Mechanism of Oxidation of Magnetite to γ-Fe2O3

Gallagher, K. J.; Feitknecht, W.; Mannweiler, U.

doi:10.1038/2171118a0

Cited by 221 publications

(174 citation statements)

References 12 publications

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“…The different behavior depending on the particle size was explained by the lattice strain developing during oxidation. This conclusion was based on the model proposed by Gallagher et al, 27 who predicted that 'during oxidation a high concentration gradient of cation holes would develop in the monocrystalline particles, leading to a gradient in the lattice constant; thus lattice strain would develop.' Hence the lattice strain was assumed to be the driving force for the nucleation of˛-Fe 2 O 3 .…”

Section: Experiments On Powdered Magnetitementioning

confidence: 99%

“…5), which is in a very good agreement with literature data on the oxidation of magnetite in air. 27 A further increase in illumination power leads to a rapid growth of peaks of hematite accompanied by a gradual deterioration of the modes of magnetite. Figure 8 summarizes the evolution of mode wavenumbers of magnetite and hematite during the process of oxidation.…”

Section: Calculation Of Temperature From the Thermodynamic Grüneisen mentioning

confidence: 99%

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Raman study of magnetite (Fe₃O₄): laser‐induced thermal effects and oxidation

Shebanova

Lazor

2003

J Raman Spectroscopy

537

307

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Section: Experiments On Powdered Magnetitementioning

confidence: 99%

Section: Calculation Of Temperature From the Thermodynamic Grüneisen mentioning

confidence: 99%

Raman study of magnetite (Fe₃O₄): laser‐induced thermal effects and oxidation

Shebanova

Lazor

2003

J Raman Spectroscopy

537

307

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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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“…This contradiction is eliminated if we assume that in our experiments the application of a more active oxidizer (H 2 O 2 ) originally leads to the formation of the Fe 3 O 4 phase in a nanodisperse state, which is subsequently oxidized by hydrogen peroxide to γ-Fe 2 O 3 by a topotactical solidstate reaction mechanism. The possibility of Fe 3 O 4 → γ-Fe 2 O 3 transformation occurring in oxygen-containing aqueous media has been reported previously [3,19].…”

Section: Fig 2 the Average Crystal Size D (Nm) Of Phases Formed In mentioning

confidence: 99%

“…In conclusion, let us consider the nature of the water of hdration in γ-Fe 2 O 3 . According to [9,19,21], the nanodisperse samples of γ-Fe 2 O 3 , as distinct from coarse crystalline ones, have a spinel-type defect structure and regular defects in the cationic sublattice. The structural formula of nanodisperse γ-Fe 2 O 3 is Fe 8 2.67 Fe 13.33 O 32 , where is a vacancy in the octahedral cationic positions.…”

Section: Fig 2 the Average Crystal Size D (Nm) Of Phases Formed In mentioning

confidence: 99%

Nanodisperse oxide compounds of iron formed in the FeSO4 – KOH – H2O – H2O2 system (4.0 ≤ pH ≤ 13.0)

Жеребцов¹,

Мирасов²,

Kleschev³

et al. 2015

Nanosist.: fiz. him. mat.

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The regularities of phase formation during oxidation of aqueous solutions of FeSO 4 and (or) suspensions of Fe(OH) 2 at quasi-constant temperature and pH values have been studied for wide intervals of temperature (20 -85• C) and (4.0 -13.0) of the reaction medium. The produced nanodisperse materials have been examined by X-ray phase analysis, IR spectroscopy, scanning electron microscopy and X-ray fluorescence analysis, as well as by thermogravimetric analysis combined with thermal analysis and mass spectrometric analysis of released gases. The dependences of the phase, chemical and disperse compositions of the formed precipitates on the synthesis parameters have been revealed.

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Mechanism of Oxidation of Magnetite to γ-Fe2O3

Cited by 221 publications

References 12 publications

Raman study of magnetite (Fe₃O₄): laser‐induced thermal effects and oxidation

Raman study of magnetite (Fe₃O₄): laser‐induced thermal effects and oxidation

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

Nanodisperse oxide compounds of iron formed in the FeSO4 – KOH – H2O – H2O2 system (4.0 ≤ pH ≤ 13.0)

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Mechanism of Oxidation of Magnetite to γ-Fe2O3

Cited by 221 publications

References 12 publications

Raman study of magnetite (Fe3O4): laser‐induced thermal effects and oxidation

Raman study of magnetite (Fe3O4): laser‐induced thermal effects and oxidation

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

Nanodisperse oxide compounds of iron formed in the FeSO4 – KOH – H2O – H2O2 system (4.0 ≤ pH ≤ 13.0)

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Raman study of magnetite (Fe₃O₄): laser‐induced thermal effects and oxidation

Raman study of magnetite (Fe₃O₄): laser‐induced thermal effects and oxidation