A Comparison Between the Densification Kinetics of Colloidal and Polymeric Silica Gels

Brinker, C. Jeffrey; Drotning, W. D.; Scherer, George W.

doi:10.1557/proc-32-25

Cited by 36 publications

(18 citation statements)

References 5 publications

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“…The structure of the gel is highly dependent upon the SiO 2 precursor (typically tetraethylorthosilicate [TEOS]), water level, pH (acid or base concentration), temperature, aging/curing time, and subsequent calcination conditions. As noted in Chapter 1 of Brinker et al, 10 acid-catalyzed gels with low water addition were clear and rubbery, which was consistent with a weekly cross-linked system. Base-catalyzed gels were often brittle and cloudy, indicating a highly cross-linked system.…”

Section: Sio 2 -Surface-coated Caer Catalysts Using Acidic Precipisupporting

confidence: 75%

“…As reported by Brinker et al, 10 Brinker and Scherer, 11 and Klein, 12 silica that is acid-catalyzed in an alcohol solvent system with only a low level of water forms a fractal structure that is somewhat linear with an open structure. Base-catalyzed silica is more highly cross-linked and brittle.…”

Section: Sio 2 -Surface-coated Caer Catalysts Using Acidic Precipimentioning

confidence: 72%

“…Again, there is an extensive literature on the formation of fractal structures. The Symposia Proceedings of Brinker et al, 10 the book of Brinker and Scherer, 11 the collection of manuscripts edited by Klein,12 and the text of Zallen 13 present a good background of the subject.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Shape-selective catalysts for Fischer-Tropsch chemistry : iron-containing particulate catalysts. Activity report : January 1, 2001 - December 31, 2004.

Cronauer¹

2006

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Section: Sio 2 -Surface-coated Caer Catalysts Using Acidic Precipisupporting

confidence: 75%

Section: Sio 2 -Surface-coated Caer Catalysts Using Acidic Precipimentioning

confidence: 72%

See 1 more Smart Citation

Shape-selective catalysts for Fischer-Tropsch chemistry : iron-containing particulate catalysts. Activity report : January 1, 2001 - December 31, 2004.

Cronauer¹

2006

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“…A gel sinters at relatively low temperatures, because of its very large surface area (which makes n a large number). In addition, the large number of nonbridging bonds caused by retained OR (hydroxy or alkoxy) groups, reduces the viscosity of the solid phase below that of a conventional glass of the same composition; during sintering, those groups are eliminated, and the viscosity increases [6,7]. The OR groups have other important consequences.…”

Section: Principles Of Sinteringmentioning

confidence: 99%

Sintering of sol-gel films

Scherer

1997

J Sol-Gel Sci Technol

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Abstract. The sintering of films differs from that of bulk gels in several ways. The initial state of a film is generally denser and less crosslinked than a bulk gel made from the same sol, and these factors enhance the densification rate of the film. The substrate constrains the shrinkage of the film, leading to high stresses that retard densification and can influence phase changes. The substrate is a site for heterogeneous nucleation, and crystallization makes densification more difficult, so the competition between sintering and crystallization is particularly important for films. Fast heating favors densification over crystallization, so rapid thermal annealing usually produces denser films. The high surface to volume ratio of a thin film makes it susceptible to degradation by reaction with the substrate and the atmosphere, so choosing compatible materials and avoiding over-firing is essential.

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“…Again, there is an extensive literature on the formation of fractal structures. The Symposia Proceedings of Brinker et al, 11 the book of Brinker and Scherer, 12 the collection of manuscripts edited by Klein,13 and the text of Zallen 14 present a good background of the subject.…”

Section: Introductionmentioning

confidence: 99%

Shape-selective catalysts for Fischer-Tropsch chemistry : atomic layer deposition of active catalytic metals. Activity report : January 1, 2005 - September 30, 2005.

Cronauer¹

2011

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SummaryArgonne National Laboratory is carrying out a research program to create, prepare, and evaluate catalysts to promote Fischer-Tropsch (FT) chemistry-specifically, the reaction of hydrogen with carbon monoxide to form long-chain hydrocarbons. In addition to needing high activity, it is desirable that the catalysts have high selectivity and stability with respect to both mechanical strength and aging properties. The broad goal is to produce diesel fraction components and avoiding excess yields of both light hydrocarbons and heavy waxes. Originally the goal was to prepare shapeselective catalysts that would limit the formation of long-chain products and yet retain the active metal sites in a protected "cage." Such catalysts were prepared with silica-containing fractal cages. The activity was essentially the same as that of catalysts without the cages. We are currently awaiting follow-up experiments to determine the attrition strength of these catalysts.A second experimental stage was undertaken to prepare and evaluate active FT catalysts formed by atomic-layer deposition [ALD] of active components on supported membranes and particulate supports. The concept was that of depositing active metals (i.e. ruthenium, iron or cobalt) upon membranes with well defined flow channels of small diameter and length such that the catalytic activity and product molecular weight distribution could be controlled. In order to rapidly evaluate the catalytic membranes, the ALD coating processes were performed in an 'exploratory mode' in which ALD procedures from the literature appropriate for coating flat surfaces were applied to the high surface area membranes. Consequently, the Fe and Ru loadings in the membranes were likely to be smaller than those expected for complete monolayer coverage. In addition, there was likely to be significant variation in the Fe and Ru loading among the membranes due to difficulties in nucleating these materials on the aluminum oxide surfaces.The first series of experiments using coated membranes demonstrated that the technology needed further improvement. Specifically, observed catalytic FT activity was low. This low activity appeared to be due to: 1. low available surface area, 2. atomic deposition techniques that needed improvements, and 3. insufficient preconditioning of the catalyst surface prior to FT testing. Therefore, experimentation was expanded to the use of particulate silica supports having defined channels and reasonably high surface area. This later experimentation will be discussed in the next progress report. Subsequently, we plan to evaluate membranes after the ALD techniques are improved with a careful study to control and quantify the Fe and Ru loadings. The preconditioning of these surfaces will also be further developed. (A number of improvements have been made with particulate supports; they will be discussed in the subsequent report.)In support of the above, there was an opportunity to undertake a short study of cobalt/promoter/support interaction using the Advanced Photon Sou...

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A Comparison Between the Densification Kinetics of Colloidal and Polymeric Silica Gels

Cited by 36 publications

References 5 publications

Shape-selective catalysts for Fischer-Tropsch chemistry : iron-containing particulate catalysts. Activity report : January 1, 2001 - December 31, 2004.

Shape-selective catalysts for Fischer-Tropsch chemistry : iron-containing particulate catalysts. Activity report : January 1, 2001 - December 31, 2004.

Sintering of sol-gel films

Shape-selective catalysts for Fischer-Tropsch chemistry : atomic layer deposition of active catalytic metals. Activity report : January 1, 2005 - September 30, 2005.

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