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

Abstract

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.

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

“…The samples prepared as above were crushed and sieved into powders with the particle diameter of 38-75 μm, and subsequently the samples were subjected to reduction experiments using a high temperature XRD apparatus. This experiment is also the same as in the previous work, 13,15) the explanation of which is repeated for reference in the following. Figure 1 shows the experimental conditions of temperature and gas composition.…”

“…Table 1 gives nominal chemical compositions of each sample. The preparation method has been described in the previous reports, 13,15) the outline of which is repeated as follows:…”

“…On the other hand, there is a report where the diameters of FeO and CW phases in reduced sinters are 30-40 μm or even smaller, 12) in which case the effect of the iron layer structure on the reduction rate would be minimized. 9) For example, the authors have measured the reducibilities of FeO and CW using high temperature X-ray diffraction (XRD) analysis on reduced sinter powders sieved into the particle diameter of 38-75 μm, 13) and have found that FeO is more reducible than CW, which is in conflict with many previous studies but supports the results reported by Sakamoto et al 14) Focusing on morphology, there are at least two types of CW: a) columnar CW with slag which is reduced from columnar SFCA with slag and b) acicular CW with fine pores which is reduced from acicular SFCA with fine pores. 15) To examine the effect of the morphology of CW, the authors have also investigated the reducibility of acicular-SFCA-origin and columnar-SFCA-origin CW powders with 38-75 μm, which is larger than the size of CW phase, using high temperature XRD analysis, to examine the effect of the morphology of CW phase including its surrounding structure.…”

Comparison between Reducibilities of Columnar Silico-ferrite of Calcium and Aluminum (SFCA) Covered with Slag and Acicular SFCA with Fine Pores

“…Figure 2 shows the experimental conditions of temperature and gas composition in the present study, which are the same as in the previous work. 7) Oxygen partial pressure in the furnace was adjusted using gas mixtures of CO-CO 2 , the ratio of which was changed depending on temperature to simulate a blast furnace condition. To improve X-ray diffraction intensity, the gas mixture was further diluted with 50 vol% of helium gas although there is no helium gas added in the actual blast furnace condition.…”

“…[4][5][6] Comparison between Reducibilities of Columnar Silico-ferrite of Calcium and Aluminum (SFCA) Covered with Slag and Acicular SFCA with Fine Pores Boyuan CAI, 1) * Takashi WATANABE, 2) Chikashi KAMIJO, 3) Masahiro SUSA 2) and Miyuki HAYASHI It is noted that there are two types of wüstite in reduced sinters: one is wüstite (denoted by FeO) reduced from Fe 2 O 3 containing less impurities and the other is calcio-wüstite (denoted by CW) reduced from SFCA -both FeO and CW have the rock-salt structure. In the previous work, 7) it has been found from high temperature X-ray diffraction (XRD) analysis that the reducibility of FeO is higher than that of CW. Now it should also be noted that there are two types of SFCA that produces CW: one is columnar SFCA covered with slag and the other is acicular SFCA with fine pores.…”