Abstract
The reduction of magnetite pellets is studied by thermogravimetry in a hydrogen flow upon linear heating. A multiple decrease in the reduction rate is observed at the degrees of metallization higher than 70% in a temperature range of 920–950°C. The observed effect of a decrease in the reduction rate by four to five times on heating is related to the α → γ phase transition of iron. Temperature cycling (heating–holding–heating–holding…) in the phase transition range shows that this effect is reversible; i.e., the reduction rate increases on cooling, unlike that on heating. The average temperature of the beginning of the effect in heating–cooling cycles (913°C) turns out to be close to the thermodynamic temperature (911°C) of the α → γ phase transition of iron. Isothermal studies of the reduction rate of pellets in a temperature range of 900–1000°C also confirm this phenomenon. The effect of a decrease in the reduction rate is assumed to appear due to a decrease in the effective coefficient of gas diffusion in γ-iron as compared to α-iron.
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References
S. T. Rostovtsev, T. E. Nizhegorodova, V. K. Simonov, and L. I. Medvedeva, “Physicochemical laws of the reduction of iron-ore materials by hydrogen and carbon monoxide at various pressures,” in Intensification of Reduction Processes (Nauka, Moscow, 1980), pp. 52–67.
O. A. Teplov, “Kinetics of the low-temperature hydrogen reduction of magnetite concentrates,” Russ. Metall. (Metally), No. 1, 12–28 (2012).
B. I. Bondarenko, Reduction of Metal Oxides in Complicated Gas Systems (Naukova Dumka, Kiev, 1980).
O. A. Teplov, “Gas permeability of sintering porous randomly packed media,” Russian Metallurgy (Metally), No. 4, 283–293 (2003).
O. A. Teplov, I. G. Voropaev, G. K. Demenskii, and Yu. V. Tarasenko, “Kinetics of hydrogen reduction of single-crystal magnetite,” in Theory and Practice of the Direct Iron Making (Nauka, Moscow, 1986), pp. 156–160.
Janaf Thermochemical Tables (NBS, Washington, 1971).
L. G. Berg, Introduction to Thermography (Nauka, Moscow, 1969).
R. Kohlhaas, P. Dimner, and N. Schmitz-Pranghe, “Uber die temperaturabhan-gigkeit der gitterparameter von eisen, kobalt und nickel im bereich hoher temperaturen,” Z. Angew. Phys. 23 (4), 245–249 (1967).
O. A. Teplov, I. G. Voropaev, V. G. Dyubanov, and L. I. Leont’ev, “Hydrogen reduction kinetics of electrometallurgical slime,” Russian Metallurgy (Metally), No. 4, 266–275 (2007).
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Original Russian Text © O.A. Teplov, 2018, published in Metally, 2018, No. 1, pp. 17–22.
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Teplov, O.A. Influence of Phase Transitions on the Macrokinetics of the Gaseous Reduction of Iron Oxide. Russ. Metall. 2018, 14–18 (2018). https://doi.org/10.1134/S0036029518010123
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DOI: https://doi.org/10.1134/S0036029518010123