SynopsisDirect observation of lattice images by TEM of magnetite reduced f rom hematite made clear ultramicroscopic partial distortion due to solid solution o f A12O3. Furthermore, the effect o f solid solution of A12O3 with hematite on strain of magnetite, which had reduced grains of the hematite with a mixture gas of CO C02, was estimated by line-broadenings of peaks of X-ray diffraction. It revealed that increasing amounts o f A12O3 increased the strain of magnetite.Fracture strength of the minerals in sintered ore was estimated quantitatively by Vickers indentation, indicating crack propagation-arrest characteristics. Fracture toughness of both glassy silicate and calcium ferrite resulted in values of the same order with a little effect of A12O3. Calcium ferrite, however, had the lowest value for " critical load", indicating crack initiation characteristic among all the minerals tested.An experimental study of the crystallization mechanism of skeletal hematite indicated that magnetite coexisting with liquid silicate decomposed, melted and was oxidized at the falling stage of sintering.

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The mechanism of degradation of agglomerates during reduction is studied with pellets made from powdery ingredients of chemical reagent grade, and the changes in mineral phases due to certain oxides leading to degradation, are examined quantitatively. The results obtained are summarized as follows: (1) Microscopic observations suggest that cracking occurs in the skeletal hematite and the calcium ferrite phases. Analysis by line-broadening measurements of X-ray diffraction reveals no strain both in the bulky and in the skeletal hematites regardless of the amount of alumina held in solid solution. Micropores are generated in magnetite as it is reduced from hematite to give rise to a stress when reduced at a low temperature, and stress concentration occurs around inclusions of small radius of curvature to cause cracking of skeletal hematite grains. (2) The quaternary calcium ferrite is expected to be reduced to metallic iron in the blast furnace through dicalcium ferrite or wustite. Nonferrous oxides form gehlenite and j3-dicalcium silicate. Calcium ferrite is not only fragile but its amount to increase with the basicity under existence of A12O3. (3) The amount of skeletal hematite depends mainly on the degree of supersaturation of iron ions in slag and on the dissociation temperature of hematite. The addition of TiO2 in sinters enhanced greatly the crystal growth of skeletal hematite in the case of induration at above THM, whereas bulky hematite at below THM.

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SynopsisThe solution property of Mg0 containing materials into the CaOFe203 system and the melting property of Mg0 containing sinter during reduction were investigated. The results obtained are summarized as follows:(1) The formation of high viscosity silicate and magnetite prevents the homogenization of slag and therefore, Cr slag and Ni slag remain unslagged. The formation of dicalcium ferrite prevents the dissolution of periclase into the CaO-Fe203 system.(2) During reduction unslagged Mg0 makes the shell of Mg0-FeO solid solution with FeO in glassy silicate and its solution is negligibly low.(3) For both normal sinter and pellet, all silicate minerals dissolve above about 1240°C.(4) Mg0 addition in sinter is effective to decrease the slag quantity during reduction but the melting property of sinter is not so improved as that of pellet. The proper basicity for sinter and pellet is about 1.4.