Morphology of Oxide Particles Made by the Emulsion Combustion Method

Abstract

Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X‐ray diffraction. Hollow γ‐Al2O3 particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid α‐Al2O3 particles. Hollow spheres were obtained also for TiO2, ZrO2, and Y2O3 by ECM of TiCl4, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe2O3, CeO2, and MgO from aqueous solutions of their corresponding nitrates.

Growth of zirconia particles made by flame spray pyrolysis

“…Essentially little is known on how droplets are converted to particles, given that in situ measuring of flame and particle characteristics is rather challenging in these particleladen flames. Such data are needed to understand some of the intriguing FSP results such as the formation of solid or hollow Al 2 O 3 by replacing air with O 2 as oxidant/dispersion gas (Tani et al, 1998(Tani et al, , 2003 or Bi 2 O 3 by controlling the composition of the precursor solution fed to FSP .…”

Band-Gap Engineering in ZnO-MgO Films Prepared by Combustion Flame Pyrolysis of Solution Precursors

“…[1][2][3] Their excellent material properties are promising for blue and UV photon emitters and detectors. 4,5 In optoelectronic devices, modulation of the optical constant and band-gap energy of the constituent layers, while keeping their lattice constant close to each other, is important for constructing appropriate heterostructures.…”

Secondary atomization as a mechanism for controlling the size of ceramic nanoparticles produced by combustion aerosol synthesis

“…Predominantly shell-like particles were observed in water in kerosene emulsion combustion studies (Takatori et al, 1999;Tani et al, 2003). Here, the shell-like fragments were also found to be larger than one micron in the TEM micrographs of the particles collected with the ESP.…”

“…This is attributed to the invariability of the vapor nucleation temperature as a function of water concentration in waterhydrocarbon emulsions. As noted above, the use of water in kerosene emulsions (Takatori et al, 1999;Tani et al, 2003) reported in the literature produced material that was primarily shell-like when the size of the aqueous droplets in the emulsion was 1-2 m. These water in kerosene studies did not appear to induce droplet fragmentation controllably, but rather the organic phase (kerosene) served to provide a source of heat to pyrolyze the precursor suspended in the aqueous phase (Tani et al, 2003). Consequently, the ÿnal particles resulted from a process similar to spray pyrolysis with the kerosene acting as the heat source.…”

“…This rapid expansion will cause each droplet to fragment into numerous smaller droplets. While this phenomenon has been extensively studied in the combustion literature as a means of improving the combustion of heavy hydrocarbons (Lasheras, Fernandez-Pello, & Dryer, 1979, 1981aLasheras et al, 1980;Lasheras, Kennedy, & Dryer, 1981b) and has been inferred from studies of particle formation in water in kerosene emulsions (Takatori, Tani, Naoyoshi, & Nuobo, 1999;Tani, Naoyoshi, Takatori, & Pratsinis, 2003), it has not been applied in a hydrocarbon system as a method for controlling the size of the ÿnal ceramic nanoparticles.…”