In an ultra high vacuum heterogeneous gas reactions such as 2 C + O2G → 2 COG and C + CO2G → 2 COG often show a less complicated reaction path than under normal pressure. In the present study the graphite sample is a commercial light‐bulb filament, which is extremely resistant against oxidation. Under low pressure the combustion reaction is of first order with a continuous transition to zero order at temperatures between 900 and 1300 K depending on the oxygen pressure. The Boudouard reaction behaves similarly but obeys zero order only around 2000 K and for CO2 pressures around 1 bar. The measured and the statistically calculated reaction rates agree well. An insight of the details of the reaction and chemisorption is determined by the evaluation of experiments carried out in an ultra high vacuum using isotopes such as 13CO2G. The Boudouard equilibrium for graphite can be reached only catalytically, e.g., with sponge iron in statu nascendi.
Investigations of the plasma smelting reduction of iron ore have been carried out on a laboratory scale using a transferred argonhydrogen plasma arc. Pyrometric measurements show that the surface temperature near the arc foot is about 2600 K when the hydrogen is mixed with the plasma-gas in front of the cathode, about 2250 K when the hydrogen is introduced laterally into the arc and ca. 2150 K when a pure argon plasma is used. With the help of thermodynamic plasma data the corresponding arc temperatures have been estimated to be 13 000 K. 11 000 K and 9500 K.lt has been shown that the reduction rate after the smelting phase remains constant and is practically independent of the manner of addition of the hydrogen. The measured efficiencies of utilization of hydrogen were 43 % and 50 % and thus correspond closely to the equilibrium FeO + H 2 = Fe+ H 20. A combination of the rate constants obtained for the plasma smelting reduction with those found in literature for lower temperatures leads to an activation energy of approximately 67 kJ/mol. This value lies in the range of energies reported for the reduction of wustite after precipitation of the iron phase. It is therefore not unlikely, that in the case of plasma smelting reduction also, the rate determining step is the reaction Had +OH ad -+ H 2 0 Bd•
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 ...
On the basis of MIP development several process concepts for primary ironmaking technology were investigated. In the smelting reduction process described the reduction of iron ore occurs in three stages: in the first step the ore is preheated and prereduced in a cyclon‐heat exchanger system. In the second step it is melted. The final reduction of the partially reduced and melted ore to metallic iron takes place in the MIP reactor.
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