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This thesis investigates montmorillonite clay particles, which are plate-like and have a hydrophilic surface, a high surface charge and a high specific area. Four studies were carried out and new results relating to polyetheramine adsorption on clay, clay suspension structure and clay-stabilised emulsions are reported. Protonated amines are known to adsorb to clay due to charge interactions. However the adsorption of polymers with primary amine end group at high pH has not previously been studied. We carry out the first such study on the adsorption of polyetheramines at a pH higher than the pKa of the amines. Our results reveal that the adsorption happens via an ion-exchange mechanism. In the adsorption process, the primary amine end-groups get protonated and release hydroxyl ions. The adsorbed molecules adopt a touching mushroom configuration. The effect of the polyetheramine adsorption on the suspension was initially observed due to the obvious change of suspension viscosity. At full coverage of the polyetherarnine, rheological data reveal that the sol/gel transition of the suspension is shifted from 3wt% to 6 wt% clay. Using scattering techniques, large scale string-like structures are found in the bare clay suspensions, which subsequently disappear upon the addition of polyetheramine. This thesis also includes the study of clay particles at interfaces. Surface-modified clay particles are found to stabilise oil-in-water Pickering emulsions. The clay particles at the droplet surface are found to adopt an orientation parallel to the droplet surface, and there are on average four layers of clay particles at the interface. Using Pickering emulsions as a template, well-defined clay microcapsules were prepared by cross-linking the clay particles at the droplet surface. The conclusion on clay orientation is further substantiated by direct observation of the microcapsule surface using SEM.

The importance of Tricalcium Silicate (3CaO. SiO2 ) arises from its occurrence in Portland Cement. Portland Cement is manufactured by the sintering in a rotary kiln of a mixture usually of limestone and clay. The final product is such that the oxides CaO, MgO, Si02,1-1l203 and Fe203 together account for from 95-99-5% of the whole. Tornebohm, examining the clinker of Portland cement under the microscope, distinguished four components, the most important of which he named 'Alite'. Towards the end of the 19th century, Le Chatelier showed that it had the probable formula 3Ca0., Si02. The controversy which subsequently arose over the question, "What is Alite? " has lasted until the present day. Bogue, in his recent book (1947) has summarised the main features of this controversy. Although he gives a reference in a footnote (pg. 116) to one paper since 1931 on this subject, he considers that the controversy had ended by that date and quotes Guttmann and Gille (1931) as closing the debate with the following statement: 'Alite, the chief constituent of high-lime Portland cement is neither (a) a lime-enriched dicalcium silicate (Dyckerhioff) nor (b) a solid solution of a lime-rich aluminate or Janeckite and 3Ca0.Si02 (Kuhl), nor (c) a solid solution chiefly of 3Ca0. Si02 and 3Ca0. A1203 (Guttmann and Gille), nor (d) a solid solution of Janeckite and 2CaO. Si02 (Janecke), nor (e) essentially 2Ca0. Si02 (Nacken) but Alite is tricalcium silicate. Thus, after fifty years, the question "What is Alite? " has been answered'. BY 1939, however, evidence (summarised in the next section) already existed showing that C38* could take up other constituents in solid solution, and some of the evidence indicated that this was accompanied by a change in structure.

The study aimed to enhance the textural properties of the synthetic hectorite clay Laponite RD. In the early 1990s Mobil Research and Development Corporation produced the first ordered mesoporous molecular sieves. This family of materials, M41S, were fabricated via liquid crystal templating (LCT), a technique involving the condensation and hydrolysis of a silica source around an organic template. As clays are primarily silicates, the question arises "Why not apply the same principles to enhance porosity characteristics of other silicates such as clays?" Optimization of reagent concentrations, template choice, synthesis protocol and template removal strategy led to a maximum total pore volume of 0.95 cm3 g-1. This was achieved through templating Laponite RD with the neutral surfactant polyoxyethylene (20) sorbitan trioleate (Tween 85). This more than trebled the original total pore volume of Laponite RD, 0.27 cm3 g-1. An increase in modal pore diameter was also observed after use of this template; from 36.6 A to 52.3 A. Synthesis of Laponite-like compounds within the laboratory led to enhancement of porosity characteristics without templating; a total pore volume of 0.44 cm3 g-1 was observed for this synthetic hectorite (KP). Use of a template further enhanced the porosity characteristics of these samples. The cationic surfactant CTMA+ (used in the original Mobil synthesis) led to a total pore volume of 0.60 cm3 g-1 for modified hectorite KP. A similar result, 0.65 cm3 g-1, was achieved through templating Laponite RD with this same surfactant. Sorption and exchange properties of the newly modified hectorites were assessed by simple equilibrium batch testing methods using both single metal and multi-metal solutions. Hectorite KP samples removed a greater percentage of metal ions from aqueous solution than its Laponite RD analogues. For 5 mg dm-3 single element solutions CTMA+ modified hectorite removed > 95% of all eight metals tested. For solutions containing higher concentrations of ions the removal efficiency of all tested clays were reduced due to greater competition between ions. Partial interlayer collapse was observed during powder XRD studies, due to the acidic nature of the metal ion solutions.

The recent development of clay-polymer nanocomposite materials has led to an increased interest in the structure and properties of clay minerals. In this thesis the reactivity of the clay mineral montmorillonite is explored by means of density functional theory based calculations. In particular three aspects are considered: catalytic properties, cation migration and dehydroxylation. The origin of the catalytic properties of the clay mineral is investigated in the context of the synthesis of clay-polymer nanocomposite materials, by in sttu, intercalative polymerisation. It is found that catalysis is most likely to occur at the clay mineral lattice-edge where exposed aluminium atoms act as Lewis acid sites. Migration of lithium cations into the clay mineral lattice is explored by means of first principles molecular dynamics. Comparison of calculated hvdrox-vl stretching frequencies, with those from experiment indicates that cations migrate to vacant octahedral sites, as oppose to the ditrigonal cavities. Dehydroxylation of the clay mineral is examined by consideration of a cis-vacant pyrophyllite structure. It is shown that dehydroxylation leads to formation of a tyan8-vacant structure, with aluminium in trigonal bipyramidal coordination and a highly distorted tetrahedral layer. Differences in the dehydroxylation behaviour of cm and tran8-vacant pyrophyllite are shown to be due to the fact that in the former adjacent hydroxyl groups bridge different pairs of aluminium atoms, while in the latter they are both bonded to the same pair. Overall density functional theory based calculations are shown to be a powerful tool for the studly of the structure and reactivity of clay minerals.

Στην παρούσα διατριβή ειδίκευσης παρασκευάστηκαν πέντε νανοσύνθετα υλικά διοξειδίου του τιτανίου (στη μορφή του ανατάση) – αλλοϋσίτη σε αναλογίες 60:40, 70:30, 75:25, 80:20, 85:15 αντίστοιχα, για την περιγραφή και μελέτη των νέων βελτιωμένων χαρακτηριστικών τους και την εφαρμογή τους ως φωτοκαταλύτες στη διάσπαση αέριων ρύπων. Τα νανοσύνθετα παρήχθησαν με τη μέθοδο κολλοειδούς διαλύματος σε πήκτωμα (sol-gel) χρησιμοποιώντας αλκοξείδιο του τιτανίου (Ti(OC3H7)4) σαν διάλυμα διασποράς-επικάθισης. Οι ιδιότητες του φυσικού δείγματος αλλοϋσίτη (από τις Η.Π.Α.), καθώς επίσης και των τροποποιημένων δειγμάτων, χαρακτηρίστηκαν με τις τεχνικές περιθλασιμετρίας ακτινών Χ (XRD), υπέρυθρης φασματοσκοπίας μετασχηματισμού κατά Fourier (FTIR-ATR), ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) και μέτρησης πορώδους και ειδικής επιφάνειας (BET). Επιτεύχθηκε η διασπορά των νανοσωματιδίων (3-10nm) του διοξειδίου του τιτανίου στην επιφάνεια του αλλοϋσίτη και τα αποτελέσματα της υπέρυθρης φασματοσκοπίας έδειξαν την δημιουργία δεσμών υδρογόνου μεταξύ τους. Τα τροποποιημένα δείγματα έδειξαν αύξηση της ειδικής τους επιφάνειας συγκριτικά με το φυσικό δείγμα και μεσοπορώδη δομή (5,7nm). Η μακροπορώδης δομή του αλλοϋσίτη (εσωτερικό κενό των επιμήκων κρυστάλλων) δεν ανιχνεύτηκε στα νανοσύνθετα διότι καλύφθηκε, εν μέρει, από τα νανοσωματίδια του TiO2 με αποτέλεσμα να προκύψει ένα υλικό με μικρότερο μέγεθος πόρων. Όλα τα νανοσύνθετα (και τα πέντε) έδειξαν ικανοποιητικά αποτελέσματα ως προς τη φωτοκαταλυτική τους ικανότητα στη διάσπαση αέριων ρύπων υπό την επίδραση φωτός του ορατού φάσματος αλλά και υπεριώδους ακτινοβολίας σε σύγκριση με τα αποτελέσματα που έδωσε το πρότυπο TiO2 P25. Όσον αφορά τα οξείδια του αζώτου, υπό την επίδραση της ορατής ακτινοβολίας, το νανοσύνθετο διοξειδίου του τιτανίου - αλλοϋσίτη σε αναλογία 70:30, συγκριτικά με το πρότυπο TiO2 P25, έδειξε 16,6 φορές καλύτερα αποτελέσματα ενώ υπό την υπεριώδη ακτινοβολία η φωτοκαταλυτική του ικανότητα ήταν μεγαλύτερη κατά 1,83 φορές. Στο τολουόλιο 4,8 φορές καλύτερα αποτελέσματα έδειξε το νανοσύνθετο με αναλογία 75:25. Η αυξημένη φωτοκαταλυτική δράση των νανοσύνθετων σε σχέση με τον πρότυπο φωτοκαταλύτη οφείλεται κυρίως στην καλή διασπορά των ννοκρυστάλλων ανατάση στις επιφάνειες του αλλοϋσίτη. / Five TiO2-halloysite nanocomposites (Ti-Hall 60:40, 70:30, 75:25, 80:20, 85:15) were prepared by depositing TiO2, in the form of anatase, on the halloysite surfaces using titanium isopropoxide under hydrothermal treatment at 180˚C. The nanocomposites were characterized by X-Ray diffraction (XRD), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and N2 specific surface area (SSA) analysis by BET method. Good dispersion of 3-10nm TiO2 particles on halloysite external surfaces was achieved in the TiO2- halloysite nanocomposites and ATR-FTIR results showed the formation of hydrogen bonding between TiO2 and the outer surfaces of halloysite tubes. After treating with TiO2, the nanocomposites largely showed interparticle mesopores of about 5.7nm. However, the macropores of halloysite (lumen or central hole in halloysite tubes) were not detected as a result of plugging of the lumens in halloysite tubes by TiO2 nanoparticles, at least partially. These nanocomposites were tested for their photocatalytic activities in decomposing NOX gas under visible-light irradiation and UV-visible light irradiation compared to that of the standard commercial titania photocatalyst, P25. Generally the nanocomposites showed significantly increased photocatalytic activities, while the most effective nanocomposite in decomposing NOX gas was the Ti-Hall 70:30 (16.6 and 1.83 times in visible light and UV respectively) and for tolouene the Ti-Hall 75:25 (4.8 times) compared to the commercial titania. The enhanced photocatalytic activities observed in the nanocomposites are a result of the good dispersion of the TiO2 nanocrystals on the surface of the halloysite.

Les matériaux et minéraux argileux, abondent au Gabon. Les travaux pionniers révèlent la présence d’argiles rouges dans la série barrémienne de l’Agoula et d’argiles rouges à violettes dans la série néocomienne de Ndombo. Les argiles constituent une ressource précieuse et abondante qui a été largement valorisée tant en constructions traditionnelles de terre crue qu'en terre cuite en divers endroits du pays. Les présentes recherches sont initiées pour inventorier les ressources en différentes argiles facilement accessibles au Gabon, et dédiées à sélectionner des gisements à potentiel applicatif, selon la nature des argiles. Ce travail a été réalisé dans les régions de Libreville et de Tchibanga. Les échantillons prélevés font l’objet d’analyses macroscopique, microscopique, chimique, structurale et superficielle. Des essais de formulation font l’objet d’applications dans les domaines des briques, tuiles et celui des réfractaires. La croissance démographique de la République Gabonaise engendre une demande importante en divers matériaux locaux qui satisfassent les besoins de la vie courante. L’accent est mis sur les applications relatives aux terres cuites : briques, tuiles et carreaux. Des zones d'intérêt à potentiel économique sont identifiées. Les argiles de la région de Libreville, riches en kaolinites et illite sont intéressantes pour des applications en terre cuite. La caractérisation des propriétés minéralogiques des roches argileuses, est réalisée dans le but d'identifier les usages industriels les plus intéressants. Les caractérisations et les tests d’applications, identifient des matières premières pour la construction, la céramique, mais aussi dans bien d'autres domaines comme la pharmacologie (galénique), la papeterie, la cosmétique, l’agro-alimentaire, le caoutchouc, la peinture, le génie civil, le génie de l’environnement. Comme dans tous les pays d’Afrique Centrale, le développement durable passe inéluctablement par une maîtrise des ressources locales. La caractérisation fine des argiles du crétacé de Libreville est réalisée par : diffraction des rayons X, spectrométrie infrarouge à transformée de Fourier, microscopie électronique à balayage, détermination de la capacité d’échange cationique, granulométrie, analyses chimiques, indice de plasticité, test de céramique. Selon la diffraction des rayons X, ces argiles sont à kaolinite, et/ou illite et montmorillonite, quartz, ± muscovite, ± microcline, ± hématite, ± rutile, ± anatase. L’observation en Microscopie Electronique à Balayage et le traitement à l’Ethylène Glycol ou chauffé à 550°C analysé en DRX confirme la présence prépondérante de ces minéraux / Materials and clayey minerals abound in the Gabon. The pioneers works reveal the presence of red clays in the barrémian series of Agoula and red clays with violets in the neocomian series of Ndombo. Clays constitute a precious and plentiful resource which was widely beneficiated as well in traditional constructions of green clays as in terra-cotta in diverse places of the country. The present researches aim at inventorying the resources in various clays easily accessible in Gabon, and in the study of selection of deposits with application potential, according to the nature of clays. This work is carried on in the regions of Libreville and Tchibanga. The collected samples are the object of macroscopic, microscopic (tiny), chemical, structural and superficial analyses. Trials of formulation are the object of applications in the domains of bricks, tiles and refractories. The population growth of the Gabonese Republic generates a demand in diverse local materials satisfying the needs for the current life. The emphasis is put on the applications concerning terra-cottas: bricks, roof tiles and floor tiles. Zones of interest with economic potential are identified. Clays of the region of Libreville, rich in kaolinites and illite are interesting for applications in terra-cotta. The characterization of the mineralogical properties of the clayey rocks is realized with the aim of identifying the most interesting industrial uses. Characterizations and tests of applications, identify raw materials for the construction, the ceramic, but also in many other domains as pharmacology (galenic), paper industry, cosmetics, food-processing industry, rubber, paint, civil engineering and environment engineering. As in all the countries of Central Africa, the sustainable development passes inevitably by a control of the local resources. The fine characterization of clays of the Cretaceous of Libreville is realized by: X-ray Diffraction, Fourier transform infrared spectroscopy, scanning electronic microscopy, determination of the cation exchange capacity, particle size analysis, chemical analyses, plasticity index, ceramic tests. According to the X-ray diffraction, these clays are mixtures of kaolinite, and/or illite and montmorillonite, quartz, ± muscovite, ± microcline, ± hematite, ± rutile ± anatase. The observation in Scanning Electron Microscopy and the treatment with Ethylène Glycol or heating at 550°C in XRD confirms the dominating presence of these minerals

Les suspensions minérales de particules fines sont connues pour leur comportement non-Newtonien pendant l'écoulement. Les interactions particule-particule dans de tels systèmes (c’est-à-dire, suspensions minérales) ne sont pas limitées au contact physique, e.g. collision et frottement. La capacité des minéraux de développer une charge dans l'environnement aqueux justifie des comportements différents des systèmes similaires de première vue. C’est à dire qu’étant caractérisées avec la même fraction volumétrique, composition chimique et granulométrie des solides et densité de dispersant, deux suspensions peuvent montrer un comportement rhéologique différent en raison de la chimie de la solution. Dans ce cas, la composition ionique du dispersant définira la charge des particules, et donc le degré d'agglomération/dispersion dans la suspension. Les argiles phyllosilicates sont connues pour être particulièrement problématiques dans les processus de valorisation des minéraux. L’origine de ces minéraux phyllosilicates implique leur inhomogénéité chimique spatiale, ce qui signifie que le bord et la face de la particule montrent des propriétés chimiques et physiques différentes. La présence de tels minéraux dans les dispositifs d'agitation (réservoirs d'agitation, cellules de flottation) est souvent caractérisée par la coexistence de volumes de suspension stagnants et agités, ce qui a un impact négatif sur l'efficacité de l'agitation. Dans ce travail, les suspensions aqueuses diluées de Na-bentonite ont été examinées par vélocimétrie par imagerie par résonance magnétique afin d'étudier l'influence du pH et du type d'électrolyte monovalent sur leur comportement rhéologique local. Les résultats ont montré que les suspensions contenant 0,1% de solide en volume peuvent présenter une bande de cisaillement, une localisation de cisaillement ou aucun phénomène local en fonction de la chimie du milieu de suspension. Il a été suggéré que l’existence d’une «master curve» (ou courbe d’écoulement globale) pour les suspensions diluées dépendait de l’organisation des particules de bentonite dans la suspension, cette organisation est influencée par la chimie de solution et l’historique des contraintes précédentes. Dans l'étape suivante, une seconde et troisieme phases minérales (hématite et quartz) ont été ajoutées dans la matrice de bentonite. L’intérêt dans tels systèmes est lié au comportement sous écoulement des matrices formées avec des types de contacts différents entre particules. Les types de contacts établis dans les suspensions avec une chimie différente du milieu ont été discutés, ainsi que leurs propriétés d’écoulement / Fine particle mineral slurries are known to exhibit non-Newtonian behavior under the load. The particle-particle interactions in such suspensions go beyond physical contact due to the collision and friction. An ability of minerals to gain the charge in the aqueous environment justifies different behaviors of the similar systems. Being characterized with the same volumetric fraction, chemistry and particle size distribution of solids, and specific gravity of dispersing media, two suspensions can possess different rheological behavior due to the chemistry of the solution. In this case, the ionic composition of the media defines particle charging, and thus the degree of agglomeration/dispersion in the suspension. Phyllosilicate clays are known to be particularly problematic in the mineral beneficiation processes. Their nature leads spatial chemical inhomogeneity, meaning that the particle edge and face possess different chemical and physical properties. The presence of such minerals in the stirring devices (stirring tanks, flotation cells) is often characterized with coexistence of stagnant and agitated volumes of slurry, which negatively impacts the efficiency of stirring. In this work, the dilute aqueous Na-bentonite suspensions were examined via magnetic resonance imaging velocimetry to investigate the influence of pH and type of monovalent electrolyte on their local rheological behavior. The results indicated that suspensions with 0.1 vol.% solid can exhibit shear banding, shear localization or no local phenomenon as a function of chemistry of the suspending media. It was suggested that the existence of master curve (or global flow curve) for dilute suspensions was dependent on the bentonite particle organization in the suspension, which was influenced by the chemistry of the environment and the previous flow history. In the next step, second mineral phase (hematite or quartz) was added to the bentonite matrix. The interest in examination of such systems is related to the flow behavior of matrix formed with different kinds of inter-particle contacts. For example, at pH 4 the resulting electrostatic interaction between positively charged bentonite edge and negatively charged quartz is attractive, whereas at the same pH it is repulsive with the positively charged hematite. These electrostatic interactions result in different organization of matrix particles around another mineral phase. In the system with solely repulsive interactions between all sites of all mineral phases (e.g., quartz and bentonite, pH 10) the deviation from Newtonian behavior is justified by the shear-induced particle rearrangements, collision and friction. The difference in the arrangement of bentonite particle aggregates around the hematite or quartz particles was observed using SEM. As a next step the third mineral phase was added. The types of contacts established in the suspensions with different chemistry of the media were discussed along with their flow propperties

Thesis (Ph.D (Physics)) --University of Limpopo, 2005 / We have derived a potential model for °uorapatite Ca10(PO4)6F2, ¯tted to structure, elastic constants and vibrational frequencies of the phosphate groups, which is compatible with existing calcite and °uorite potential mod- els. We then modelled the structure and stabilities of the dry and hydrated f0 0 0 1g, f1 0 1 0g, f1 0 1 1g, f1 1 2 0g, f1 0 1 3g and f1 1 2 1g surfaces, which calculations con¯rmed the experimental dominance of the f0 0 0 1g surface, which is prominently expressed in the calculated thermodynamic morphologies. The dehydrated morphology further shows the experimental f1 1 2 1g twinning plane, while the f1 0 1 0g cleavage plane is expressed in the hydrated morphology. Molecular adsorption of water has a stabilising e®ect on all six surfaces, where the surfaces generally show Langmuir be- haviour and the calculated hydration energies indicate physisorption (73 - 88 kJ mol¡1). The chains of °uoride ions surrounded by hexagonal calcium channels can become distorted in two major ways during relaxation: either by a shortening/lengthening of the FF distances, when the channel is perpendicular to the surface, or by distortion of the CaF bonds when the channel is parallel to the surface. Both distortions occur when the channel runs at an angle to the surface. Other relaxations include compression of the calcium sub-lattice and rotation of surface phosphate groups. We have modelled adsorption of a range of organic molecules onto dif- ferent °uorapatite surfaces, due to the importance of organic/ inorganic in- teractions in biological situations. We have selected organic molecules that represent a model for the carboxylic acids, alkyl hydroxamates and those 3 that contain both the aldehyde and hydroxyl functional groups. Adhesion of these organic molecules on the surfaces has shown strong interaction between the surface's Ca ions and the molecule's oxygens, more especially the car- bonyl oxygens than any other interactions. It was found that the number of interactions between the ions of adsorbate molecule and the mineral surfaces thus contribute signi¯cantly to the exothemicity of adsorption. Further more, simulations of apatite thin ¯lms at a range of ®-quartz surfaces have shown how the strength of adhesion between thin ¯lms of ap- atite material and ceramic silica surfaces is crucially dependent upon both the orientation of the ¯lm relative to the substrate and the nature of the silica surfaces, a ¯nding that is important in a wide number of applications, from basic geological research on intergrowth of phosphate and silicate rock minerals to the search for more e®ective surgical implant materials. It was shown that although the unrelaxed quartz surface is more reactive toward the apatite ¯lm, the more regular thin ¯lm structures grown at the pre-relaxed quartz surfaces lead to more stable interfaces. Film growth at the unrelaxed quartz surface is energetically increasingly unfavorable, whereas growth at the pre-relaxed surface is calculated to continue beyond the ¯rst layer, where the adhesion energy is convergent with the layer growth of the thin ¯lm. Ad- hesion of apatite thin ¯lm on hydroxylated surfaces of ®-quartz has shown to be energetically less favourable than at dry surfaces. This was because the thin ¯lm interact mainly with the hydroxyl ions on the surface of quartz. However, the adhesion energy is still convergent with layer growth of the thin ¯lm on the hydroxylated surfaces. / National Research Foundation of South Africa (NRF), Council for Scientific and Industrial research (CSIR), and the University of the North