engleski

Investigation of crystalline phases in the a-Fe2O3/a-Al2O3 system

Mixtures containing the desired weight ratios of a-Fe2O3 and a-AlOOH were homogenized in the planetary mill, then pressed into tablets and heated up to 1200 oC. 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 a-(AlxFe1-x)2O3 were found ; one solid solution was closely related to a-Fe2O3, the other to a-Al2O3. The terminal solid solubility limits, 27.0 &plusmn ; 0.5 mole % of a-Al2O3 in a-Fe2O3 and 9.0 &plusmn ; 0.5 mole % of a-Fe2O3 in a-Al2O3, were determined. The Mössbauer spectra showed a broadening of spectral lines and a decrease in the hyperfine magnetic field of a-Fe2O3 with incorporation of Al3+ ions in the a-Fe2O3 structure. For mole fractions between x=0.40 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 a-(AlxFe1-x)2O3 system.

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

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