Formation of particles in a H₂O₂ 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 SiO_x (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 SiO_x particles.