Synthesis of nanostructured goethite and magnetite particles from the oxidation of Fe(OH)(2) in a high-oxygen-flow-rate medium

Results on the oxidation of ferrous hydroxide under different oxygen flow rates are reported. Oxidation under air produced mainly magnetite (Fe3O4) with a small amount of goethite (alpha-FeOOH), but as the oxygen flow rate was increased, their relative content and their crystallite size varied; the higher the oxygen flow rate, the higher the superparamagnetic goethite content and the smaller the crystallite size (nanometric scale) of both oxidation products. Slight quantitative differences were found between the Mossbauer and the XRD analysis while estimating the goethite and magnetite contents. These differences were associated with the fitting procedures but may also be due to different Debye Waller factors between the goethite and magnetite. Additionally, HRTEM images showed that distorted nano-fibers were characteristic for the goethite, and nano-platelets for the magnetite. (C) 1997 Acta Metallurgica Inc.