Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 48-49). Also available via the Internet.

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Inaugural-Diss.--Mathematisc-Naturwissenschaftlichen Fakultät--Bonn--Rheinischen Friedrich-Wilhelms-Universität, 1992. / Bibliogr. p. 142-154.

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Please read the abstract (Synopsis) in the section 00frontof this document / Thesis (PhD (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

The mechanical properties of particulate filled polymers are influenced significantly by interfacial interactions. The adhesion between the polymer and the filler depends on the area of the interface and the strength of the interaction. The former is related to specific area of the filler while the strength of the interaction can be modified by surface treatment. This study is focused on comparing the reinforcing ability of muscovite and phlogopite with and without surface treatment. Muscovite and phlogopite are two common forms of mica. Mechanical properties such as Young's modulus, tensile strength, elongation and impact strength were used to compare the reinforcing ability of muscovite and phlogopite in EVA composites. The Young's modulus of the surface treated and non-surface treated composites increased with an increase in filler loading. Composites reinforced with muscovite had similar moduli compared to composites reinforced with phlogopite. The tensile strength of phlogopite reinforced composites increased with an increase in filler content while that of muscovite reinforced composites remained constant. Surface modification by both silane and stearic acid reduced the tensile strength of phlogopite reinforced composites. The tensile strength of stearic acid treated muscovite reinforced composites improved but not to the same extent as the silane treated composites. Both muscovite and phlogopite lead to a lowering of the impact strength at high filler loadings while the tensile impact strength of both muscovite and phlogopite reinforced composites improved when using silane and stearic acid. In non-surface treated systems, muscovite reinforced composites showed an initial increase in elongation while the elongation of phlogopite reinforced composites decreased with an increase in filler loading. Elongation at maximum load values, however, increased at low filler loadings, when using stearic acid. It can be concluded that stearic acid is not an effective coupling agent for mica/EVA composites and that the use of silane for phlogopite reinforced composites does not offer any improvement in mechanical properties. / Dissertation (MSc (Chemical Technology))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

The behavior during dissolution of edge and basal surfaces of the mica phlogopite were examined using in situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) in an attempt to characterize the reactive surface area during dissolution. Mica minerals are the ideal material for this study because they offer a high degree of structural anisotropy. Therefore surfaces with different structures are easily identified. Dissolution is shown to proceed preferentially by removal of material from {hk0} edges. Dissolution rates were calculated by measuring the volume of material removed from etch pits, and normalizing to either the "reactive" surface area of {hk0} edges exposed at pit walls, or to a total "BET-equivalent" surface area. Rates normalized to total surface area are in the range of dissolution rates reported in the literature. Edge surface normalized rates are about 100 times faster. Long-term in situ AFM observations of phlogopite dissolution reveal that exposed (001) surfaces also display a distinct reactivity, though it operates on a different time scale. The top layer is shown to expand between 39 and 63 hours in contact with pH 2 HCl solution. Subsequent LEED analysis shows that the (001) surface becomes amorphous upon reacting with pH 2 HCl. Compositional characterization of the phlogopite after reaction shows that for pitted phlogopite surfaces, dissolution is characterized by leaching of octahedral cations and polymerization of the silica-enriched residual layer. No chemical changes or polymerization are observed for freshly cleaved unpitted phlogopite after reaction with pH 2 HCl for 24 hours. This suggests a gallery access mechanism is facilitated by edge attack, and is only significant on exposed (001) surfaces after a certain amount of dissolution by edge attack. / Master of Science

A commercial solid-state batch process for the manufacturing of synthetic fluorophlogopite (KMg3A1Si3010F2) mica powder was evaluated and standardized. The minimum firing temperature and time for this process was determined to be 1000°C for 10 hours to both ensure the complete reaction of the raw materials and to limit the decomposition of the mica into secondary phases that occurs during overfiring. The addition of an excess amount of the fluoride K2SiF 6 to compensate for the loss of fluorine that occurs during firing was found to increase the formation of fluorophlogopite. Additionally, enclosing the material within closed containers also limits the loss of fluorine from the batch. The practice of pressing the raw material blend into cakes before firing was found to have no effect on the formation of fluorophlogopite and is, therefore, an unnecessary processing step. Finally, a quality control testing procedure that will be used in industry was developed to determine the amount of mica formed during a given heat. / Master of Science

Des liquides riches en K2O ( K2O > 2 pds. % ; K2O/Na2O > 1) sont observés dans la majeure partie des contextes géodynamiques sur Terre. Ces liquides sont principalement caractérisés par leurs teneurs en K2O variant entre 3 et 13 pds. % et des rapports K2O/Na2O de 1 – 40. Les compositions chimiques des différents groupes de liquides riches en K2O observés sont extrêmement variables, depuis des termes très sous-saturés en silice (kamafugites, kimberlites, lamproïtes madupitiques à olivine) à des termes sur-saturés en silice (shoshonites, lamproïtes à phlogopite). Ces fortes teneurs en K2O et les rapports K2O/ Na2O élevés ne peuvent pas être obtenus par la fusion de péridotites fertiles ou réfractaires. Des expériences de fusion partielle en piston-cylindre ont été réalisées sur des péridotites à phlogopite ± amphibole dans les domaines de stabilité du spinelle et du grenat (1 et 3 GPa) afin de déterminer la capacité du manteau lithosphérique à produire des liquides riches en K2O. La présence de faibles teneurs en fluor dans le matériel de départ stabilise le phlogopite à des températures supérieures aux études antérieures. Les faibles degrés de fusion obtenus à 1 GPa sont sur-saturés en silice et leur teneur en K2O est tamponnée à 4 – 6 pds. % par la présence de phlogopite résiduel pour des péridotites fertile et réfractaire, respectivement. Les expériences réalisées à 3 GPa montrent que les premiers degrés de fusion sont sous-saturés en silice mais plus riches en K2O (6 – 8 pds. % pour la lherzolite et la harzburgite, respectivement) que dans le domaine du spinelle, démontrant l’importance de la pression sur la genèse de liquides riches en K2O. Les modélisations réalisées montrent également que l’augmentation de la proportion de phlogopite dans la source ne modifie pas la teneur en K2O des liquides formés mais diminue leurs rapports K2O/Na2O. Par conséquent, la fusion de péridotite à phlogopite dans la gamme de pression étudiée ne permet pas d’obtenir des liquides aussi riches en K2O que certains lamproïtes et kamafugites. Une série d’expériences réalisée sur du phlogopite pur à 1 et 3 GPa montrent que les liquides dérivés de telles sources sont très riches en K2O (12 – 14 pds. %) et comparables aux lamproïtes. Les différentes lithologies dans le manteau ne permettent cependant pas d’expliquer la grande gamme de composition des liquides riches en K2O et nécessitent des conditions riches en éléments volatils (H2O, CO2, F) et des fugacités d’oxygène réductrices. / K2O-rich melts (K2O > 2 wt. %; K2O/Na2O > 1) have been described in all of the major geodynamic settings on Earth. These melts are mainly characterized by their huge K2O content, ranging between 2 – 13 wt. % and K2O/Na 2 O ratios of 1 – 40. The chemical compositions of the different K2O-rich melt groups span a very high variability, from strongly silica undersaturated melts (kamfugites, kimberlites, madupitic lamproites) to silica-rich terms (shoshonites, phlogopite lamproites). These very high K2O contents together with strong K2O/Na2O ratios cannot be derived from partial melting of fertile or depleted peridotites. Partial melting experiments have been conducted in piston cylinder apparatus on phlogopite ± amphibole-peridotite in the spinel and garnet stability fields (1 – 3 GPa) in order to determine the ability of the lithospheric mantle to produce K2O-rich melts. The presence of small amounts of fluorine in the starting material leads to stabilize phlogopite at higher temperatures than previously determined. The first degrees of melting at 1 GPa are silica-rich and their K2O contents are buffered to 4 – 6 wt. % in the presence of residual phlogopite, depending on the source fertility (lherzolite and harzburgite, respectively). In the garnet stability field at 3 GPa, low-degree melts are silica-undersaturated but are enriched in K2O, compared to the garnet stability field: from 6 to 8 wt. % in lherzolite and harzburgite sources, respectively. These results suggest that pressure is a key parameter in the mantle to produce K2O-rich melts. Partition coefficient modelings show that increasing the phlogopite proportion in the mantle source does not modify the K2O content of derived melts, but decreases their K2O/Na2O ratios. Consequently, partial melting of phlogopite-peridotite in this range of pressure cannot accounts for the highest K2O contents observed in natural lamproites and kamafugites. A series of experiments has been realized on pure phlogopite at 1 and 3 GPa, showing that derived melts are strongly enriched in K2O (12 – 14 wt. %) and share chemical affinities with lamproites. Peridotite or pyroxenite melting in the presence of phlogopite, however, do not permit to reproduce the high chemical variability of natural K2O-rich melts requires volatile-rich conditions (H2O, CO2, F) and reduced oxygen fugacities.

The development of an appropriate solid-state kinetic model which represents the leaching process of phlogopite was investigated. Phlogopite samples were leached with nitric acid solutions of different concentrations, at different temperatures and for different reaction times. Leach liquors were analysed by ICP-OES for concentration, while the raw phlogopite and the acid-leached solid residues were analysed by XRF, XRD, ATR-FTIR, BET, TGA-DTG and SEM-EDS for characterisation to support the reaction rate model selection. It was found that the reaction was diffusion-controlled and the model which represents onedimensional diffusion through a flat plate (model D1) most accurately predicts the leaching behaviour. The observed activation energies and preexponential constants varied with initial acid concentration. The observed activation energies decreased from 98.8 – 88.9 kJ mol-1 as the initial acid concentration increased from 2 – 4 M, while the observed preexponential constants decreased from 3.30 x 10+12 – 2.30 x 10+11 min-1. Additional experiments were conducted at different temperatures, using different initial acid concentrations and over different reaction times to test the model. The experimental data points obtained (“testing data”) were in agreement with the predicted values. Analyses of the solid residues also revealed complementary results with respect to the leaching model selection. The raw phlogopite was found to be highly crystalline (XRD). Therefore, the absence of defects in the lattice means that the motion of H+ ions permeating into the lattice is restricted (Ropp, 2003; Schmalzried, 1995). This confirms that the leaching is internal diffusion-controlled since the mobility of constituents into the system is the controlling factor, and since the phlogopite particles are plate-like (SEM-EDS, BET) in shape, the use of the D1 model for one-dimensional diffusion through a flat plate is the recommended model to represent the leaching process. Furthermore, results obtained from the different analytical techniques were supportive of each other. It was also found that the amount of acid consumed is inequivalent to the amount theoretically required. Using the theoretically required acid concentration (2.45 M) results in incomplete conversion (< 80 % according to Kgokong (2017)). When initial acid concentrations between 2.4 – 2.6 M were used, only 88 – 91 % conversion was obtained after 6 hours of leaching at 65 °C, leaving behind excess H+ in solution. If fertiliser is the desired end product, it would be favourable to minimise the H+ concentration of the leach liquor. Therefore, the leaching process should be optimised so that the acidity of the leach liquor is minimised while obtaining complete leaching of all cations from the phlogopite particles into solution. Furthermore, since the SiO2 by-product is highly porous (surface area of 517 m2 g-1), its application in industrial adsorbents, catalysts, polymers, pigments, cement, etc. should be further explored. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2020. / Chemical Engineering / MEng (Chemical Engineering) / Unrestricted