Thesis (Ph. D.) - Harvard University, 1960. / Bibliography: leaves [90-93]

Un nouveau procédé, basé sur une adaptation innovante du principe de protection cathodique des ouvrages métalliques en milieu marin, consiste à favoriser la précipitation d’un agglomérat calcomagnésien sur plusieurs centimètres d’épaisseur. En présence de sable et de coquillages, cet agglomérat pourrait permettre de stabiliser des zones littorales en cours d’érosion ou d’améliorer l’ancrage d’enrochements brise-lames. L’objectif de ce travail est d’étudier et de comprendre les mécanismes réactionnels de formation de cet agglomérat permettant une précipitation en volume loin de la cathode afin d’en optimiser la vitesse de formation ainsi que ses propriétés mécaniques. Premièrement, il a été montré dans ces travaux que le milieu électrolytique pouvait influer sur la croissance du dépôt, avec une possible inhibition de formation de carbonate de calcium pour les faibles potentiels. L’influence des produits de corrosion dans le mécanisme de protection cathodique a également été mise en évidence grâce à des polarisations effectuées dans NaCl, eau de mer artificielle et naturelle. Deuxièmement, des essais d’un mois en courant imposé ont été menés du laboratoire jusqu’au site naturel, afin de se rapprocher des conditions réelles. La densité de courant appliquée ainsi que les conditions hydrodynamiques sont des facteurs clefs étroitement liés l’un à l’autre, influant sur la masse et le rapport Ca/Mg. Ces travaux ont aussi permis de mettre en avant l’influence du temps de polarisation sur la composition du dépôt calcomagnésien, présentant une cinétique de croissance stable mais une fluctuation de composition après 15, 30 et 60 jours. Cette variation interne du rapport Ca/Mg, attribuée à un processus de « dissolution/précipitation » dépendant du gradient de pH, ainsi que la répartition de ces éléments au sein du dépôt pourraient jouer un rôle majeur dans l’évolution de la tenue mécanique du dépôt au cours du temps. / A new method, based on an innovative adaptation of cathodic protection principle of metal structures in marine environment, is to promote the precipitation of a calcareous agglomerate several centimeters thick. In the presence of sand and shells, this cluster could stabilize coastal areas being eroded or improve anchorage of breakwater riprap. The objective of this work is to study and understand the reaction mechanisms allowing to create a voluminous calcareous deposit away from the cathode and to optimize deposition time as well as its mechanical properties. First, it was shown in this work that the electrolytic medium could affect the growth of the deposit, with a possible inhibition of formation of calcium carbonate fot the low potential. The influence of corrosion products in the cathodic protection mechanism was also highlighted through polarizations performed in NaCl, artificial and natural sea water. Second, one month test with impressed current were conducted from laboratory to natural site, in order to get closer of real conditions. Current density and hydrodynamic conditions are key factors closely bonded to each other, affecting the mass and composition of the Ca/Mg ratio. This work has also helped to highlight the influence of the polarization time on the composition, with stable growth kinetics but a composition’s evolution after 15, 30 and 60 days. This internal variation of the Ca/Mg ratio attributed to a process of « dissolution/precipitation » is pH dependent and the distribution of these elements within the deposit could play a major role in the evolution of the mechanical strength of deposit over time.

L'augmentation rapide du niveau de concentration de dioxide de carbone dans l'air ambiant à la suite de diverses activités humaines est l'un des principaux défis environnementaux du XXIe siècle. Par conséquent, la résolution des problèmes d'émissions de carbone est l'une des principales tâches de la société moderne. Diverses technologies ont été développées et testées au cours des dernières décennies pour atténuer ce problème. La carbonatation minérale est reconnue comme l'une des technologies les plus sûres permettant de capturer et de stocker en permanence du carbone sous forme de carbonates thermiquement stables. La minéralisation passive du carbone par les résidus miniers en tant que processus naturel a lieu dans des conditions environnementales, partout où l'accès de l'air et de l'eau au tas de résidus miniers est possible. Le présent travail explore l'utilisation de la thermographie infrarouge comme méthode non destructive de surveillance du comportement exothermique au cours de la capture passive du carbone par la brucite. La configuration de carbonatation à deux cellules, consolidée avec une caméra infrarouge, a été conçue pour surveiller simultanément les variations thermiques de la surface du matériel dues à l'absorption de CO2 ainsi que le flux de chaleur échangé entre la brucite et son environnement. Les résultats montrent une influence significative de la température ambiante sur le système qui a contribué à l'échange thermique de la couche réactive avec l'environnement. La comparaison des profils de température entre les demi-cellules de référence et réactives montre des différences dans les variations thermiques par rapport à la température adiabatique à cause de l'influence de la température ambiante. L'élévation de température adiabatique par rapport aux profils de température de surface démontre une différence substantielle dans le taux de génération de chaleur de carbonatation en raison de l'échange de flux de chaleur avec l'environnement pendant le processus. / Rapid increment of the level of carbon concentration in ambient air in consequence of various human activities is one of the major environmental challenges of 21st century. Therefore, solving carbon emissions issues is one of the main tasks of the modern society. Variety of technologies have been developed and tested over the past decades to alleviate this concern. Mineral carbonation is recognized as one of the safest technologies that allows to capture and permanently store carbon in the form of thermally stable carbonates. Passive mineral carbonation by mining residues as a naturally occurring process takes place under environmental conditions anywhere where the air and water access to mining residue heap can be obtained. The present work explores the use of infrared thermography as a non-destructive method of monitoring exothermal behavior of passive carbon capture by brucite. Dual-cell carbonation setup consolidated with an infrared camera was designed in order to provide simultaneous monitoring of thermal variations on the surface of the material due to CO2 uptake as well as exchange of heat fluxes between brucite and its surroundings. The results show a significant influence of room temperature on the system that contributed to heat exchange of the reactive layer with the surrounding. The temperature profiles comparison between reference and reactive half-cells demonstrates striking differences in thermal variations than the adiabatic temperature due to the room temperature influence. Adiabatic temperature rise in comparison with surface temperature profiles demonstrates a substantial difference in carbonation heat generation rate due to heat fluxes exchange with surrounding during the process.

The thesis deals with the study of magnesium oxide burned by various burning regimes and his possibilities of its usage as potential expansion additive. The theoretical part of the thesis concerns mainly the volume changes and how they can be influenced. The practical part focuses on monitoring morphology, phase composition and the hydration process of magnesium oxide.

Le monzogranite hercynien de Costabonne est intrusif dans une série précambrienne à cambrienne. Des roches métasomatiques se sont développées dans l'auréole de contact. L'étude des différentes séquences métasomatiques développées dans les métasédimants et d'une minéralisation en scheelite postérieure est un des objectifs d'un projet CCE. Les deux résultats principaux de ce travail sont : (1) Un modèle d'évolution de la lithologie "marbre à brucite" (2) un modèle expliquant la variation des paragénèses des zones dans les veines métasomatiques.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-10T12:37:20Z No. of bitstreams: 1 deysegomesdacosta.pdf: 10386782 bytes, checksum: a18ce8ca7fd4c235c246f70bc4f6f946 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-17T15:04:53Z (GMT) No. of bitstreams: 1 deysegomesdacosta.pdf: 10386782 bytes, checksum: a18ce8ca7fd4c235c246f70bc4f6f946 (MD5) / Made available in DSpace on 2017-05-17T15:04:53Z (GMT). No. of bitstreams: 1 deysegomesdacosta.pdf: 10386782 bytes, checksum: a18ce8ca7fd4c235c246f70bc4f6f946 (MD5) Previous issue date: 2011-07-29 / Os hidróxidos duplos lamelares (HDL) ou compostos tipo-hidrotalcita vêm sendo muito estudados devido a suas inúmeras aplicações. No campo da catálise, estes compostos podem atuar como catalisadores, suportes para catalisadores ou precursores de catalisadores. É sabido que a morfologia do suporte tem grande influência sobre a dispersão, a atividade e a seletividade apresentada pelo catalisador. Nestes caso, o conhecimento detalhado dos efeitos do suporte e dos sítios catalíticos exigem a compreensão da estrutura do HDL. Entretanto, por causa da desordem estrutural, muitas vezes inerente ao material, torna-se a determinação completa da estrutura, via difração de raios X, raramente possível. As bandas largas presentes na análise do IV, fazem a atribuição das mesmas ambígua. Devido à complexidade dos HDL e à dificuldade de se adquirir ou interpretar os resultados experimentais, foi proposto um modelo para simular as características estruturais dos compostos tipo-hidrotalcita com o politipo 3R1, usando condições periódicas de contorno e cálculos ab initio dentro da teoria do funcional da densidade (DFT). As informações estruturais da hidrotalcita, obtidas experimentalmente, foram usadas para verificar a validade do modelo teórico. Os resultados mostraram boas concordâncias com os padrões de raios X do pó experimentais. O espectro na região do infravermelho, a entalpia e energia livre de Gibbs, também foram calculadas. Os cálculos de frequências vibracionais mostraram que as moléculas de água intercaladas são altamente organizadas devido às fortes interações intermoleculares com outras moléculas de água, com ânions interlamelares e com as hidroxilas das lamelas. A presença destas interações é refletida na presença do estiramento O-H das moléculas de água deslocadas para baixas frequências. A perda da degenerescência dos modos vibracionais v3 e do v4 foi observada, indicando a redução da simetria do íon carbonato. As modificações termodinâmicas e estruturais resultantes da substituição do íon presente no HDL Zn-Al-Cl também formam analisadas. O íon Cl- do HDL precursor foi trocado por uma série de ânions como o F-, Br-, OH-, NO3-, ClO4-, CO32- e SO42-. Os resultados mostraram que a intercalação do HDL com diferentes íons, afeta o gap de energia e a basicidade da lamela tipo-brucita. A entalpia e a energia livre de Gibbs, a densidade de estados (DOS) e a densidade de estados projetada (PDOS) foram avaliadas para todos os HDL. / The layered double hydroxide (LDH) or hydrotalcite-like compounds have been widely studied due to many applications they have. In catalysis field these compounds can act as catalyst, catalyst support or precursor for supports and catalysts. It is well known that the support morphology has larger influence on the dispersion, activity and selectivity of catalysts. In this case, detailed knowledge about support effects and catalytic sites requires understanding the LDH structure. However, because of the inherent structural disorder, complete structure determination using X-ray diffraction is rarely possible. The IR analysis present broad bands, which makes their assignment ambiguous. Due to the complexity of the LDH and the difficult of acquiring experimental data, we proposed a model to simulate structural features of the hydrotalcite-like compounds with 3R1 polytypes using periodic boundary conditions and ab initio density functional theory (DFT) calculations. The structural information of hydrotalcite from experiments were used to verify the validity of theoretical model. Our results showed good agreements to the powder X-ray patterns. The infrared spectroscopy, enthalpy and Gibbs free energy, also was calculated. The IR calculations showed that intercalated water molecules are highly ordered due the strong intermolecular interactions with other water molecules, interlayer anions and layer hydroxyls. These interaction is reflected by the presence of downshift vibrational frequencies of OH-stretching of interlayer water. The loss of degeneracy of the v3 and v4 vibrational modes are observed, indicating the reduction of the carbonate anion symmetry. The thermodynamic and structural modifications derived from anion exchange on a LDH containing Zn-Al-Cl was also analyzed. The Cl- ion to the LDH precursor was exchanged for a series of anions as F-, Br-, OH-, NO3-, ClO4-, CO32- and SO42-. The resulted show that intercalation of LDH with different anions affect their gap energy and basicity of brucite-like layer. The enthalpy and Gibbs free energy, density of charge, density of state (DOS) and projected density of state (PDOS) were evaluated for all substituted materials.