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Title: Thermal properties of organic and modified inorganic aerogels

Abstract

Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. Improvements in the thermal insulating properties of aerogels are possible by synthesizing new organic varieties, by using additives within existing aerogel matrix, and by optimizing their nanostructures. We discuss these approaches and give some examples of aerogels which demonstrate the improvements.

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (United States)
Sponsoring Org.:
DOE; USDOE, Washington, DC (United States)
OSTI Identifier:
6622514
Alternate Identifier(s):
OSTI ID: 6622514; Legacy ID: DE93009230
Report Number(s):
UCRL-JC-111333; CONF-9210332--1
ON: DE93009230
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: 1992 international chlorofluorocarbon (CFC) and halon alternatives conference, Washington, DC (United States), 1 Oct 1992
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; FOAMS; THERMAL CONDUCTIVITY; THERMAL INSULATION; DENSITY; GELS; SOL-GEL PROCESS; COLLOIDS; DISPERSIONS; PHYSICAL PROPERTIES; THERMODYNAMIC PROPERTIES 360606* -- Other Materials-- Physical Properties-- (1992-); 320107 -- Energy Conservation, Consumption, & Utilization-- Building Systems-- (1987-)

Citation Formats

Pekala, R.W., and Hrubesh, L.W. Thermal properties of organic and modified inorganic aerogels. United States: N. p., 1992. Web.
Pekala, R.W., & Hrubesh, L.W. Thermal properties of organic and modified inorganic aerogels. United States.
Pekala, R.W., and Hrubesh, L.W. Sat . "Thermal properties of organic and modified inorganic aerogels". United States. doi:.
@article{osti_6622514,
title = {Thermal properties of organic and modified inorganic aerogels},
author = {Pekala, R.W. and Hrubesh, L.W.},
abstractNote = {Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. Improvements in the thermal insulating properties of aerogels are possible by synthesizing new organic varieties, by using additives within existing aerogel matrix, and by optimizing their nanostructures. We discuss these approaches and give some examples of aerogels which demonstrate the improvements.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Aug 01 00:00:00 EDT 1992},
month = {Sat Aug 01 00:00:00 EDT 1992}
}

Conference:
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  • Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. Improvements in the thermal insulating properties of aerogels are possible by synthesizing new organic varieties, by using additives within existing aerogel matrix, and by optimizing their nanostructures. We discuss these approaches and give some examples of aerogels which demonstrate the improvements.
  • Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. This paper examines the three major contributions to thermal transport through porous materials; solid, gaseous, and radiative, to identify how to reduce the thermal conductivity of air-filled aerogels. We find that significant improvements in the thermal insulation property of aerogels are possible by; (i) employing materials with a low intrinsic solid conductivity, (ii) reducing the average pore size within aerogels, and (iii) affecting an increase of the infrared extinction in aerogels. Theoretically, polystyrene is the best of the organic materials andmore » zirconia is the best inorganic material to use for the lowest achievable conductivity. Significant reduction of the thermal conductivity for all aerogel varieties is predicted with only a modest decrease of the average pore size. This might be achieved by modifying the sol-gel chemistry leading to aerogels. For example, a thermal resistance value of [ital R]=20 per inch would be possible for an air-filled resorcinol-formaldehyde aerogel at a density of 156 kg/m[sup 3], if the average pore size was less than 35 nm. An equation is included which facilitates the calculation of the optimum density for the minimum total thermal conductivity, for all varieties of aerogels.« less
  • Organically modified silica aerogels were prepared by NH{sub 4}OH-catalyzed hydrolysis and condensation of RSi(OMe){sub 3} / Si(OMe){sub 4} mixtures, followed by supercritical drying of the alcogels with methanol or CO{sub 2}. Terminal alkyl or aryl groups, bridging groups or functional organic (methacryloxypropyl or glycidoxypropyl) groups were employed for R. By the proper choice of the organic groups, the RSi(OMe){sub 3} / Si(OMe){sub 4} ratio and the drying conditions, hydrophobic aerogels, being insensitive towards moisture, were obtained with no residual SiOH or Si-OMe groups left. The transparency and porosity of the organically modified aerogels was only slightly diminished relative to unmodifiedmore » silica aerogels. The elastic constant of the aerogels was significantly influenced by the kind of organic groups. By pyrolysis of the phenyl-substituted aerogels, nanometer-sized carbon structures were generated. They partly coat the primary aerogel particles and provide a very high mass specific extinction in the wavelengths interval critical for thermal radiative transport.« less
  • This report briefly covers Lawrence Livermore National Laboratory's research and development into aerogels. 7 refs. (JDL)
  • Organically substituted silica aerogels were prepared from RSi(OR`){sub 3}/Si(OR`){sub 4} mixtures, followed by supercritical drying. The typical microstructure and the resulting physical properties of silica aerogels are retained, if the portion of R-Si units is below 10-20%. However, new properties are supplemented, such as hydrophobicity (which makes the aerogels insensitive towards moisture), a higher compliance, and the possibility to incorporate functional organic groups. Controlled pyrolysis of the organically substituted aerogels allows to coat the inner surface of the aerogels with nanometer-sized carbon structures. This results in a very efficient infrared opacification and improved heat insulation properties at high temperatures. 5more » refs., 2 figs.« less