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The topic of this dissertation is the solidification of a binary melt. The investigation is separated into three portions: An experimental investigation on the NH₄Cl--H₂O system; the development of a Cellular Automata code; and the development of a pair of coupled partial differential equations governing the evolution of an array of dendrites. Any necessary concepts are reviewed in the introduction. The experimental investigation focuses on the morphological transition from "slow" <100> dendrites to "fast" <111> dendrites. It is shown how the very complicated structures occurring during the transition actually have a simple explanation. The "slow-to-fast" transition has been previously investigated in the literature, and the relationships obtained in those studies can not account for the data collected in the present study. When "slow" dendrites are cooled into the "fast" regime, a curious stagnation of growth has also been observed. Additionally, two mechanisms are proposed as possible contributions to the order-of-magnitude jump in speed at the slow-to-fast transition. One mechanism is that of a "herringbone structure", and the other is that of a vortical fluid flow occurring at the tip of the dendrite. A relationship is also found which further indicates the importance of fluid flow. The cellular automata model developed in this dissertation has proven to be a valuable tool in gaining insight into the solidification process. The simulated growth is governed predominantly by the diffusion of solute and the Gibbs-Thomson effect. Solutal diffusion, is accurately treated, diffusing differently through liquid than through solid. The interface curvature is approximated using a template method, into which crystalline anisotropy has also been introduced. Several features were added to explore interface kinetics, solute partitioning, and fluid flow due to shrinkage. Simulations on a 100 x 100 system typically required less than a minute on a workstation, and only qualitative agreement with the experiments was sought. The partial differential equations for the evolution of a growing array of dendrites are derived taking into account only diffusion. It is explicitly shown how the non-conservative equations conserve all of the material in the solidifying system.

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A series of experiments were conducted to explore the hydration state of the mineral lausenite. The experiments of Posnjak and Merwin (1922) were recreated and the conclusion is reached that lausenite is of mineral formula Fe2(SO4)3∙5H2O, rather than Fe2(SO4)3∙6H2O as suggested by Posnjak and Merwin (1922). This conclusion is based on the X-ray diffraction data which found that the Posnjak and Merwin experiments produced a phase whose pattern matched that of the pentahydrate identified by Majzlan (2005). The refractive index data and morphology of this phase is also a match for the mineral described previously as a hexahydrate by Posnjak and Merwin (1922) and Lausen (1928). Synchrotron X-ray diffraction data was collected from a possible new phase in the hydrous ferric sulfate system. The data were analyzed and a unit cell was identified with monoclinic unit cell dimensions of a = 7.532(3)Å b = 12.551(6)Å c = 7.077(4)Å and β = 96.775(8)° with a unit cell volume of 664.4Å3. This phase was determined to grow only at temperatures above 85°C and at a RH of ~23%. The atomic structures of the minerals quenstedtite [Fe2(SO4)3∙11H2O] and romerite [Fe2+Fe3+2(SO4)4∙14H2O] are refined, hydrogen positions are identified and hydrogen bonding scheme is discussed. The weakest hydrogen bonds are found to occur between layers of differently coordinated tetrahedral groups in both romerite and quenstedtite. The transition from romerite to quenstedtite involves the oxidation of the ferrous iron in romerite converting into a Fe3+(SO4)∙5H2O cluster. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-09-02 10:11:21.232

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The Nopal I uranium deposit located in northern Chihuahua Mexico has been the focus of study for the past 40 years. Information regarding to its formation and evolution through time demonstrate that it has a very complex history. Uranium mineralization occurs in two different styles: uranium oxide uraninite and a secondary phases of silicates (uranophane, soddyite) and oxyhydroxides (schoepite and ianthinite). Petrographic studies have revealed that uraninite is found encapsulated within the host rock (ignimbrites) as fine grains while secondary uranium minerals are filling fractures and micro-veins. Chemical dates from the uranium minerals give a wide range from 0 to 611 Ma; many of the ages may be overestimated since the host rock is 44 Ma. U/Pb isotopic studies demonstrate the presence of common Pb, and after a correction was applied, a new range of dates from 1< to 7 Ma was obtained.

A minor eruption of Mount Saint Helens in Washington State U. S. A. in 1984, triggered the formation of a debris flow in the headwaters of the North Fork Toutle River. As the debris flow progressed downstream it transformed through the incorporation of water and the loss of sediment and within 34 kilometres became a muddy flood. The deposits produced by the transforming flow and associated recessional flows that followed in its wake, exhibited a coarse grained depositional continuum from debris flow to stream flow, including deposits with intermediate sedimentological characteristics termed "hyperconcentrated flow deposits".The systematic and detailed sedimentological analysis of these deposits, combined with information concerning the characteristics of the flow, has allowed the delineation of hyperconcentrated flow deposits within the debris flow/stream flow depositional continuum and hence the establishment of criteria for the recognition of coarse grained hyperconcentrated flow deposits in the volcaniclastic environment of Mount Saint Helens. Hyperconcentrated flow deposits are generally homogeneous, matrix-supported, unstratified (except where defined by sub units), have sorting characteristics intermediate between debris flow and stream flow and can exhibit a bimodal, generally non imbricate, clast fabric as a function of clast size. Coarse-tail inverse grading may occur but it is weak, or restricted to sub units. Use of these criteria enabled the recognition of hyperconcentrated flow deposits within depositional sequences produced earlier in the eruptive history of Mount Saint Helens.The analysis of Permo-Triassic alluvial fan deposits on the Isle of Lewis Scotland, revealed that elements of the debris flow/stream flow depositional continuum could be recognised by the application of the criteria established in the volcaniclastic environment of Mount Saint Helens.

The Ostracoda from nine sections of the Lower Fars Formation, Northern Iraq, Tel-Hajer well-1, Sheikh Ibrahim locality, Dohuk locality, Sheikhan locality, Bashiqa locality, Kirkuk well-208, Bai-Hassan well-33, Hamrin well-2 and the Naft Khana well-34, have been studied in detail.One hundred and nine Ostracod species/subspecies belonging to 50 genera/subgenera are described, of which one genus, one subgenus and 70 species are new. Five species are assigned to species previously described from western India. Five species are compared with other species from W. India, Iran, Turkey and France. Three species are regarded as having affinities with new species described in this thesis and 26 species are left under open nomenclature mainly because of lack of material or the impossibility of observing the internal details.Biostratigraphically, the Lower Fars Formation in the Sinjar area is divided into three Assemblage Zones, these zones are applicable only to N. Iraq, but make a starting point for future work in the area. In the Kirkuk area, the saliferous beds proved completely barren, but the upper Red, Seepage and Transition beds yield Ostracods although the assemblages recognised are at present only regarded as tentative, because the samples are ditch cuttings.Palaeoecology is discussed in terms of oxygenation, alaeoclimate, salinity and the trends in the depositional environment of the Lower Fars Formation.The affinities of the present genera and species are discussed from a palaeogeographical view point in relation to the adjacent and related regions. Three Miocene Ostracod provinces are proposed, namely a western India province, a Zagros shelf province and a southeast Turkey province.