Evaluation of Sintering of Nanometer-Sized Titania Using Aerosol Method

Seto, Takafumi; Shimada, Manabu; Okuyama, Kikuo

doi:10.1080/02786829508965303

Cited by 127 publications

(88 citation statements)

References 29 publications

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“…When performing electrical mobility measurements, the classified mobility (mobility equivalent diameter, D m ) of the fractal-like aggregate is proportional to its projected area. [46,49] The results obtained from the mobility scan using the DMA and CNC showed that the geometric mean D m values of the aggregates increase with an increase in precursor evaporation temperatures. The change in precursor vapor pressure (Figure 1 a) does not result in any substantial change in the primary-particle diameters as proven by TEM.…”

Section: Particle Growth Investigationmentioning

confidence: 99%

“…It involves vapor-phase chemical reaction, nucleation of the supersaturated vapor to form primary particles, primary-particle growth by vapor condensation and/or heterogeneous chemical reactions, coagulation by particle-particle collisions induced by their Brownian motion, and coalescence or sintering between particles. [46,47] For many metal oxides produced by oxidation of organometallic precursors using aerosol reactors or in flames, it has been found that nucleation of the oxide species is virtually instantaneous due to the very rapid oxidation and high concentration of the precursor vapor, and only the physical coagulation and coalescence process determine the final particle morphology. [47,48] In the present study this was verified by increasing the precursor vapor pressure through increasing the evaporation temperature and keeping the decomposition furnace temperature constant at 300 8C to minimize any postsintering effect.…”

Section: Particle Growth Investigationmentioning

confidence: 99%

“…[51,52] The most accepted expression to calculate the characteristic sintering time, t, is derived for the initial stage of sintering from the two-sphere model with the assumption that it holds true for all stages of sintering. [46][47][48][51][52][53] To calculate t, it is important to determine the rate-controlling transport mechanism(s) for sintering. ZnO has a melting point of 1975 8C, and it is therefore rather unlikely that viscous flow plays any significant role in the sintering mechanism for T 900 8C as in our experiments.…”

Section: Particle Growth Investigationmentioning

confidence: 99%

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Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Polarz

Roy

Merz

et al. 2005

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ZnO can be regarded as one of the most important metal oxide semiconductors for future applications. Similar to silicon in microelectronics, it is not only important to obtain nanoscale building blocks of ZnO, but also extraordinary purity has to be ensured. A new gas-phase approach to obtain size-selected, nanocrystalline ZnO particles is presented. The tetrameric alkyl-alkoxy zinc compound [CH 3 ZnOCH(CH 3 ) 2 ] 4 is chemically transformed into ZnO, and the mechanism of gas-phase transformation is studied in detail. Furthermore, the morphological genesis of particles via gas-phase sintering is investigated, and for the first time a detailed model of the gas-phase sintering processes of ZnO is presented. Various analytical techniques (powder XRD, TEM/energy-dispersive X-ray spectroscopy, magic-angle spinning NMR spectroscopy, FTIR spectroscopy, etc.) are used to investigate the structure and purity of the samples. In particular, the defect structure of the ZnO was studied by photoluminescence spectroscopy.

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Section: Particle Growth Investigationmentioning

confidence: 99%

Section: Particle Growth Investigationmentioning

confidence: 99%

Section: Particle Growth Investigationmentioning

confidence: 99%

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Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Polarz

Roy

Merz

et al. 2005

Small

156

108

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“…There are many studies on the hydrolysis and thermal decomposition of TTIP. The rate constants are 3.96 × 10 5 exp(−8479.7/T) for gas phase thermal decomposition (Okuyama et al 1990) and 3 × 10 15 exp(−1013.9/T) for gas phase hydrolysis (Seto et al 1995). Hydrolysis clearly is much faster than thermal decomposition.…”

Section: Aerosol Reactor Experiments Vanadium Precursor Characterizationmentioning

confidence: 99%

A Mechanistic Study of Vanadium-Sorbent Surface Interaction at High Temperature

Lee

Andino

2007

Aerosol Science and Technology

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A mechanistic study of vanadium-sorbent interaction at high temperature was conducted to investigate the underlying mechanisms of sorbent injection for controlling vanadium emissions from combustion systems. Both calcium-and silica-based sorbents successfully reduced the formation of vanadium submicron particles. The capture of vanadium was found to correlate well with sorbent surface area, demonstrating that the dominant mechanism was condensation. Bimodal lognormal modeling based on the experimental conditions verified that condensation on injected sorbents was a very effective means of scavenging vanadium vapor. However, if vanadium vapor quickly nucleated (e.g., through gas phase hydrolysis in the studied system) to form a large number of ultrafine particles, their much larger specific surface area overshadowed that of the sorbent particles and scavenged the rest of the vanadium vapor. Using the residence times employed in this study, intra-coagulation of and condensation onto these ultrafine vanadium particles was not an effective means of growing the particles to the supermicrometer range. Such a scenario decreased the effectiveness of the sorbent technique. Consequently, enhancing direct vanadium condensation onto sorbent particles and suppressing vanadium nucleation is critical to successful reduction of vanadium emissions from combustion sources.

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“…Schmidt-Ott argued that the fractal dimension of the aggregates could be inferred from the exponent of the power law. The kinetics of the structural rearrangements due to the sintering of agglorncrate particles have been probed by processing an agglomerate aerosol through a high-temperature furnace betwecn the two DMAs (SchmidtOtt, 1988;Shimada et al, 1994;Lunden, 1995;Seto et al, 1995). The resulting densification is seen as a decrease in the mobility equivalent size.…”

Section: Particle Structure and Densitymentioning

confidence: 99%

History of Electrical Aerosol Measurements

Flagan

1998

Aerosol Science and Technology

218

117

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ABSTRACT. Early studies of atmospheric electricity suggested that the electrical conductivity of the atmosphere should be sufficient to dissipate the charge on the surface of the earth in a matter of minutes. Efforts to understand how substantial electric fields could be maintained globally in spite of the high dissipation rates were propelled into the forefront of physics research at the turn of the century when it was observed that the newly discovered X-rays produced ions that behaved much like those in the atmosphere. Many of the approaches that are now employed in electrical measurements of aerosols were first conceived during the first three decades of this century. Initially the focus was on gas ions, but they were found to consist of charged clusters of water molecules that exhibited a number of distinct mobilities that were substantially lower than those that resulted after long efforts to dry the gas. The coaxial condenser mobility analyzer, introduced by McClelland in 1898 and enhanced by Zeleny in 1900, was used to measure atmospheric ions as early as 1901 by Ebert. Based upon atmospheric measurements with this device in 1905, Langevin reported on the existence of ions with mobilities 3000 times lower than those observed in the laboratory studies. These so-called large ions correspond to particles in what we now know as the accumulation mode of the atmospheric aerosol. The aspiration condenser dominated measurements of atmospheric ions for six decades even though Erikson developed a differential mobility analyzer by 1921, and Rohmann produced a differential mobility sampler in 1923. Only after electronics was improved in the 1950s and 1960s were these instruments reintroduced. It was based upon condenser measurements of atmospheric "ions" that Junge first described the structure of the ultrafine particle size distribution in 1955.The development of the Whitby Aerosol Analyzer in 1966 built upon earlier developments, including the Faraday cup electrometer that was used by both Zeleny and McClelland at the turn of the century, and a long history of mobility analyzers. This instrument represented a breakthrough nonetheless since it was the first mobility aerosol analyzer that was sufficiently refined and robust to be commercially produced. That instrument was refined into the electrical aerosol analyzer ( E M ) that became the primary tool for characterizing ultrafine aerosol particles in the atmosphere for a number of years. At the same time that the E M was developed, the differential mobility analyzer was reintroduced in a form that quickly became the standard for production of submicron calibration aerosols. Early efforts to transform that instrument from a calibration tool to a measurement device met with limited success due to the lack of a suitable detector. The introduction of a continuous flow condensation nucleus counter was followed quickly by the development of computerized differential mobility analysis of particle-size distributions and later accelerated through the introduction of scannin...

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Evaluation of Sintering of Nanometer-Sized Titania Using Aerosol Method

Cited by 127 publications

References 29 publications

Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

A Mechanistic Study of Vanadium-Sorbent Surface Interaction at High Temperature

History of Electrical Aerosol Measurements

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