Diagnostics and modeling of nanopowder synthesis in low pressure flames

Laser-induced fluorescence, thermophoretic sampling, laser light scattering, and emission spectroscopy have been used to probe low pressure hydrogen/oxygen flames in which 3-50 nm, loosely agglomerated oxide nanopowders have been synthesized at high production rates by the pyrolysis of precursor vapors, followed by condensation in the gas phase. These measurements have enabled the identification of pyrolysis, condensations, and particle growth regions in the flame. Flame simulations using a one-dimensional stagnation flow model, with complex chemistry, demonstrate that the chemical and thermal flame structure can be accurately predicted for flames without a precursor. Furthermore, some flame structure changes induced by the addition of a precursor can be simulated by addition of analogous species to the chemical mechanism.