Thesis supervisor: Michelle M. Scherer. Includes bibliographic references (p. 198-215).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / 2 folded maps in pocket. Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MTech: Chemical Engineering))--Cape Peninsula University of Technology, 2012 / The microbial ferrous-iron oxidation process plays a significant role in bioleaching, providing ferric-iron (Fe3+) − a strong oxidising agent for the dissolution of most sulphide minerals. An extensive literature review has shown that several studies have been carried out on microbial ferrous-iron oxidation, mostly in stirred tank reactors and in conditions close to optimum. However, limited studies have been carried out on this subject in the context of heap bioleach situation. Despite the fact a packed column system may be used to represent heap bioleaching, most of the studies on microbial ferrous-iron oxidation in such systems were carried out under flooded/fluidised conditions which do not adequately represent solution flow dynamics in a heap system. The microbial ferrous-iron oxidation kinetics of Leptospirillum ferriphilum were studied at substrate loading rates of 0.17 – 0.5 g.L-1h -1 (dilution rates 0.033 – 0.1 h-1). The study was conducted in a packed column with a view to investigating the kinetics in a system which simulates the solution flow dynamics of a typical heap bioleach operation. Glass marbles, 15 mm in diameter, were used as reactor packing. The microbial oxidation kinetics were investigated in a continuous mode at the desired loading rates. The pH of the bioreactor was maintained at pH 1.45 ± 0.05 and the aeration at 15 mL.s-1. Both Monod and Hansford models were used to describe the biooxidation kinetics.

Nutrient pollution from industrial activity is an environmental problem that persists in water bodies near urban settings, and has been a primary contributor to eutrophication, bacterial contamination, and harmful algal blooms. Biogenic iron oxides offer a potential solution to the treatment of lakes and rivers containing high concentrations of phosphate, the limiting nutrient in aquatic systems. Soluble ferrous iron can act as an electron donor for iron-oxidizing bacteria, which thrive in low-oxygen environments. This results in the formation of insoluble ferric iron minerals, ideal adsorbents for negatively charged phosphate. Conversely, iron-reducing bacteria reduce ferric iron to form ferrous iron, resulting in the formation of secondary minerals depending on the chemistry of the particular environment. This project investigates the chemical conditions at which biogenic iron oxides have the maximum adsorptive capacity, especially with respect to organic carbon content. A simplified model of natural biogenic iron oxides was synthesized by co-precipitating the mineral ferrihydrite (a common iron oxide) with the polysaccharide alginate, an analogue to bacterial exopolysaccharides. At the levels of carbon investigated, organic matter was not found to affect the adsorptive capacity of iron oxides at the C/Fe ratios analyzed. Similarly, organic matter did not appear to significantly influence the rate of reduction of ferrihydrite by the iron-reducing bacterium Shewanella putrefaciens CN32. Presence of organics did however influence rates of reduction and the mineralogy of the post-reduction precipitates. Phosphate adsorbed to iron oxides prior to microbial reduction greatly increased both the rate and the extent of ferric iron reduced, and also had an impact on the secondary minerals that formed (vivianite, green rust). An improved understanding of these conditions could contribute to a more efficient process by which iron-oxidizing bacteria are used for large-scale industrial water treatment.

Iron oxyhydroxides are ubiquitous in surface environments, playing a key role in many biogeochemical processes. Their characterization is made challenging by their nanophase nature. Magnetometry serves as a sensitive non-destructive characterization technique that can elucidate intrinsic physical properties, taking advantage of the superparamagnetic behaviour that nanoparticles may exhibit. In this work, synthetic analogues of common iron oxyhydroxide minerals (ferrihydrite, goethite, lepidocrocite, schwertmannite and akaganéite) are characterized using DC and AC magnetometry (cryogenic, room temperature), along with complementary analyses from Mössbauer spectroscopy (cryogenic, room temperature), powder X-ray diffraction and scanning electron microscopy. It was found that all of the iron oxyhydroxide mineral nanoparticles, including lepidocrocite, schwertmannite and akaganéite were superparamagnetic and therefore magnetically ordered at room temperature. Previous estimates of Néel temperatures for these three minerals are relatively low and are understood as misinterpreted magnetic blocking temperatures. This has important implications in environmental geoscience due to this mineral group’s potential as magnetic remanence carriers. Analysis of the data enabled the extraction of the intrinsic physical parameters of the nanoparticles, including magnetic sizes. The study also showed the possible effect on these parameters of crystal-chemical variations, due to elemental structural incorporation, providing a nanoscale mineralogical characterization of these iron oxyhydroxides. The analysis of the intrinsic parameters showed that all of the iron oxyhydroxide mineral nanoparticles considered here have a common magnetic moment formation mechanism associated with a random spatial distribution of iv uncompensated magnetic spins, and with different degrees of structural disorder and compositional stoichiometry variability, which give rise to relatively large intrinsic magnetization values. The elucidation of the magnetic nanostructure also contributes to the study of the surface region of the nanoparticles, which affects the particles’ reactivity in the environment.

Poly(dimethylsiloxane) (PDMS) fluids containing magnetite nanoparticles stabilized with carboxylic acid-functionalized PDMS were prepared. PDMS-magnetite complexes were characterized using transmission electron microscopy, elemental analysis, and vibrating sample magnetometry. PDMS-magnetite complexes containing up to 67 wt% magnetite with magnetizations of ~52 emu gram-1 were prepared. The magnetite particles were 7.4 ± 1.7 nm in diameter. Calculations suggested that the complexes prepared using mercaptosuccinic acid-functionalized PDMS (PDMS-6COOH) complexes contained unbound acid groups whereas the mercaptoacetic acid-functionalized PDMS (PDMS-3COOH) complexes did not. Calculations showed that the PDMS-3COOH and PDMS-6COOH covered the same surface area on magnetite. Calculations were supported by molecular models and FTIR analyses. The complexes were dispersed into PDMS carrier fluids by ultrasonication, resulting in magnetic PDMS fluids with potential biomedical applications. Magnetite particles (100 nm to 1 mm in diameter) were prepared by crystallization from goethite/glycol/water solutions under pressure. Two methods for particle growth were investigated in which the crystallization medium was varied by adjusting the amount of water or by adding itaconic acid. Particle surfaces were analyzed by x-ray photoelectron spectroscopy (XPS). Particles with clean surfaces were coated with carboxylic acid-functionalized poly(e-caprolactone) stabilizers. Adding itaconic acid to the reactions afforded particles ~100 nm in diameter. The magnetite particles displayed magnetic hysteresis. The particles were dispersed into vinyl ester resins by ultrasonication and it was demonstrated that the ~100 nm particles remained dispersed for three days without agitation. These dispersions have applications in magnetic induction heating for composite repair. Living polymerizations of hexamethylcyclotrisiloxane were terminated with dimethylchlorosilane, phenylmethylchlorosilane, or diisopropylchlorosilane (DIPCS). Platinum-catalyzed hydrosilation of the hydrosilane-terminated PDMS with allyloxyethanol afforded a systematic series of hydroxyalkyl-terminated PDMS. The reactions were successful except for the hydrosilation of the sterically-hindered DIPCS-functionalized PDMS where no reaction was observed. Hydroxyalkyl-terminated PDMS oligomers were successful in initiating the stannous octoate-catalyzed copolymerization of e-caprolactone, which afforded PDMS-b-PCL diblock copolymers of controlled composition. / Ph. D.

Lee Wai Tak Joseph = Fe₃₋xZnxO₄的真空熱處理效應及磁隧道結 / 李懷德. / On t.p. "-x" and "x" is subscript. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Lee Wai Tak Joseph = Fe₃₋xZnxO₄ de zhen kong re chu li xiao ying ji ci sui dao jie / Li Huaide. / Acknowledgement --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of contents --- p.iv / List of Figures --- p.ix / List of Tables --- p.xiv / Table of Contents / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction to Magnetite Fe3O4 and Zinc Ferrite Fe3.-xZnxO4 --- p.1-1 / Chapter 1.1.1 --- Crystal structure and Properties of Fe304 and Fe3-xZnxo4 --- p.1-1 / Chapter 1.1.2 --- Transformation of Iron Oxides --- p.1-6 / Chapter 1.2 --- Verwey transition --- p.1-10 / Chapter 1.2.1 --- Introduction --- p.1-10 / Chapter 1.2.2 --- Charge-orbital ordering --- p.1-15 / Chapter 1.3 --- Trilayer Magnetic Tunneling Junction (MTJ) --- p.1-18 / Chapter 1.3.1 --- Half-metallic Fe3O4 --- p.1-18 / Chapter 1.3.2 --- Tunneling Magnetoresistance (TMR) --- p.1-19 / Chapter 1.4 --- Research Motivation --- p.1-20 / Chapter 1.5 --- Scope of this thesis --- p.1-21 / References --- p.1-22 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Sample Preparation --- p.2-1 / Chapter 2.1.1 --- Vacuum System --- p.2-1 / Chapter 2.1.2 --- Facing-target Sputtering (FTS) Technique --- p.2-3 / Chapter 2.2 --- Sample Treatment --- p.2-7 / Chapter 2.2.1 --- Vacuum Annealing (VA) --- p.2-7 / Chapter 2.2.2 --- Silver Electrode Coating System --- p.2-9 / Chapter 2.3 --- Sample Characterization --- p.2-11 / Chapter 2.3.1 --- Four-point-probe DC Resistivity Measurement --- p.2-11 / Chapter 2.3.2 --- Current-Voltage Measurement (IV) --- p.2-11 / Chapter 2.3.3. --- X-ray Diffraction (XRD) --- p.2-13 / Chapter 2.3.4 --- X-ray Fluorescence (XRF) Method --- p.2-14 / Chapter 2.3.5 --- Alpha-step Surface Profiler --- p.2-14 / Chapter 2.3.6 --- Atomic Force Microscope (AFM) --- p.2-15 / References --- p.2-16 / Chapter Chapter 3 --- Fabrication of Fe3- xZnxO4Thin Films / Chapter 3.1 --- Thin Film Deposition --- p.3-1 / Chapter 3.1.1 --- Review of Deposition Procedures --- p.3-1 / Chapter 3.1.2 --- Preparation of Substrates --- p.3-6 / Chapter 3.1.3 --- Deposition of Fe3-xZnxO4 thin films --- p.3-7 / Chapter 3.2 --- Characterization of Fe3-xZnxO4 thin films --- p.3-9 / Chapter 3.2.1 --- Surface Morphology --- p.3-9 / Chapter 3.2.2 --- Temperature-Dependent Resistivity Measurement --- p.3-11 / Chapter 3.3 --- Factors affecting the Quality of films --- p.3-18 / Chapter 3.3.1 --- Effect of Substrates --- p.3-18 / Chapter 3.3.2 --- Effects of Sputtering Power --- p.3-21 / Chapter 3.3.3 --- Effects of Temperature --- p.3-24 / Chapter 3.3.4 --- Effects of Thickness --- p.3-29 / Chapter 3.4 --- Chapter summary --- p.3-32 / References --- p.3-33 / Chapter Chapter 4 --- Vacuum Annealing of Fe3-xZnxO4 Thin Films / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.2 --- Post-Annealing Effect in the Presence of Oxygen --- p.4-6 / Chapter 4.3 --- Vacuum Annealing of Fe3-xZnx04 thin films --- p.4-12 / Chapter 4.3.1 --- First Stage of Vacuum Annealing --- p.4-12 / Chapter 4.3.2 --- Second Stage of Vacuum Annealing --- p.4-17 / Chapter 4.3.3 --- Third Stage of Vacuum Annealing --- p.4-25 / Chapter 4.4 --- Chapter summary --- p.4-32 / References --- p.4-33 / Chapter Chapter 5 --- Trilayer Magnetic Tunneling Junction (MTJ) / Chapter 5.1 --- Introduction --- p.5-1 / Chapter 5.2 --- Fabrication of Trilayer Magnetic Tunneling Junction --- p.5-3 / Chapter 5.3 --- Tunneling Magnetoresistance (TMR) --- p.5-5 / Chapter 5.3.1 --- Current-Voltage Characteristic Curve (IV curve) --- p.5-5 / Chapter 5.3.2 --- Magnetoresistance Measurement --- p.5-8 / References --- p.5-10 / Chapter Chapter 6 --- Conclusions / Chapter 6.1 --- Conclusions --- p.6-1 / Chapter 6.2 --- Further research --- p.6-2 / References --- p.6-3

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Ph.D.

The mixed metal compound, Chromated Copper Arsenate, or CCA, has been widely used as a wood preservative. The metal ions in CCA, CrO��������, Cu�����, and AsO��������, have been found in contaminated surface and subsurface soils and groundwater nearby some wood preservative facilities and nearby wood structures. Iron oxides are a ubiquitous soil-coating constituent and are believed to be a main factor in controlling the transport and fate of many metals in the soil solution. In this research, iron-oxide-coated sand (IOCS) is used as a surrogate soil to investigate the adsorption and transport behavior of the mixed metals solution, copper, chromate, and arsenate, in the subsurface environment. Copper adsorption increases with increasing pH. The presence of arsenate in the solution slightly increases, while chromate has minimal effect, on the amount of copper adsorbed. Chromate adsorption decreases with increasing pH. With arsenate present in solution, chromate adsorption is significantly suppressed over the pH range studied. In contrast, the presence of copper slightly increases chromate adsorption. Similar to chromate, arsenate adsorption decreases with increasing pH. The presence of chromate or copper does not affect the amount of arsenate adsorbed over the range of concentrations studied. Two surface complexation models, the triple layer model (TLM) and the electrostatic implicit model (EIM), were used to simulate equilibrium adsorption in both single-metal and multi-metal systems. Simulations using the specific surface complexation equilibrium constants derived from either the single-metal or the multi-metal systems with both the TLM and the EIM were successful in fitting the adsorption data in that respective single or multi-metal system. The local equilibrium assumption using batch-derived sorption isotherm parameters from the EIM failed to predict the copper and arsenate transport, while it adequately described chromate transport. The breakthrough curves of all three metals were asymmetrical and showed long-tailing behavior. This nonideal behavior is caused by nonlinear sorption and/or non-equilibrium conditions during transport. The two-site chemical non-equilibrium model, which accounts for the kinetically controlled adsorption sites, was able to fit the observed breakthrough curves for all three metals in single-metal systems. However, the model was partially successful in predicting transport in multi-metal systems. / Graduation date: 2002

Seven iron ore pellets, two sinters, and one lump ore were studied in CO-CO₂-H₂-N₂ atmospheres from 350°C to 750°C, simulating the upper stack of the ironmaking blast furnace. Experiments were performed in a flowing gas reactor on single specimens of each type of substrate. Two different measurements were made: (1) the carbon deposition and concurrent iron oxide reduction rate at 550°C in 30%CO, 10%CO₂, 2%H₂, and 58%N₂; and (2) the amount of carbon deposited during a programmed increase in temperature and change in CO-CO₂ ratio simulating the descent of an ore specimen in the blast furnace stack. The rates of the concurrent reaction were determined from mass balances based on gas chromatographic analyses of the CO, CO₂H₂, and N₂ in both the inlet and outlet gases and the continuously recorded mass of the specimen. The materials were examined as to chemical composition, internal structure, porosity, and surface area. Elemental analyses of single iron oxide grains were made by electron microprobe. Slag materials and composition, and crystallinity were determined by microprobe and X-ray diffraction. The results of the experiments show that carbon deposition occurs only in the presence of metallic iron which is produced from the concurrent reduction of Fe₃O₄. The degree of reduction is controlled largely by the structure of the substrate, but the carbon deposition is controlled only by the chemical composition of the substrate--specifically, silicon in the iron and the CaO to MgO ratio. In the blast furnace simulation, the carbon deposition increases for pellets fluxed with dolomite to a maximum with lime-fluxed pellets. The effects of H₂ and CO₂ on the reactions were investigated in the isothermal experiments using an Empire pellet. The CO₂ controlled only the reduction, and this by diffusion of the CO₂. The hydrogen in very small amounts enhanced the deposition of carbon, probably by eliminating the presence of the inactive iron carbides. Under blast furnace conditions, the changes in the operation when the chemistry of the ore feed is changed to fluxed pellets will be due more to the shifts in the available heat within the stack from carbon deposition than to the low temperature reduction of the ores, which does not change with the addition of the flux materials.