Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 99 (2013), No. 6

  • Reaction Behavior in Packed Bed Considering Bed Structure and Reaction Properties of Particles

    pp. 391-400

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    DOI:10.2355/tetsutohagane.99.391

    To decrease the reducing agent ratio in the blast furnace, various measures such as mixed charging are being pursued. Coke mixed charging is considered to improve permeability in the cohesive zone and the reducing behavior of ore particles. Conventionally, these researches were frequently carried out with a small packed bed. However, the information obtained by these experiments was based on a macroscopic analysis. In the present research, a DEM-CFD model developed by the authors was applied to precisely analyze reaction behavior under various packed bed structures, such as that with coke mixing. Moreover, the effect of high reactivity coke on the reduction rate of ore was examined using this model. According to the results, coke mixed charging has little influence on the reduction rate. When high reactivity coke was charged to the ore layer, the particle temperature decreased due to the endothermic reaction by high reactivity coke. Accordingly, the reduction rate of the ore particles was suppressed as a result of the temperature change. This phenomenon was relatively noticeable in the packed bed structure with high reactivity coke set up in the lower part.
  • Effect of Material Particle Size on Reduction rate of Hematite and Quaternary Calcium Ferrite Mixtures

    pp. 401-406

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    DOI:10.2355/tetsutohagane.99.401

    It is important to know the reduction kinetics of iron ore sinter that is main iron resource of blast furnace. Iron ore sinter has various mineral phases such as hematite, magnetite and calcium ferrite, and equilibrium gas compositions of these minerals are different. Size and shape of these mineral phases are various, and these morphology is related in the reduction rate of iron ore sinter. However relationship between size of mineral phase and reduction rate has not been researched. In this study, we clarified the relationship between them.
    We prepared mixed samples made from iron oxide having particle size range of -45, 45-75, 75-125 and 125-250 μm and calcium ferrite having particle size range of -45, 45-75 and 75-125 μm. The reduction experiments were carried out with 100% CO.
    The results obtained in this study are follows:
    (1)The effect of particle size under 250 μm on the reduction rate was negligible below 1000°C. It caused by the reduction degradation of iron oxide reduced from hematite to magnetite during pre-reduction.
    (2)Reduction of mixed samples having particle size 125-250 μm of iron oxide and 45-75 μm of calcium ferrite at 1100°C were extremely slow. It is caused by the formation of melt having three-component system of Al2O3-CaO-FeO.
  • Influence of Lowering the Thermal Reserve Zone Temperature on Reduction Rate of Wustite

    pp. 407-414

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    DOI:10.2355/tetsutohagane.99.407

    As lowering the thermal reserve zone temperature in blast furnace is known to reduce the reducing agent rate and enhance the productivity effectively, this work aim at elucidating influence of pre reduction temperature of iron oxide samples to wustite (FeO) on reduction rate of FeO to Fe by using a thermobalance.
    As a result, for samples of sinter, commercial pellet, and iron ore, it was found that decrement of pre reduction temperature led to enhancement of reduction rate of FeO to Fe, giving to a largest extent for iron ore.
    These enhancements of reduction rate of FeO to Fe would be mainly because the wustite samples had larger specific surface area for lower pre reduction temperatures.
  • Crevice Corrosion Behavior of Various Stainless Steels under Marine Environments

    pp. 415-424

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    DOI:10.2355/tetsutohagane.99.415

    Exposure tests of various stainless steels have been conducted for 10 years with actual sea water. Corrosion resistance of each stainless steel under marine environments was evaluated by two types of tests which were atmospheric corrosion test and seawater spray test. The test results showed that spraying sea water enhanced the proceeding of corrosion. It has been proved that the super austenitic stainless steels defined by Pitting Resistance Equivalent (PRE=%Cr+3.3×%Mo+16×%N) over 40 have excellent corrosion resistance. The corrosion mechanism in this environment was basically estimated as crevice corrosion between the specimen surface and condensed substance originated from adhered chloride ions. In addition, microbes contained in sea water were considered to enhance the corrosion progress.
    Repassivation potential for crevice corrosion measurements were further carried out for Cl- ion to understand the corrosion mechanism assuming the critical potential of 500mV accounting for the existence of microbes. The obtained curves well support the exposure test results; the steel grades with PRE values over 40 were proved not to corrode under the present test conditions including temperature and Cl- ion concentrations. As a conclusion, the corrosion behavior of stainless steels can be explained by repassivaition potential for crevice corrosion considering microbes.
  • Electrodeposition Behavior of Zn-Ni alloy from Alkaline Zincate Solution Containing Ethylenediamine

    pp. 425-431

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    DOI:10.2355/tetsutohagane.99.425

    Electrodeposition behavior of Zn-Ni alloys was investigated at current densities of 5-500 A∙m–2 and a charge of 5×104 C∙m–2 in an unagitated zincate solution containing ethylenediamine, which forms a stable complex with Ni2+ ions at 308 K, and was compared with that from the solution containing triethanolamine. In a solution containing triethanolamine, the Zn-Ni alloy exhibited normal codeposition at low current densities, wherein electrochemically more noble Ni deposited preferentially and it exhibited anomalous codeposition at high current densities, wherein less noble Zn deposited preferentially, while in a solution containing ethylenediamine, it exhibited anomalous codeposition at high current densities, however, even at low current densities, the Ni content in deposit was almost identical with the composition reference line, showing the behavior close to anomalous codeposition. In a solution containing ethylenediamine, Ni deposition and H2 evolution were significantly suppressed in the larger region of current densities, showing the formation of an inhibitor for deposition, which results from Zn2+ ions in the cathode layer. The dependence of current efficiency for alloy deposition on the current density was smaller in a solution containing ethylenediamine than triethanolamine. In a solution containing triethanolamine, the underpotential deposition of Zn apparently occurred with Ni, while in a solution containing ethylenediamine, the underpotential deposition of Zn never occurred because Ni deposition was suppressed by the coexistence of Zn2+ ions even at low current densities. The throwing power of Zn-Ni alloy was better in a solution containing ethylenediamine than triethanolamine.

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