Mechanism of the low temperature oxidation of synthetic magnetites

Sidhu, P. S.; Gilkes, R. J.; Posner, A. M.

doi:10.1016/0022-1902(77)80523-x

Cited by 119 publications

(123 citation statements)

References 14 publications

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“…Magnesium and other cations would have migrated out of the flakes to surfaces where they were released to soil solution. Several mineral alteration processes involve retention of anion layers and diffusion of cations, for example magnetite may alter topotaxially to maghemite (Sidhu et al, 1977).…”

Section: Discussionmentioning

confidence: 99%

Biotite Alteration in Deeply Weathered Granite. II. The Oriented Growth of Secondary Minerals

Gilkes

1979

Clays and clay miner.

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Abstract--Single grain X-ray and electron diffraction patterns of weathered biotite flakes exhibit groupings of 001 and hk reflections of biotite, vermiculite, mixed-layer clay minerals, and kaolinite indicating that the secondary minerals are in parallel crystallographic orientation to the parent biotite. Asterism of biotite reflections is enhanced by weathering. Gibbsite crystals developed in parallel basal orientation to biotite flakes. Most goethite in weathered biotite occurs as aggregates of randomly oriented crystals in cleavages and on grain surfaces. Some goethite is present on micaceous fragments as 0.05-/~m size, lathlike crystals in a hexagonal arrangement with their (100) face resting on the (001) biotite face. Selected area electron diffraction patterns of aggregates of lathlike goethite crystals contain 0k~, lk~, and 2k( reflections due to undulation of the aggregates and the extreme thinness of the crystals. These patterns indicate that the close packed anion layers in goethite coincide with the brucite-like layer of the micaceous minerals.

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Section: Discussionmentioning

confidence: 99%

Biotite Alteration in Deeply Weathered Granite. II. The Oriented Growth of Secondary Minerals

Gilkes

1979

Clays and clay miner.

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“…[15][16][17][18] Magnetite is an inverse spinel with Fe 2+ and Fe 3+ cations distributed among octahedral sites and Fe 3+ cations at tetrahedral sites.…”

Section: Introductionmentioning

confidence: 99%

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

et al. 2010

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The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic-acidcoated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic-acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe Ledge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic-acid-coated sample. However, O K-edge absorption spectroscopy observed a ~0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase, and exert an effect on the global electronic and optical properties of the material.This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO 2 .

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“…The standards of maghemite and hematite were obtained by heating precipitated magnetite at 220 ~ and 700~ for 3 hr, respectively (Sidhu et al, 1980). Changes in the shape of particles which accompanied the transformation of maghemite to hematite were studied by TEM using a Hitachi HU 11 instrument and the procedure described by Sidhu et aL (1977). Infrared (IR) spectra were recorded on a Perkin Elmer Model 337 Grating Spectrophotometer using KBr as the matrix.…”

Section: Transformation Of Maghemite To Hematitementioning

confidence: 99%

“…Sidhu et al (1977) showed that the presence of trace elements reduced the rate of oxidation of magnetite to maghemite. The present paper describes the effect of these trace elements on the transformation of maghemite to hematite.…”

Section: Introductionmentioning

confidence: 99%

Transformation of Trace Element-Substituted Maghemite to Hematite

Sidhu

1988

Clays and clay miner.

102

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Abstract--X-ray powder diffraction (XRD), transmission electron microscopy, infrared spectroscopy, differential thermal analysis, and surface area (BET) measurements were employed to investigate the transformation of microcrystalline maghemite to hematite. At 500~ pure maghemite was completely altered to hematite in 3 hr, whereas maghemites containing small amounts (< 1%) of Co, Ni, Zn, Cu, Mn, A1, V, and Cr required much longer heating times. The maghemite-to-hematite transformation temperature varied from 540* to 650"C. XRD line widths suggest that each particle of maghemite and hematite may have been a mosaic of many independent, coherently diffracting crystals. The transformation of maghemite to hematite at 650~ was accompanied by a reduction in surface area due to sintering of particles.

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Mechanism of the low temperature oxidation of synthetic magnetites

Cited by 119 publications

References 14 publications

Biotite Alteration in Deeply Weathered Granite. II. The Oriented Growth of Secondary Minerals

Biotite Alteration in Deeply Weathered Granite. II. The Oriented Growth of Secondary Minerals

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Transformation of Trace Element-Substituted Maghemite to Hematite

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