Influence of Mn-dopant on the properties of α-FeOOH particles precipitated in highly alkaline media

The effects of Mn-dopant on the fort-nation of solid solutions alpha-(Fe, Mn)OOH in dependence on the initial concentration ratio r = [Mn]/([Mn] + [Fe]), as well as on the size and morphology of the corresponding particles were investigated using Mossbauer and Fr-IR spectroscopies, high-resolution scanning electron microscopy (FE SEM) and an energy dispersive X-ray analyser (EDS). The value of the hyperfine magnetic field of 34.9 T, as recorded for the reference alpha-FeOOH sample at RT, decreased linearly up to 21.4 T for sample with r = 0.1667. Only a paramagnetic doublet at RT was recorded for sample with r = 0.2308, a ferrite phase was additionally found for r = 0.3333. Fe-OH bending IR bands, delta(OH) and gamma(OH), were influenced by the Mn-substitution as manifested through their gradual shifts. FE SEM micrographs showed a great elongation of the starting acicular particles along the c-axis with an increase in Mn-doping. For r = 0.1667 and 0.2308 star-shaped and dendritic twin alpha-(Fe, Mn)OOH particles were observed. The length of these alpha-(Fe, Mn)OOH particles decreased, whereas their width increased. The alpha-Fe2O3 phase was not detected in any of the samples prepared. (c) 2006 Elsevier B.V. All rights reserved.