High voltage microscopy of the reduction of hematite to magnetite

Swann, P. R.; Tighe, N. J.

doi:10.1007/bf02696936

Cited by 86 publications

(55 citation statements)

References 8 publications

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“…[36][37][38][39] The rate of this surface reaction has been shown to be proportional to the partial pressure of the reductant gas. 28,36,37,39,40 In the current study, TGA runs were performed with p H2 varying from 0.003 to 0.08 atm, which validated that the rate of reduction was proportional to p H2 .…”

Section: Resultsmentioning

confidence: 99%

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: 99%

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Ndlela

Shanks

2003

Ind. Eng. Chem. Res.

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“…Normal swelling up to 20 vol-% occurs during the transformation of the pellets from hematite to magnetite in the initial stages of reduction, in which the crystal structure changes from hexagonal to cubic. 2,7,8) Singh and Björkman 2) state that conversion from magnetite to wüstite can also lead to swelling to some extent. Abnormal swelling occurs during the transformation of wüstite to metallic iron in the latter stages of reduction and is generally believed to be caused by the growth of iron whiskers in the reduction of wüstite.…”

Section: Introductionmentioning

confidence: 99%

Dynamic and Isothermal Reduction Swelling Behaviour of Olivine and Acid Iron Ore Pellets under Simulated Blast Furnace Shaft Conditions

Iljana

Mattila²,

Alatarvas

et al. 2012

ISIJ Int.

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Pellet swelling has been widely studied, being simultaneous with reduction reactions and common in the operation of blast furnaces. A tube furnace equipped with a camera recording system was used here to study the dynamic and isothermal reduction swelling behaviour of olivine and acid pellets under simulated BF shaft conditions. The olivine pellets were magnetically separated into three fractions, containing low, medium and high amounts of magnetite in the core. The divalent iron (FeO) content of these fractions was 0.1 wt-%, 0.2 wt-% and 2.9 wt-%, respectively. Pellets with a large magnetite nucleus were observed to encompass numerous cracks, which was reflected in a poor LTD test value, while SiO2-rich reference pellets with a different slag chemistry had more restrained swelling and cracking behaviour in dynamic reduction. Swelling in the olivine pellets was associated with cracking at the boundary between the original magnetite nucleus and the hematite shell.The dynamic reduction swelling test results showed lower reduction swelling indices (max 17% in volume) than under isothermal conditions (max 51% in volume), in which case the pellets were suddenly exposed to a strongly reducing atmosphere. It is thus suggested that the reduction swelling behaviour of iron ore pellets should preferably be studied dynamically under simulated blast furnace conditions in order to achieve a realistic understanding of their swelling behaviour in a blast furnace.

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“…Meanwhile, the values of n = 1−2 represent the 1D growth of nuclei [28]. Thus, this equationindicates that this phase transition of hematite to magnetite proceeded through a 1D growth process, suggesting that the newly generated magnetite nuclei wereneedle-like, which wasalso proven by Et-Tabirou, Swann, and Bahgat [29][30][31]. Additionally, the kinetic constant (k) values for different roasting temperatures could be obtained from the experimental α = f (t) data through the Avrami-Erofe'ev equation (n = 1.58).…”

Section: Determination Of the Kinetic Modelmentioning

confidence: 73%

Mechanism and Kinetics of the Reduction of Hematite to Magnetite with CO–CO2 in a Micro-Fluidized Bed

Han

et al. 2017

Minerals

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Abstract:The mechanism and kinetics of the reduction of hematite to magnetite in a laboratory-scale, micro-fluidized bed reactor were isothermally investigated. The procedure consisted of the isothermal heating in a flow of a 20%CO-80%CO 2 mixture at temperatures from 500 • C to 600 • C. It was found that the Avrami-Erofe'ev model of nucleation and 1D growth (n = 1.58) successfully described the phase transition of hematite to magnetite, and the value of activation energy ∆E a of the reaction was estimated to be 48.70 kJ/mol. The microstructure properties for specimens with different conversion degrees were analyzed using the Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). The results showed that the magnetite nuclei were needle-like, and the hematite specimens became thoroughly porous after complete reduction to magnetite. The physical and chemical processes of the reaction were also discussed.

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High voltage microscopy of the reduction of hematite to magnetite

Cited by 86 publications

References 8 publications

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Reducibility of Potassium-Promoted Iron Oxide under Hydrogen Conditions

Dynamic and Isothermal Reduction Swelling Behaviour of Olivine and Acid Iron Ore Pellets under Simulated Blast Furnace Shaft Conditions

Mechanism and Kinetics of the Reduction of Hematite to Magnetite with CO–CO2 in a Micro-Fluidized Bed

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