Observation of Soot Superaggregates with a Fractal Dimension of 2.6 in Laminar Acetylene/Air Diffusion Flames

Sorensen, C. M.; Kim, Wongyo; Fry, D.; Shi, Dan; Chakrabarti, Amitabha

doi:10.1021/la034063h

Cited by 58 publications

(54 citation statements)

References 26 publications

(39 reference statements)

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“…Recently, in work from this laboratory [17] soot aggregates in an acetylene/air laminar diffusion flame were studied using small angle light scattering. An inhomogeneous aggregate structure was observed at higher heights above the burner orifice, i.e., late aggregation times.…”

Section: Chapter 3 -Results and Discussionmentioning

confidence: 99%

The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

Mokhtari

Sorensen

Cheng

et al. 2008

Journal of Colloid and Interface Science

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Section: Chapter 3 -Results and Discussionmentioning

confidence: 99%

The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

Mokhtari

Sorensen

Cheng

et al. 2008

Journal of Colloid and Interface Science

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“…There also are situations where aggregates are found with larger fractal dimensions as a result of processes following the aggregation processes such as shear restructuring or cloud processing. More recently hybrid superaggregates with D f = 1.8 on short length scales and D f = 2.6 on larger length scales have been discovered (Sorensen et al 2003;Kim et al 2004Kim et al , 2006. Regardless of these variants, here we will consider the canonical DLCA aggregates which represent the great majority.…”

Section: Fractal Aggregatesmentioning

confidence: 99%

The Mobility of Fractal Aggregates: A Review

Sorensen

2011

Aerosol Science and Technology

306

298

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A review of the experimental and theoretical literature describing the mobility of fractal aggregates over the previous three decades is presented. Aggregates are those formed via both diffusion and reaction limited cluster-cluster aggregation processes, DLCA and RLCA, which form aggregates with fractal dimensions and prefactors of ca. 1.78 and 1.3 and 2.1 and 0.94, respectively. Emphasis is placed on DLCA aggregates. The entire Knudsen number range from continuum to free molecular is reviewed. The review finds a simple and general consensus description of mobility for the entire range.

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“…The stronger power-law decay of the scattered intensity at low q can be explained as the appearance of superaggregates with a fractal dimension of ca. 2.6, which we have shown can occur in dense aerosols near the gel point (Sorensen et al 2003;Kim et al 2004Kim et al , 2006. On the other hand, this could also be an artifact of the collapsing of the aerosol gel while shipping and handling to NCNR (Sorensen et al 1998b).…”

Section: Morphology Of the Silica Aggregatesmentioning

confidence: 73%

Synthesis of Silica Aerosol Gels via Controlled Detonation

Dhaubhadel

Rieker

Chakrabarti

et al. 2012

Aerosol Science and Technology

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Silica (SiO 2 ) aerosol gels were formed via Brownian aggregation of silica nanoparticles in a closed reaction chamber. A sudden and quick detonation reaction of pyrophoric silane (SiH 4 ) with either oxygen or nitrous oxide created silica nanoparticles with diameters ranging from ∼22 to 90 nm in the presence of an inert background gas with a volume fraction of ca. 10 −4 , conditions necessary for gelation. The background gas was necessary for quick thermal quenching of freshly formed silica molecules and molten nanoparticles and some control of the particle size could be achieved by variation of the gas. The silica aerosol gels were found to have very low densities in the range 4-15 mg/cm 3 and high specific surface areas of 300-500 m 2 /g. Wide angle X-ray diffraction showed that the nanoparticles were amorphous silica. Neutron scattering showed that they were arranged in networks with a fractal dimension of 1.75 between 10 and 1000 nm length scales. INTRODUCTIONIn previous work, we presented an aerosol gelation method to produce porous materials with high specific surface area and extremely low density (Dhaubhadel et al. 2007). The method involved the gelation of nanoparticles in the aerosol phase to yield a material that we have named an "aerosol gel." Unlike wellknown aerogel materials which begin with a liquid phase sol-gel step, aerosol gels are made in the gas phase. Simply said a cloud of smoke in a volume gels or freezes to form a volume spanning, very light weight, porous body; truly "frozen smoke." The initial aerosol is composed of nanometer-sized particles produced rapidly by exploding in a chamber a hydrocarbon precursor with an oxidizer, e.g., oxygen. The nanometer particles so produced aggregate and then gel on the order of tens of seconds to form the aerosol gel. The carbon materials we made previously have densities as low as 2.5 mg/cc. The current state-of-the-art Address correspondence to C. M. Sorensen, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA. E-mail: sor@phys.ksu.edu for manufacture of aerogel materials is the sol-gel/supercriticaldrying method (Brinker and Scherer 1990; Hüsing and Schubert 1998). The gas phase aerosol gelation method is a significantly different than this state-of-the-art and hence might offer advantages because (1) there is no need for a supercritical drying step as for aerogels and (2) the aerosol gel method should be applicable to a greater variety of substances. Disadvantages of our method lie in the current need for a detonation which could be hard to scale up, and it is a batch process.Gelation is a consequence of random aggregation of noncoalescing particles to form ramified fractal aggregates. Fractal aggregates have a mass-size scaling exponent, the fractal dimension D f , that is less than the spatial dimension, d, and this inequality represents a fundamental condition for gelation (Sorensen and Chakrabarti 2011). Because of this, the ratio of aggregate mean nearest neighbor separation to aggregate size declines as the aggreg...

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Observation of Soot Superaggregates with a Fractal Dimension of 2.6 in Laminar Acetylene/Air Diffusion Flames

Cited by 58 publications

References 26 publications

The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

The Mobility of Fractal Aggregates: A Review

Synthesis of Silica Aerosol Gels via Controlled Detonation

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