<p> The kinetics of the hematite to rnagnetite reduction have been studied in H2-H2O, and H2-H2O-N2 gas mixtures, using natural as well as synthetic specimens. The reactivity of hematite was found to be related to the structural defects formed during the preparation of the specimens. The type of defects formed and their effect on reactivity are discussed. Kinetic studies are performed on the specimens with reproducible properties. Rate expressions based upon suitable reaction mechanisms are derived and their validity checked with the experimental data. Reaction rate parameters for the expressions accurately interpreting the experimental results are evaluated, and the effect of nitrogen is separately established. Values of enthalpies and entropies for the mechanistic steps a.re calculated from the temperature dependence of these parameters, which reasonably support the proposed mechanism. </p> / Thesis / Doctor of Philosophy (PhD)

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This dissertation focuses on the use of novel polyethers and polydimethylsiloxanes in the stabilization of magnetite nanoparticles as well as biomedical applications. The colloidal stabilities of magnetite nanoparticles coated with polyethers containing various functional endgroups were studied. Different variables (e.g. polymer loading, polyether molecular weight and type of functional anchor group) were investigated to determine their effect on the long-term physiological stability of the polyether magnetite complexes. One-part PDMS-magnetite nanoparticle fluids were synthesized using a high shear process and magnetic separation techniques. These one-part fluids are unique in the fact that they do not require the addition of a non-functional PDMS oligomer solvent to generate a magnetic hydrophobic fluid. A series of PDMS-magnetite nanoparticle fluids containing different molecular weight stabilizers were synthesized. A magnetic separation study was performed to determine if PDMS molecular weight influences the magnetic separation profiles of the fluids. Well-defined PDMS-b-PtBA and PDMS-b-poly(acrylic acid) copolymers were synthesized using living free radical techniques from novel PDMS precursors as well as PDMS-based ionenes with different hard segment groups. / Ph. D.

Cancer is one of the challenges for today's medicine and therefore a great deal of effort is being put into improving known methods of treatment and developing new ones. A new method that has been proposed is magnetic hyperthermia where magnetic nanoparticles linked to the tumor dissipate heat when subjected to an alternating magnetic field and will thus increase the temperature of the tumor. This method makes the tumor more susceptible to radiation therapy and chemotherapy, or can be used to elevate the temperature of the tumor cells to cause cell death. The particles proposed for this are single core and often have a size in the range of 10 nm to 50 nm. To achieve an effective treatment the particles should have a narrow size distribution and the proper size. In this work, a theoretical model for predicting the heating power generated by magnetic nanoparticles was evaluated. The model was compared with experimental results for magnetite particles of size 15 nm to 35 nm dissolved in water. The properties of the particles were characterized, including measurements of the magnetic saturation, the effective anisotropy constant, average size and size distribution. To evaluate the results from the model the AC susceptibility and heating power were experimentally determined. The model is a two-step model. First the out-of-phase component of the AC susceptibility as a function of frequency is calculated. Then this result is used to calculate the heating power. The model gives a correct prediction of the shape of the out-of-phase component of the susceptibility but overestimates its magnitude. Using the experimentally determined out-of-phase component of the susceptibility, the model estimation of the heating power compares quite well with the measured values.

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187Re-187Os analysis of magnetite and other oxide minerals from various well dated geological settings (kimberlites, lamprophyres, Manicouagan impact melt rock, Great Bear magmatic zone iron ore deposits and Laramie Anorthosite complex) worldwide have been used to investigate the potential for precise geochronology. 187Re-187Os isotopes in groundmass oxide minerals from kimberlites and lamprophyres are not suitable for emplacement geochronology due to low Re contents and large quantities of un-radiogenic Os. TRD and TMA ages can be calculated however, and correlate well with previously published depletion ages and large magmatic events in the overlying crust, indicating the effectiveness of this technique. Geochronology using magnetite from the remaining settings is im-precise due to very low Re and Os contents but the ages produced are in the correct area. Young ages produced from the Laramie anorthosite complex indicate that magnetite may have a low closure temperature to Os diffusion (~200-300C).

Thesis (M.Sc.)--University of Alberta, 2010. / Title from PDF file main screen (viewed on July 9, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science, [Department of] Earth and Atmospheric Science, University of Alberta. Includes bibliographical references.

The use of magnetite as a medium in the wet processing of coal has been used since the early days of dense medium separation. The high magnetic susceptibility and density of magnetite make it an ideal medium to use in wet coal beneficiation because it is relatively easily and successfully recoverable. Owing to the need for more sustainable technologies, Coaltech has been investigating alternative dry processing processes: the Bohou process (developed in China) was identified as a possible feasible option. The Bohou process comprises dry dense medium separation using magnetite as the medium. The recovery and re-use of magnetite are, however, problematic. The aim of this investigation was to determine how efficiently magnetite can be recovered and to identify the factors influencing the magnetite losses during this dry processing. The test work for the project was divided into two phases. The aim of Phase 1 was to identify the magnetite losses to the oversize coal fraction for different moisture conditions of the coal and magnetite. In Phase 2, magnetite and high-titanium magnetite (an alternative source of magnetite) were used to conduct test work to determine which medium could be successfully recovered from fine coal. Magnetite or high-titanium magnetite was mixed with the coal sample as a medium. During Phase 2, the effects of using different screens and different moisture conditions were investigated. For both phases, the samples received were divided into three categories containing different moisture contents: dry coal and dry magnetite, dry coal with wet magnetite (4% to 4.4%), and wet coal (3.5% to 6.5%) with dry magnetite. In Phase 1, the coal samples were screened at 13.2 mm, the oversize mixed with magnetite, and then screened again with a 13.2 mm screen: the magnetite losses were then recorded. For Phase 2, the prepared samples were screened at 3 mm, 13.2 mm, and with a 3 mm high-frequency screen. The undersize was passed through a low-intensity magnetic separator. The recovered magnetite was then passed over a magna chute to recover additional magnetite. ii The results for both phases indicated that the highest recovery of magnetite occurred when dry magnetite and dry coal samples were used. The samples with wet magnetite also gave high recovery, but the samples with wet coal were detrimental to recovery and significant losses were observed. It was found that the magnetite stuck to the surface moisture of the coal. The use of a high-frequency screen improved recovery of the magnetite from the wet coal samples from 45.38% to 74.27%. Recovery from the high-frequency screen for both dry and wet magnetite samples was lower than that achieved with a conventional 3 mm screen. The test results indicated that magnetite can be recovered in the dry beneficiation of coal when the surface moistures of both the coal and magnetite are controlled. Use of a high-frequency screen can improve recoveries only for conditions where the surface moisture of the coal is high. / Dissertation (MSc (Metallurgy))--University of Pretoria, 2021. / CoalTech / Materials Science and Metallurgical Engineering / MSc (Metallurgy) / Unrestricted

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