Relations between the texture of silica aerogels and their preparation

Ehrburger‐Dolle, Françoise; Dallamano, Julien; Elaloui, E.; Pajonk, G.M.

doi:10.1016/0022-3093(95)00036-4

Cited by 26 publications

(14 citation statements)

References 19 publications

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“…Ehrburger-Dolle et al performed a comparative study of resulted aero-gels dried by HTSCD and LTSCD methods. They reported that the micro porosity of CO2-dried aero-gels is significantly larger than that of the corresponding MeOH-dried aero-gels [99]. However, the micro and mesoporous textures of the CO2-dried aero-gel are equivalent to those of the alco-gel [100].…”

Section: Comparison Of Htscd and Ltscdmentioning

confidence: 99%

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

Прасад

Pandey

2012

Bull. Chem. React. Eng. Catal.

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In recent years, silica gels have developed a lot of interest due to their extraordinary properties and their existing and potential applications in science and technology. Silica gel has a wide range of applications such as a desiccant, as a preservation tool to control humidity, as an adsorbent, as a catalyst and as a cata-lyst support. Silica gel is a rigid three-dimensional network of colloidal silica, and is classified as: aqua-gel, alco-gel, xero-gel and aero-gel. Out of all known solid porous materials, aero-gels are particularly known for their high specific surface area, high porosity, low bulk density, high thermal insulation value, ultra low dielectric constant and low index of refraction. Because of these extraordinary properties silica aero-gel has many commercial applications such as thermal window insulation, acoustic barriers, super-capacitors and catalytic supports. However, monolithic silica aero-gel has been used extensively in high energy physics in Cherenkov radiation detectors and in shock wave studies at high pressures, inertial confinement fusion (ICF) radio-luminescent and micrometeorites. Silica gel can be prepared by using various sol gel precursors but the rice husk (RH) is considered as the cheapest source for silica gel production. Rice husk is a waste product abundantly available in rice producing countries during milling of rice. This review article aims at summarizing the developments carried out so far in synthesis, properties, characterization and method of determination of silica, silica gel, silica aero-gel and silica xero-gel. The effect of synthesis parameters such as pH, temperature of burning the rice husk, acid leaching prior to formation of rice husk ash (RHA) on the properties of final product are also described. The attention is also paid on the application of RH, RHA, sil-ica, silica aero-gel and silica xero-gel. Development of economically viable processes for getting rice husk silica with specific properties assumes importance at this juncture. Copyright © 2012 by BCREC UNDIP. All rights reserved.

Received: 23th November 2011, Revised: 09th January 2012, Accepted: 10th January 2012

[How to Cite: R. Prasad, and M. Pandey. (2012). Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview. Bulletin of Chemical Reaction Engineering & Catalysis, 7 (1): 1-25. doi:10.9767/bcrec.7.1.1216.1-25]

[How to Link / DOI: http://dx.doi.org/10.9767/bcrec.7.1.1216.1-25 ]

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Section: Comparison Of Htscd and Ltscdmentioning

confidence: 99%

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

Прасад

Pandey

2012

Bull. Chem. React. Eng. Catal.

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Received: 23th November 2011, Revised: 09th January 2012, Accepted: 10th January 2012

[How to Link / DOI: http://dx.doi.org/10.9767/bcrec.7.1.1216.1-25 ]

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“…All these kinds of shrinkages affect the porous network, but when applied to a wet gel, supercritical drying mostly affects the larger pores that involve network dimensions beyond the fractal scale, while drying by evaporation to obtain a xerogel in addition leads to a drastic shrinkage of the mesopores. Furthermore, concerning supercritical drying, the silica aerogels obtained by the HOT process tend to possess a lower specific microporosity but a similar specific mesoporosity to those obtained by the COLD process [35,109,110].…”

Section: Texturementioning

confidence: 99%

SiO2 Aerogels

Pierre

Rigacci

2011

Aerogels Handbook

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International audienceThis chapter focuses on one of the most studied aerogel materials, silica aerogels. It aims at presenting a brief overview of the elaboration steps (sol-gel synthesis, aging, and drying), the textural and chemical characteristics (aggregation features, porosity, and surface chemistry), the main physical properties (from thermal, mechanical, acoustical, and optical, to biological, medical, etc.), and a rather broad panel of related potential applications of these fascinating nanostructured materials. It cannot be considered as an exhaustive synopsis but must be used as a simple tool to initiate further bibliographic studies on silica aerogels

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“…Indeed, extensive investigations carried out in the eighties by Rabinovich et al. , focused mainly on the mechanisms of fluoride ion operation in a silanol environment and less on xerogel texture. Only very recently several papers reported on the effect of reactant concentration on the porous texture of aerogels obtained from the process catalyzed by NH 4 F , or the two-component system of NH 4 F and NH 4 OH. , The mechanism of fluoride anion operation is still not entirely clear,14a and hence it can hardly facilitate prediction of the F - concentration influence on the resulting gels' morphology. Experimental evaluation of this effect is the issue tackled in the current work.…”

Section: Introductionmentioning

confidence: 99%

Morphology of Silica Aerogels Obtained from the Process Catalyzed by NH₄F and NH₄OH

et al. 1997

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Twelve samples of silica aerogels were synthesized using different concentrations of catalysts (NH4F, NH4OH), and their morphology was investigated by means of small-angle X-ray scattering (SAXS), N2 adsorption, and transmission electron microscopy. Both SAXS and the nitrogen adsorption method consistently show a different influence of the catalysts; fluoride anions promote formation of a tenuous branched-polymeric structure, with mass fractal dimension Dm = 2.3-2.5, while addition of hydroxyl ions results in a sparser structure (Dm = 2.1-2.2) self-similar over a narrower range. The morphology of aerogels obtained from the process catalyzed by fluoride hydroxide resembles that of aerogels produced by the two-step method. This may suggest similar mechanisms of gel formation in both processes, and, consequently, a dramatic acceleration of the hydrolysis reaction caused by NH 4F.

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Relations between the texture of silica aerogels and their preparation

Cited by 26 publications

References 19 publications

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

SiO2 Aerogels

Morphology of Silica Aerogels Obtained from the Process Catalyzed by NH₄F and NH₄OH

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Relations between the texture of silica aerogels and their preparation

Cited by 26 publications

References 19 publications

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

SiO2 Aerogels

Morphology of Silica Aerogels Obtained from the Process Catalyzed by NH4F and NH4OH

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Morphology of Silica Aerogels Obtained from the Process Catalyzed by NH₄F and NH₄OH