Characterization of Fine Particles of Different Iron Oxides Formed in Aqueous Media

Abstract

Small-angle X-ray scattering (SAXS) measurements using synchrotron radiation and transmission electron microscopy (TEM) observation have been carried out for characterizing fine particles of ferric oxides including hydroxides and oxyhydroxides. A compact chamber was designed for SAXS measurements at BL15XU of SPring-8, Japan. SAXS profiles of reference particles of ferric oxyhydroxides, namely, α-FeOOH (goethite), β-FeOOH (akaganetite), and γ-FeOOH (lepidocrocite), obtained using the measurement system were compared with their morphologies observed by TEM. SAXS profiles of fine particles of ferric oxides, that were converted from condensed Fe(OH)3 gel to β-FeOOH and α-Fe2O3 by aging, were also measured. While TEM observation provided information on the characteristic microstructure of well-crystallized fine particles of ferric oxides in a selected area of a sample, information regarding fine particles including poorly crystallized ferric oxides in the entire sample was obtained by SAXS measurements. The SAXS and TEM results indicated that the addition of foreign anions of sulfate or silicate to the gel delayed the conversion processes of the gel to β-FeOOH and α-Fe2O3. A combination of SAXS measurement with TEM observation and X-ray diffraction measurement is shown to be effective in the characterization of fine particles of different iron oxides, which are formed by aging in aqueous media. [DOI: 10.1380/ejssnt.2006.352]