The effect of iridium(III) ions on the formation of iron oxides in a highly alkaline medium

The effect of the presence of Ir3+ ions on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRD), Fe-57 Mossbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Monodispersed lath-like alpha-FeOOH (goethite) particles precipitated by hydrothermal treatment in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. The presence of Ir3+ ions in the precipitation system strongly influenced the phase composition, magnetic, structural and morphological properties of obtained samples. The formation of alpha-Fe2O3 (hematite) along with alpha-FeOOH in the first stage of hydrothermal treatment and the transformation of alpha-FeOOH and alpha-Fe2O3 to Fe3O4 (magnetite) by a longer hydrothermal treatment was caused by the presence of Ir3+ ions. Ir3+ for Fe3+ substitution in the structure of alpha-FeOOH brought about changes in unit-cell dimensions, crystallinity, particle size and shape, hyperfine magnetic field and infrared bands positions. Ir3+ for Fe3+ substitution in the structure of alpha-Fe2O3 led to an increase in the temperature of the Morin transition; Mossbauer spectroscopy showed the presence of alpha-Fe2O3 in the antiferromagnetically ordered state at 293 K. (C) 2011 Elsevier B.V. All rights reserved.