FORMATION OF PARTICLES IN A H-2-O-2 COUNTERFLOW DIFFUSION FLAME DOPED WITH SIH4 OR SICL4

Formation of particles in a H2O2 counterflow diffusion flame doped with SiH4 or SiCl4 was investigated. When SiH4 is used as precursor, the species that nucleate in the flame depend on the SiH4 concentration as well as on the flame temperature. At low SiH4 concentrations and/or when a high-temperature flame is used, SiO2 is the species that nucleates. At high SiH4 concentrations and/or when a low-temperature flame is used, nucleation of SiOx (x = 0 and/or 1) in addition to SiO2 is believed to occur in the flame. When SiCl4 is used as precursor, SiO2 is the species that nucleates under all the experimental conditions studied here. Laser light scattering and extinction measurements indicate a specific region in the flame where growth of the particles by coagulation occurs, and the particles were always amorphous. When SiH4 is used as precursor, most of the particles are in the form of agglomerate of small particles (mostly 20-40 nm diameter) with some larger, spherical particles (mostly 80-150 nm diameter). When SiCl4 is used as precursor, the particles are all agglomerates of small particles (mostly 20-30 nm diameter). When SiH4 is used as precursor, a second flame, orange in color, appears below the H2O2 flame when the SiH4 concentration is increased beyond a certain value. This orange flame cannot be ascribed to radiation from SiO2 particles and is suspected to be due to SiOx particles. © 1991.