Synthesis of pure amorphous Fe 2 O 3
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Synthesis of pure amorphous Fe2 O3 X. Cao Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel, 52900
R. Prozorov Department of Physics, Bar-Ilan University, Ramat-Gan, Israel, 52900
Yu. Koltypin and G. Kataby Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel, 52900
I. Felner Racah Institute of Physics, Hebrew University, Jerusalem, Israel
A. Gedanken Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel, 52900 (Received 1 April 1996; accepted 26 August 1996)
A method for the preparation of pure amorphous Fe2 O3 powder with particle size of 25 nm is reported in this article. Pure amorphous Fe2 O3 can be simply synthesized by the sonication of neat Fe(CO)5 or its solution in decalin under an air atmosphere. The Fe2 O3 nanoparticles are converted to crystalline Fe3 O4 nanoparticles when heated to 420 ±C under vacuum or when heated to the same temperature under a nitrogen atmosphere. The crystalline Fe3 O4 nanoparticles were characterized by x-ray diffraction and M¨ossbauer spectroscopy. The Fe2 O3 amorphous nanoparticles were examined by Transmission Electron Micrography (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Quantum Design SQUID magnetization measurements. The magnetization of pure amorphous Fe2 O3 at room temperature is very low s,1.5 emuygd and it crystallizes at 268 ±C.
I. INTRODUCTION
Amorphous metal oxides have many important applications, including that in the fields of solar-energy transformation, magnetic storage media, electronics, and catalysis.1–5 Amorphous metal oxides can be prepared by rapidly quenching the molten mixture of metal oxides and a glass former, such as P2 O5 , V2 O5 , Bi2 O3 , SiO2 , and CaO,1,6–8 or by thermal decomposition of some easily decomposed metal compounds.4,9 Amorphous metal oxide thin films on a substrate can be prepared by means of ion beam sputtering, electron beam evaporation, and thermal evaporation.10 So far, only a few amorphous metal oxides, such as Cr2 O3 , V2 O5 , MnO2 , and PbO2 powders, have been prepared by means of thermal decomposition,4,9 but it is difficult to control their purities. Other amorphous metal oxides are usually in the form of hydrous oxides.5,11 The cooling rates that are generally required for the preparation of amorphous metals are 105 –107 Kys. Since the thermal conductivities of metal oxides are usually much lower than those of the metals, faster cooling rates are needed to prepare amorphous metal oxides. This is the reason that glass formers, whose purpose is preventing crystallization, are added if the quenching method is applied. No pure amorphous iron oxide has ever been reported as being 402
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J. Mater. Res., Vol. 12, No. 2, Feb 1997
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successfully prepared. Suslick and his co-workers have reported the preparation of amorphous iron,12 amorphous cobalt, and amorphous FeyCo alloy,13 as well as amorphous molybdenum carbide,14 all as powders having nanometer s
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