FE-57 MOSSBAUER, FT-IR AND TEM INVESTIGATIONS OF FE-OXIDE POWDERS OBTAINED FROM CONCENTRATED FECL3 SOLUTIONS

The chemical and microstructural properties of oxide phases precipitat ed from concentrated FeCl3 solutions were investigated using Fe-57 Mos sbauer spectroscopy, Fourier transform infrared spectroscopy and trans mission electron microscopy. The initial pH of the precipitation syste m (acidic or highly alkaline medium) determined the mechanism of phase transformations. In a highly alkaline medium two competitive mechanis ms exist: (a) the nucleation and crystal growth of alpha-Fe2O3 inside the condensed Fe(OH)(3) gel and (b) the crystallization of alpha-FeOOH which transforms to alpha-Fe2O3 by a dissolution/reprecipitation mech anism. In the present work, spectroscopic results indicated that befor e a-FeOOH was detectable (or formed) at 60 degrees C, superparamagneti c and/or amorphous Fe-oxide particles (probably alpha-Fe2O3) were form ed. Once alpha-FeOOH was formed, its fraction in the precipitate incre ased rapidly. In an acidic medium (partially neutralized FeCl3 solutio n) alpha-Fe2O3, was formed from beta-FeOOH by a dissolution/reprecipit ation mechanism. The complete interpretations of Fe-57 Mossbauer and F T-IR spectra were given. TEM observation showed that the particle size and morphology of the oxide phases were very dependent on the experim ental parameters. (C) 1998 Elsevier Science S.A. All rights reserved.