Optical Properties of Combustion-Synthesized Iron Oxide Aggregates

Measurements of scattering /extinction and asymmetry ratios at both polarization orientations, along with depolarization and reciprocity ratios, corresponding to nanosized Fe2 O3 aggregates were carried out in an Fe(CO)5 -seeded CO air-diffusion flame as a function of the position above the burner surface. The measurements were combined with an exact light-scattering theory to yield, for the first time, the complex refractive index, the primary particle-size parameter, the aspect ratio, and the number density and volume fractions of the Fe2 O3 chainlike aggregates under flame conditions. An effective complex refractive index of 1.96 +- 6.9% to 0.20 +- 14.5% was inferred from the data analysis at a wavelength of 488 nm and in the temperature range of 894 -924K. The corresponding primary particle size was found to be 48 nm +- 13%, and the aggregate aspect ratio was in the range of 6 -7. Comparisons of the size parameters are made with transmission electron microscopy results, and the possible sources of uncertainties in the inferred results pertaining to temperature, polydispersity effects, and the departure from the straight configuration are discussed.