TiO 2 Produced by Vapor‐Phase Oxygenolysis of TiCI 4

384

225

Recent advances in aerosol generation of materials are reviewed. Gas-to-particle and spray processes (spray pyrolysis) for powder generation and various routes for film generation are discussed from the experimental and theoretical perspectives. The range of materials generated by these routes has increased in recent years to include fullerenes and ceramic superconductors. Many metals and various oxide and nonoxide ceramics have also been added to the list of materials generated by gas-phase routes. Established aerosol routes such as vapor condensation have found widespread applications for generation of nanophase materials. The formation of quantum dots via aerosol approaches has also been demonstrated. The theoretical understanding of gas-to-particle conversion routes has advanced to include the finite rate of particle fusion or sintering occurring after collisions of particles. The modeling of spray pyrolysis systems has provided insight into the control of particle morphology and reactor design. In this review, these recent developments in aerosol generation of powders and films via gas-phase and spray routes are discussed with an emphasis on the material chen~istries involved and the synthesis of nanophase materials.

Section: Effect Of Particle Charging On Aerosol Coagulationmentioning

confidence: 99%

Aerosol Processing of Materials

Gurav,

Kodas,

Pluym

et al. 1993

384

225

“…Two different chemical precursors have been used: titanium tetrachloride (TiCl 4 ) and titanium tetraisopropoxide (TTIP). Particles were synthesized by either oxidation of TiCl 4 (Suyama and Kato 1976;Morooka et al 1989;Akhtar et al 1991;Jang and Jeong 1995;and Windeler et al 1997), thermal decomposition of TTIP (Kanai et al 1985;Komiyama et al 1984;Okuyama et al 1986;Okuyama et al 1990), or hydrolysis of TTIP (Kashima and Sugiyama 1990). These investigations focused on the effect of reaction temperature, precursor concentrations, and residence time on either the primary particle or aggregate size.…”

Section: Chemical Pathways To Titanium Dioxide Formationmentioning

confidence: 99%

Size Distribution Change of Titania Nano-Particle Agglomerates Generated by Gas Phase Reaction, Agglomeration, and Sintering

Nakaso¹,

Fujimoto

Seto³

et al. 2001

In the manufacturing of nanometer-sized material particlulates by aerosol gas-to-particle conversion processes, it is important to analyze how the gas-phase chemical reaction, nucleation, agglomeration, and sintering rates control the size distribution and morphology of particles. In this study, titania particles were produced experimentally by the thermal decomposition of titanium tetraisopropoxide (TTIP) and oxidation of titanium tetrachloride (TiCl 4 ) using a laminar ow aerosol reactor. The effect of reaction temperature on the size and morphology of the generated particles was investigated under various conditions. The size distributions of agglomerates were measured using a DMA/CNC system. The size distributions of primary particles were measured using TEM pictures of the agglomerates sampled by a thermophoretic aerosol sampler. In order to model the growth of both agglomerates and primary particles simultaneously, a two-dimensional discrete-sectional representation of the size distribution was employed, solving the aerosol general dynamic equation for chemical reaction, agglomeration, and sintering. Qualitative agreement between the experimentally observed results and the simulation are satisfactory for the large variations in reactor temperature explored.

“…Commonly, these processes are those in which an evaporated precursor is subsequently reacted to produce particles that form through chemical reaction and nucleation from the gas phase. This can be achieved by reacting the vapors of volatile metal chlorides in high temperature furnaces (Suyama and Kato 1976) or ames . The process is widely employed in industry for the large scale production of the oxides of silicon and titanium.…”

Section: Introductionmentioning

confidence: 99%

A Novel Aerosol Combustion Process for the High Rate Formation of Nanoscale Oxide Particles

Kilian¹,

Morse²

2001

We report a new method for the high rate formation of nanophase ZrO 2 and Al 2 O 3 powders. In the experimental arrangement, a solution of metal alkoxides in their parent alcohols is converted into an aerosol of approximately 30 ¹ diameter droplets by means of an ultrasonic spray nozzle. The aerosol is mixed with oxygen immediately after formation and combusted in a specially designed burner at high temperature. The resulting oxide particles are thermophoretically collected and examined using TEM and X-ray diffractometry. A novel, patented, burner design permits a signicant reduction in temperature gradients normal to the ame. As a consequence, it is possible to obtain signi cantly better control over particle size and morphology and, in addition, hard agglomerates are absent. This is a signi cant departure from the process found in a typical ame reactor. With this technique, spherical, unnecked particles in the range from 5 to 140 nm (peaking sharply at 40 nm) are produced. There is no correlation between the initial liquid droplet size and the nal particle size. The method was successfully applied to the formation of zirconium and aluminum oxide at synthesis rates in excess of 3 g/min. Experiments to measure the ame temperature using an optical technique yielded temperatures between 2300 K and 3000 K, depending on the position in the ame and the type of precursor solution used. We note that this technique can be readily extended to more complex oxides such as YAG and BaSrTiO 3 . INTRODUCTIONDuring the past several years a large number of methods for the production of nanoscale oxide particles have been reported. Oxide powders with particles sizes in the range below 100 nm are important in many applications that include ceramic products, catalysts, and paint opaci ers. The approaches taken in their synthesis can be divided into wet chemical and gas phase (aerosol) methods. Among the former is the precipitation of particles from a suitable homogeneous precursor solution (Ciftcioglo and Majo 1990) and the wet hydrolysis of metal alkoxides in solution (Smith et al.; Ingebrethsen and Matijevi).