The Behaviour of Softening and Melting of Hematite Pellet and Sinter during Heating in a Reducing Atmosphere

Mori, Ken-ichiro; Hidaka, Ryoichi; Kawai, Yasuji

doi:10.2355/tetsutohagane1955.66.9_1287

Cited by 12 publications

(4 citation statements)

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“…The second step is of particular importance in practice because the reaction rate at higher temperatures dominates the overall reduction efficiency of a blast furnace. [4][5][6] There are two types of wüstite in reduced sintered ores: one is wüstite (donated as FeO) reduced from hematite containing less impurities and the other is calcio-wüstite (donated as CW) reduced from CF: both FeO and CW have the rock-salt structure. CW contains CaO and other gang components such as MgO, SiO 2 and Al 2 O 3 as solutes, and thus its reducibility could be different from that of FeO.…”

Section: Introductionmentioning

confidence: 99%

Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

et al. 2017

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Reducibilities of wüstite and calcio-wüstite have been examined using high temperature X-ray diffraction analysis including the effect of hydrogen on the reducibility. Fe 2 O 3 reagent powders and hematite ore powders were used for reduction of wüstite (denoted as FeO) and sintered ore powders were used for reduction of FeO and calcio-wüstite (denoted as CW). High-temperature X-ray diffraction was applied to these samples in a flow of CO-CO 2 -He mixtures with and without 3.9 vol% of hydrogen during the heating cycle which simulates a blast furnace condition. The diffraction angle was scanned in the range from 33° to 55°. In experiment on sintered ore powders without hydrogen, the main peak around 48.5° shifted to lower angles with increasing temperature. This shift also continued while temperature was kept at 1 000°C where wüstite was saturated with iron; on the contrary, the peak shift did not take place for hematite ore powders. This main peak is associated with wüstite (200), which is actually composed of peaks due to FeO and CW for sintered ore powders. The peak shift reflects that the peak intensity of CW increases relative to that of FeO, which suggests that the reduction of FeO proceeds faster than that of CW, and the reducibility of FeO is higher. In contrast, the peak shift did not take place in experiment on sintered ore powders with hydrogen additions. This suggests that the reducibility of CW is comparable to that of FeO in the presence of hydrogen.

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Section: Introductionmentioning

confidence: 99%

Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

et al. 2017

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“…To achieve efficient and stable operations under such conditions, it is important to clarify and control the phenomena in the cohesive zone. Estimations of the gas permeability, [1][2][3] melting-softening behavior, 4,5) and reduction behavior [6][7][8][9] in the cohesive zone have been the subjects of previous research. 10) According to Mori et al, 4) the initial melt formation temperature of the pellets and sinters increases with the degree of reduction.…”

Section: Introductionmentioning

confidence: 99%

Influence of CaO/SiO2 on the Reduction Behavior of Sintered Fe2O3–CaO–SiO2–Al2O3 Tablets at the Softening and Melting Temperatures

et al. 2020

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Reduction experiments were conducted with sintered Fe 2 O 3 -CaO-SiO 2 -Al 2 O 3 tablets at (mass%CaO)/ (mass%SiO 2 ) (C/S) of 1.5, 2.0, and 2.5 at 1 000, 1 050, 1 100, 1 150, and 1 200°C. From the reduction behaviors, we investigated the relationship between the reduction rate and C/S at the softening and melting zone temperatures of blast furnaces. The reduction rates at C/S = 2.0 and 2.5 increased with temperature in the range of 1 000 to 1 200°C. The reduction rate at C/S = 1.5 increased with temperature in the range of 1 000 to 1 150°C; however, at 1 200°C, it decreased to the same value obtained at 1 000°C. The microstructures of these samples, after sintering at 1 270°C, pre-reduction at 900°C, and reduction at 1 200°C, were analyzed through SEM-EDS. Fe 2 O 3 particles, SFCA, slag, and pores among Fe 2 O 3 particles existed in the samples after sintering. The matrix components in the pre-reduced sample were suggested to be calcium silicate slag containing FeO x and Al 2 O 3 at C/S = 1.5, and to be 'FeO x ' originated from SFCA at C/S = 2.0 and 2.5. The porosity of the open pores at C/S = 1.5 decreased to 16%. It was found that the reduction rate at 1 200°C decreased due to this lower porosity. By contrast, the porosity of the open pores after reduction at C/S = 2.0 and 2.5 was much higher than that after pre-reduction. The reduction rates of these samples at 1 200°C were found to not decrease as a result of maintaining a higher porosity.

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“…There are various characteristics of sinters to be considered for the blast furnace operation, one of which is the reducibility of sinters; [1][2][3] in particular, the reducibility of wüstite is the most important because it controls the overall reduction efficiency of a blast furnace. [4][5][6] Wüstite in reduced sinters roughly falls into two types: 1) wüstite (denoted by FeO) reduced from Fe 2 O 3 and Fe 3 O 4 with less impurities and 2) calcio-wüstite (denoted by CW) reduced from SFCA; both FeO and CW have the rock-salt structure. There have been many studies on the reducibilities of FeO and CW in terms of chemical reaction and diffusion, and there is a consensus that the reduction of wüstite is promoted by CaO dissolved in wüstite [7][8][9][10][11] from the following findings: reduction of FeO forms a dense iron layer in the outer part of the sample, which layer is a resistance to diffusion of reducing gas, whilst reduction of CW forms a porous iron layer which facilitates gas diffusion.…”

Section: Introductionmentioning

confidence: 99%

Dominant Factor Affecting Reducibility of Calcio-wüstite Originating from Silico-ferrite of Calcium and Aluminum

2020

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The reducibility of calcio-wüstite (CW) originating from silico-ferrite of calcium and aluminum (SFCA) has been investigated from the perspectives of the morphology of SFCA and the concentration of FeO in CW. Two types of SFCA sample were prepared: columnar SFCA and acicular SFCA. The former was synthesized from reagent grade powders of Fe 2 O 3 , CaCO 3 , SiO 2 and Al 2 O 3 , and contained columnar SFCA grains covered with slag. The latter was synthesized from iron ore and reagent grade CaCO 3 , and contained acicular SFCA grains, which were smaller than the columnar SFCA grains and had fine pores nearby. These samples were reduced in an XRD apparatus for high temperature use in a condition simulating a blast furnace where the oxygen partial pressure was controlled by CO-CO 2 mixtures. The microstructures of the samples before and after reduction were observed by electron probe microanalysis (EPMA). XRD profiles indicated: (i) both SFCA samples were reduced to Fe via CW at 1 000°C and (ii) acicular-SFCA-origin CW was reduced to Fe earlier than columnar-SFCA-origin CW, which suggests that the reducibility of acicular-SFCA-origin CW is higher than columnar-SFCA-origin CW. EMPA indicated: (i) most residual parts of acicular-SFCA-origin CW phase kept the morphologic feature of having fine pores as acicular SFCA during reduction as well and (ii) the FeO concentration in acicular-SFCA-origin CW was lower than that in columnar-SFCA-origin CW. Hence, it is concluded that the reducibility of SFCA-origin CW is dominated by the morphology of CW but not by the concentration/activity of FeO in CW.

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The Behaviour of Softening and Melting of Hematite Pellet and Sinter during Heating in a Reducing Atmosphere

Cited by 12 publications

References 1 publication

Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

Influence of CaO/SiO<sub>2</sub> on the Reduction Behavior of Sintered Fe<sub>2</sub>O<sub>3</sub>–CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> Tablets at the Softening and Melting Temperatures

Dominant Factor Affecting Reducibility of Calcio-wüstite Originating from Silico-ferrite of Calcium and Aluminum

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