a1 Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899–0001
a2 Aerosol and Air Quality Research Laboratory, Department of Environmental Engineering, University of Cincinnati, Cincinnati, Ohio 45221–0071
a3 Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899–0001
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.
(Received April 03 1995)
(Accepted January 03 1996)
c1 Author to whom correspondence should be addressed.
a) National Research Council/NIST postdoctoral fellow.
b) Work performed while on sabattical at NIST.