SYNTHESIS AND CHARACTERIZATION OF NANOPHASIC GOETHITE

X-ray diffraction, Mossbauer spectroscopy surface area and positron an nihilation lifetime measurements were carried out to characterize alph a-FeOOH crystals as produced from the oxidation of Fe(OH)(2) using dif ferent oxygen flow rates at 298 K. From the resulting oxidation rates, average sized a-FeOOH crystals that ranged from 7 to 48 nm were obtai ned. Of these, crystals from 7 to 13 nm mainly showed superparamagneti c behavior and a surface area of about 200 m(2)/g; those from 23 to 48 nm were characterized by their hyperfine magnetic Mossbauer spectrum and an intermediate surface area of about 100 m(2)/g. Positron annihil ation data showed that these nanometer-sized alpha-FeOOH crystals cont ained a high concentration of crystal defects. Three lifetime componen ts were needed to fit the data, and the relative intensity of the defe ct-lifetime (tau(2)) increased as the average crystal size of the goet hite decreased. Depending on the crystal size of the goethite, the cry stal defects may or may not contribute to the surface area. By correla ting the crystal size, the surface area, and the concentration of crys tal defects, one may be able to assess the crystallinity of these goet hites. (C) 1998 Acta Metallurgica Inc.