Aerosol Gelation: Synthesis of a Novel, Lightweight, High Specific Surface Area Material

Dhaubhadel, Rajan; Gerving, Corey S.; Sorensen, Christopher M.

doi:10.1080/02786820701466291

Cited by 27 publications

(25 citation statements)

References 15 publications

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“…Thus one might question whether or not a volume spanning aerosol gel ever formed. For carbon aerosol gels, a thickly coated interior was also typically found, but occasionally the chamber was opened to find a volume spanning gel that subsequently collapsed to form a thick layer (Dhaubhadel et al 2007). Perhaps the silica did the same.…”

Section: Gelsmentioning

confidence: 99%

“…Such conditions were met in our initial discovery of aerosol gelation in an acetylene flame (Sorensen et al 1998a) and our first work to create an aerosol gel in which we reacted 596 SYNTHESIS OF SILICA AEROSOL GELS 597 hydrocarbons, most notably acetylene, explosively with oxygen under fuel-rich conditions (Dhaubhadel et al 2007). The rapid reaction led to nanometer-sized carbon particles that gelled via random Brownian motion on the order of 100 s. The resulting material had very low density and high specific surface area.…”

Section: Introductionmentioning

confidence: 99%

“…Under the conditions of spherical, same-sized monomers, and monodisperse aggregates, simple kinetic arguments (Dhaubhadel et al 2007) lead to an expression for the gel time as…”

Section: Introductionmentioning

confidence: 99%

“…In 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."…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Gelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Under the conditions of spherical, same-sized monomers, and monodisperse aggregates, simple kinetic arguments (Dhaubhadel et al 2007) lead to an expression for the gel time as…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Synthesis of Silica Aerosol Gels via Controlled Detonation

Dhaubhadel

Rieker

Chakrabarti

et al. 2012

Aerosol Science and Technology

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“…1 shows a transmission electron microscope (TEM) picture of part of a carbon-soot aggregate captured in an open-burning acetylene flame [9]. This aggregate is composed of roughly spherical carbon monomers.…”

Section: Aggregate Morphologymentioning

confidence: 99%

Internal fields of soot fractal aggregates

Berg

Sorensen

2013

J. Opt. Soc. Am. A

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This work uses the discrete dipole approximation (DDA) to examine the internal electric field within a simulated carbon soot fractal aggregate in fixed and random orientations. For fixed orientations, deviations of the internal field magnitude up to 50% from that assumed by the Rayleigh-Debye-Gans Approximation (RDGA) are found. Given the refractive index of the aggregate monomers and conditions for the validity of the approximation, such large deviations are no surprise. Yet despite this deviation, the far-field scattered intensity from such aggregates agrees surprisingly well with that described by the RDGA. Moreover, if the average over an ensemble of many random aggregate-orientations is calculated, both the DDA and RDGA scattered intensities obey the well-known power-law functionality in terms of the scattering wave vector and show a forward-angle intensity-maximum proportional to the square of the number of monomers. The explanation for this lies in the over and under estimations made by the approximation of the internal field, which apparently mostly cancel upon integration to yield the scattered intensity. It is shown that this error cancellation is related to the fractal structure of the aggregate and that the agreement between the DDA and RDGA improves with aggregates of increasing size provided the fractal dimension is less than two. Overall, the analysis suggests that both the special fractal character of the aggregate and its orientational averaging is important to account for the experimentally observed validity of the RDGA despite its poor description of the internal fields.

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Synthesis of turbostratic nanoscale graphene via chamber detonation of oxygen/acetylene mixtures

et al. 2021

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A study of the detonation synthesis method to make graphene and the properties of the resulting graphene is presented. The gaseous precursors are mixtures of oxygen and acetylene with oxygen/carbon molar ratios of O/C = 0.25 to 0.75. Chamber pressure and temperature data indicate pressures ≤ 300 psi and temperatures of 2550 ± 100K after initiation of the reaction mixture. The graphene material collected from the chamber after the detonation was characterized by Raman, XRD (X‐ray diffraction), BET, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and so on. The material properties divide into two groups: low O/C (≤ 0.45) and high O/C (≥ 0.5). Low O/C graphene appears as a low density, aerosol gel with ∼8 weakly associated, disordered turbostratic layers with a lateral extent of 20 to 30 nm. High O/C graphene appears as a denser powder with ∼30 weakly associated turbostratic layers, with a lateral extent of 100 to 200 nm. We conclude, as we have previously, that the high detonation temperature during the reaction is the primary reason that graphene is formed rather than soot. Differentiation into two types of graphene products is hypothesized to be a result of aggregation kinetics to form a static gel that pre‐empts layering (stacking) when O/C is low.

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Aerosol Gelation: Synthesis of a Novel, Lightweight, High Specific Surface Area Material

Cited by 27 publications

References 15 publications

Synthesis of Silica Aerosol Gels via Controlled Detonation

Synthesis of Silica Aerosol Gels via Controlled Detonation

Internal fields of soot fractal aggregates

Synthesis of turbostratic nanoscale graphene via chamber detonation of oxygen/acetylene mixtures

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