Solid State Diffusion in the Reduction of Magnetite

Edström, J. O.; Bitsianes, G.

doi:10.1007/bf03377566

Cited by 19 publications

(15 citation statements)

References 5 publications

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“…To explain the following results better, we can use a typical pure iron oxidation process at the dense grain level shown in Figure 2. 10 It can be seen that iron cations and electrons diffuse from the pure iron phase through the initial gas−solid interface onto the new gas− solid interface to react with oxygen gas. As a result, the iron oxide layer grows outward at the gas−solid interface.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Reactive Solid Surface Morphology Variation via Ionic Diffusion

2012

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In gas-solid reactions, one of the most important factors that determine the overall reaction rate is the solid morphology, which can be characterized by a combination of smooth, convex and concave structures. Generally, the solid surface structure varies in the course of reactions, which is classically noted as being attributed to one or more of the following three mechanisms: mechanical interaction, molar volume change, and sintering. Here we show that if a gas-solid reaction involves the outward ionic diffusion of a solid-phase reactant then this outward ionic diffusion could eventually smooth the surface with an initial concave and/or convex structure. Specifically, the concave surface is filled via a larger outward diffusing surface pointing to the concave valley, whereas the height of the convex surface decreases via a lower outward diffusion flux in the vertical direction. A quantitative 2-D continuum diffusion model is established to analyze these two morphological variation processes, which shows consistent results with the experiments. This surface morphology variation by solid-phase ionic diffusion serves to provide a fourth mechanism that supplements the traditionally acknowledged solid morphology variation or, in general, porosity variation mechanisms in gas-solid reactions.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Reactive Solid Surface Morphology Variation via Ionic Diffusion

2012

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“…The characteristic ''rate minimum''-the unusual decrease of reaction rate around 873 K (600°C) despite the increase in reaction temperature-observed in many investigations [13,14,31,35,36] proves this claim since wustite becomes stable above 843 K (570°C). As the grown wustite islands coalesce and cover the whole surface, an additional interface labeled as ''a 3 '' arises between ''a 1 '' and ''a 2 '' interfaces as seen in Figures 2(c) and 2(d).…”

Section: ½4mentioning

confidence: 83%

“…This situation shows that wustite islands [13,14,35] whose trace entities cannot be sensed by any increase on reduction degree are on the way to spread to the whole surface of the particle with an extremely slow nucleation rate. As is known, equilibrium state for a reaction can be predicted by thermodynamics but it gives no information on how fast this equilibrium can be approached.…”

Section: Evaluation Of the First Regionmentioning

confidence: 99%

“…[12] Reduction kinetics of iron oxides have been widely investigated by numerous researchers until today, and remarkable progress involving increasingly complex models has been achieved. [13][14][15][16][17][18][19][20][21][22][23][24] Major part of the aforementioned researches has been performed by using fluidized bed reactors since they minimize effects of external heat and mass transfer resistances on reaction kinetics. [25] Besides that, due to the relatively smaller particle size of iron ores which is a requirement for fluidized bed, intraparticle diffusion effects are also restricted.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Direct Reduction Mechanism of Attepe Iron Ore by Hydrogen in a Fluidized Bed

Dilmaç

Yörük

Gülaboğlu

2015

Metall Mater Trans B

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“…Edstrom [3] and Edstrom and Bitsianes [4] used optical microscopy to study the relationship between microstructure and reduction rate, and observed that the reduction of hematite occurred more rapidly when there was early and extensive formation of pores in the solid reaction products, and concluded that the nucleation and growth of the solid reaction products were important for iron oxide reduction. Ei-Rahaiby and Rao [5] used a polycrystalline specimen of wustite, carried out hydrogen reduction at 238°C to 417°C, and observed the reaction between the oxide and the gas.…”

Section: Introductionmentioning

confidence: 99%

Microreaction mechanism in reduction of magnetite to wustite

Guo

Sasaki

Kashiwaya

et al. 2004

Metall Mater Trans B

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In order to understand the microreaction mechanism of the reduction of magnetite to wustite, hydrogen ions were implanted into magnetite at room temperature by an ion accelerator. The crystalloid transformation during the reduction process was investigated by using selected-area electron diffraction patterns. The experimental results showed that {220} planes on the surface of magnetite were changed first because the concentration of oxygen ions on the {220} planes is higher than other planes to follow the reaction of oxygen ions with hydrogen ions, leaving the {220} planes and resulting in rearrangement of ions. On the other hand, oxygen ions migrate more difficultly than iron ions in magnetite; therefore, {220} planes in the bulk are more stable than other planes. Based on the experimental facts, two kinds of microreaction mechanisms in reduction of magnetite to wustite are suggested. It was found that (1) wustite with [001] direction was formed on the magnetite with [001] direction, (2) (220) and (200) planes of wustite were parallel with (220) and (400) planes of magnetite, respectively, in crystal structure between parent phase and new phase, (3) some {220} planes were formed earlier than other ones in wustite during the reduction process. These results can be considered as due to the similar geometric distribution of oxygen ions between magnetite and wustite.

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Solid State Diffusion in the Reduction of Magnetite

Cited by 19 publications

References 5 publications

Reactive Solid Surface Morphology Variation via Ionic Diffusion

Reactive Solid Surface Morphology Variation via Ionic Diffusion

Investigation of Direct Reduction Mechanism of Attepe Iron Ore by Hydrogen in a Fluidized Bed

Microreaction mechanism in reduction of magnetite to wustite

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