Wachstum der Eisenphase auf Wüstit während der Reduktion in Wasserstoff-Wasserdampf-Gemischen

Pluschkell, Wolfgang; Yoshikoshi, Hideyuki

doi:10.1002/srin.197001649

Cited by 17 publications

(7 citation statements)

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“…These data show excellent internal agreement. Regression analysis of the data shown in The activation energy of 71 400J/g•mol found here agrees reasonably well with those reported by Turkdogan and Vinters 2 ) and Feinman and Drexler.6) The activation energy values reported by Pluschkell and Yoshikoshi 7 ) and Yoshikoshi et at. 8 ) are smaller than the value found in the present study.…”

Section: R Esults and Discussionsupporting

confidence: 91%

Kinetics of Reduction of Wustite by Hydrogen-Helium Gas Mixtures at Modest Temperatures

El-Rahaiby

Rao

1980

ISIJ Int.

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The kinetics of reduction of wustite by hydrogen-helium gas mixtures were investigated at relatively modest temperatures, namely, 295° and 334°C. At each temperature, the effect of the partial pressure of hy drogen on the reduction kinetics was studied. Extremely thin specimens of wustite which were p repared by oxidizing thin foils (1.5 to 2 mils thick) qf iron in 54% CO-46% C0 2 gas mixture at 885° were employed. The use qf such thin specimens together with the choice of modest temperatures ensured that the measurements represented the chemical kinetics of the wustite reduction. The values of the nominal rate constant for the interfacial reaction, ". , were determined from the experimental data. These were combined with the results from an earlier work of the same authors to obtain the following equation. k. • = O.246(± O.048)exp [-714:i±950)] (g. atom O/cm 2 .sec .atm) The activation energy of 71 400 J ig • mol was found to be in reasonably good agreement with the published values. The rate of reduction of wustite, at airy given temperature, was fou nd to exhibit a firs to rder dependance with respect to the partial pressure of hydrogen.

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Section: R Esults and Discussionsupporting

confidence: 91%

Kinetics of Reduction of Wustite by Hydrogen-Helium Gas Mixtures at Modest Temperatures

El-Rahaiby

Rao

1980

ISIJ Int.

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“…(5) Figure 7 shows that the requirement In v E x implied by equation (5) is satisfactorily confirmed by the measured values. The constants fa and k*a can be determined from the slopes and intercepts of the curves.…”

Section: Resultssupporting

confidence: 61%

“…Assuming a first-order reaction with respect to the concentration c* of the 'hot' H 2 molecules, the following equation is applicable to the excess reaction rate caused by the catalyst at constant T: The solid curves in figures 3 to 5 were calculated by entering the constants fa and k*a in equation (5). The excess reaction rate v E was calculated with the same constants for varying H 2 concentrations and is shown in figure 8.…”

Section: Resultsmentioning

confidence: 99%

Influence of metal-wustite separation on the reduction of wustite with hydrogen

Barin

Leber²,

Lemperle

1985

Steel Research

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The reduction rate of wustite with hydrogen at 1133 to 1233 K and for hydrogen pressures between 1.6 and 5 mbar has been measured gravimetrically upon varying the separation between tablets made of wustite and iron or nickel. The reduction rate of wustite is increased by a factor 2.4 prior to precipitation of iron on wustite when the wustite-metal distance is changed from 2 mm to 0.35 at Hz pressures of 1.6 mbar and 2.3 mbar respectively. It has thus been demonstrated for the first time, that the catalytic effect of the metal phase on wustite reduction also exists when metal and wustite are separated. To describe this catalytic effect mathematical relations have been derived on the basis of a reaction model. These relations are in good accord with the results of the measurements. From recently published experimental findings, it may be concluded that, as a result of heterogeneous reactions, translationally 'hot' Hz molecules are desorbed from the metal surface. These induce a rapid reaction at wustite unless they have been deactivated by molecular collisions within the bulk gas between the tablets. EinfluB des Metall-Wustit-Abstandes auf die Reduktion von Wustit mit Wasserstoff. Die Geschwindigkeit der Reduktion von Wustit mit Wasserstoff wurde bei Variation des Abstandes zwischen Tabletten aus WGstit und Eisen oder Nickel bei WasserstoffdrGcken von 1,6 bis 5 mbar und Temperaturen von 1133 bis 1233 K gravimetrisch gemessen. Bei Anderung des WGstit-Metallabstandes von 2 auf 0,35 mm wird die Reduktionsgeschwindigkeit des Wustits bei Hz-Drucken von 1,6 und 2,3 mbar vor Ausscheidung der arteigenen Eisenphase um den Faktor 2,4 erh6ht. Damit wurde erstmalig gezeigt, daB der katalytische EinfluB der Metallphase auf die Wustitreduktion auch bei raumlicher Trennung des Metalls von Wustit vorhanden ist. Zur Beschreibung dieses katalytischen Effektes wurden auf der Basis eines Reaktionsmodells Beziehungen abgeleitet, die mit den Messungen gut Gbereinstimmen. Bisherige experimentelle Befunde lassen den Schlufs zu, daB von der Metalloberflache als Foige von Heterogenreaktionen translatorisch .heifse' Hz-MolekGle desorbiert werden, die an Wustit eine schnelle Reduktion bewirken, sofern sie nicht durch Moiekularst6Be im Gasraum desaktiviert werden.The accelerating effect of iron and other metals on the reduction of iron oxides, in particular of wustite, has been investigated systematically by Morawietz and Schafer')'), by Neuschiitz and Towhidi 3 )4), and by Pluschkell and Yoshikoshi'). It was shown that accelerated reduction takes place not only after formation of the iron phase on wustite but from the very beginning if the oxide to be reduced is in contact with metals such as Fe, Ni, Co and Cu.In an effort to explain this effect, Morawietz and Schafer') discussed the nuclei-forming role played by metallic phases. However, Neuschiitz and Towhidi') showed in addition, that the degradation of oxygen from wustite within the latter's range of homogeneity, is accelerated through contact with nickel powder.Pluschkell and Yoshikoshi ...

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“…The direct measurement of iron metal growth kinetics on iron oxide surface have been reported for wustite reduction in H 2 /H 2 O/N 2 28, 29, and H 2 /N 2 and CO/N 2 29 gas mixtures between 650 and 850 °C. These data were obtained by observing, using optical microscopy, the growth of individual iron nuclei in controlled temperature and gas conditions.…”

Section: Iron Oxide Reductionmentioning

confidence: 99%

Analysis of Product Morphologies and Reaction Mechanisms on Gaseous Reduction of Iron Oxides

Hayes

2011

steel research int.

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It is well established that in gaseous reduction processes solid iron oxides exhibit a wide range of reducibilities. Using the interface stability criteria developed to describe the decomposition of metal compounds in reactive gas atmospheres, together with microstructural evidence obtained under well characterised reaction conditions, the relationships between product structures, and the mechanisms and the kinetics of reduction of iron oxides have been examined. It is shown that the structures and reaction rates can be explained through the occurrence of four principal mechanisms; continuous gas pore formation, dense metal layer growth, discontinuous metal layer breakdown and continuous coupled growth of metal and pores. Through identification of the critical conditions for these different mechanisms, the maximum rates of reduction of a given starting material as a function of temperature, thermal history and gas conditions can be more clearly understood.

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Wachstum der Eisenphase auf Wüstit während der Reduktion in Wasserstoff-Wasserdampf-Gemischen

Cited by 17 publications

References 0 publications

Kinetics of Reduction of Wustite by Hydrogen-Helium Gas Mixtures at Modest Temperatures

Kinetics of Reduction of Wustite by Hydrogen-Helium Gas Mixtures at Modest Temperatures

Influence of metal-wustite separation on the reduction of wustite with hydrogen

Analysis of Product Morphologies and Reaction Mechanisms on Gaseous Reduction of Iron Oxides

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