Mechanism of Metastable Wüstite Formation in the Reduction Process of Iron Oxide below 570℃

Chen, Zhi Yuan; Chou, Kuo‐Chih; Morita, Kazuki

doi:10.2320/matertrans.m2016147

Cited by 12 publications

(6 citation statements)

References 41 publications

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“…in wüstite-magnetite (FeO@Fe 3 O 4 ) core-shell nanoparticles. The lattice mismatch between FeO and Fe 3 O 4 has been theoretically and experimentally shown to range from approximately 2.3%-4.6%, falling within the range required for coherent strain conditions [15]. Elucidating the mechanisms of oxidation for iron oxide nanoparticles is an important problem as their magnetic properties depend on their crystal structure, and the formation of defects during oxidation can significantly affect their performance [16].…”

Section: Introductionmentioning

confidence: 94%

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

Poerwoprajitno,

Baradwaj,

Singh

et al. 2023

J. Phys. Mater.

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The use of transmission electron microscopy (TEM) to observe real-time structural and compositional changes has proven to be a valuable tool for understanding the dynamic behaviour of nanomaterials. However, identifying the nanoparticles of interest typically require an obvious change in position, size, or structure, as compositional changes may not be noticeable during the experiment. Oxidation or reduction can often result in subtle volume changes only, so elucidating mechanisms in real-time requires atomic-scale resolution or in-situ electron energy loss spectroscopy (EELS), which may not be widely accessible. Here, by monitoring the evolution of diffraction contrast, we can observe both structural and compositional changes in iron oxide nanoparticles, specifically the oxidation from a wüstite-magnetite (FeO@Fe3O4) core-shell nanoparticle to single crystalline magnetite, Fe3O4 nanoparticle. The in-situ TEM images reveal a distinctive light and dark contrast known as the "Ashby-Brown contrast", which is a result of coherent strain across the core-shell interface. As the nanoparticles fully oxidize to Fe3O4, the diffraction contrast evolves and then disappears completely, which is then confirmed by modelling and simulation of TEM images. This represents a new, simplified approach to tracking the oxidation or reduction mechanisms of nanoparticles using in-situ TEM experiments.

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Section: Introductionmentioning

confidence: 94%

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

Poerwoprajitno,

Baradwaj,

Singh

et al. 2023

J. Phys. Mater.

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“…Thus, even a small amount of metastable wüstite could have formed, it would be difficult to observe it in the experiments. Based on the second conjecture, theoretical analysis has been carried out [31]. It indicates that additives and crystal structure deformation can increase the possibility of metastable wüstite formation.…”

Section: Phase Transformationmentioning

confidence: 99%

Reduction Kinetics of Hematite Powder in Hydrogen Atmosphere at Moderate Temperatures

Chen

Dang

et al. 2018

Metals

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Hydrogen has received much attention in the development of direct reduction of iron ores because hydrogen metallurgy is one of the effective methods to reduce CO2 emission in the iron and steel industry. In this study, the kinetic mechanism of reduction of hematite particles was studied in a hydrogen atmosphere. The phases and morphological transformation of hematite during the reduction were characterized using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. It was found that porous magnetite was formed, and the particles were degraded during the reduction. Finally, sintering of the reduced iron and wüstite retarded the reductive progress. The average activation energy was extracted to be 86.1 kJ/mol and 79.1 kJ/mol according to Flynn-Wall-Ozawa (FWO) and Starink methods, respectively. The reaction fraction dependent values of activation energy were suggested to be the result of multi-stage reactions during the reduction process. Furthermore, the variation of activation energy value was smoothed after heat treatment of hematite particles.

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“…Suspicion to the traditional mechanisms has never stopped since 1970s according to Romanov and his partners' experimental results. [7,8] Chen [19] presented the meatastable wustite was formed in 400-500 °C. What more confusing is that wustite was found by Khader et al [9] as the final reduction product of hematite at 300-400 °C.…”

Section: Introductionmentioning

confidence: 99%

The Ideal and Regular Mechanisms of Hematite Reduction Reactions

Zhang

Xue

Zou

et al. 2022

Crystal Research and Technology

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The thermodynamic data of iron oxides reduction reactions from the most recognized thermodynamic database (NIST‐JANAF) show remarkable difference between stoichiometric and nonstoichiometric iron oxides. Iron oxides reduction equilibria in both CO‐CO2 and H2‐H2O atmospheres are calculated with Dieckmann's and Weiss’ defect models. Relevant literatures are investigated and reduction experiments are carried out to complement and interpret the newly calculated equilibrium diagram. The results suggest a conjecture of two routes for hematite reduction reactions. With the ideal and widely accepted mechanism, hematite is reduced to magnetite and then to iron below 576 °C, while the reduction route follows the sequence of Fe2O3 → Fe3−δO4 → FexO → Fe above 576 °C. With the regular but always unrecognized mechanism, the reduction process of hematite experiences Fe3O4, FeO, and Fe step by step in all possible temperature above 156 °C. In the regular mechanism, sufficient scattered impurities occupy crystal interstices of magnetite and prevent the newly produced FeO unit cell from dissolving into the solid solution of magnetite, and then the FeO will accumulate above 156 °C. Actually the regular mechanism is hard to realize and usually confused with the ideal mechanism. The presence of the regular mechanism is proved by experimental phenomena of the drop of eutectoid temperature.

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Mechanism of Metastable Wüstite Formation in the Reduction Process of Iron Oxide below 570℃

Cited by 12 publications

References 41 publications

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

Reduction Kinetics of Hematite Powder in Hydrogen Atmosphere at Moderate Temperatures

The Ideal and Regular Mechanisms of Hematite Reduction Reactions

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