Experimental Method Samples PreparationSFCAM samples were prepared by a solid state reaction technique from the chemical reagents of Fe 2 O 3 (99 %), CaCO 3 (99 %), MgO (99 %), Al 2 O 3 (99 %) and SiO 2 (99 %). ISIJ International, Vol. 45 (2005), No. 4, © , Zϭ2) were determined by the single crystal X-ray diffraction. The structure of SFCAM is iso-structural with aenigmatite and well demonstrated by an alternating stacking of the tetrahedral and octahedral layers. The tetrahedral sites of oxygen are occupied either by Fe, Al and Si. The octahedral sites of oxygen are occupied either by Fe, Mg and Al and this feature contrasts with that of the Mg-free SFCA phase where Al prefers tetrahedral sites, only. In particular, Si 4ϩ and Mg 2ϩ prefer the tetrahedral T1, T2 and T4 sites and octahedral M5 and M6 sites, respectively, by producing a structural slab similar to that of aluminous diopside. Such local concentration of divalent Mg 2ϩ and tetravalent Si 4ϩ in the structure of SFCAM is strongly favored in order to compensate the local charge valance. The SFCAM phase indicates the superior structural flexibility for a variety of cations and this feature is promising for the chemical design of the bonding phase in the sinter ore.KEY WORDS: crystal structure; sinter ore; aenigmatite; X-ray diffraction; SFCAM.The powder mixtures with initial chemical compositions listed in Table 1, were pressed into pellets. The pellet samples were held in Al 2 O 3 crucibles and sintered at 1 250°C for more than 24 h in air. The sintered pellets were quenched to room temperature and subsequently ground into fine powders. After repeating this procedure two times for homogenization, powder X-ray diffraction patterns of the obtained samples were measured by using Cu Ka radiation with a pylolitic graphite monochromater in the diffracted beam path and the chemical compositions of the obtained SFCAM phases were analyzed by the electron probe microanalysis (EPMA). As an example, Fig. 1 shows the diffraction patterns of SFCAM08 together with that for the typical SFCA phase (SFCA125) prepared by the similar procedure. Although the peak positions for SFCAM08 are systematically shifted toward the smaller d-space region, the features in the intensity profiles correspond to each other. This result strongly suggests that SFCAM08 was mainly composed by the SFCAM phase with the aenigmatite structure. Similarly, the SFCAM phase was confirmed as a major constituent in the samples of SFCAM03, SFCAM05, SFCAM06 and SFCAM07. Crystals of the SFCAM phase found in the samples of SFCAM03 SFCAM05, SFCAM06, SFCAM07 and SFCAM08 were less than 30 mm in size and not suitable for the single crystal X-ray diffraction, another heating sequence was introduced for Mg-rich samples of SFCAM10 and SFCAM15 in order to produce crystals more than 100 mm in size. Samples of SFCAM10 and SFCAM15 were melted in Pt crucibles at 1 350°C for 12 h and subsequently cooled down to 900°C with a speed of 10°C/h. Figure 2 indicates the typical image of SFCAM15 taken by using a scanning elec...

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