Formation of mixed oxide powders in flames: Part II. SiO₂−GeO₂ and Al₂O₃−TiO₂

Abstract

SiO2−GeO2 and Al2O3−TiO2 mixed oxide powders were synthesized using a counterflow diffusion flame burner. SiCl4, GeCl4, Al(CH3)3, and TiCl4 were used as source materials for the formation of oxide particles in hydrogen-oxygen flames. In situ particle sizes were determined using dynamic light-scattering. Powders were collected using two different methods, a thermophoretic method (particles are collected onto carbon coated TEM grids) and an electrophoretic method (particles are collected onto stainless steel strips). Their size, morphology, and crystalline form were examined using a transmission electron microscope and an x-ray diffractometer. A photomultiplier at 90° to the argon ion laser beam was used to measure the light-scattering intensity. The formation of the mixed oxides was investigated using Si to Ge and Al to Ti ratios of 3:5 and 1:1, respectively. Heterogeneous nucleation of the SiO2 on the surface of the GeO2 was observed. In Al2O3−TiO2 mixtures, both oxide particles form at the same temperature. X-ray diffraction analysis of particles sampled at temperatures higher than 1553 K showed the presence of rutile, γ–Al2O3, and aluminum titanate. Although the particle formation process for SiO2−GeO2 is very different from that for Al2O3−TiO2, both mixed oxides result in very uniform mixtures.

Morphology and crystal structure of A1-doped TiO2 nanoparticles synthesized by vapor phase oxidation of titanium tetrachloride

“…He concluded that oxygen vacancies promoted crystallite growth and the anatase to rutile transformation. Hung et al [12] obtained a mixture of TiO 2 , Al 2 O 3 and aluminum titanate on a microscopic scale when they synthesized TiO 2 -Al 2 O 3 composite particles in a counter flow diffusion flame. Powell et al [13] prepared titania particles from the oxidation of titanium tetrachloride in a hot-wall, tubular, aerosol reactor and directly coated by SiO 2 in the gas phase.…”

Synthesis and Properties of Nanocomposites

“…Earlier attempts by Hung and Katz to produce mixed oxide powders nanoparticles of the core/shell type by flame synthesis. [10,11] lead to coated clusters, too. Entirely different is the approach of Jiao et al applying a modified Krätschmer-method to coat Fe, Co and Ni nanopar-REVIEWS ticles with amorphous carbon or graphite.…”

Controlling Surface Composition and Zeta Potential of Chemical Vapor Synthesized Alumina‐Silica Nanoparticles

“…Preparation of silica-coated particles by wet chemical process can be found, for example, in the literature. [8,9] Hung et al [10] report on the formation of mixed oxide powders consisting of silica, alumina, germania, and titania using a counterflow diffusion flame burner. Hartmann et al [11] present the production of highly dispersed ZrO 2 -, Al 2 O 3 ±TiO 2 -, and SiO 2 -doped powders by high-temperature hydrolysis of gaseous metal chlorides.…”