S. Music et al., FE-57 MOSSBAUER, FT-IR AND TEM INVESTIGATIONS OF FE-OXIDE POWDERS OBTAINED FROM CONCENTRATED FECL3 SOLUTIONS, Journal of alloys and compounds, 278(1-2), 1998, pp. 291-301
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.