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In this work, we characterize the hollow hematite (α-Fe2O3) micro spheres obtained by two non-template techniques: i) sol gel and ii) spray roasting process. Both techniques allow the production of high yield hollow hematite spheres up to 100 g for the case of sol gel and up to 500 kg for the case of spray roaster process. The samples were characterized by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. The results indicate nearly uniform hollow spheres with diameters of around 1–1.5 μm and consisting of polycrystalline hematite. The Mӧssbauer spectroscopy reveals the signal change of quadrupole shift values evidencing the occurrence of the Morin transition and that the samples show an antiferromagnetic order at 77 K as in bulk hematite. The Morin temperature (TM) for both samples was obtained from the measurements of the magnetic moments as a function of the temperature in zero field cooling (ZFC) and field cooling (FC) modes. The values of TM for both samples are lower than that reported for bulk hematite (TM(bulk) = 263 K). Remarkably, the ZFC and FC loops do not overlap in both samples, revealing irreversible Morin transition. However, the sample obtained by sol gel presents thermal hysteresis with TM values of 260 K (in ZFC) and 248 K (FC). Whereas, the sample obtained by spray roaster process presents complete irreversibility and TM values of 252 K (in ZFC) and 242 K (in FC). Keywords: Hollow spheres, Hematite, Morin transition, Thermal hysteresis

The physical nature of formation of nanoparticles of the disperse phase in isotropic electrical steel, as a scientific basis of development new and perfection of existing technologies of its production, is considered. Account of a volume fraction of redundant phases is bought at disintegration of a overvibrant solid solution during production of steel. On the basis of the offered model it is received kinetics of coalescence of nanoparticles of the disperse phase at hot rolling. The effect of micro additives of aluminum on coalescence of nanoparticles and on magnetic properties of steel is shown.