In situ characterization of vapor phase growth of iron oxide-silica nanocomposites: Part I. 2-D planar laser-induced flu
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In situ characterization of vapor phase growth of iron oxide-silica nanocomposites: Part I. 2-D planar laser-induced fluorescence and Mie imaging Brian K. McMillina) Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-0001
Pratim Biswasb) Aerosol and Air Quality Research Laboratory, Department of Environmental Engineering, University of Cincinnati, Cincinnati, Ohio 45221-0071
Michael R. Zachariahc) Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-0001 (Received 3 April 1995; accepted 3 January 1996)
Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained during flame synthesis of iron-oxide/silica superparamagnetic nanocomposites. The theory and application of laser-induced fluorescence, the spectroscopy of FeO(g), and the experimental approach for measurement of gas phase precursors to particle formation are discussed. The results show that the vapor phase FeO concentration rapidly rises at the primary reaction front of the flame and is very sensitive to the amount of precursor added, suggesting nucleation-controlled particle growth. The FeO vapor concentration in the main nucleation zone was found to be insensitive to the amount of silicon precursor injected, indicating that nucleation occurred independently for the iron and silicon components. Light scattering measurements indicate that nanocomposite particles sinter faster than single component silica, in agreement with TEM measurements.
I. INTRODUCTION
An area of current interest in materials processing is the synthesis of structures on an atomic to nanometer scale. Particles with dimensions of less than 100 nm are referred to as “nanoparticles,” and these nanophase materials possess unique advantages with respect to their processing and, more importantly, their properties.1– 4 Flame aerosol reactors offer a potential route for the production of large quantities of nanostructured materials,5 but at present the formation and nucleation of nanophase particles from the gas phase are not well understood. Developing a better understanding of the gas phase chemistry is important, though, because the chemistry and interaction of the gas phase precursors in this high temperature environment are critical in establishing the final particle characteristics (sizes and chemical composition). In situ measurements aimed at investigating the gas phase species’ concentrations, temperature field, and
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National Research Council/NIST postdoctoral fellow. performed while on sabattical at NIST. Author to whom correspondence should be addressed.
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particle size and distributions are therefore of great interest, because they can lead to a better understanding of the underlying chemical/transport phenomena that occur during particle synthesis. While conventional diagnostic tools such as thermocouples and
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