Thesis (M.S.) in Earth Sciences--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 90-95).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 65 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 60-64).

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Molecular orbital calculations have been successively applied to mineralogical studies of equilibrium molecular geometry, electronic charge distributions, electronic spectra and bulk modulus calculations. To date, these studies have modelled bonding at atmospheric pressure. With the ever increasing interest in high pressure phases and mantle mineralogy, bonding studies of molecular groups at simulated high pressure can be an invaluable aid to understanding high pressure crystal chemistry, bond energetics and electronic spectra. This investigation tests the feasibility of various models to simulate pressure in ab initio SCF MO calculations on common metal-oxygen polyhedra. Pressure is simulated in the cluster, H₆Si₂O₇, by systematically stepping helium atoms directed^ along the Si-O bridging vectors toward the bridging oxygen. Changes in the Si-0 bond lengths, SiOSi angles and Si-0 force constants are monitored with increasing pressure. For an increase of 60 kbar pressure, the Si-0 bond length and SiOSi angle decrease 0.30% and 4.5%, respectively, which compares well with the 0.30% and 6.6% decrease observed in c-quartz for a similar increment of pressure. The linear correlation of Si-0 bond length and -sec(SiOSi), known to occur at one bar, holds at elevated pressure. In addition, the Si-0 stretching and SiOSi bending force constants show a percentage increase in the ratio 1:6 up to an estimated pressure of 140 kbar. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The chemical properties of guanidinium tris(catecholato)siliconate, (H2N)2C=NH2J2(Si(C6H402)j]-XH20 (0 This same compound was, upon addition of' (H2N)2C=NH.HC1, isolated from 0.2, M aqueous catechol solutions buffered at pH 10 and containing the silicate minerals albite, andradite, muscovite, pyrophyllite, talc, and wollastonite, and also from unbuffered catechol solutions containing wollastonite and andradite. It is concluded from this work that the formation of an anionic catechol-silicon complex, Si(C6H402)32~ is largely responsible for the dissolution of the minerals mentioned above. From this conclusion, it is proposed that naturally occurring members of the class of organic compounds to which catechol belongs, the aromatic vic-diols, may play a role in chemical weathering, in the development of certain soil profiles, and in the entry and accumulation of silica in plants.

Samples of garnet-grade Ashe formation schists, gneisses, and amphibolites from two drill holes through the Great Gossan Lead in southwestern Virginia have been studied petrographically and chemically. Metamorphic temperatures determined from the muscovite-paragonite solvus, the muscovite-calcite-quartz system, and Fe⇄Mg distribution in biotite and garnet are approximately 400-460°C. Using the sphalerite geobarometer, metamorphic pressures were found to have been equal to or greater than 4 kbar. Fine- to medium-grained garnet-chlorite-biotite-quartz-muscovite schists and gneisses predominate. Other lithologies include thin layers of hornblende amphibolite, sulfide ore, quartz veins, thin layers of hornblendic gneiss, marble lenses and minor solution cavities. The coarser-grained ore zone lithologies are dominated by chlorite, hornblende and actinolite-tremolite with cummingtonite rims, calcite, and quartz. Garnet-chlorite and garnet-biotite selvages are also occasionally found in the ore zone. The ferromagnesian minerals show marked iron depletion within 2-5 feet of the sulfide ore. Ore zone chlorite and biotite show a significant increase in magnesium; garnets show a similar increase in manganese. The cores of garnets from the ore zone show the influence of the ore even at the earliest stages of garnet growth, indicating that the ore was present prior to the peak of metamorphism. The distribution coefficients for Fe - Mg exchange reactions for garnet-biotite and garnet-chlorite also indicate that the ore and the surrounding rocks were metamorphosed together. Therefore, hypotheses for a synsedimentary or early hydrothermal origin for the ore are favored over those suggesting a post-metamorphic hydrothermal origin. / Master of Science

The inversion temperature of cristobalite was investigated by incorporating TiO₂, AlPO₄, and BPO₄ into the cristobalite phase using solid state reactions. The combination of TiO₂ and AlPO₄ proved to be most effective in lowering the inversion temperature of cristobalite. Phase diagrams at the high silica corner were constructed for the respective systems. High cristobalite was stabilized for compositions prepared from the CaO-Al2₂O₃-SiO₂ and CuO-Al₂O₃-SiO₂ system using sol-gel processing. The stabilization mechanism is attributed to the surface energy effect resulting from the formation of fine crystals. The structural evolution from the x-ray amorphous gel to high cristobalite was examined by FTIR and Raman spectroscopy. The thermal expansion of the stabilized high cristobalite was characterized by high temperature x-ray. Changes in bond angle continue to dominate the thermal expansion of high cristobalite. / Ph. D.

Equilibrium relations between garnet and orthopyroxene have been investigated by reversal experiments in the range of 20-45Kb and 975-1400°C in the FeO-MgO-Al₂O₃-SiO₂(FMAS) system. The Fe-Mg exchange reaction seems to have little or no compositional dependence at these conditions. The experimental results can be fitted adequately by the linear relation: ln K(D) = 2243/T°K - 0.9522 at 25Kb where K(D) = (X(Fe)/X(Mg))ᴳᵗ/(X(Fe)/X(Mg))ᴼᵖˣ. Combination of the available data for the mixing properties of garnet and V° for the Fe-Mg exchange reaction with the above experimental results yields the following geothermometric expression for the common natural assemblages that can be represented essentially within the system CaO-MnO-FeO-MgO-Al₂O₃-SiO₂. T°K = (1968 + 11P(Kb) + 1510(X(Ca)+X(Mn))ᴳᵗ)/(ln K(D) + 0.9522). The stability field of pyrope+quartz, defined by the reaction pryope+quartz=opx+sill, has been calculated as a function of P,T,X(Fe)ᴳᵗ in the FMAS system using the reversal experimental data of Perkins (1983) in the MAS system, and the present data on K(D)(Fe-Mg) between garnet and orthopyroxene. This reaction is very sensitive to pressure and compositional effects. Combination of P,T conditions for the garnet stability and that defined by (K(D)(Fe-Mg))ᴳᵗ⁻ᴼᵖˣ yields a simultaneous solution for both P and T of equilibration of garnet and orthopyroxene in the presence of Al₂SiO₅ and SiO₂. The effect of FeO on Al₂O₃ solubility in orthopyroxene in equilibrium with garnet has been determined experimentally at several pressures at 975 and 1200°C. These data have been modeled to develop a thermodynamic method for the calculation of Al₂O₃ in orthopyroxene as a function of P,T and composition. The Al₂O₃ isopleths have moderate P-T slopes, and provide virtually the only means of determining the pressure of mantle derived rocks.

Cement has three sequential states in most applications: fluid, setting and hardened. This thesis focuses on the effect of nanoclays and diutan gum on rheological, chemical and mechanical properties corresponding to the three states. Water transport properties are critically important in many applications, such as oil well cementing and 3D concrete printing. The effect of nanoclays and diutan gum on water transport properties of cement pastes were investigated. Bleeding, water retention under suction pressure, and evaporation under air flow were measured. The nanoclay was found to reduce bleeding but had no effect on water retention or evaporation. The diutan gum was found to reduce bleeding, improve water retention, and decrease evaporation loss. The rheological properties of the pastes and their interstitial solution were also characterized to resolve the mechanisms underlying the water transport behaviors. Good correlation between the measured rheological parameters and water transport properties was found. In addition to water retention, the static yield stress build-up plays a major role in the successful oil well cementing and 3D concrete printing. Linear models are commonly used to describe the early structural build-up of cement-based materials. However, some studies have shown that there exists a faster non-linear phase before the linear phase. A simple non-linear thixotropy model is presented to describe the structural build-up process. It was quantified using static yield stress and storage modulus, which are measured through the stress growth protocol and small amplitude oscillatory shear (SAOS) tests, respectively. The effect of pre-shear, rest condition and nanoclay and diutan gum on the build-up behavior are studied. The results showed distinctly different trends between static yield stress and storage modulus. This may be attributed to the two different structures of fresh cement pastes, i.e. floc structures and C-S-H structures, measured by the stress growth protocol and SAOS test, respectively. Phase characterization of cement paste was performed through synchrotron x-ray diffraction technique. This allowed for real-time, in-situ measurements of x-ray diffraction patterns to be obtained, and subsequently the continuous formation and decomposition of select phases over time (up to 8 hours). Phases of interest included alite, ferrite, portlandite, ettringite, monosulfate, and jaffeite (crystalline form of calcium silicate hydrate). The effects of elevated temperatures at elevated pressure, as well as the effect of nanomaterial addition were investigated. Rate of conversion of ettringite to monosulfate increased with increasing temperature, and monosulfate became unstable when temperatures reached 85ºC. The synchrotron x-ray diffraction setup appeared to have captured the seeding effect of nano-sized attapulgite clays at 0.5% addition by mass of cement, where acceleration in the rate of formation of portlandite and jaffeite was observed. Finally, the investigated system was upscaled from cement paste to cement mortar incorporating the fly ash and the slag. The effect of the nanoclays on the mechanical properties was evaluated in comparison with the carbon nanotube. Compressive strength and tensile strength were evaluated. Results indicated that although the nanoclays are utilized primarily as a rheological modifier, they can also enhance mechanical properties.

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [55]-[60]).