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

Abstract

The effect of the presence of Ir 3+ ions on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRD), 57Fe Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Monodispersed lath-like α-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 Ir 3+ ions in the precipitation system strongly influenced the phase composition, magnetic, structural and morphological properties of obtained samples. The formation of α-Fe 2O 3 (hematite) along with α-FeOOH in the first stage of hydrothermal treatment and the transformation of α-FeOOH and α-Fe 2O 3 to Fe 3O 4 (magnetite) by a longer hydrothermal treatment was caused by the presence of Ir 3+ ions. Ir 3+ for Fe 3+ substitution in the structure of α-FeOOH brought about changes in unit-cell dimensions, crystallinity, particle size and shape, hyperfine magnetic field and infrared bands positions. Ir 3+ for Fe 3+ substitution in the structure of α-Fe 2O 3 led to an increase in the temperature of the Morin transition; Mössbauer spectroscopy showed the presence of α-Fe 2O 3 in the antiferromagnetically ordered state at 293 K.