Particle aggregation in alumina aerogels

Keysar, S.; Hazan, Yoram de; Cohen, Yachin; Aboud, T.; Grader, Gideon S.

doi:10.1557/jmr.1997.0063

Cited by 17 publications

(18 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A homogeneous packing of very small globular particles 2--4 nm size is observed. This is the basic aggregate size in the alumina system prepared by this procedure, in agreement with our previous TEM and SAXS results [7].…”

Section: Resultssupporting

confidence: 92%

“…2. Sols were prepared at acid/Al ion concentration 0.07 since this ratio was found to produce aerogels with maximal surface area [7]. Both gels and sols were used to coat the substrates, however the identical final morphology was obtained.…”

Section: Resultsmentioning

confidence: 99%

“…We propose the following mechanism for the formation of this morphology: During phase separation the initial sol and gel, which consists of nanometer sized particles, forms aggregates that are 0.1-0.2/zm in size. This aggregation occurs by diffusion limited cluster cluster aggregation DL-CCA [7,11]. Due to the small thickness of the film (about 1/zm), the process occurs throughout the whole (This is not expected to happen in monoliths or thick films.)…”

Section: Resultsmentioning

confidence: 99%

“…This procedure does not allow an easy way to study the properties of the gel prior to the drying stage. We performed the gelation and coating stages under atmospheric conditions so that the gelation stage can be studied separately from the final SCD step [7]. This procedure enabled straightforward additional manipulations of the film prior to drying.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Grader

Rifkin

Cohen

et al. 1997

J Sol-Gel Sci Technol

Self Cite

View full text Add to dashboard Cite

Abstract. Alumina aerogel thin films were formed by a new synthesis route. Sols were prepared by the Yoldas process. Gels were formed by sol evaporation in a few hours. Films were prepared by dip coating glass or alumina substrates into both the sols and the gels. Aerogel films with special morphology were produced for the first time by exchanging the film solvent with acetone after the dip coating, followed by supercritical drying. The morphology of the films, studied by SEM and TEM, consists of fiber-like network of round chains (N0.1/zm thick), and pores (0.1-0.5/zm in diameter). It is shown that the fibers contain a homogeneous arrangement of sol particles, 2-4 nm in size. Formation of this microstructure can be attributed to phase separation in the alumina-water-acetone system in a 2D film geometry. A conceptual model for the film development is proposed.

show abstract

Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Grader

Rifkin

Cohen

et al. 1997

J Sol-Gel Sci Technol

Self Cite

View full text Add to dashboard Cite

show abstract

“…Results for alumino-silicates (Pouxviel, Boilot, Lecomte & Dauger, 1987 ;Dauger, Lecomte, Vesteghem, Guinebretière & Fargeot, 1991) and non-silicate systems like TiO 2 (Lebon, Merignan & Appell, 1992;Kallala, Sanchez & Cabane, 1993), ZrO 2 (Chaumont, Craievich & Zarzicky, 1992) or Al 2 O 3 (Keysar, De Hazan, Cohen, Aboud & Grader, 1997) are also reported.…”

Section: Introductionmentioning

confidence: 94%

Dynamical scaling property of colloidal aggregation in a zirconia-based precursor sol during gelation

2000

View full text Add to dashboard Cite

Zirconia precursor gels, prepared in the zirconium n-propoxide, npropanol, acetylacetone and water system, are studied by small angle X-ray scattering (SAXS). The SAXS intensity pattern exhibits a pronounced maximum for a scattering vector q different from zero. The intensity maximum of the finite q-vector peak increases during gelation while its position q m moves towards smaller and smaller qvectors. The SAXS intensity distribution is well accounted for by recent direct numerical calculations of diffusion-limited cluster aggregation (DLCA). The structural aspects of cluster growth can be described by scaling assumptions. The position q m of the intensity maximum and the structure function S(q/q m ,t) are shown to scale according to S(q/q m ,t) = q m (t) -d F(q/q m ) where F(q/q m ) is a timeindependent scaling function. This scaling requires d=D f , the fractal dimension of the clusters, instead of d=3 for spinodal decomposition. The gel structure is made up of connected fractal clusters, around 50 nm in size, with an apparent fractal dimension of 1.7, resulting from the aggregation of very small primary particles about 2.5 nm in diameter.

show abstract

Mechanochemical redox synthesis of interstitial mesoporous Co_xFe_1‐_xO_y catalyst for CO₂ hydrogenation

et al. 2021

View full text Add to dashboard Cite

The study on CoOx‐FeOx catalysts gives a profound insight into the synthesis and the application of multitransition metal oxide catalysts. A facile and solid‐state mechanochemical redox strategy was developed to obtain CoxFe1‐xOy from CoCl2·6H2O and KMnO4 with simply two‐round of ball milling (BM) operation. The process was witnessed by the Brunauer—Emmett—Teller (BET), X‐ray diffraction (XRD), scanning transmission electron microscope (STEM), inductively coupled plasma emission spectrometry (ICP), and X‐ray photoelectron spectroscopy (XPS) characterization, confirming the contribution of the mechanical force and frictional heating in the occurrence of redox reaction, the dispersion of metal species, and the generation of interstitial pores. Importantly, as‐made CoxFe1‐xOy‐BM sample possessed abundant porosity, and the specific surface area of it (131 m2 g−1) was much higher than that of coprecipitation route (49 m2 g−1) and sol‐gel route (33 m2 g−1). The as‐prepared catalysts CoxFe1‐xOy‐BM exhibited excellent performance in reverse water gas shift reaction, reaching 43% of CO2 conversion rate at 500°C with high selectivity (over 80%) during the whole temperature range, while the conversion for both control samples were below 20%. Moreover, continuous 120 hr CO2 hydrogenation at 500°C presented the enhancement of thermal stability and the possible change of active sites. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

show abstract

Particle aggregation in alumina aerogels

Cited by 17 publications

References 18 publications

Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Dynamical scaling property of colloidal aggregation in a zirconia-based precursor sol during gelation

Mechanochemical redox synthesis of interstitial mesoporous Co_xFe_1‐_xO_y catalyst for CO₂ hydrogenation

Contact Info

Product

Resources

About

Particle aggregation in alumina aerogels

Cited by 17 publications

References 18 publications

Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Dynamical scaling property of colloidal aggregation in a zirconia-based precursor sol during gelation

Mechanochemical redox synthesis of interstitial mesoporous CoxFe1‐xOy catalyst for CO2 hydrogenation

Contact Info

Product

Resources

About

Mechanochemical redox synthesis of interstitial mesoporous Co_xFe_1‐_xO_y catalyst for CO₂ hydrogenation