Some properties of γ-Fe2O3 obtained by hydrogen reduction of α-Fe2O3

Aharoni, Amikam; Frei, E. H.; Schieber, M.

doi:10.1016/0022-3697(62)90512-7

Cited by 66 publications

(15 citation statements)

References 26 publications

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“…In addition, the maghemite phase is present. Previous studies with hematite have shown that maghemite forms as an intermediate phase upon reduction to magnetite, [29][30][31] so the presence of maghemite in the 700°C sample further supports the initiation of reduction. Studies by Lecznar have shown that the transformation of hematite to maghemite occurs in the 550-750°C temperature range.…”

Section: Resultsmentioning

confidence: 59%

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Ndlela

Shanks

2003

Ind. Eng. Chem. Res.

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There is economic incentive to operate the ethylbenzene dehydrogenation reaction at low steam/ ethylbenzene ratios. To develop catalysts capable of performing under these conditions, it is necessary to understand the mechanism whereby the concomitant activity loss occurs. A potentially important mechanism is the reduction of the iron oxide. Thermogravimetric analysis in conjunction with X-ray diffraction is used to characterize the reduction properties resulting from potassium addition to iron oxide. The impacts of potassium addition on the temperature required to initiate reduction with hydrogen and on the apparent activation energy of reduction are determined. Reducibility of the potassium/iron oxide system in the presence of other dehydrogenation catalyst promoters is also presented. There is economic incentive to operate the ethylbenzene dehydrogenation reaction at low steam/ ethylbenzene ratios. To develop catalysts capable of performing under these conditions, it is necessary to understand the mechanism whereby the concomitant activity loss occurs. A potentially important mechanism is the reduction of the iron oxide. Thermogravimetric analysis in conjunction with X-ray diffraction is used to characterize the reduction properties resulting from potassium addition to iron oxide. The impacts of potassium addition on the temperature required to initiate reduction with hydrogen and on the apparent activation energy of reduction are determined. Reducibility of the potassium/iron oxide system in the presence of other dehydrogenation catalyst promoters is also presented.

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Section: Resultsmentioning

confidence: 59%

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Ndlela

Shanks

2003

Ind. Eng. Chem. Res.

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“…Bulk coercive force Hc also increased from 1000 to 200°C [ Fig. 4C; see also (15,23)]. These changes cannot result from subdivision of originally MD grains, because the MD fraction is small; therefore, SP grains must be growing to stable SD size.…”

Section: Ozden Ozdemir and David J Dunlopmentioning

confidence: 80%

“…The Ms values indicate about 40% hematite and 60% maghemite after the 656'C run. Curie temperatures of the spinel phase were 6020 to 614°C after these runs, compared to 590°C (14,15) to 645°C (16) for maghemite.…”

Section: Ozden Ozdemir and David J Dunlopmentioning

confidence: 99%

Chemico-Viscous Remanent Magnetization in the Fe ₃ O _4-y Fe ₂ O ₃ System

Özdemir

Dunlop

1989

Science

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The chemical remanent magnetization (CRM) acquired when single-domain size magnetite (Fe(3)0(4)) oxidizes to maghemite (gammaFe(2)O(3)) in a 50-microtesla field at a series of 13 temperatures from 1000 to 6560C is of similar intensity to viscous remanent magnetization (VRM) acquired under the same field and temperature conditions by unoxidized magnetite. The remanences of the oxidized and unoxidized phases also have similar resistances to demagnetization. These similarities imply that the remanence of the oxidized material is a chemico-viscous remanent magnetization (CVRM) having some of the characteristics of both classic growth CRM and thermally activated VRM. At low temperatures in partially oxidized grains, VRM of the magnetite core and growth CRM of the maghemite surface layer contribute about equally to CVRM. Near the Curie point, intensity of CVRM increases to a Hopkinson-type peak. High-temperature CVRM is more resistant to demagnetization than the thermoremanent magnetization (TRM) produced from cooling through the Curie point.

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“…A defect spinel (r) phase is ubiquitous in this class of basalts and is formed through oxidation of Q phase minerals Schmidt and Vermaas, 1955;Lepp, 1957;Colombo et a1, 1964;Aharoni et al, 1962;Nicholls, 1955;Ozima and Larson, 1967;Kobayashi, 1959). The r phase is considered to be the intermediate step in the Q-r-a transformation.…”

Section: Resultsmentioning

confidence: 99%

Magnetization of Ocean Basalts

Wasilewski¹

1968

J. geomagn. geoelec

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Some properties of γ-Fe2O3 obtained by hydrogen reduction of α-Fe2O3

Cited by 66 publications

References 26 publications

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Chemico-Viscous Remanent Magnetization in the Fe ₃ O _4-y Fe ₂ O ₃ System

Magnetization of Ocean Basalts

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Some properties of γ-Fe2O3 obtained by hydrogen reduction of α-Fe2O3

Cited by 66 publications

References 26 publications

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Chemico-Viscous Remanent Magnetization in the Fe 3 O 4-y Fe 2 O 3 System

Magnetization of Ocean Basalts

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Chemico-Viscous Remanent Magnetization in the Fe ₃ O _4-y Fe ₂ O ₃ System