmatic and metamorphic crustal rocks because it contains high concentrations of Th, and to a lesser extent U. Insensitive to lead diffusion, it possibly records high temperature geological events without resetting. On the other hand, monazite strongly controls the lanthanide and actinide budget in the host-rock and is involved in numerous chemical reactions, which makes it a good petrogenetic tracer as well. Therefore, the coupling of age and chemical data in monazite allows an accurate interpretation of the geological event which is recorded by monazite crystallization. However, monazite is very sensitive to interactions with fluids, which possibly result in its partial or complete dissolution, followed by recrystallization of new grains. The present study has shown that the behavior of monazite during fluid-rock interaction is controlled by several parameters: fluid and rock composition, ligands, pH and temperature. At low temperatures (350°C - 450°C) in a microgranite, monazite is easily disturbed by dissolutionprecipitation in presence of F and CO2 -rich fluid, while an alkali-bearing fluid has no effects on it. By contrast, at higher temperatures (> 600 ° C) in metapelitic rocks, the same alkalibearing fluid induces dissolution-precipitation of monazite. The impact of this process on the geochronometer of depends on Pb, Th and U mobility in the fluid: as a result, the newly formed grained record either the same age as the initial crystal, the age of fluid/rock interaction, or an apparent age without any geological significance. The U-Pb and Th-Pb isotopic systems in monazite can also be affected by the incorporation of common Pb during crystallization (up to several hundred ppm), then increasing artificially the recorded ages. This work has demonstrated that the correct interpretation of the age data in monazite relies on a careful characterization of each geological example and cannot rely simply on commonly accepted paradigms. In the future, optimizing the use of monazite as geochronometer implies to (1) improve the analytical methods (increasing spatial resolution to solve geological problems at the nanometric scale, use of homogeneous monazites as standards) and (2) use a range of geochemical tools (major- and trace elements, U-Th-Pb dating, oxygen isotopes). This would help to better interpret the ages recorded by monazite.

A green synthesis method for the synthesis of hydrotalcite has been previously developed but this process has not yet been optimised. The main focus of this dissertation was on aluminium-based LDHs. The purpose of this investigation were; to determine optimum synthesis conditions for the formation of hydrotalcite using the dissolution-precipitation method and to determine the possibility of partial substituting the divalent metal species in hydrotalcite and hydrocalumite with other metal species. During the optimisation process for the formation of hydrotalcite using the dissolution precipitation method, the formation of hydromagnesite was proved to be dominant reaction at lower reaction temperatures. With the increase in reaction time and temperature the decomposition of hydromagnesite occurred to form magnesite. At low temperatures the formation of Mg-Al-CO3 LDH is limited due to the low solubility of gibbsite. Mg-Al-CO3 LDH formation of 80 % was achieved at 140 oC after 2 hours reaction time, but crystallinity was low. To achieve an Mg-Al-CO3 LDH conversion higher than 96 % a reaction temperature of 160 oC for a minimum of 4 hours is required, but is achieved within 1 hour at 180 oC. A 99.37 % conversion was achieved at 180 oC for 5 hours with a high crystallinity and homogeneity. The surface area for Mg-Al-CO3 LDH at 180 oC after 5 hours reaction time proved to be 9.19 m2/g. The average particle size obtained for a high crystalline LDH was in the range of approx. 3 μm and 6.8 μm at temperatures of 160 oC and above for a minimum of 3 hours reaction time. The following are recommended for future work:  Determine the effect of mixing speed on the shape of the platelets.  Determine the difference between freshly precipitated metal oxides/hydroxides as reagents compared to aged metal oxides/hydroxides. The presence of Mg(OH)2 and Ca(OH)2 in solution (respectively) did increase the pH enough for the dissolution of gibbsite and most of the Mx+ metal species. A reaction time and temperature of 5 hours at 180 oC in a carbonate environment proved to be close to the ideal conditions for the formation of Mg/Mo-Al-CO3 LDH and Mg/Zn-Al-CO3 LDH. The results for the formation of Mg/Ti-Al-CO3 LDH were inconclusive. Isolation of the possible Mg/Ti-Al-CO3 LDH is recommended to determine the degree of substitution. The conditions for the dissolution of the metal species for the following experiments were proven to be successful:  Ca/Mn(lV)-Al  Ca/Mo-Al  Ca/Ni-Al  Ca/Ti-Al The following recommendations are made for the improvement on the formation of an Mx+-impregnated LDH/precursor:  Determine the effect of different reaction time and temperature.  Determine the effect of adding the carbonate source at temperatures above 100 oC under pressure.  Determine the effect of synthesising at different pH conditions. Cobalt and tin showed no/negligible amount of possible solubility. / Dissertation (MSc)--University of Pretoria, 2014. / Chemical Engineering / MSc / Unrestricted

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High performance liquid chromatography (HPLC) is one of the major techniques in separat-ion sciences. Faster separation and higher efficiency are required to meet ever-growing demands. Despite numerous studies and achievements on improving mass transfer in particulate packings discontinuity seems to be the cornerstone drawback in their development. Macroporous continuous beds or monoliths are therefore a promising alternative to the particle medium. This thesis deals with preparation of new monoliths used as carrier for HPLC. Two different approaches were developed for two polymer systems. One was based on polycondensation of epoxy resins and polyamines which were components of an oil-in-water emulsion. An epoxy resin mixture was dispersed in aqueous polyamine phase with the aid of a surfactant. The other involved a traverse of a ready-made polymer solution around its upper critical solution temperature (UCST). In other words, linear polyamides, non-covalently crosslinked polymers, dissolved in a solvent at temperature higher than their UCST followed by slow cooling to below the critical temperature to precipitate the polymers. Partly re-established hydrogen bonds resulted in the formation of crystallites that interconnected into a network structure. Factors controlling morphology and porosity of final products were investigated. The study also deals with surface modifying for chromatographic applications. Functionalization pathways attempted in the thesis were quaterization of inherent amine of the epoxy-based monoliths and grafting tentacle ion groups via glycidyl methacrylate by atom transfer radical polymerization (ATRP) for ion exchange chromatography (IEC).

This thesis focuses on my endeavors to prepare new porous polymeric monoliths that are viable to use as supports in flow-through processes. Polymer monoliths of various porous properties and different chemical properties have been prepared utilizing the thermally induced phase separation (TIPS) phenomenon and step-growth polymerization reactions. The aim has been to find appropriate synthesis routes to produce separation supports with fully controlled chemical, physical and surface properties. This thesis includes preparation of porous monolithic materials from several non-cross-linked commodity polymers and engineering plastics by dissolution/precipitation process (i.e. TIPS). Elevated temperatures, above the upper critical solution temperature (UCST), were used to dissolve the polymers in appropriate solvents that only dissolve the polymers above this critical temperature. After dissolution, the homogeneous and clear polymer-solvent solution is thermally quenched by cooling. A porous material, of three dimensional structure, is then obtained as the temperature crosses the UCST. More than 20 organic solvents were tested to find the most compatible one that can dissolve the polymer above the UCST and precipitate it back when the temperature is lowered. The effect of using a mixture of two solvents or additives (co-porogenic polymer or surfactant) in the polymer dissolution/precipitation process have been studied more in depth for poly(vinylidine difluoride) (PVDF) polymers of two different molecular weight grades. Monolithic materials showing different pore characteristics could be obtained by varying the composition of the PVDF-solvent mixture during the dissolute­ion/precipitation process. Step-growth polymerization (often called polycondensat­ion reaction) combined with sol-gel process with the aid of porogenic polymer and block copolymer surfactant have also been used as a new route of synthesis for production of porous melamine-formaldehyde (MF) monoliths. In general, the meso- and macro-porous support materials, for which the synthesis/preparation is discussed in this thesis, are useful to a wide variety of applications in separation science and heterogeneous reactions (catalysis).

Ce travail entre dans le cadre de l’étude des interactions eau-roche dans le cas du stockage du CO2 en milieu géologique. Un intérêt particulier est accordé aux hétérogénéités des paramètres associés aux phénomènes géochimiques. Ces hétérogénéités peuvent s’observer à différentes échelles: celle des grains (les minéraux présentent des défauts de cristallinité et des impuretés), et l’échelle centimétrique/pluri-décamétrique. En particulier, les paramètres thermodynamiques (logK) et de cinétique chimique (dans ce travail nous avons considéré le produit de la constante cinétique k par la surface spécifique S soit kS comme "paramètre de cinétique chimique") sont connus à partir des expériences de laboratoire pour des échantillons de quelques centimètres de dimension, alors que l’on s’intéresse aux réactions minéralogiques à l’échelle des réservoirs.Nous avons évalué les caractéristiques géostatistiques de la variabilité spatiale après réaction à travers des simulations de transport réactif dans lesquelles différents paramètres (logK et kS) sont perturbés avec une première variabilité imposée. Une combinaison de deux approches est ainsi abordée : déterministe et géostatistique. Le code du transport-réactif COORES (IFP-EN et Ecole nationale supérieure des mines de Saint-Etienne) a été utilisé pour les simulations déterministes et le système géochimique étudié concerne la dissolution du diopside avec précipitation de minéraux secondaires comme la calcite et la magnésite.Après analyse par la méthode des plans d’expériences, les résultats montrent qu’une corrélation spatiale élevée combinée avec une grande variance de dispersion des minéraux favorise une réactivité importante des minéraux lorsqu’on perturbe le paramètre de cinétique chimique kS. Par ailleurs une vitesse d’injection élevée accélère le processus de dissolution du minéral étudié. La variabilité spatiale du paramètre thermodynamique n’a cependant pas d’effet significatif sur les résultats, le système se comporte comme dans le cas homogène. Du point de vue de l’homogénéisation du paramètre kS, on retrouve l’influence de l’historique de dissolution. / The present work is based on the study of water-rock interactions in the case of CO2 storage in geological media. Particular attention is devoted to heterogeneities at different observation scales geochemical phenomena. These heterogeneities can be observed at different scales: the grain (mineral crystallinity present defects and impurities), and the centimeter scale / multi- decametric (rocks are heterogeneous at different scales). In particular, the thermodynamic parameters logK and chemical kinetics kS (in this work we considered the product of the rate constant k by the specific surface area S is kS as "chemical kinetics parameter") are known from laboratory experiments to a few centimeters in size, while we are interested in mineralogical reactions across tanks.We propose to evaluate the geostatistical characteristics of the local variability after reaction through simulations of reactive transport on a small scale in which various parameters (logK and kS) are perturbed with a first spatial variability imposed. A combination of both approaches is discussed: deterministic and geostatistical for the study of geochemical problems at different scales. The reactive transport code - COORES (IFP - EN and Ecole nationale supérieure des mines de Saint -Etienne) was used for deterministic simulations and the geochemical system studied concerns the dissolution of diopside with precipitation of secondary minerals such as calcite and magnesite.After analysis by the method of design of experiments, the results show that high spatial correlation variance combined with high dispersion of minerals promotes a high reactivity when minerals chemically disturbing is the kinetic parameter kS. In addition, a high velocity injection accelerates the dissolution of the mineral studied. However, the effect of spatial variability of the thermodynamic parameter, did not significantly affect the results, the system behaves as in the homogeneous case. From the standpoint of homogenizing the parameter kS, include the influence of the history of dissolution.

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The aim of this work was to study the separate effect of fission fragment damage on the structural integrity and matrix dissolution of uranium dioxide in water. Radiation damage similar to fission damage was created by irradiating bulk undoped and doped ‘SIMFUEL’ disks of UO2, undoped bulk CeO2 and thin films of UO2 and CeO2 with high energy Xe and U ions. The UO2 thin films, with thicknesses in the range of 90 – 150 nm, were deposited onto (001), (110) and (111) orientations of single crystal LSAT (Al10La3O51Sr14Ta7) and YSZ (Yttria-Stabilised Zirconia) substrates. The CeO2 thin films were deposited onto single crystal silicon (001) substrates. Part of the bulk UO2 and CeO2 samples, the thin films of UO2 on the LSAT substrates and the thin films of CeO2 were irradiated with 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate the damage produced by fission fragments in uranium dioxide nuclear fuel. Part of the bulk UO2 and CeO2 samples and the thin films of UO2 on the YSZ substrates were irradiated with 110 MeV 238U31+ ions to a fluence of 5 × 1010, 5 × 1011 and 5 × 1012 ions/cm2 to study the accumulation of the damage induced. The irradiated and unirradiated samples were studied using scanning electron microscopy (SEM), focused ion beam (FIB), atomic force microscopy (AFM), energy dispersive X-ray (EDX) spectroscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) techniques to characterise the as-produced samples and assess the effects of the ion irradiations. Dissolution experiments were conducted to assess the effect of the Xe ion irradiation on the dissolution of the thin film UO2 samples on the LSAT substrates and the bulk and thin film CeO2 samples. The solutions obtained from the leaching of the irradiated and unirradiated samples were analysed using inductively coupled plasma mass spectrometry (ICP-MS). XRD studies of the bulk UO2 samples showed that the ion irradiations resulted in an increased lattice parameter, microstrain and decreased crystallite size, as expected. The irradiated UO2 thin films on the LSAT substrates underwent significant microstructural and crystallographic rearrangements. It was shown that by irradiating thin films of UO2 with high energy, high fluence ions, it is possible to produce a structure that is similar to a thin slice through the high burn-up structure. It is expected that the ion irradiation induced chemical mixing of the UO2 films with the substrate elements (La, Sr, Al, Ta). As a result, a material similar to a doped SIMFUEL with induced radiation damage was produced.