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Title: A comparison of mechanical properties and scaling law relationships for silica aerogels and their organic counterparts

Abstract

Aerogels are a special class of open-cell foams derived from the supercritical extraction of highly crosslinked, inorganic or organic gels. The resultant materials have ultrafine cell/pore sizes (< 100 nm), high surface areas (350--1000m{sup 2}/g), and a microstructure composed of interconnected colloidal-like particles or polymeric chains with characteristic diameters of 10 nm. TEM and SAXS show that this microstructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Traditional silica aerogels are prepared via the hydrolysis and condensation of tetramethoxy silane (TMOS) or tetraethoxy silane (TEOS). Factors such as pH and the (H{sub 2}O)/(TMOS) ratio affect the microstructure of the dried aerogel. It is generally accepted that polymeric' silica aerogels result from acid catalysis while colloidal'silica aerogels result from base catalysis. Recently, Hrubesh and Tillotson developed a new condensed silica' procedure for obtaining silica aerogels with densities as low as 0.004g/cc, i.e. only 3{times} the density of air. Organic aerogels are formed from the aqueous, polycondensation of (1) resorcinol/formaldehyde or (2) melamine/formaldehyde. The microstructure of the resorcinol-formaldehyde (RF) aerogels is dictated by the amount of base catalyst used in the sol-gel polymerization. In addition, these materials can be pyrolyzed in an inertmore » atmosphere to form vitreous carbon aerogels. Melamine- formaldehyde (MF) aerogels that are both colorless and transparent are only formed under acidic conditions (i.e. pH = 1--2). In this paper, the microstructural dependence and scaling law relationships for the compressive modulus of silica, carbon, RF, and MF aerogels will be discussed in detail. 17 refs., 1 fig.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (USA)
Sponsoring Org.:
DOE/DP
OSTI Identifier:
6824462
Report Number(s):
UCRL-JC-104279; CONF-901105-13
ON: DE91000282
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Fall meeting of the Materials Research Society, Boston, MA (USA), 24 Nov - 1 Dec 1990
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; GELS; MECHANICAL PROPERTIES; SYNTHESIS; FOAMS; FORMALDEHYDE; MELAMINE; MICROSTRUCTURE; RESORCINOL; SILICA; ALDEHYDES; AMINES; AROMATICS; AZINES; CHALCOGENIDES; COLLOIDS; CRYSTAL STRUCTURE; DEVELOPERS; DISPERSIONS; HETEROCYCLIC COMPOUNDS; HYDROXY COMPOUNDS; MINERALS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PHENOLS; POLYPHENOLS; SILICON COMPOUNDS; SILICON OXIDES; TRIAZINES; 360603* - Materials- Properties; 360601 - Other Materials- Preparation & Manufacture

Citation Formats

Pekala, R W, Hrubesh, L W, Tillotson, T M, Alviso, C T, Poco, J F, and LeMay, J D. A comparison of mechanical properties and scaling law relationships for silica aerogels and their organic counterparts. United States: N. p., 1990. Web.
Pekala, R W, Hrubesh, L W, Tillotson, T M, Alviso, C T, Poco, J F, & LeMay, J D. A comparison of mechanical properties and scaling law relationships for silica aerogels and their organic counterparts. United States.
Pekala, R W, Hrubesh, L W, Tillotson, T M, Alviso, C T, Poco, J F, and LeMay, J D. Wed . "A comparison of mechanical properties and scaling law relationships for silica aerogels and their organic counterparts". United States. https://www.osti.gov/servlets/purl/6824462.
@article{osti_6824462,
title = {A comparison of mechanical properties and scaling law relationships for silica aerogels and their organic counterparts},
author = {Pekala, R W and Hrubesh, L W and Tillotson, T M and Alviso, C T and Poco, J F and LeMay, J D},
abstractNote = {Aerogels are a special class of open-cell foams derived from the supercritical extraction of highly crosslinked, inorganic or organic gels. The resultant materials have ultrafine cell/pore sizes (< 100 nm), high surface areas (350--1000m{sup 2}/g), and a microstructure composed of interconnected colloidal-like particles or polymeric chains with characteristic diameters of 10 nm. TEM and SAXS show that this microstructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Traditional silica aerogels are prepared via the hydrolysis and condensation of tetramethoxy silane (TMOS) or tetraethoxy silane (TEOS). Factors such as pH and the (H{sub 2}O)/(TMOS) ratio affect the microstructure of the dried aerogel. It is generally accepted that polymeric' silica aerogels result from acid catalysis while colloidal'silica aerogels result from base catalysis. Recently, Hrubesh and Tillotson developed a new condensed silica' procedure for obtaining silica aerogels with densities as low as 0.004g/cc, i.e. only 3{times} the density of air. Organic aerogels are formed from the aqueous, polycondensation of (1) resorcinol/formaldehyde or (2) melamine/formaldehyde. The microstructure of the resorcinol-formaldehyde (RF) aerogels is dictated by the amount of base catalyst used in the sol-gel polymerization. In addition, these materials can be pyrolyzed in an inert atmosphere to form vitreous carbon aerogels. Melamine- formaldehyde (MF) aerogels that are both colorless and transparent are only formed under acidic conditions (i.e. pH = 1--2). In this paper, the microstructural dependence and scaling law relationships for the compressive modulus of silica, carbon, RF, and MF aerogels will be discussed in detail. 17 refs., 1 fig.},
doi = {},
url = {https://www.osti.gov/biblio/6824462}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1990},
month = {8}
}

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