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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.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references. / Microfiche. / xxi, 170 leaves, bound ill. 29 cm

[Truncated abstract] In the past decade, the synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) has received considerable attention due to their potential applications in biomedical fields. However, success in size and shape control of the SPIONs has been mostly achieved through organic routes using large quantities of toxic or/and expensive precursors in organic reaction medium at high reaction temperature. This has limited the biomedical applications of SPIONs and therefore, development of a synthetic method under aqueous condition that is reproducible, scalable, environmentally benign, and economically feasible for industrial production is of paramount importance in order to fully realise their practical applications. Spinning Disc Processing (SDP) has been used to synthesise superparamagnetic magnetite (Fe3O4) nanoparticles at room temperature via a modified chemical precipitation method under continuous flow condition and offer a potential alternative to be applied to SPIONs production. SDP has extremely rapid mixing under plug flow conditions, effective heat and mass transfer, allowing high throughput with low wastage solvent efficiency. The synthesis process involves passing ammonia gas over a thin aqueous film of Fe2+/3+ which is introduced through a jet feed close to the centre of a rapidly rotating disc (500-2500 rpm). Synthetic parameters such as precursor concentrations, temperature, flow rate, disc speed, and surface texture influence the particle sizes. ... Magnetic silica microspheres are receiving great attention for possible applications in magnetic targeting drug delivery, bioseparation and enzyme isolation. However, the current available methods for preparation suffer from the setback of low loading of Fe3O4 nanoparticles in the silica microsphere, which result in low magnetic moment, thereby limiting their practical applications. Therefore it is of considerable importance to develop new alternative synthetic methods for fabricating magnetic silica microspheres with high magnetic nanoparticles loading. Superparamagentic Fe3O4 nanoparticles (8-10 nm diameter) and curcumin have been encapsulated in mesoporous silica in a simple multiplestep self assembly approach process with high Fe3O4 nanoparticles loading (37%). The synthesis involves loading of curcumin in the Cetyltrimethylammonium bromide (CTAB) micellar rod in the presence of superparamagnetic Fe3O4 nanoparticles via a parallel synergistic approach. The synthesised magnetic mesoporous silica composite material is stable, superparamagnetic with high saturation magnetisation before and after curcumin leaching experiment. Under physiological pH in phosphate buffer, the curcumin is slowly released over several days. These magnetic mesoporous silica are expected to have great potential as targeted drug delivery systems.

Thesis (Ph. D.)--Murdoch University, 1995. / Thesis submitted to the School of Mathematical and Physical Sciences. Includes bibliographical references (leaves 274-288).

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on May 7, 2009) Includes bibliographical references.

Thesis (Ph. D.)--Johns Hopkins University, 1930. / Date in imprint changed in manuscript to 1931. Biographical note. Bibliography: p. 82-87.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.