Mineral textures, preserved in the metamorphosed sedimentary sequences that are exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. In this thesis the textural record of anatexis and melt transfer in the Himalayan metamorphic core is decoded and the controls that these processes exert on the tectonic evolution of the Himalaya are explored. The problem is divided into two parts, corresponding to variations in protolith lithostratigraphy: melt source - the pelitic region where melt was first generated, and melt sink - the psammitic region where melt accumulated and crystallised. Dehydration melting of muscovite has long been recognized as a critical reaction for the generation of anatectic melt in the Himalaya, but a textural understanding of how this reaction progresses is limited by the inherent difficulties in identifying specific reaction products. Using samples collected from the Langtang area in central Nepal, a mechanistic model for muscovite dehydration melting was constructed, and a set of textural criteria were developed, which were used to distinguish peritectic K-feldspar from K-feldspar grains formed during melt crystallisation. Melt is transferred from the source to the sink in two stages: firstly along a pervasive network of mineral grain boundaries, and secondly via a channelised network of sills and dykes in the melt sink where it solidified as leucogranite. Variation in the primary mineral assemblage and appearance of leucogranite bodies reflect the degree of interaction that occurred between the melt and metasedimentary country rock, rather than a change in primary melt composition. The modal proportion of K-feldspar in the melt source requires vapour-absent conditions during muscovite dehydration melting and leucogranite formation, indicating that the generation of large volumes of granitic melts in orogenic belts is not necessarily contingent on an external source of fluids. The crystallisation of hydrous minerals in leucogranite consumes <15.5 % of water released by the breakdown of muscovite. These results indicate that anatexis efficiently dehydrates the middle crust and suggests that the continents have limited potential to store water over geological time.

This thesis concentrates on gaining a fundamental understanding of the crystallisation, phase behaviour, and melting in relatively simple fat/oil blends. This is the first reported study of hot stage microscopy (HSM) experiments on tripalmitin (PPP)/triolein (OOO), 1,3-dipalmitoyl-2-oleoylglycerol (POP)/OOO, and cocoa butter (CB)/hazelnut oil (HZ) systems. The HSM technique allows the visualisation of the initial crystallisation, polymorphic transformations, and melting of fat crystals; melting points can also help identify polymorphic form. Supporting experiments were also performed using differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD). In PPP-OOO samples, HSM visualised for the first time a melt-mediated transformation from β' to β across a small liquid gap between the untransformed (β') and transformed (β) material. This behaviour was not seen with pure PPP. Melting points obtained by HSM for the PPP/OOO system were above those predicted by the Hildebrand equation, but this is attributed to the non-equilibration of concentration gradients within the system. This was evidenced by the fact that a rapid cooling rate (to produce a finer microstructure with smaller crystals, and hence reduce diffusion distances) combined with a slower remelt rate enabled samples to melt close to ideal. Indeed, final melting points obtained via HSM were consistently higher than DSC results across all systems; convection and the more three-dimensional system in DSC (as compared with the two-dimensional HSM system) may have aided melting. The POP/OOO system displayed complex remelting behaviour, especially when warmed at a relatively slow rate; this also resulted in a higher production of β. Liquid oil content was shown to not only be important in aiding transformation of lower forms to β, but also reduced the number of polymorphs observed upon remelting, as compared with pure fat samples. Liquid oil content was also shown to be crucial for transformation to β in the CB/HZ experiments; very few β crystals were seen in pure CB samples. Experiments carried out on DSC for both CB and CB-HZ cooling at 1°C/min or faster produced both α and β' crystals, but for CB-HZ this also then led to some transformation from α to β. The β polymorph was not observed when only β' was formed at slower cooling rates. A curious result was that the effect was stronger the longer the samples were held at 0°C before rewarming, with the α becoming more resilient against transforming to β' and instead transforming directly to β. More extensive transformation to β occurred if the sample was held for 30 min at 18°C or 22°C during the rewarming step. As well as showing differences in melting temperatures, the HSM and DSC results also did not always match with respect to polymorphic form. Small quantities of β crystals were seen in HSM samples that were not always seen in thermograms of equivalent DSC samples. This either highlights the limitations of DSC or suggests that polymorphic behaviour in the more fluid DSC system differs to that in HSM, or both. Growth rate analysis of PPP (in OOO) showed that both reduced supersaturation and supercooling can be correlated with the growth rates of β' and β. Growth rates of β that occurred via the melting of β' were well correlated with driving forces that took into account that the concentration of PPP in the liquid gap between β' and β (from which the β crystal was growing) was limited by the solubility of β' at the sample temperature. Whilst temperature is often seen as a key driver in governing polymorphic transformation, part of the temperature effect may be an indirect effect via the extra amount of liquid content at higher temperatures. The ability of oil to aid transformation to β may be relevant to food systems where this higher polymorphic form is the preferred type, such as chocolate. Potential applications could include producing novel fat blends with relatively stable fat network structures at a lower overall saturate level, or developing blends with bloom inhibiting properties.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Nesta tese, estudamos as propriedades estruturais e dinÃmicas, bem como, a fusÃo de sistemas coloidais. Inicialmente, abordamos o problema de determinar as estruturas de mÃnima energia e o espectro de fÃnons de um sistema de dipolos magnÃticos carregados, organizados em uma estrutura de bicamadas e orientados perpendicularmente ao plano das camadas. Este sistema pode ser sintonizado atravÃs de seis diferentes fases cristalinas, atravÃs da variaÃÃo de parÃmetros tais como a separaÃÃo entre as camadas e/ou a carga e/ou o momento de dipolo das partÃculas. A presenÃa de carga elÃtrica nas partÃculas dipolares à responsÃvel pela nucleaÃÃo de cinco fases onde as camadas nÃo estÃo alinhadas verticalmente e uma fase desordenada, que nÃo sÃo encontradas no sistema em bicamadas de dipolos magnÃticos previamente apresentado na literatura. Estas fases extras sÃo uma consequÃncia da competiÃÃo entre a repulsÃo coulombiana e a interaÃÃo atrativa entre os dipolos em diferentes camadas. As estruturas de mÃnima energia sÃo sumarizadas em um diagrama de fases associado à separaÃÃo entre camadas e a importÃncia relativa entre as interaÃÃes elÃtrica e magnÃtica. Determinamos, ainda, a ordem das transiÃÃes estruturais entre as vÃrias configuraÃÃes de mÃnima energia. O espectro de fÃnons do sistema foi calculado usando a aproximaÃÃo harmÃnica. Um comportamento nÃo-monotÃnico do espectro de fÃnons à encontrado como funÃÃo da interaÃÃo efetiva entre as partÃculas. A estabilidade termodinÃmica das diferentes fases à determinada. Em seguida, estudamos o sistema de bicamadas de dipolos magnÃticos carregados para temperaturas diferentes de zero, investigando a fusÃo do sistema atravÃs do critÃrio de Lindemann modificado, em funÃÃo dos parÃmetros: (i) a distÃncia entre as camadas η e (ii) a intensidade relativa da interaÃÃo magnÃtica com respeito à interaÃÃo elÃtrica λ. Para λ suficientemente grande, uma das fases (a fase hexagonal com alinhamento vertical) exibe um comportamento reentrante na temperatura de fusÃo em funÃÃo de η. Uma vez que a carga e o momento de dipolo magnÃtico das partÃculas coloidais pode ser alterado, por exemplo, pela variaÃÃo do pH da soluÃÃo na qual estÃo imersos e por um campo magnÃtico externo, respectivamente, este sistema pode ser em princÃpio verificado experimentalmente. Por Ãltimo, um sistema bidimensional (2D) coloidal binÃrio consistindo de dipolos interagentes à investigado. Dentro da aproximaÃÃo harmÃnica, calculamos o espectro de fÃnons do sistema em funÃÃo da composiÃÃo, da razÃo entre os momentos de dipolo e da razÃo entre as massas das partÃculas pequenas e grandes. AtravÃs de uma anÃlise sistemÃtica dos espectros de fÃnons, determinamos a regiÃo de estabilidade das diferentes estruturas das ligas coloidais. As lacunas no espectro de frequÃncia dos fÃnons, as frequÃncias Ãticas no limite de longos comprimentos de onda e a velocidade do som sÃo tambÃm discutidos. Usando o critÃrio de Lindemann modificado e dentro da aproximaÃÃo harmÃnica, estimamos a temperatura de fusÃo da sub -rede gerada pelas partÃculas grandes. / This thesis presents the study of the structural and dynamical properties, as well as, melting of colloidal systems. Initially, we study the structure and phonon spectrum of a system of charged magnetic dipoles, organized in a bilayer structure and oriented perpendicular to the plane of the layers. This system can be tuned through six different crystalline phases by changing parameters such as the interlayer separation and/or the charge and/or dipole moment of the particles. The presence of the electric charge on the dipole particles is responsible for the nucleation of five staggered phases and a disordered phase which are not found in the magnetic dipole bilayer system previously presented in the literature. These extra phases are a consequence of the competition between the repulsive Coulomb and the attractive dipole interlayer interaction. The minimum energy structures are summarized in a phase diagram associated to the separation between the layers and to the relative importance between the magnetic and electric interactions. We determine the order of the structural phase transitions. The phonon spectrum of the system was calculated within the harmonic approximation. A non-monotonic behavior of the phonon spectrum is found as a function of the effective strength of the inter-particle interaction. The thermodynamic stability of the different phases is determined. Then, we study the bilayer system of charged magnetic dipoles for nonzero temperatures, investigating the melting behavior of the system through the modified Lindemann criterion, as a function of the parameters: (i) the distance between the layers η and (ii) the relative intensity of the magnetic interaction with respect to the electric interaction λ. For large enough λ, one of the phases (the matching hexagonal phase) exhibits a re-entrant melting behavior as a function of η. Since the charges and the magnetic dipole moment of the colloidal particles can be altered, for example, by changing the pH of the solution in which they are immersed or an external magnetic field, respectively, this system can be in principle verified experimentally. Last, a two-dimensional (2D) binary colloidal system consisting of interacting dipoles is investigated. Within the harmonic approximation, we obtained the phonon spectrum of the system as a function of the composition, dipole moment ratio and mass ratio between the small and big particles. Through a systematic analysis of the phonon spectra, we are able to determine the stability region of the different lattice structures of colloidal alloys. The gaps in the phonon frequency spectrum, the optical frequencies in the long-wavelength limit and the sound velocity are discussed as well. Using the modified Lindemann criterion and within the harmonic approximation, we estimated the melting temperature of the sub-lattice generated by the big particles.

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Thermodynamic relationships are used to predict several physicochemical properties of organic compounds. As described in chapter one, the UPPER model (Unified Physicochemical Property Estimation Relationships) has been used to predict nine essential physicochemical properties of pure compounds. It was developed almost 25 years ago and has been validated by the Yalkowsky group for almost 2000 aliphatic, aromatic, and polyhalogenated hydrocarbons. UPPER is based on a group of additive and nonadditive descriptors along with a series of well-accepted thermodynamic relationships. In this model, the two-dimensional chemical structure is the only input needed. Chapter (1) extends the applicability of UPPER to hydrogen bonding and non-hydrogen bonding aromatic compounds with several functional groups such as alcohol, aldehyde, ketone, carboxylic acid, carbonate, carbamate, amine, amide, nitrile as well as aceto, and nitro compounds. The total data set includes almost 3000 compounds. Aside from the enthalpies and entropies of melting and boiling, no training set is used for the calculation of the properties. The results show that UPPER enables a reasonable estimation of all the considered properties. Chapter (2) uses modification of the van't Hoff equation to predict the solubility of organic compounds in dry octanol as explained in chapter two. The equation represents a linear relationship between the logarithm of the solubility of a solute in octanol to its melting temperature. More than 620 experimentally measured octanol solubilities, collected from the literature, are used to validate the equation without using any regression or fitting. The average absolute error of the prediction is 0.66 log units. Chapter (3) compares the use of a statistic based model for the prediction of aqueous solubility to the existing general solubility equation (GSE).

The present work studies the microstructure and corrosion behaviour of 25 vol.% SiCp/AA2124-T4 metal matrix composites (MMCs) and AA2124-T4 aluminium alloy; and also the capability of excimer laser surface melting (LSM) to improve the corrosion resistance of the SiCp/AA2124 MMC and the monolithic alloy (MA). Microstructural characterization has shown significant influence of the presence and size of SiC particles on the fine Al2Cu precipitate and Mg segregation at SiC/Al interfacial regions. Such precipitates are revealed to be active sites for corrosion initiation in the MMCs, while the preferential sites for corrosion initiation in the MA are the coarse intermetallics. Corrosion evaluation performed in a 0.6 M NaCl solution suggests that the corrosion resistance of the MMC reinforced with micrometre-sized SiC particles is inferior to that of the MA and the MMC reinforced with submicrometre-sized SiC particles. The submicrometre-sized SiC particles have little adverse effect on the corrosion resistance of the MMC due to the reduced interfacial precipitates. Thin films of up to several micrometres have been achieved by excimer LSM on both the MMC and the MA. The surface roughness and the thickness of the melted layer increase with increasing laser fluence. High number of pulses (40 P) results in significant porosity in the MA and networks of cracking in the MMC. A homogeneous layer without chemical segregation except the Cu-rich segregation bands has been obtained on the MA; while complex microstructures are observed for the MMC, including the Cu-rich segregation bands, Al-Si eutectic structure and microsegregation-free structure laid in sequence from the bottom of the melted layer to the top surface. The modelling work suggest that the presence of SiC particles gives rise in high temperatures in the melt pool, which is useful to explain the materials responses upon laser irradiation, such as decomposition of SiC, evaporation of matrix alloy, and oxides formation. The fast cooling rate up to 1011 K/s is responsible for the formation of microsegregation-free structure. Corrosion evaluation has indicated improvement of corrosion resistance of the MMC and the MA after excimer LSM due to the reduction of the intermetallics. For the laser-melted MA, the corrosion behaviour is governed by the surface morphology and the porosity. The significant rippled structure obtained under high laser fluence could lead to crevice corrosion in the valley between the ripples whilst the pores could provide penetrating routes for the chloride solution to reach the Cu-rich segregation bands, leading to the delamination of the melted layer. For the laser-melted MMC, corrosion mainly initiated at the SiC remnants, which are rich in Si. The corrosion sites of the laser-melted MMC are in the form of small cracked blisters.

The ignition temperature of the aluminium copper oxide (Al-CuO) thermite was measured using differential thermal analysis (DTA) at a scan rate of 50 °C/min in an inert nitrogen atmosphere. Thermite reactions are difficult to start as they require very high temperatures for ignition, e.g. for the Al-CuO thermite comprising micron particles it is ca. 940 °C. It was found that the ignition temperature is significantly reduced when the binary Si-Bi2O3 system is used as sensitiser. Further improvement is achieved when nano-sized particles are used. For the composition CuO + Al + Bi2O3 + Si (65.5:14.5:16:4 wt %), when all components except the aluminium fuel are nano-sized, the observed ignition temperature is reduced to ca. 615 °C and results in a thermal runaway. / Dissertation (MSc)--University of Pretoria, 2011. / Chemical Engineering / unrestricted