Cax Fe3-x O4 samples, with x _ < 0.28, prepared from α-Fe 2 O 3 and CaO by the Bridgman method were investigated by means of 57 Fe Mossbauer spectroscopy. Room temperature spectra gave evidence that the samples were multiphase, the calciómagnetite being the dominant phase with a contribution of 73% to 99%, depending on the sample. Analysis of the subspectra associated with the calciomagnetite gave evidence that Ca-ions reside on the tetrahedral (A) sites and have not random distribution. Their presence on those sites causes a reduction of the hyperfine field at Fe nuclei occupying the octahedral positions (B) by 12.3(1.0) kOe per one Ca-ion and a decrease in the average hf field, (ΗB)/dx, at the rate of 29 kOe/mol% for x < 0.07 and of 387 kOe/mol% for larger x. In addition, a linear correlation between (ΗB) and the average isomer shift, (IB), was revealed to hold. It indicates that addition of Ca-ions into the magnetite causes a decrease in the spin-density and an increase in the charge-density at Fe nuclei occupying the B-sites.

Iron oxides doped with calcium occur in such natural metallurgical materials as sinters and lumps for the blast furnace process. In this work the Ca-doped magnetite phase Fe3 _yCayO4 with 0 < y <~ 0.55 was produced and studied as a pattern phase for investigation of the magnetit0 phase in sinters.The synthesis process was studied by means of simultaneous thermal analysis, while the synthesized products were studied by diffraction analysis, scannipg and optical microscopy, and spectral analysis in microareas.The solubility limits for Ca in magnetite were estimated, and an explanation of the shapes of the thermal curves was given.A precise identification of the oxide phases in blast furnace sinters is very difficult, due to the complex and inhomogeneous chemical composition of the phases.A possible modification of the blast furnace technology could be reached only if the properties of all the phase components of the sinter are known. Therefore, in this study we first synthesized a sinter with chemical composition close to that of the blast furnace sinter and determined its physico-chemical properties. This enabled us to find a proper investigation techniquewhich could be applied to study some blast furnace sinters.The magnetite phase doped ~vith calcium was produced and then studied as a pattern phase for the subsequent investigations of the magnetite phase in the blast furnace sinter.

Investigations of metallurgical materials such as blast furnace sinters and pellets require the syntheses of the standard phases contained in these materials.Synthetic pure and calcium-doped iron oxides were studied Calcium ferrite phases originated in the intergranular space and strongly affected the reducibility of the sinter, besides haematite and magnetite.Studies of the formation and physicochemical properties of the synthetic calcium ferrites CaFe204 and Ca2Fe2Os, identified in polycrystalline calciomagnetite and caiciowustite samples, are described. ExperimentalThe calcioferrites CaFe204 and Ca2Fe205 have been obtained by thermal dissociation [1][2][3][4][5][6] and following the sintering of stoichiometric CaCO3-Fe203 mixtures at 1150 ~ in air [7]. The products were subjected to microscopic and diffractometric examination and also to microregion spectral analysis.In order to determine the conditions of ferrite formation, thermal analyses were carried out with a Q-15000 Paulik-Paulik-Erdey derivatograph. TG, DTG, DTA analyses were performed in air atmosphere, using 500 mg samples. The temperature was increased at a rate of 7.5 deg/min.As can be seen in Fig. 1, the TG and DTG analyses of a 1:1 molar mixture of in the temperature range 525-880 ~ indicate the complex character of the weight loss (16.4%) process. The process involving a slow increase in the weight loss rate between 325 and 825 ~ turns into the next step with an altered rate up to 880 ~ . The complexity of the weight loss process is confirmed by DTA. There are initially endothermic effects conJohn Wiley & Sons, Limited, Chichester Akadgmiai Kind6, Budapest

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