The System Iron—Oxygen. II. Equilibrium and Thermodynamics of Liquid Oxide and Other Phases

Darken, L. S.; Gurry, R. W.

doi:10.1021/ja01209a030

Cited by 704 publications

(199 citation statements)

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“…The stoichiometry of the phase here described falls within the most puzzling region of the Fe-O phase diagram, between wüstite and magnetite (7,(16)(17)(18)(19). With increasing temperature, at ambient pressure, the Fe-O phase diagram at 44 at.…”

Section: Energetics and Stability Ofmentioning

confidence: 65%

Discovery of the recoverable high-pressure iron oxide Fe₄O₅

Lavina

Dera

Kim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

134

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Phases of the iron–oxygen binary system are significant to most scientific disciplines, directly affecting planetary evolution, life, and technology. Iron oxides have unique electronic properties and strongly interact with the environment, particularly through redox reactions. The iron–oxygen phase diagram therefore has been among the most thoroughly investigated, yet it still holds striking findings. Here, we report the discovery of an iron oxide with formula Fe 4 O 5 , synthesized at high pressure and temperature. The previously undescribed phase, stable from 5 to at least 30 GPa, is recoverable to ambient conditions. First-principles calculations confirm that the iron oxide here described is energetically more stable than FeO + Fe 3 O 4 at pressure greater than 10 GPa. The calculated lattice constants, equation of states, and atomic coordinates are in excellent agreement with experimental data, confirming the synthesis of Fe 4 O 5 . Given the conditions of stability and its composition, Fe 4 O 5 is a plausible accessory mineral of the Earth’s upper mantle. The phase has strong ferrimagnetic character comparable to magnetite. The ability to synthesize the material at accessible conditions and recover it at ambient conditions, along with its physical properties, suggests a potential interest in Fe 4 O 5 for technological applications.

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Section: Energetics and Stability Ofmentioning

confidence: 65%

Discovery of the recoverable high-pressure iron oxide Fe₄O₅

Lavina

Dera

Kim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

134

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“…[8][9][10] Taylor et al 9) have measured the thermal diffusivities of iron oxide scales on iron substrates from 450 to 1 250 K using the laser flash method. 11) The scale phase composition and amounts of Fe 3 O 4 and Fe produced by the FeO decomposition are not considered, although they are thermodynamically possible below 843 K. 12) In fact, these form easily and very rapidly at 623 to 723 K in dynamics, as shown in a study of FeO decomposition dynamics by Tanei and Kondo. 13) Baud et al 14) have also reported that significant numbers of magnetite seams are generated in the temperature range of 648 to 748 K. More recently, Endo et al 8) have measured the thermal diffusivity of an actual oxide scale formed on a steel slab during hot rolling using the laser flash method following the analysis proposed by Baba.…”

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Thermal Diffusivity and Conductivity of FeO Scale Produced on Iron by Thermal Oxidation

Endo

Akoshima³

et al. 2017

ISIJ International

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The thermal diffusivity/conductivity of FeO scales produced on iron substrates by thermal oxidation have been determined as functions of temperature. Iron plates (99.99%) were oxidised at 973 K in air to obtain oxide scales of FeO, Fe 3 O 4 , and Fe 2 O 3 , and then were reduced at 1 273 K in nitrogen to obtain FeO-only. The densities of these scales were 5.85-6.05 g cm − 3 . The laser flash method was used to measure the apparent thermal diffusivity of the whole sample from room temperature to 1 164 K during the heating/ cooling cycles. This was converted to the thermal diffusivity of the scale only, which in turn was converted to the thermal conductivity. However, these values depended on the scale thickness, which suggests an interfacial heat resistance occurs between the scale layer and iron substrate. In addition, scanning electron microscopy (SEM) observations revealed that the scales contained Fe and Fe 3 O 4 phases after heating. The scale thermal diffusivity/conductivity were corrected considering the interfacial heat resistance and dispersed phases to derive the corresponding values for FeO only. The interfacial heat resistance derived from the thickness dependence of the scale thermal conductivity was 8.3 × 10 − 6 m 2 K W − 1 . Using this value, the thermal diffusivity of FeO was derived as 3.7 × 10 − 7 -5.8 × 10 − 7 m 2 s − 1 and the thermal conductivity as 1.8-2.5 W m − 1 K − 1 between room temperature and 1 164 K. The temperature coefficients of the thermal conductivity were mostly negative, which would be dominated by the phonon mean free path.

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“…Because magnetite possesses a higher oxygen content than wüstite, precipitation can only occur, without the co-precipitation of iron, if accompanied by a local decrease in oxygen content in the surrounding wüstite. This is accommodated by the large range in stoichiometry of wüstite, which is evident from the Fe-Fe 2 O 3 phase diagram (Darken & Gurry, 1946) (the stoichiometry of magnetite only varies slightly below 1000 ° C). This also results in a stoichiometry gradient across the wüstite layer between the scale/substrate interface (low oxygen content) and the wüstite/magnetite interface (high oxygen content) (Engell, 1958).…”

Section: Introductionmentioning

confidence: 99%

Phase determination and microstructure of oxide scales formed on steel at high temperature

West

Birosca

Higginson

2005

Journal of Microscopy

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SummaryEven in simple low-alloy steels the oxide scales that form during hot working processes are often a complex mixture of three iron oxide phases: haematite, magnetite and wüstite. The mechanical properties, and hence descalability, are intimately linked with phase distribution and microstructure, which in turn are sensitive to both steel composition and oxidation conditions. In this study electron backscatter diffraction in the SEM has been used to characterize the microstructures of oxide scales formed on two compositions of low-alloy steel. The technique can unambiguously differentiate between the candidate phases to provide the phase distribution within the scale. This is used to investigate grain orientation relationships both within and between phase layers. It has been found that the strength of the orientational relationship between the magnetite and wüstite layers is dependent on steel composition, and in particular Si content. In a low-Si (0.01 wt%) alloy only a very weak relationship was found to exist for a range of oxidation temperatures (800 -1000 ° C), whereas for the higher Si (0.37 wt%) alloy a strong relationship was observed under the same oxidation conditions. These orientational relationships are particularly important because, in this temperature range, the majority of oxide scale growth occurs at the magnetite/ wüstite interphase boundary.

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The System Iron—Oxygen. II. Equilibrium and Thermodynamics of Liquid Oxide and Other Phases

Cited by 704 publications

References 0 publications

Discovery of the recoverable high-pressure iron oxide Fe₄O₅

Discovery of the recoverable high-pressure iron oxide Fe₄O₅

Temperature Dependence of Thermal Diffusivity and Conductivity of FeO Scale Produced on Iron by Thermal Oxidation

Phase determination and microstructure of oxide scales formed on steel at high temperature

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The System Iron—Oxygen. II. Equilibrium and Thermodynamics of Liquid Oxide and Other Phases

Cited by 704 publications

References 0 publications

Discovery of the recoverable high-pressure iron oxide Fe4O5

Discovery of the recoverable high-pressure iron oxide Fe4O5

Temperature Dependence of Thermal Diffusivity and Conductivity of FeO Scale Produced on Iron by Thermal Oxidation

Phase determination and microstructure of oxide scales formed on steel at high temperature

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Product

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Discovery of the recoverable high-pressure iron oxide Fe₄O₅

Discovery of the recoverable high-pressure iron oxide Fe₄O₅