O estudo do interior da Terra apresenta diversos desafios, principalmente devido à impossibilidade de observações diretas de suas propriedades. Ondas sísmicas liberadas por terremotos são a melhor fonte de informação sobre a estrutura do planeta, mas sua correta interpretação depende do conhecimento das propriedades de seus elementos constituintes. Entretanto, estes estudos devem ser feitos nas condições extremas de temperatura e pressão do interior terrestre, condições difíceis de serem alcançadas em laboratório. Neste contexto, o estudo teórico de materiais tem sido muito importante na elaboração de modelos sobre a estrutura interna da Terra e na correta interpretação de dados sísmicos. Pesquisas recentes têm mostrado que a quantidade de carbono no manto inferior da Terra é maior do que se pensava anteriormente, e é importante compreender seus efeitos no interior profundo da Terra. Apesar da importância de entender os efeitos do carbono no interior da Terra, existem poucos estudos deste elemento nestas condições extremas de pressão e temperatura. Neste trabalho, utilizamos métodos e técnicas da física do estado sólido para estudar as propriedades de compostos de carbono nas condições de pressão e temperatura do manto inferior terrestre. Estudamos, primeiramente, as propriedades estruturais, eletrônicas e elásticas do MgSiO3 nas estruturas perovskita e pós-perovskita, considerado o principal mineral do manto inferior. Os resultados obtidos para as velocidades acústicas neste mineral mostraram variações maiores em relação às direções cristalinas, quando comparadas com mudanças devido à transição de fase estrutural. Isso indica que uma orientação preferencial dos eixos (anisotropia) pode ajudar a explicar algumas regiões com aumento descontínuo nas velocidades sísmicas. Posteriormente, foram obtidas as propriedades do MgCO3 e do CaCO3 em suas estruturas mais estáveis, em função da pressão. Nossos resultados foram comparados com os do MgSiO3 , mostrando que carbonatos de cálcio e de magnésio são estáveis nas condições do manto terrestre e que sua formação é energeticamente favorável. Resultados dos cálculos dos coeficientes elásticos e das velocidades acústicas nestes minerais mostram que as velocidades são menores que aquelas no MgSiO 3 . Dessa forma, em regiões ricas em carbono deve ocorrer a formação destes carbonatos e, por conseguinte, as velocidades sísmicas seriam menores nessas regiões. Isso pode explicar a existência das zonas de baixa velocidade na fronteira do manto inferior com o núcleo. Foram estudadas, também, as consequências da introdução de efeitos térmicos. Entretanto, obteve-se que os resultados não apresentam alterações significativas, de modo que mesmo nas altas temperaturas do interior da Terra nossas conclusões permanecem válidas, onde propomos que as regiões de baixa velocidade no manto inferior possam ser provocadas pela presença de carbono na forma de carbonatos e que a formação destes seria um modelo adicional para explicar onde e como o carbono pode ser armazenado no manto profundo. / Investigations on the Earths interior face several challenges, especially due to the infeasibility of direct observations of its properties. Earthquake seismic waves are the best information source about our planets structure, but its correct interpretation depends on the knowledge of its forming elements. However, these studies must consider the extreme pressures and temperatures of the Earths interior, hard to achieve experimentally. In this way, theoretical methods have emerged as an essential tool in elaborating models for the Earth internal structure and in the correct interpretation of seismic data. Recent studies have shown that the Earth must have much more carbon than previous thought, and it is important to understand its effects on the Earths deep interior. Despite its importance, there are few studies on carbon in these extreme conditions of pressure and temperature and on its effects in the Earths interior. In this investigation, we use theoretical solid state physics methods to investigate the properties of carbon compounds in the pressure and temperature conditions of Earths deep interior. First of all, we studied the electronic and elastic properties of MgSiO3 in the perovskite and post perovskite structures. This silicate is considered the main mineral in the Earths lower mantle. Our results show that seismic velocities have a larger variation with respect to the propagation direction than that with the phase transition. This indicates that a lattice preferred orientation can explain some seismic discontinuities. Thereafter, the properties of the MgCO3 and CaCO3 minerals were obtained in their more stable structures with respect to pressure. The results were compared with those of the MgSiO3, showing that calcium and magnesium carbonates are stable in the Earths mantle and that their formation is energetically favorable. The elastic coefficients and the acoustic velocities in these carbonates show seismic velocities considerably lower than those in the MgSiO3 . In this way, in regions with high carbon concentration the formation of carbonates could favorably occur and therefore the seismic velocities would be lower in those regions. This may explain the existence of low velocity zones near the bottom of Earths lower mantle. We also studied the consequences of the introduction of thermal effects. However, our results do not show any significant variation with temperature. Hence, even in the high temperatures of Earths interior, our conclusions are still valid where we propose that low velocity regions can be caused by the presence of carbon in the form of carbonates. Its formation could provide an additional model to explain where and how carbon can be stored in the deep mantle.

La minéralisation induite par l'activité microbienne joue un rôle majeur dans le fonctionnement des écosystèmes passés et présents. Cette étude présente les données expérimentales de précipitation de CaCO3 à partir de cultures pures de deux types de bactéries anoxygéniques phototrophiques (APB) : Rhodovulum steppens A-20s haloalcaphilique et Rhodovulum sp. S-17-65 neutrophilique halophilique, ainsi que de cyanobactéries Gloeocapsa sp.. Ces bactéries représentent deux groupes importants d'organismes photosynthétiques depuis les temps les plus anciens jusqu'à nos jours. Dans ce contexte, cette thèse a pour objectif principal de caractériser les processus biologiques de précipitation de CaCO3 et d'évaluer l'existence d'un processus métabolique protégeant les bactéries étudiées contre la minéralisation de carbonates à leur surface. Pour cela, des expériences cinétiques, des mesures de potentiel zêta et d'adsorption de Ca à la surface bactérienne, couplées à des observations par Microscopie Electronique à Balayage (MEB), en Transmission (MET) et des analyses chimiques par émission et diffraction de rayons X (EDX et XRD) ont été menées. Les résultats de cette étude démontrent que les bactéries étudiées prennent une part active dans la précipitation de CaCO3 . Les mesures de potentiel zêta suggèrent l'existence d'un mécanisme de protection de la cellule pour les APB étudiées, basé sur le maintien métabolique d'une charge de surface plus positive à pH alcalin, préservant les bactéries actives de l'adsorption de Ca2+ et de la précipitation subséquente de carbonates à leur surface. L'existence d'un tel mécanisme n'est pas confirmée pour Gloeocapsa sp. Ainsi, deux mécanismes différents de nucléation de CaCO3 peuvent être mis en évidence : un premier mettant en jeu une sursaturation non-spécifique pour les bactéries anoxygéniques phototrophiques (APB), et un deuxième par nucléation spécifique au niveau de la membrane cellulaire pour les cyanobactéries Gloeocapsa sp..

L'écoulement ductile d'une roche, en présence de fluide, peut s'effectuer par transfert de matière autour de domaines constituants cette roche, sous l'effet de différences de contrainte normale, ou de différences d'énergie élastique, plastique, ou de surface. Les stylolites, schistosités, fentes ou cavités colmatées,témoignent de ce fluage par dissolution-cristallisation dans la croûte supérieure. Différents modèles théoriques en ont été établis, avec des vitesses de déformation limitées par chacun des processus successifs de la transformation (cinétique des réactions solide/fluide, ou vitesse des transferts par diffusion ou infiltration). Puis ces modèles ont été testés en distinguant l'effet de plusieurs paramètres (géométrie des domaines, conditions P.T., nature des matériaux, valeurs des coefficients de transfert) . Pour l'aspect expérimental on a réalisé des dissolutions-cristallisations du quartz et de la calcite, autour de cavités ou autour de grains sous contrainte, en maintenant ces minéraux plusieurs mois au contact de fluides chauds et sous pression (eau, Na OH, NH4 CI) . Différentes forces motrices peuvent intervenir (énergie de surface autour des cavités, contrainte normale autour des grains). Différents processus peuvent limiter les vitesses des déformations (cinétique de réaction pour les cavités, vitesse de diffusion pour les grains). Pour l'aspect naturel. des analyses chimiques comparatives au sein de roches à déformation hétérogène (plissement, cisaillement, poinçonnement, boudinage) permettent de faire un bilan des quantités transférées. On montre que !e transfert peut s'effectuer par diffusion ou par infiltration, sous de faibles déviateurs de contrainte, avec une mobilité variable des minéraux selon les conditions P.T . Les possibilités et les conditions du transfert imposent en priorité le type de modèle de dissolution-cristallisation et la vitesse de cette déformation. On discute de l'initiation et du développement des zones de dissolution et de cristallisation et de l'acquisition d'un litage tectonique dont l'orientation, la géométrie et les compositions reflètent les conditions de la déformation. Des applications sont données pour des processus voisins (métamorphisme, diagenèse) et pour des problèmes particuliers (déformation interne des roches, concentration des minéralisations, glissement asismique des failles).

Cette thèse concerne l'étude expérimentale et la modélisation de la déformation des roches polyminérales par le mécanisme de la dissolution cristallisation sous contrainte. D'une part, il est montré qu'une augmentation de la proportion de grains peu solubles dans une roche diminue la résistance à la déformation. Cela indique une compétition entre deux mécanismes: d'une part la dissolution sous contrainte aux contacts des grains accélère la déformation, et d'autre part la cicatrisation de ces contacts inhibe la dissolution et ralentit le fluage. D'autre part, il a été réalisé des expériences de poinçonnement de monocristaux de calcite en présence de fluide. La vitesse de déformation de la calcite est de deux ordres de grandeur plus élevée que prévu par la théorie. Cet effet peut être expliqué par le développement de microfissures dans la calcite au contact du poinçon. Ces résultats sont appliqués au comportement des sites de stockage de déchets radioactifs et de séquestration du CO2.

Les propriétés mécaniques de différents types de matériaux géologiques sont étudiées en laboratoire. Ce sont d'abord les propriétés d'agrégats artificiels de calcite et de quartz, mettant en évidence le comportement rhéologique volumique et la réduction de porosité en fonction du temps, des pressions de confinement appliquées et de la température. Le second type de matériau est un diabase, roche basaltique microcristalline dont le comportement est étudié â la température de 1000°C. La diminution de la pression de confinement entraine le passage d'un comportement ductile à un comportement fragile, cet te transition dépendant de la vitesse de déformation. Le troisième système étudié est constitué de deux matériaux séparés par une interface. L'auteur analyse la relation entre les propriétés mécaniques des matériaux constitutifs et les propriétés de l'interface. Les expériences sont interprétées en parallèle à une simulation numérique et les valeurs des paramètres déterminées selon leur utilisation dans le calcul. Finalement l'auteur présente une étude technique sur l'inversion des données de stéréologie relatives à la quantification d'un réseau de fractures. Une inversion analytique simple est comparée à une technique numérique en plusieurs phases.

Στο πλαίσιο της παρούσας εργασίας έγινε προσπάθεια για την ανάπτυξη αναλυτικών μεθοδολογιών με στόχο την ταυτοποίηση και την ποσοτική ανάλυση σε περιπτώσεις ταυτόχρονης συνύπαρξης και των τριών φάσεων του άνυδρου κρυσταλλικού ανθρακικού ασβεστίου. Η Φασματοσκοπία Raman και η Φασματοσκοπία Υπερύθρου ήταν οι δύο αναλυτικές τεχνικές οι οποίες χρησιμοποιήθηκαν σαν βάση για την ανάπτυξη των ανάλογων αναλυτικών μεθοδολογιών. Η χρήση της Φασματοσκοπίας Raman οδήγησε στην ανάπτυξη μιας μη καταστροφικής αναλυτικής μεθοδολογίας, στην οποία όμως μόνο τα σχετικά ποσοστά των τριών φάσεων έγινε δυνατόν να προσδιοριστούν. Για την δημιουργία των ευθειών αναφοράς, κατασκευάστηκαν δυαδικά μίγματα, ενώ χρησιμοποιήθηκαν οι κορυφές στα 711cm-1 για τον ασβεστίτη, στα 700cm-1 για τον αραγωνίτη και στα 750cm-1 για τον βατερίτη. Τα όρια ανίχνευσης προσδιορίστηκαν 0.13mol%, 0.18mol% και 1.3mol% για τον ασβεστίτη, αραγωνίτη και βατερίτη αντίστοιχα, ενώ τα σφάλματα κατά τον προσδιορισμό τριαδικού μίγματος γνωστής σύστασης βρέθησαν να είναι 1.6mol% για τον ασβεστίτη, 0.3mol% για τον αραγωνίτη και 1.1mol% για τον βατερίτη. Στην προσπάθεια επιλογής των κατάλληλων δονήσεων Raman, έγινε μελέτη των φασμάτων Raman των καθαρών κρυσταλλικών φάσεων και απόδοση των κορυφών. Τέλος με την χρήση της Φασματοσκοπίας IR έγινε δυνατός ο προσδιορισμός των απόλυτων ποσοστών των τριών φάσεων, κάνοντας χρήση των δονήσεων στα 714cm-1 για τον ασβεστίτη, στα 700cm-1 και 714cm-1 για τον αραγωνίτη και στα 745cm-1 για τον βατερίτη. Οι απόρροφητικότητες των κορυφών (σε mg-1CaCO3 mm-2) βρέθηκαν ίσες με: α 63.38 714 = για τον ασβεστίτη, α .30 700 = 19 και α .43 714 = 40 για τον αραγωνίτη και α .79 745 = 21 για τον βατερίτη. Τα όρια ανίχνευσης (σε mgCaCO3/mm2) προσδιορίστηκαν σε: 714 -4 C O.A. =6.6 ×10 για τον ασβεστίτη, 700 -3 A O.A. =2.2 ×10 και 714 -3 A O.A. =1.1×10 για τον αραγωνίτη και 745 -3 V O.A. =1.9 ×10 για τον βατερίτη. / In the present work new analytical methodologies were developed for the study of calcium carbonate polymorphs (calcite, aragonite, vaterite). Two vibrational techniques were employed for the simultaneous quantitative analysis of mixtures of crystalline materials; Raman Spectroscopy (non-destructive technique), Infrared Spectroscopy (destructive technique). Using binary mixtures from known quantities of the crystal phase the calibration curves were constructed using the Raman bands at 711cm-1 for calcite, 700cm-1 for aragonite and 750cm-1 for vaterite. Detection limits (DL) were found to be 0.13, 0.18 and 1.3mol % for calcite, aragonite and vaterite, respectively, while the relative errors in determining the mol % of a known ternary mixture of calcium carbonate polymorphs were 1.6% for calcite, 0.3% for aragonite and 1.1% for vaterite. Infrared Spectroscopy was used, in order to determinate the absolute concentration of the calcium carbonate crystal phases, using the bands at 714cm-1 for calcite, at 700cm- 1 and 714cm-1 for aragonite and at 745cm-1 for vaterite. The asborptivities were found to be α 63.38 714 = for calcite, α .30 700 = 19 and α .43 714 = 40 for aragonite and α .79 745 = 21 for vaterite. The detection limits were also established and found to be 714 -4 C D.L. = 6.6 ×10 for calcite, 700 -3 A D.L. = 2.2 ×10 and 714 -3 A D.L. =1.1×10 for aragonite and 745 -3 V D.L. = 1.9 ×10 for vaterite.

Σημαντικός αριθμός μνημείων και έργων τέχνης είναι κατασκευασμένα από πέτρα, μάρμαρο κατά πρώτο λόγο, και έπειτα από ασβεστόλιθο και από άλλα πυριτικά υλικά. Η παρούσα εργασία επικεντρώθηκε στη μελέτη της διάλυσης του μαρμάρου σε διάφορες συνθήκες με απώτερο στόχο την αποκάλυψη του μηχανισμού της φυσικοχημικής αυτής διεργασίας τόσο για την περίπτωση ασβεστιτικών όσο και δολομιτικών μαρμάρων. Η κατανόηση του μηχανισμού του προβλήματος είναι απαραίτητη για την κατάλληλη προσέγγιση και επιλογή των μεθόδων προστασίας. Έτσι, στην παρούσα εργασία επιχειρήθηκε: α) Ο προσδιορισμός του μηχανισμού διάλυσης από πειράματα μέτρησης της κινητικής της διάλυσης του μαρμάρου σε ακόρεστα ως προς το βασικό συστατικό (ασβεστίτης, δολομίτης) διαλύματα και σε διαφορετικές συνθήκες ακορεστότητας. β) Η αναστολή της διάλυσης με την προσθήκη υδατοδιαλυτών τασιενεργών ουσιών και η διερεύνηση του μηχανισμού δράσης τους. γ) Η δημιουργία δυνητικά προστατευτικών επικαλύψεων των επιφανειών του (ασβεστιτικού) μαρμάρου με στρώματα ανόργανων αλάτων. δ) Η σύγκριση των αποτελεσμάτων μέτρησης του ρυθμού διάλυσης τόσο παρουσία όσο και απουσία προσθέτων ουσιών με βιβλιογραφικές αναφορές, και αποτελέσματα από πειράματα υπαίθριας έκθεσης και από πειράματα έκθεσης δοκιμίων σε συνθήκες επιταχυνόμενης διάβρωσης σε θάλαμο αλατονέφωσης (παρουσία και άλλων παραγόντων, όπως μικροοργανισμοί, μικροβιοκτόνες ενώσεις). Ο στόχος της σύγκρισης αυτής ήταν η επιλογή του καταλληλότερου μοντέλου για την αξιόπιστη δοκιμή νέων υλικών και μεθόδων προστασίας του μαρμάρου. Για τη διεξαγωγή των δοκιμών, επιλέχθηκαν τρεις τύποι μαρμάρου που απαντώνται σε μνημεία και γλυπτά στην Ευρώπη: Carrara (ασβεστίτης >98%), Πεντελικό (ασβεστίτης >98%) και Ekeberg (δολομίης ~93%). Τα διαλύματα που χρησιμοποιήθηκαν στις μετρήσεις, κινητικής της διάλυσης ήταν ακόρεστα ως προς ασβεστίτη και παρασκευάζονταν με την αραίωση κατάλληλων όγκων stock διαλυμάτων CaCl2, MgCl2, NaHCO3, NaCl, και η αρχική τιμή του pH ρυθμιζόταν στο 8.25 με προσθήκη 0.01N NaOH. Μετά την αποκατάστασης ισορροπίας στα ακόρεστα διαλύματα εργασίας, γινόταν προσθήκη ακριβώς ζυγισμένης σκόνης μαρμάρου ή η εμβάπτιση των δοκιμίων (στερεωμένων σε ειδικό στήριγμα). Τρεις μέθοδοι χρησιμοποιήθηκαν για τις μετρήσεις της κινητικής της διάλυσης του μαρμάρου: συνθήκες ελεύθερης μεταβολής (free drift), συνθήκες σταθερού pH (pH-stat), συνθήκες σταθερού κορεσμού. Για τα ασβεστιτικά μάρμαρα, οι μετρήσεις του ρυθμού διάλυσης τόσο του μαρμάρου (κονιοποιημένου ή δοκιμίων) όσο και της πρότυπης ένωσης αναφοράς (ασβεστίτης) συναρτήσει της ακορεστότητας των διαλυμάτων έδειξαν γραμμική εξάρτηση. Σε όλες τις περιπτώσεις, οι ρυθμοί που υπολογίσθηκαν ήσαν της αυτής τάξης μεγέθους με τους αντίστοιχους ρυθμούς του καθαρού ασβεστίτη. Η θερμική κατεργασία του Πεντελικού μαρμάρου οδήγησε σε σημαντική αύξηση του ρυθμού διάλυσης, και η εξάρτηση των μετρούμενων ρυθμών, R, από τον σχετικό υπερκορεσμό, σ, ήταν μη γραμμική, με n>1. Για το δολομιτικό μάρμαρο Ekeberg, από το διάγραμμα του ρυθμού διάλυσης συναρτήσει της σχετικής ακορεστότητας σ, η προσαρμογή των δεδομένων στην R=kdσn έδωσε την τιμή n=2, οπότε εξήχθη το συμπέρασμα, ότι το στάδιο που καθορίζει τη διάλυση του δολομιτικου μαρμάρου είναι η επιφανειακή διάχυση. Μετρήθηκε και η διαλυτότητα τόσο του δολομιτικού όσο και των λοιπών τύπων μαρμάρου. Τα ασβεστιτικά μάρμαρα Πεντελικό και κρυσταλλίνα Θάσου έδωσαν τιμές για το γινόμενο διαλυτότητας κοντά στην αντίστοιχη τιμή για τον καθαρό ασβεστίτη (8.48) ενώ τα υπόλοιπα ασβεστιτικά (Carrara, Σπηλιά, Διονύσου) έδωσαν υψηλότερες τιμές διαλυτότητας. Τα δύο δολομιτικά μάρμαρα έδωσαν την αυτή τιμή για τη σταθερά διαλυτότητας, η οποία ευρίσκεται εντός των ορίων τιμών που έχουν αναφερθεί στην βιβλιογραφία για στοιχειομετρικό δολομίτη. Σε όλες τις περιπτώσεις ο ρυθμός διάλυσης του μαρμάρου βρέθηκε ότι ελέγχεται από την επιφανειακή διάχυση των δομικών λίθων στο οριακό στρώμα του υγρού. Η ρόφηση κάποιας ουσίας πάνω στο στερεό θα μπορεί να δεσμεύει τα ενεργά κέντρα και θα έχει αποτελεσματική δράση στην επιβράδυνση της διάλυσης. Έγινε μελέτη ρόφησης ουσιών με ιοντιζόμενες φωσφορικές και φωσφονικές ομάδες σε σκόνες των μαρμάρων Πεντελικού, Carrrara και Ekeberg (ισόθερμοι ρόφησης). Το HEDP μελετήθηκε σε μεγαλύτερη έκταση, τόσο γιατί η παρουσία του στα ακόρεστα διαλύματα είχε ως αποτέλεσμα τη σημαντικότατη αναστολή της διάλυσης, όσο και διότι ως ουσία με ιονιζόμενες δραστικές ομάδες αποτελεί μοντέλο για την μελέτη της επίδρασης ανάλογων ουσιών σε κρυσταλλικά στερεά τα οποία διαθέτουν κατιόντα μετάλλων στην επιφάνειά τους. Η προσθήκη του αναστολέα HEDP στα ακόρεστα διαλύματα είχε ως αποτέλεσμα τη μείωση του ρυθμού διάλυσης σε ανάλογο βαθμό με την προ-ρόφησή του. Η προσθήκη του HΕDP στα ακόρεστα διαλύματα, έδωσε μικρότερους ρυθμούς διάλυσης σε σύγκριση με τους αντίστοιχους ρυθμούς οι οποίοι ελήφθησαν από δείγματα στα οποία η ουσία αυτή είχε προ-ροφηθεί στο στερεό (πειράματα σε σκόνες και δοκίμια ασβεστιτικών μαρμάρων). Το HEDP εκτός από την επιβράδυνση της διάλυσης (ακόμα και κατά 80-90 %), βρέθηκε ότι είχε αρνητική επίδραση στη μορφολογία των κρυστάλλων του μαρμάρου. Ο στόχος της επόμενης σειράς πειραμάτων ήταν η δημιουργία επικαλύψεων σε συμπαγή δοκίμια μαρμάρου. Οι επικαλύψεις αυτές, αποτελούντο από ανόργανα άλατα, μικρότερης διαλυτότητας σε υδατικά διαλύματα, σε σύγκριση με τον ασβεστίτη. Τα διαλύματα αντιδραστηρίων κατεργασίας (HCl, ΕDTA, γαλακτικού οξέος, oξικού οξέος, H3PO4, HEDP, NTMP , N(phosphomethyl-) imino diacetic acid) εφαρμόσθηκαν με: α) επίχριση με πινέλο, β) επίθεση εμποτισμένων υφασμάτων, γ) εμβάπτιση των δοκιμίων στα αντίστοιχα διαλύματα. Αποτελεσματικότερος τρόπος εφαρμογής ήταν η εμβάπτιση. Ο χαρακτηρισμός των επιφανειών, και των αντίστοιχων επιστρώσεων και η ταυτοποίησή τους έγινε με XRD, FΤ-IR και SEM. Στην συνέχεια, τα σύνθετα υλικά (μάρμαρο+επικάλυψη), υποβλήθηκαν σε πειράματα διάλυσης σε διαλύματα ακόρεστα ως προς ασβεστίτη προκειμένου να δοκιμασθεί η αποτελεσματικότητά τους στην προστασία της επιφάνειας του μαρμάρου από τη διάβρωση. Η επεξεργασία με φωσφορικό οξύ, είχε ως αποτέλεσμα την δημιουργία παχέος στρώματος διένυδρου, όξινου φωσφορικού ασβέστιου (CaHPO42H2O, DCPD). Με δεύτερη εμβάπτιση σε διάλυμα όξινου φωσφορικού νατρίου η υδρόλυση των αρχικά σχηματισθέντων κρυστάλλων DCPD, οδήγησε στον σχηματισμό ψευδομορφικών κρυστάλλων OCP οι οποίοι και σχηματίζουν στρώμα περίπου 100 μm, το οποίο καλύπτει πλήρως την επιφάνεια του μαρμάρου και παρουσιάζει εξαιρετική πρόσφυση στην επιφάνεια. Οι δοκιμές διάλυσης σε ακόρεστα διαλύματα, έδειξαν ότι διαλύεται μόνο η επικάλυψη. Υπαίθρια Έκθεση. Επαληθεύθηκε η ανασταλτική δράση του HΕDP στην διάλυση των δοκιμίων του μαρμάρου τα οποία εκτέθηκαν στους σταθμούς υπαίθριας έκθεσης. Γενικά, οι τασιενεργές ουσίες που δοκιμάσθηκαν προστάτευσαν τα δοκίμια του μαρμάρου σε μεγαλύτερο βαθμό από τις υδρόφοβες ουσίες γεγονός το οποίο υπογραμμίζει την σημασία της αλληλεπίδρασης ουσίας-υποστρώματος και το οποίο είναι σε συμφωνία με τα ευρήματα από τα πειράματα που διεξήχθησαν στους αντιδραστήρες batch.. Θάλαμος αλατονέφωσης. Σε συνθήκες επιταχυνόμενης διάβρωσης, επαληθεύθηκε για μια ακόμα φορά η ανασταλτική δράση ουσιών όπως το HΕDP, οι οποίες μπορούν να αλληλεπιδράσουν με το μάρμαρο. Είναι αξιοσημείωτο ότι τα αποτελέσματα των μετρήσεων της κινητικής της διάλυσης τα οποία ελήφθησαν από την υπαίθρια έκθεση δοκιμίων ήσαν συγκρίσιμα με τα αποτελέσματα των μετρήσεων σε αντιδραστήρες τύπου batch. . Η μέθοδος μέτρησης της κινητικής της διάλυσης σε ακόρεστα διαλύματα και σε συνθήκες σταθερού κορεσμού, έχει τη δυνατότητα σε μικρό σχετικά χρονικό διάστημα να δώσει ικανοποιητικές πληροφορίες σχετικά με τη συμπεριφορά των δοκιμίων μαρμάρου σε διαβρωτικό περιβάλλον αλλά και να χρησιμεύσει σε δοκιμές ελέγχου και προκαταρκτικής αξιολόγησης (screening) σειράς υποψήφιων για την προστασία του μαρμάρου ουσιών. / A significant number of historic monuments and artworks have been made of stone, mainly of marble, lime and silicate materials. The work in the present thesis, is focused on the investigation of the kinetics of marble dissolution under various conditions. These studies contribute to the understanding of the mechanism of dissolution, for of calcitic and dolomitic marbles. Understanding the mechanism of the problem is essential for the selection and the implementation of methods for the protection of monuments. More specifically, in the present work it was attempted to achieve the following tasks: a) Determination of dissolution mechanism, through measurements of the kinetics of marble dissolution in solutions undersaturated with respect to the main component (calcite, dolomite) under various undersaturation conditions at controlled conditions. b) Dissolution inhibition by addition of water soluble compounds and investigation of the mechanism of their interaction with the calcitic surfaces. c) Formation of potentially protective coatings on marble surface consisting of sparingly soluble inorganic salts. d) Comparison of marble dissolution rates (in the presence and in the absence of different water soluble substances) with the respective values reported in the literature and with results from marble specimens exposed outdoors or under accelerated weathering conditions in a salt spray chamber (with or without other agents, including colonization with microorganisms, treatment with biocides). The aim of this comparison was the selection of the best model for the reliable testing of novel methods and materials for the protection of marble. Three marble types were selected in the present investigation. These types have been frequently used as building materials in monuments and sculptures in Europe: Carrara (>98% calcite), Pentelic (>98% calcite) and Ekeberg (>93% dolomite). A number of compounds were selected for the investigation of their effectiveness of protection against marble weathering due to wet precipitation: VPA3-7 (surfactant) and HEDP (organophosphorus compounds), Hydrophase superfici (hydrophobic substannce) and Algophase  (biocide). To study the effect of microorganisms on the weathering of marble specimens exposed outdoors, they were inocculated with a bacteria culture consisting of (Geodermatophilus sp BC 508 isolated from limestone rock (Noto, Syracuse, Italy) , Micromonospora sp. BC 562 isolated from Pentelic marble), fungi (Coniosporium apolliniis MC518 isolated from marble from Tarragona Cathedral (Spain) and Coniosporium uncinatum MC557 isolated from Carrara marble statue (Messina, Italy).) The aim of the measurements of the rates of marble dissolution in solutions undersaturated with respect to calcite, as a function of the relative undersaturation was the attainment of a better understanding for the mechanism underlying marble dissolution. Undersaturated working solutions were prepeared by dilution of proper stock solutions of CaCl2, MgCl2, NaHCO3, NaCl, and pH was initially adjusted to 8.25 with 0.01N NaOH. After equilibration of undersaturated solutions in the reactor, known amount of marble was introduced, either in powder form (suspension) or in rod form (fixed on special scaffold). Depending on the control of the parameters possible the following types of experiments were done and the dissolution rates were measured: free drift (all variables change with the exception of temperature), constant pH (pH only is kept constant), constant undersaturation (the activities of all species in the undersaturated solutions are kept constant). The dissolution rates of calcitic marble (both in powders and slabs) and calcite powder showed linear dependence on the relative undersatutation. In all cases, the rates of dissolution were of the same order of magnitude with the rates corresponding to (synthetic) calcite powder. Thermal pretreatment of pentelic marble powder resulted to higher dissolution rates. In this case, the dependence of the rates measured with respect to the relative undersatutation was found to be non-linear, (R=Kdσn , n>1). In the case of Ekeberg marble, the dependence of the rates of dissolution on the relative undersatutation was found to be non-linear, as well with n = 2. It may therefore be concluded that the dissolution is surface diffusion controlled. In the present work, solubilities for different types of marbles investigated in aqueous solutions were calculated from measurements of specimens equilibrated with electrolyte solutions over a time period exceeding the 2 years. For Pentelic and Crystallina Thassou marbles, values of solubility products were close to the value of pure calcite, while those for the rest of the calcitc marbles (Carrara, Spilia, Dionysoy) were higher. For the dolomitc marbles Ekeberg and Thassos White, the values obtained were almost identical and close to the values reported for stoichiometric dolomite. In all cases, the rate of dissolution was found to be controlled by surface diffusion. The adsorption of a substance on marble surface could possibly affect the dissolution process. The adsorption of substances posessing ionisable phosphate and phosphonate groups on marble powders (Pentelic, carrara, Ekeberg) was investigated through the respective adsorption isotherms. HEDP was mainly studied in this section, because its presence in undersaturated solutions inhibited dissolution to a large extent, and also because it could be considered as a model substance for the investigation of the effect of substances with similar functional groups on crystalline solids with metal cations on their surface. The presence of HEDP in the undersaturated solutions resulted in the reduction of the marble dissolution rates, proportionally to the extent of HEDP adsorption on the substrate. The dissolution rates obtained were lower than those obtained in experiments were HEDP was pre-adsorbed on the substrate (both in marble powder and in marble rod tests). HEDP showed strong inhibition effect (even by 80-90%) but also showed negative effect on the morphology marble crystallites. The aim of the next series of experiments was the formation of coatings on pentelic marble slabs. The coatings tested in the present investigation, consisted of inorganic salts , less soluble than calcite. Treatment solutions (HCl, ΕDTA, lactic acid, H3PO4, HEDP, NTMP , N(phosphomethyl-) imino diacetic acid) were applied by:a) brush, b) impregnated patch and c) immersion. The most effective way was impregnation. XRD, FT-IR and SEM were used for the characterization of the surfaces and of the composition of the coatings. The “new” composite (marble + coating) materials were then subjected to dissolution experiments in solutions undersaturated with respect to calcite. Treatment of marble with phosphoric acid resulted in formation of a thick layer of CaHPO42H2O, DCPD. Following a second treatment with sodium hydrogen phosphate solution, the iniatially formed DCPD crystals were hydrolyzed to pseudomorfic OCP crystals, resulting to a layer of 100 um thickness with complete coverage of the surface and good adhesion on the substrate. Dissolution experiments showed that only the coating was dissolved. T Outdoors exposure. The inhibiting effect of HEDP on dissolution was verified in the case of the exposed marble specimens. The surfactant substances tested seemed to protect the specimens more than the hydrophobic compounds, which empasizes the importance of substance-substrate interaction and is in good agreement with batch experiment results. Salt spray chamber. The inhibiting effect of HEDP on dissolution was again verified in the case of the marble specimen exposedunder accelerated weathering conditions. Results of the measurements of the kinetics of marble dissolution obtained from outdoors exposure tests of marble slabs, were comparable to those obtained from batch reactor experiments. Measurement of dissolution kinetics in working solutions under constant undersaturation conditions is a method capable of providing satisfactory information on the behaviour of marble specimen under weathering conditions and a useful tool on testing and evaluating the efficiency of candidate protective methods and products in a short time (suitable as preliminary screening tool).

O estudo do interior da Terra apresenta diversos desafios, principalmente devido à impossibilidade de observações diretas de suas propriedades. Ondas sísmicas liberadas por terremotos são a melhor fonte de informação sobre a estrutura do planeta, mas sua correta interpretação depende do conhecimento das propriedades de seus elementos constituintes. Entretanto, estes estudos devem ser feitos nas condições extremas de temperatura e pressão do interior terrestre, condições difíceis de serem alcançadas em laboratório. Neste contexto, o estudo teórico de materiais tem sido muito importante na elaboração de modelos sobre a estrutura interna da Terra e na correta interpretação de dados sísmicos. Pesquisas recentes têm mostrado que a quantidade de carbono no manto inferior da Terra é maior do que se pensava anteriormente, e é importante compreender seus efeitos no interior profundo da Terra. Apesar da importância de entender os efeitos do carbono no interior da Terra, existem poucos estudos deste elemento nestas condições extremas de pressão e temperatura. Neste trabalho, utilizamos métodos e técnicas da física do estado sólido para estudar as propriedades de compostos de carbono nas condições de pressão e temperatura do manto inferior terrestre. Estudamos, primeiramente, as propriedades estruturais, eletrônicas e elásticas do MgSiO3 nas estruturas perovskita e pós-perovskita, considerado o principal mineral do manto inferior. Os resultados obtidos para as velocidades acústicas neste mineral mostraram variações maiores em relação às direções cristalinas, quando comparadas com mudanças devido à transição de fase estrutural. Isso indica que uma orientação preferencial dos eixos (anisotropia) pode ajudar a explicar algumas regiões com aumento descontínuo nas velocidades sísmicas. Posteriormente, foram obtidas as propriedades do MgCO3 e do CaCO3 em suas estruturas mais estáveis, em função da pressão. Nossos resultados foram comparados com os do MgSiO3 , mostrando que carbonatos de cálcio e de magnésio são estáveis nas condições do manto terrestre e que sua formação é energeticamente favorável. Resultados dos cálculos dos coeficientes elásticos e das velocidades acústicas nestes minerais mostram que as velocidades são menores que aquelas no MgSiO 3 . Dessa forma, em regiões ricas em carbono deve ocorrer a formação destes carbonatos e, por conseguinte, as velocidades sísmicas seriam menores nessas regiões. Isso pode explicar a existência das zonas de baixa velocidade na fronteira do manto inferior com o núcleo. Foram estudadas, também, as consequências da introdução de efeitos térmicos. Entretanto, obteve-se que os resultados não apresentam alterações significativas, de modo que mesmo nas altas temperaturas do interior da Terra nossas conclusões permanecem válidas, onde propomos que as regiões de baixa velocidade no manto inferior possam ser provocadas pela presença de carbono na forma de carbonatos e que a formação destes seria um modelo adicional para explicar onde e como o carbono pode ser armazenado no manto profundo. / Investigations on the Earths interior face several challenges, especially due to the infeasibility of direct observations of its properties. Earthquake seismic waves are the best information source about our planets structure, but its correct interpretation depends on the knowledge of its forming elements. However, these studies must consider the extreme pressures and temperatures of the Earths interior, hard to achieve experimentally. In this way, theoretical methods have emerged as an essential tool in elaborating models for the Earth internal structure and in the correct interpretation of seismic data. Recent studies have shown that the Earth must have much more carbon than previous thought, and it is important to understand its effects on the Earths deep interior. Despite its importance, there are few studies on carbon in these extreme conditions of pressure and temperature and on its effects in the Earths interior. In this investigation, we use theoretical solid state physics methods to investigate the properties of carbon compounds in the pressure and temperature conditions of Earths deep interior. First of all, we studied the electronic and elastic properties of MgSiO3 in the perovskite and post perovskite structures. This silicate is considered the main mineral in the Earths lower mantle. Our results show that seismic velocities have a larger variation with respect to the propagation direction than that with the phase transition. This indicates that a lattice preferred orientation can explain some seismic discontinuities. Thereafter, the properties of the MgCO3 and CaCO3 minerals were obtained in their more stable structures with respect to pressure. The results were compared with those of the MgSiO3, showing that calcium and magnesium carbonates are stable in the Earths mantle and that their formation is energetically favorable. The elastic coefficients and the acoustic velocities in these carbonates show seismic velocities considerably lower than those in the MgSiO3 . In this way, in regions with high carbon concentration the formation of carbonates could favorably occur and therefore the seismic velocities would be lower in those regions. This may explain the existence of low velocity zones near the bottom of Earths lower mantle. We also studied the consequences of the introduction of thermal effects. However, our results do not show any significant variation with temperature. Hence, even in the high temperatures of Earths interior, our conclusions are still valid where we propose that low velocity regions can be caused by the presence of carbon in the form of carbonates. Its formation could provide an additional model to explain where and how carbon can be stored in the deep mantle.

Polycrystalline geological materials are not normally single phase materials and commonly contain second phases which are known to influence the grain size and mechanical properties of bulk material. Despite the well documented significance of second phases, there are relatively few detailed systematic experimental studies of the effect of second phases on isostatic high temperature grain growth in geological materials. Grain growth is a process that is fundamental to our understanding of how rocks behave in the lower crust / upper mantle where grain size is considered to play an important role in the localization of deformation in addition to determining the strength of materials at these pressure and temperature conditions. Furthermore, the effect that the spatial distribution and grain size of the second phases have on the mechanical properties of rocks is generally acknowledged, but it is not well constrained. Spatial variation is particularly significant in geological systems where a strength contrast exists between phases. With these two things in mind, a two-part study is presented in which the influence of a pore second phase on the microstructural evolution of halite during grain growth (Part I), and the influence of a calcite second phase on the mechanical behaviour of two phase calcite + halite aggregates (Part II), is investigated. In Part I, high temperature (330 °-600 °C), high confining pressure (200 MPa) isostatic grain growth experiments were carried out on 38-125 μm reagent grade halite (99.5%+ NaCl) powder over durations of 10 secs up to 108 days. After hot-pressing, the halite displays a foam texture. Some porosity remained along the grain boundaries, the size and distribution of which appears to impact significantly on the resulting grain size, growth mechanism and kinetics of halite grain growth. Halite grain growth was found to be well described by the normal grain growth equation: d^(1/n)-d0^(1/n)=k0(t-t0)exp(-H/RT) where t is the duration of the growth period, t0 is the time at which normal growth begins, d is the grain size, d0 is the grain size at t0, k0 is a constant, H is the activation enthalpy for the growth controlling process, R is the universal gas constant,T is temperature and n is a growth constant. At 330 °-511 °C, the data is best described by n = 0.25 indicating growth controlled by surface diffusion around pores that lie on the grain boundaries. An activation enthalpy of 122±34 kJ/mol was obtained using the grain size data from these data sets. At 600 °C the data is best described by n = 0.5, suggesting that a transition to interface controlled growth takes place between 511 °C and 600 °C. To investigate the impact of porosity, the Zener parameter (Z = pore size/pore volume fraction) was determined for individual grains in 10 samples. A general trend of increasing with increasing halite grain size is observed, indicating pore elimination keeps pace with pore accumulation in the growing grains. In some samples, the largest grains display a decrease in the Zener parameter corresponding with an increase in pore volume fraction. These grains are interpreted as having experienced a short-lived, abnormal growth phase shortly after t0 during which pore accumulation outpaced pore elimination. A model of pore controlled grain growth is proposed with a view to explaining these observations. In Part II, calcite + halite aggregates of constant volume fraction (0.60 calcite : 0.40 halite) and varying calcite clast size (6 μm 361 μm) were axially deformed to <1% bulk strain at room temperature in a neutron diffraction beamline. Elastic strain and stress in each phase was determined as a function of load from the neutron diffraction data. The strain (and stress) behaviour correlates well with the microstructural parameters: 1) halite mean free path and 2) calcite contiguity. Both phases behaved elastically up to aggregate axial stresses of 20-37 MPa, above these stresses the halite yielded plastically while the calcite remained elastic. Once yielding began, the rate of enhanced load transfer from halite to calcite with increasing applied load decreased with halite mean free path and increased calcite with contiguity. A Hall-Petch relationship between halite mean free path and aggregate yield stress was observed.

Concrete is a brittle material prone to cracking due to its low tensile strength. Crack repairs are not only expensive and time-consuming but also increase the carbon footprint. Designing a novel concrete material possessing the ability to self-repair cracks would enhance its sustainability. Self-healing can be defined as a material’s ability to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on an optimized mix composition, or autonomous, when additional capsules containing some healing agent and/or bacteria spores are incorporated into the binder matrix. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria precipitating calcite which are released into the crack from a broken capsule or activated by access to water and oxygen. The main disadvantages of the autonomous method are the loss of the fresh concrete workability, worsened mechanical properties, low efficiency, low survivability of the capsules and bacteria during mixing and the very high price. On the other hand, the autogenous self-healing was found to be more efficient, more cost effective, safer, and easier to implement in full-scale applications. Knowledge related to mechanisms and key factors controlling the autogenous self-healing is rather limited. Therefore, the aim of this research work was to better understand the autogenous self-healing process of concrete and to optimize the mix design and exposure conditions to maximize its efficiency. This licentiate thesis summarizes the main findings of the first 2.5 years of the PhD project. Several factors affecting autogenous self-healing were studied, including the amount of unhydrated cement, mix composition, age of material, self-healing duration and exposure conditions. The process was investigated both externally, at the surface, and deeper inside of the crack, by evaluating the crack closure and chemical composition of formed self-healing products. In addition, the flexural strength recovery was also studied. It was observed that a large amount of cement in the concrete mix does not ensure an efficient autogenous self-healing of cracks. A very dense and impermeable binder microstructure limited the transport of calcium and silicone ions to the crack and diminished the precipitation of the healing products. Addition fly ash increased the crack closure ratio close to the crack mouth, but its presence did not support the recovery of the flexural strength, presumably due to a very limited formation of load bearing phases inside the crack. Calcium carbonate was detected mainly at the crack mouth, whereas calcium silicate hydrate (C-S-H) and ettringite were found deeper inside the crack. The formation of C-S-H and ettringite presumably resulted in a regain of the flexural strength. On the other hand, calcite crystals formed close to the surface of the specimen controlled conditions inside the crack through its external closure. Healing exposure based on pure water appeared to be inefficient even despite the application of different temperature cycles and water volumes. The application of a phosphate-based retarding admixture in the curing water resulted in the highest self-healing efficiency. The admixture presumably inhibited the formation of a dense hydration shell on the surface of the unhydrated cement grains and promoted the precipitation of calcium phosphate compounds inside the crack. In addition, water mixed with microsilica particles caused a regain of the flexural strength through formation of C-S-H in the crack.