engleski

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

Mixtures containing the desired weight ratios of alpha-Fe2O3 and gamma-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 alpha-(AlxFe1-x)2O3 were found ; one solid solution was closely related to alpha-Fe2O3, the other to alpha-Al2O3. The terminal solid solubility limits, 27.0 ± ; 0.5 mol % of alpha-Al2O3 in alpha-Fe2O3 and 9.0 ± ; 0.5 mol % of alpha-Fe2O3 in alpha-Al2O3, were determined. The Mössbauer spectra showed a broadening of spectral lines and a decrease in the hyperfine magnetic field of alpha-Fe2O3 with incorporation of Al3+ ions in the alpha-Fe2O3 structure. For molar 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 alpha-(AlxFe1-x)2O3 system.

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

nije evidentirano