Original scientific paper

Investigation of Crystalline Phases in the α-Fe₂O₃/α-Al₂O₃ System

Mira Ristić orcid.org/0000-0003-0033-9840 ; Division of Materials Chemistry, Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia
Stanko Popović ; Department of Physics, Faculty of Science, P.O. Box 331, HR-10002 Zagreb, Croatia
Svetozar Musić ; Division of Materials Chemistry, Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia

Abstract

Mixtures containing the desired weight ratios of α-Fe₂O₃ and γ-AlOOH were homogenized in the planetary mill, then pressed into tablets and heated up to 1200 °C. All samples were characterized by X-ray diffraction, Mössbauer spectroscopy, Field emission scanning electron microscopy and Energy dispersive X-ray analysis. Two types of solid solutions of general formula α-(Al_xFe_1-x)₂O₃ were found; one solid solution was closely related to α-Fe₂O₃ the other to α-Al₂O₃ The terminal solid solubility limits, r = 27.0 ± 0.5 mole ratio of α-Al₂O₃ in α-Fe₂O₃ and r = 9.0 ± 0.5 of α-Fe₂O₃ in α-Al₂O₃ were determined. The Mössbauer spectra showed a broadening of spectral lines and a decrease in the hyperfine magnetic field of α-Fe₂O₃ with incorporation of Al3+ ions in the α-Fe₂O₃ structure. For mole fractions between x = 0.4 and 0.70, the Mössbauer spectra were considered as the superposition of a sextet and quadrupole doublet(s). In this concentration range the samples showed an almost constant value of hyperfine magnetic field. For x = 0.90 and 0.93, the Mössbauer spectra were considered as a superposition of two quadrupole doublets, whereas for x = 0.95 the superposition of two quadrupole doublets and one singlet was considered. The origin of this singlet with the isomer shift close to zero is not clearly understood. FE-SEM showed a strong sintering effect on the particles in all samples in the α-(Al_xFe_1-x)₂O₃ system.

Keywords

solid solutions; α-Fe₂O₃; α-Al₂O₃; XRD; ⁵⁷Fe Mössbauer; FE-SEM; EDS

Hrčak ID:

39657

URI

https://hrcak.srce.hr/39657

Publication date:

15.7.2009.

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