Preparation of Magnetite Nanoparticles by Thermal Decomposition of Hematite Powder in the Presence of Organic Solvent
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0998-J08-05
Preparation of Magnetite Nanoparticles by Thermal Decomposition of Hematite Powder in the Presence of Organic Solvent Chun-Rong Lin1, Ray-Kuang Chiang2, Chih-Jung Chen3, Hsin-Yi Lai3, Igor S. Lyubutin4, and Egor A. Alkaev4 1 Department of Mechanical Engineering, Southern Taiwan University, No.1, Nan-Tai Street, Yung-Kang City, Tainan County, 710, Taiwan 2 Department of Electronic Materials, Far East University, No.49, Chung Hua Rd., Hsin-Shih, Tainan County, 744, Taiwan 3 Department of Mechanical Engineering, National Cheng Kung University, No.1, University Road, Tainan City, 701, Taiwan 4 Institute of Crystallography, Russian Academy of Sciences, Moscow, 117333, Russian Federation
ABSTRACT Magnetite nanoparticles have been synthesized by thermal decomposition of hematite (αFe2O3) powder in the presence of high boiling point solvent. The mixture of hematite and 1octadecene solvent was heated and stirred in nitrogen gas at the temperature of 320 °C for the desired time (~2 to 28 hrs). The influence of the reaction time on transformation process was analyzed with X-ray diffraction (XRD), Mˆssbauer spectroscopy (MS), and magnetic measurements. XRD patterns show that the phase of intermediate was composed of spinel phase and corundum phase (α-Fe2O3). The 57Fe Mˆssbauer spectra show that the spinel phase originated from the magnetite particles. The structure transformation proportion of hematite to magnetite strongly depends on reaction times. After reflux for 28 hrs the hematite-magnetite transformation was complete. The mean crystallite size of pure phase of magnetite particles is about 40 nm. The saturation magnetization increases with the reaction time, which corresponds to an increase of concentration of magnetite in the samples. A pronounced feature of the Hc and σr /σs observed in samples is the steplike change which appears at 125 K and is characteristic of the Verwey transition. The hyperfine parameters of Mˆssbauer spectrum measured at low temperature also indicate that the Verwey phase transition occurs. In other words, the Verwey transition is an indication that the magnetite particles exactly grew up in the synthesized compounds. This thermal decomposition process provided a method to prepare pure magnetite as well as magnetite/hematite nanocomposites useful for various magnetic applications.
INTRODUCTION Magnetite is the focus of a great deal of recent research because of its numerous potential applications in various areas such as magnetic recording media, GMR sensors, sealing, photonic crystals and biotechnology [1-4]. Synthesis of magnetite powders using pure hematite (α-Fe2O3)
has been studied for a long time and was found to be induced by either reduction of hematite by CO/CO2 or H2 [5] or magnetomechanical activation [6]. Stoichiometric Fe3O4 has an inverse cubic spinel structure with eight Fe3+ ions on the tetrahedrally coordinates sites (A-sites) antiferromagnetically coupled with eight Fe2+ and eight Fe3+ ions on the octahedrally coordinates sites (B-sites) [7]. Moreover, the magne
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