delta-FeOOH nanoparticles were synthesized via the oxidation of precipitates obtained from the reaction of FeCl2 and N2H4 in the presence of sodium tartrate and gelatin in an alkaline condition. These delta-FeOOH particles were subsequently examined using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), Mossbauer spectroscopy, and superconducting quantum interference device (SQUID) assessment. The average size of the delta-FeOOH nanoparticles was below 10 nm, and these particles exhibited superparamagnetic behavior as a result of this small size. The precursors of the delta-FeOOH nanoparticles were also characterized as a means of elucidating the reaction mechanism. Precipitates prior to oxidation upon rinsing with water and ethanol were analyzed by obtaining XRD patterns and Mossbauer spectra of wet and frozen samples, respectively. The precipitates obtained by the reaction of FeCl2 and N2H4 were found to consist of a mixture of Fe304 and Fe(OH)(2), and it is believed that these species then rapidly oxidized into delta-FeOOH nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.