Magnetization, micro-x-ray fluorescence, and transmission electron microscopy studies of low concentrations of nanoscale
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W. Lowe, H. Anderson,a) and E. Williamsb) MHATT-CAT, Howard University, Washington, District of Columbia 20059
C. Monkres and A. Barkatt Department of Chemistry, The Catholic University of America, Washington, District of Columbia 20064 (Received 11 February 2000; accepted 14 August 2000)
Magnetization measurements, transmission electron microscopy (TEM), and high-resolution micro-x-ray fluorescence (-XRF) using a synchrotron radiation source (Advanced Photon Source) were used to examine Fe3O4 particle agglomerates of nominally 10-nm particles at low concentrations (down to 0.03%) in thick epoxy resin samples. The magnetization measurements showed that at low concentrations (1 wt%) of such particles. At low concentrations the interparticle distances become so large that it is difficult to find and focus on individual particles or small agglomerates using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). As there is no need to focus on individual particles when making magnetic measurements, magnetic studies are useful in studying low concentrations of particles, especially when coupled with other techniques. In this study commercial magnetite ferrofluids were used as a source of nanoscale Fe3O4 particles to prepare samples at low concentrations.
a)
Present address: Rutgers University at Newark, Newark, New Jersey 07102. b) Present address: MHATT-CAT APS, Argonne National Laboratory, Argonne, Illinois 60439. 2488
http://journals.cambridge.org
J. Mater. Res., Vol. 15, No. 11, Nov 2000 Downloaded: 17 Mar 2015
Superparamagnetic-size (single domain) magnetite particles behave as individual dipoles. In an aqueous solution they are free to move under the influence of thermal agitation, and therefore, due to dipole–dipole interactions, they tend to agglomerate.3 In any event, the dipoles tend to neutralize each other so that the resultant remanent magnetization of the fluid is essentially zero.4 In ferrofluids, the particles are generally coated with a surfactant that, because of its thickness, establishes a minimum interparticle distance, and prevents interactions (agglomeration) due to short-range van der Waals forces.5 At first glance, in the absence of a magnetic field the magnetite particles in a water-based ferrofluid would be expected to be uniformly dispersed. However, as pointed out by Krueger,3 agglomeration has been observed in ferrofluids in several types of experiments, particularly at high concentrations, even in the absence of an external magnetic field. Commercial water-based ferrofluids typically have concentrations of about 20 wt% Fe3O4, whereas kerosene-based ferrofluids have concentrations of about 14% magnetite. In this investigation ferrofluids containing small particles of magnetite (nominally 10 nm, but with a size distribution of 2 to 30 nm) primarily at concentrations of © 2000 Materials Research Society IP address: 152.14.136.77
A.N. Thorpe et al.: Magnetization, µ-XRF, and TEM studies of low concentrations of nanoscale Fe3O4 particles in epoxy resin
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