Controlling the particle size of amorphous iron nanoparticles
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R. Prozorov Department of Physics, Bar-Ran University, Ramat-Gan, Israel 52900
A. Gedankena) Department of Chemistry, Bar-Han University, Ramat-Gan, Israel 52900 (Received 12 May 1995; accepted 14 July 1995)
A method for controlling the particle size of amorphous iron, which was prepared by the sonication of iron pentacarbonyl [Fe(CO)5], is reported in this paper. The sonolysis was performed on neat Fe(CO)s and its solutions in decane whose concentrations were 4 M, 1 M, and 0.25 M. The iron nanoparticles were subjected to TEM (Transmission Electron Micrograph), ESR (Electron Spin Resonance), TGA (Thermogravimetric Analysis), DSC (Differential Scanning Calorimetry), and Quantum Design SQUID magnetization measurement. The measured properties demonstrated a strong dependence on the concentration of the solution, e.g., particle size.
I. INTRODUCTION Suslick and his co-workers have shown that the ultrasound irradiation of pure Fe(CO)5 or its 4.0 M solution in decane yields a black powder.1 The iron, which is the only sonochemical product, is obtained in the amorphous state and converts into crystalline form at 312 °C. The elemental analysis of the powder shows it to contain >96% iron by weight. Their transmission electron micrograph of the powder revealed that the bulk material is a composite of many smaller iron particles (about 10 nm size).1 The transmission electron micrograph confirmed the agglomerated nature of the solid.2 Later Suslick reported the formation of amorphous cobalt and amorphous Fe/Co alloy3 using similar techniques. We have recently succeeded in synthesizing amorphous nickel from the sonication of Ni(CO) 4 . 4 The magnetic properties of the amorphous iron nanoparticles were also measured by Suslick and his co-workers.5 Their results were consistent with the properties of an aggregate of amorphous iron particles of nonspherical shape, giving rise to local shape anisotropy. In this study we have prepared amorphous iron from various concentrations of iron pentacarbonyl in decane solution. Our assumption was that in a dilute solution the iron nanoparticles resulting from the sonochemical process should have a smaller size than those obtained from a more concentrated solution. We have checked this assumption by measuring the particle size, ESR, DSC, TGA, and magnetization of the amorphous iron. All the measurements showed a gradual dependence on
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to whom all correspondence should be addressed. J. Mater. Res., Vol. 10, No. 11, Nov 1995
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the concentration of the solution which is consistent with the assumed particle size.
II. EXPERIMENTAL Ultrasonic irradiation of iron pentacarbonyl Fe(CO)5 yields a dull black powder. The experimental procedure has been reported in detail elsewhere.6 Pure Fe(CO)5 (Aldrich), 4 M, 1 M, and 0.25 M Fe(CO)5 solutions in decane (Aldrich, dried with sodium) were irradiated at 0 °C with a high-intensity ultrasonic horn (Ti horn, 20 kHz) for 3 h under 1.5 atm of argon. The products were washed thoroughly wi
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