The influence of metal precursor and solvent composition on the morphology of SiO2, Bi2O3, and other oxide particles made by flame spray pyrolysis (FSP) was investigated. Silica precursors with boiling points Tbp=299–548 K dissolved in xylene were used as well as different solvents (Tbp=308–557 K) with tetraethyl‐orthosilicate (TEOS) as the silica precursor. For Bi2O3, nonvolatile bismuth nitrate pentahydrate was dissolved in solvents with Tbp=338–468 K. Product powders were characterized by nitrogen adsorption, X‐ray diffraction, and scanning and transmission electron microscopy. From these data as well as from the literature of FSP synthesis of Bi2O3, CeO2, MgO, ZnO, Fe2O3, Y2O3, Al2O3, and Mg–Al spinel, it is inferred that hollow/inhomogeneous particles are formed at low combustion enthalpy densities and when the solvent boiling point is comparable or smaller than the precursor melting or decomposition point.

Synthesis of zirconia nanoparticles by flame spray pyrolysis(FSP) at high production rates is investigated. Product powder is collected continuously in a baghouse filter unit that is cleaned periodically by air-pressure shocks. Nitrogen adsorption (BET), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) are used to characterize the product powder. The effect of powder production rate (up to 600 g/h), dispersion gas flow rate, and precursor concentration on product particle size, crystallinity, morphology, and purity is investigated. The primary particle size of zirconia is controlled from 6 to 35 nm, while the crystal structure consists of mostly tetragonal phase (80 -95 wt%), with the balance monoclinic phase at all process conditions. The tetragonal crystal size is close to the primary particle size, which indicates weak agglomeration of single crystals.

The growth of ZrO 2 particles in spray flames is studied at production rates of 100 and 300 g/h by thermophoretic sampling (TS) and image analysis of transmission electron microscope (TEM) micrographs. At each TS location, the corresponding temperature of the particle-laden spray flame is measured along the centerline by Fourier transform infrared (FTIR) spectroscopy. The product powder is analyzed by nitrogen adsorption and TEM. The measured evolution of primary particle size distribution is presented and

Rapid quenching during flame spray synthesis of Pt/TiO 2 (0-10 wt% Pt) is demonstrated as a versatile method for independent control of support (TiO 2 ) and noble metal (Pt) cluster characteristics. Titania grain size, morphology, crystal phase structure, and crystal size were analyzed by nitrogen adsorption, electron microscopy and x-ray diffraction, respectively, while Pt-dispersion and size were determined by CO-pulse chemisorption. The influence of quench cooling on the flame temperature was analyzed by Fourier transform infrared spectroscopy. Increasing the quench flow rate reduced the Pt diameter asymptotically. Optimal quenching with respect to maximum Pt-dispersion (∼60%) resulted in average Pt diameters of 1.7 to 2.3 nm for Pt-contents of 1-10 wt%, respectively.

Silica/titania composite particles were prepared by co-oxidation of titanium-tetra-isopropoxide and hexamethyldisiloxane in a co-flow diffusion flame reactor. The influence of precursor composition on product powder characteristics was studied by x-ray diffraction, nitrogen adsorption, electron microscopy, elemental mapping, and energy-dispersive x-ray analysis. The flame temperature was measured by Fourier transform infrared spectroscopy. The evolution of composite particle morphology from ramified agglomerates to spot-or fully coated particles was investigated by thermophoretic sampling and transmission/scanning electron microscopy. At 40-60 wt% TiO 2 , particles with segregated regions of silica and titania were formed, while at 80 wt% TiO 2 rough silica coatings were obtained. Rapid flame-quenching with a critical flow nozzle at 5 cm above the burner nearly halved the product particle size, changed its crystallinity from pure anatase to mostly rutile and resulted in smooth silica coatings on particles containing 80 wt% TiO 2 .