Defects and Cation Diffusion in Magnetite (VII): Diffusion Controlled Formation of Magnetite During Reactions in the Iron‐Oxygen System

Backhaus‐Ricoult, M.; Dieckmann, R.

doi:10.1002/bbpc.19860900814

Cited by 54 publications

(47 citation statements)

References 8 publications

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“…Based on available space model, the oxidation kinetics of two ferritic-martensitic steels are developed to predict in supercritical water at 400 ∘ C, 500 ∘ C, and 600 ∘ C. The iron diffusion coefficients in magnetite and Fe-Cr spinel, which are extrapolated from studies of Backhaus-Ricoult and Dieckmann [17] and Töpfer et al [18], are used for calculation of oxidation kinetics of steels under supercritical water environment. The main conclusions are as follows.…”

Section: Resultsmentioning

confidence: 99%

“…The concentration of defects is linked to the oxygen activity in oxide scales and the diffusion coefficient of Fe ions is dependent on the oxygen activity in two oxide layers. The diffusion coefficient of Fe ions in magnetite can be expressed by oxygen activity and temperature, and the equation can be written [17]:…”

Section: H the Dissociation Of Oxide Scales Is Neglectedmentioning

confidence: 99%

“…Advances in Materials Science and Engineering Dieckmann [17]. For the iron diffusion coefficient in spinel oxide, the data at 1200 ∘ C given by Töfpfer et al [18] is used and extrapolated towards lower temperature.…”

Section: Determination Of Iron Diffusion Coefficient Inmentioning

confidence: 99%

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Estimation of Oxidation Kinetics and Oxide Scale Void Position of Ferritic-Martensitic Steels in Supercritical Water

Sun

Yan

2017

Advances in Materials Science and Engineering

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Exfoliation of oxide scales from high-temperature heating surfaces of power boilers threatened the safety of supercritical power generating units. According to available space model, the oxidation kinetics of two ferritic-martensitic steels are developed to predict in supercritical water at 400 ∘ C, 500 ∘ C, and 600 ∘ C. The iron diffusion coefficients in magnetite and Fe-Cr spinel are extrapolated from studies of Backhaus and Töpfer. According to Fe-Cr-O ternary phase diagram, oxygen partial pressure at the steel/Fe-Cr spinel oxide interface is determined. The oxygen partial pressure at the magnetite/supercritical water interface meets the equivalent oxygen partial pressure when system equilibrium has been attained. The relative error between calculated values and experimental values is analyzed and the reasons of error are suggested. The research results show that the results of simulation at 600 ∘ C are approximately close to experimental results. The iron diffusion coefficient is discontinuous in the duplex scale of two ferritic-martensitic steels. The simulation results of thicknesses of the oxide scale on tubes (T91) of final superheater of a 600 MW supercritical boiler are compared with field measurement data and calculation results by Adrian's method. The calculated void positions of oxide scales are in good agreement with a cross-sectional SEM image of the oxide layers.

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Section: Resultsmentioning

confidence: 99%

Section: H the Dissociation Of Oxide Scales Is Neglectedmentioning

confidence: 99%

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Estimation of Oxidation Kinetics and Oxide Scale Void Position of Ferritic-Martensitic Steels in Supercritical Water

Sun

Yan

2017

Advances in Materials Science and Engineering

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“…Moreover it is consistent with the fact that the chemical reaction usually limits at lower temperatures. Backhaus-Ricoult and Dieckmann 33) also observed that phase interphase reaction can be the rate controlling step under these conditions.…”

Section: Limiting Stepmentioning

confidence: 83%

Reduction Behavior of Hematite to Magnetite under Fluidized Bed Conditions

et al. 2004

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Reduction kinetic tests of Mt. Newman hematite ore from Western Australia were carried out in a laboratory-scale fluidized bed reactor at temperatures from 623 to 873 K and an absolute pressure of 10 bar. The reducing gas mixture was thermodynamically in equilibrium with magnetite and consisted of a mixture of H 2 , H 2 O, CO, CO 2 and CH 4 . The effect of temperature and residence time was studied. The original ore and its mineralogical and petrographical changes with increasing reduction time were analyzed. A reflected-light microscope technique with CCD-camera was used to determine the progress and the mechanism of reduction. According to the mineralogy and texture the ore could be classified in four types (coarse hematite, microplaty hematite, limonite and martite) with different reduction characteristics. Limonite and martite showed better reducibility than coarse and fine hematite.At all ore types the growth of dense magnetite rims was observed. The thickness of these layers was found to be linear proportional to reduction time. After analyzing the single steps of the reduction process the phase interface reaction turned out to be rate controlling between 673 and 773 K. Its activation energy is 91 kJ/mol. KEY WORDS: iron ore reduction; fluidized bed; hematite; magnetite; elevated pressure; rate controlling step.

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“…Formation of outer and inner oxide scales is governed by outward diffusion of Fe ions and by inward diffusion of O ions, respectively. The diffusivity of O ions in Fe 3 O 4 is reported to be much lower than that of Fe ions, 17) so that the thickness of the inner oxide scale may decrease as the thickness of the outer oxide scale increases at temperatures between 873 K and 973 K. However, the thickness of both the outer and inner oxide scales decreased at 1 073 K compared with the thicknesses at 973 K. This could be attributed to quick formation of a Cr-and Si-enriched layer, which would act as barrier for diffusion of Fe and O ions as described below.…”

Section: Steam Oxidation Testsmentioning

confidence: 99%