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1	Étude par dynamique moléculaire du comportement élastique et vibrationnel des roches sous pression : cas du carbonate de calcium et de la strontianite / Molecular dynamics study of elastic and vibrationel behavior of rocks under pressure : the case of calcium carbonate and strontianite Taleb, Nezha 25 March 2009 (has links) Le travail de cette thèse concerne l'étude des propriétés structurales, mécaniques et vibrationnelles du carbonate de calcium et de la strontianite. Ces deux roches appartiennent à la famille des carbonates et sont abondamment présentes dans la croûte terrestre. Elles sont soumises à des contraintes géologiques qui les exposent à des pressions qui peuvent atteindre plusieurs GPa. Il est alors intéressant de pouvoir prédire leur comportement dans ces cas extrêmes en étudiant l'évolution de leurs propriétés élastiques en fonction de la pression. Pour réaliser cet objectif on a utilisé la méthode de dynamique moléculaire basée sur la connaissance d'un potentiel modèle approprié. Les grandeurs physiques permettant de caractériser le comportement de ces deux espèces de roches sont: la vitesse de propagation des ondes élastiques, les modes de vibration des phonons et la variation de l'enthalpie. Pour CaCO3 les paramètres de potentiel employés, ont permis de calculer les valeurs de l'ensemble des propriétés mécaniques. Les valeurs trouvées sont en bon accord avec les résultats expérimentaux pour les phases aragonite et post-aragonite. La variation de l'enthalpie en fonction de la pression a permis de montrer que la phase post-aragonite était stable pour des pressions supérieures à 35 GPa. Outre l'enthalpie, la transition de phase aragonite post-aragonite, est confirmée par d'autres résultats concordants. Il s'agit de la variation de la vitesse des ondes transversales et de la variation en fréquence du mode acoustique mou. Ce dernier présente un saut en fréquence lorsqu'on se trouve à la pression de transition. Pour SrCO3 on a du procéder selon la même démarche que pour CaCO3. / The aim of the present work is to study the structural, mechanical and vibrational properties of calcium carbonate and strantianite. These two rocks belong to the carbonate family and they are abandonment in the earth 's crust. They are subject to geological constraints that expose them to high pressures, which may reach several GPa. It is then interesting to predict their behaviour in these extreme cases by studying the evolution of their elastic properties as a function of pressure. To do this we have used the molecular dynamics method based on knowledge of an appropriate potential. The physical quantities used to characterize the behaviour of these two kinds of rocks are: the elastic wave velocities, the vibrational modes of phonons and the variation of enthalpy. For CaCO3 the potential parameters employed allow us to evaluate ail mechanical properties. The obtained values are in good agreement with experimental results for aragonite and post-aragonite phases. The variation of the enthalpy as a function of pressure has shown that the post-aragonite phase was stable for pressures above 35 GPa. ln addition to the enthalpy, the structural phase transition from aragonite to post-aragonite phase is confirmed by further results. These latter are the variation of the transversal wave velocities and the variation of trequency of the soft mode, which shows a abrupt jump at the transition pressure. For the SrCO3 we have followed the same procedure as for CaCO,. Strontianite
2	The vibrational spectroscopy of minerals Martens, Wayde Neil January 2004 (has links) This thesis focuses on the vibrational spectroscopy of the aragonite and vivianite arsenate minerals (erythrite, annabergite and hörnesite), specifically the assignment of the spectra. The infrared and Raman spectra of cerussite have been assigned according to the vibrational symmetry species. The assignment of satellite bands to 18O isotopes has been discussed with respect to the use of these bands to the quantification of the isotopes. Overtone and combination bands have been assigned according to symmetry species and their corresponding fundamental vibrations. The vibrational spectra of cerussite have been compared with other aragonite group minerals and the differences explained on the basis of differing chemistry and crystal structures of these minerals. The single crystal spectra of natural erythrite has been reported and compared with the synthetic equivalent. The symmetry species of the vibrations have been assigned according to single crystal and factor group considerations. Deuteration experiments have allowed the assignment of water vibrational freque ncies to discrete water molecules in the crystal structure. Differences in the spectra of other vivianite arsenates, namely annabergite and hörnesite, have been explained by consideration of their differing chemistry and crystal structures. A novel approach to the assignment of site occupancy of ions in the erythrite - annabergite solid solution has been reported. This approach has utilised vibrational spectroscopy, in conjunction with careful consideration of the crystal structures of the minerals. It has been shown that in the erythrite - annabergite solid solution Coprefers metal site 2 contrasting nickel which prefers site 1. This study in conjunction with other studies has yielded the trend that the more electronegative metal prefers to occupy site 1, with the least electronegative metal preferring to occupy site 2. Fundamentally this thesis has increased the knowledge base of the spectroscopic properties of the aragonite and the vivianite minerals. The site occupancy of metal ion substitutions in solid solution series of the vivianite group of minerals has been further enhanced, with novel method of studying the site occupancy of ions in solid solutions has been developed. A detailed knowledge and understanding of factor group analysis applied to the study of minerals has been achieved. Annabergite Aragonite Arupite Baricite Cerussite Erythrite Hörnesite Infrared Spectroscopy Köttigite Minerals Parasymplesite Raman Spectroscopy Solid Solutions Strontianite Vibrational Spectroscopy Vivianite Witherite
3	Synthesis and characterisation of substituted smithsonite and calcite Hales, Matthew Cameron January 2008 (has links) Carbonate minerals play a very important role in nature, they represent some of the most diverse and common mineral species on the Planet. They are directly involved in the carbon dioxide (CO2) cycle acting as relatively stable long term chemical storage reservoirs, moderating both global warming trends and oceanaquatic chemistry through carbonate buffering systems. A range of synthetic metal carbonates have been synthesised for analysis under multiple experimental conditions, in order to study the variation in physical and chemical properties such as phase specificity, metal substitution, hydration/hydroxy carbonate formation under varying partial pressures of CO2 and thermal stability. Synthetic samples were characterised by a variety of instrumental analysis techniques in order to investigate chemical purity and phase specificity. Some of the techniques included, vibrational spectroscopy (IR/Raman), thermal analysis (TGA-MS) (thermal Raman), X-Ray diffraction (XRD) and electron microscopy (SEM-EDX). From the instrumental characterisation techniques, it was found that single phase smithsonite, hydrozincite, calcite and nesquehonite could successfully be synthesised under the conditions used. Minor impurities of other minerals and / or phases were found to form under specific chemical or physical conditions such as in the case of hydrozincite / simonkolleite if zinc chloride was used during hydrothermal synthesis. Raman Infrared IR spectroscopy characterisation synthesis synthetic natural scanning electron microscopy SEM thermo-gravimetric analysis mass spectroscopy TGA-MS X-Ray diffraction XRD carbonate hydrogen carbonate hydroxy hydrate minerals crystal point group factor group phase symmetry elements calcite magnesite aragonite vaterite aurichalcite azurite malachite hydrozincite zincite nesquehonite strontianite witherite oxide zone partial pressure carbon dioxide CO2 geological settling coral geo-sequestration green house gas

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