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

Mixtures containing the desired weight ratios of 2 3 -Fe O α 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 12 3 -(Al Fe ) O x x α were found; one solid solution was closely related to 2 3 -Fe O , α the other to 2 3 -Al O . α The terminal solid solubility limits, 27.0 0.5 r   mole ratio of 2 3 -Al O α in 2 3 -Fe O α and 9.0 0.5 r   of 2 3 -Fe O α in 2 3 -Al O , α were determined. The Mössbauer spectra showed a broadening of spectral lines and a decrease in the hyperfine magnetic field of 2 3 -Fe O α with incorporation of 3+ Al ions in the 2 3 -Fe O α structure. For mole fractions between 0.40 x  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 0.90 x  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 1 2 3 -(Al Fe ) O x x α  system.