Preparation of low-density xerogels at ambient pressure

Smith, Douglas M.; Stein, David J.; Anderson, Jeffrey C.; Ackerman, William C.

doi:10.1016/0022-3093(95)00040-2

Cited by 168 publications

(76 citation statements)

References 6 publications

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“…Optimization of aging conditions and modification processes are of prime importance for the synthesis of monolithic silica aerogels (without cracks) at an ambient pressure. In this process, the gel undergoes a "springback effect" during the drying and preserves porosity and prevents cracks in the dried solid [21,22]. Otherwise, the gel shrinks to accommodate the loss of pore fluid, producing severe cracks in the aerogels during APD.…”

Section: Introductionmentioning

confidence: 97%

Influence of aging conditions on textural properties of water-glass-based silica aerogels prepared at ambient pressure

Sarawade

Kim

Hilonga

et al. 2010

Korean J. Chem. Eng.

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The experimental results of aging time and temperature on the textural properties of water-glass (sodium silicate)-based silica aerogels are reported and discussed. Aging of the hydrogel for different times and temperatures led to an ability to increase the stiffness and strength of the networks. These improvements enabled the gel to withstand ambient pressure drying (APD) and, consequently, preserve the highly porous silica network without collapse. The pore size and volume increased with increasing aging temperature and time, while the specific surface area decreased. Monolithic aerogels with extremely low bulk density (~0.069 g/cm 3 ), high specific surface area (820 m 2 g −1 ), large cumulative pore volume (3.8 cm 3 g −1 ), and high porosity (~96%) were obtained by aging at 60 o C for 18 hours. Therefore, easy synthesis of monolithic silica aerogels at ambient pressure is achievable using a relatively inexpensive silica precursor (sodium silicate).

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Section: Introductionmentioning

confidence: 97%

Influence of aging conditions on textural properties of water-glass-based silica aerogels prepared at ambient pressure

Sarawade

Kim

Hilonga

et al. 2010

Korean J. Chem. Eng.

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“…As the skeletons that comprise their porous morphology are too thin, aerogels are brittle, and they must be dried with the utmost care by using SCD, for example, to preserve their fragile pore structure. To overcome such challenges for silica-based aerogels, numerous attempts to strengthen the gel skeletons by aging, [6,7] crosslinking with organic polymers, [8][9][10] modifying surfaces hydrophobically, [11][12][13] and conventional drying [14,15] have been explored.Prakash et al [13] have obtained aerogel films with porosity up to 98.5 % by adding hydrophobicity through the use of trimethylchrolosilane constituents on bare silica networks. This method enables the so-called spring-back phenomenon, in which temporarily shrunk gel networks recover their original forms like a sponge.…”

mentioning

confidence: 99%

New Transparent Methylsilsesquioxane Aerogels and Xerogels with Improved Mechanical Properties

Aizawa²,

et al. 2007

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Since they were first prepared in 1931 via supercritical drying (SCD), [1] aerogels have been utilized for rather specific applications in spite of their wide range of extraordinary properties, such as high optical transparency (> 90 %), large surface areas (ca. 1000 m 2 g -1 ), low refractive indices (< 1.01), high thermal and acoustic insulation values, and low dielectric constants (ca. 1.1). An aerogel-based Cherenkov detector has been used to detect charged elementary particles, thus contributing to the development of high-energy physics. [2,3] In the field of space development, [4] the first aerogel cosmic dust collector was launched on February 7, 1999 and returned to Earth on January 15, 2006, successfully bringing back the dust of the comet "Vilt 2" after a seven-year journey.[5] Despite these applications, aerogels are not routinely found in our daily life because they collapse easily and are difficult to prepare in a large-scale industrial setting. The unique characteristics of aerogels stem from the fact that they are composed mostly of air. As the skeletons that comprise their porous morphology are too thin, aerogels are brittle, and they must be dried with the utmost care by using SCD, for example, to preserve their fragile pore structure. To overcome such challenges for silica-based aerogels, numerous attempts to strengthen the gel skeletons by aging, [6,7] crosslinking with organic polymers, [8][9][10] modifying surfaces hydrophobically, [11][12][13] and conventional drying [14,15] have been explored.Prakash et al. [13] have obtained aerogel films with porosity up to 98.5 % by adding hydrophobicity through the use of trimethylchrolosilane constituents on bare silica networks. This method enables the so-called spring-back phenomenon, in which temporarily shrunk gel networks recover their original forms like a sponge. Another prevalent approach is to use trifunctional silicon alkoxides together with conventional tetrafunctional silicon alkoxides such as tetramethylorthosilicate (TMOS) or tetraethylorthosilicate (TEOS) in a sol-gel route. [16,17] Incorporating trifunctional monomers with one hydrophobic group, such as alkyltrialkoxysilanes, also makes the resultant gel surface hydrophobic [18,19] but sacrifices the transparency aspect. [20] As silanol groups that are closely located to each other lead to persistent shrinkage by forming siloxane bonds during drying, [21] incorporating hydrophobic groups to reduce the chances of such condensations prevents persistent shrinkage. The repulsive interactions between hydrophobic moieties also promote the spring-back effect. An in situ treatment of alkyltrialkoxysilanes rather than a post treatment by a silane coupling agent on bare silica is an effective way to achieve hydrophobicity in a simple manner. However, trifunctional alkoxides usually form cyclic and cagelike closed species that hinder the homogeneous gelling of a starting solution, especially when the monomer concentration is low (unfortunately in aerogel preparation, monomer concentration must be ...

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“…The supercritical drying process of aerogel preparation have important characteristic of high specific surface area, mesoporous structures, and low density. These important characteristics lead to the various applications, such as isolators, batteries, supercapacitors, electrode materials, and others [33][34][35]. To prepare the porous crystalline materials, the method of sol-gel has also been used.…”

Section: Synthesis Of Micro and Mesoporous Materialsmentioning

confidence: 99%

Amorphous Porous Mixed Oxides: A New and Highly Versatile Class of Materials

Pandey

Mishra

2012

Intelligent Nanomaterials

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Porous solids are a rapidly developing class of materials with an ever-increasing range of applications. Among these materials, amorphous porous mixed oxides possess the extraordinary properties of fine tuning the chemical composition, microstructure, porosity and surface properties. The tailor made composition of the mixed oxides can be fabricated from the availability of variety of precursor, additives and modifiers. Besides, their performance can be found close to that of crystalline phase. These amorphous mixed oxides can easily be synthesized using acid / base catalyzed one-pot sol-gel procedure. Sol-gel processes allow for a relatively facile tailoring of the morphology of mixed oxides to the desired application in the field of nanotechnology. Pore volume, porosity, specific surface area, and surface acidity are typical parameters that can be tailored. This chapter deals with the preparation methodology, characterization techniques, and application of amorphous porous mixed oxides.

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Preparation of low-density xerogels at ambient pressure

Cited by 168 publications

References 6 publications

Influence of aging conditions on textural properties of water-glass-based silica aerogels prepared at ambient pressure

Influence of aging conditions on textural properties of water-glass-based silica aerogels prepared at ambient pressure

New Transparent Methylsilsesquioxane Aerogels and Xerogels with Improved Mechanical Properties

Amorphous Porous Mixed Oxides: A New and Highly Versatile Class of Materials

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