Dielectric properties of aerogels

Journal Article · Thu Jul 01 00:00:00 EDT 1993 · Journal of Materials Research; (United States)

DOI:https://doi.org/10.1557/JMR.1993.1736· OSTI ID:5437696

Hrubesh, L W; Keene, L E; Latorre, V R ^[1]

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1. Chemistry and Material Sciences Department, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

We have measured the real (dielectric constant) and imaginary (loss factor) components of the complex relative permittivity at 298 [degree]K using microwave frequencies (2, 10, and 18--40 GHz), for bulk SiO[sub 2]-aerogels and for two types of organic aerogels, resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF). Measured dielectric constants are found to vary linearly between values of 1.0 and 2.0 for aerogel densities from 10 to 500 kg/m[sup 3]. For the same range of densities, the measured loss tangents vary linearly between values of 2[times]10[sup [minus]4] and 7[times]10[sup [minus]2]. The observed linearity of the dielectric properties with density in aerogels at microwave frequencies shows that their dielectric behavior is more gas-like than solid-like. The dielectric properties of aerogels are shown to be significantly affected by the adsorbed water internal to the bulk material. For example, water accounts for 7% of the dielectric constant and 70% of the loss at microwave frequencies for silica aerogels. Because of their very high porosity, even with the water content, the aerogels are among the few materials exhibiting such low dielectric properties. Our measurements show that aerogels with greater than 99% porosity have dielectric constants less than 1.03; these are the lowest values ever reported for a bulk solid material.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5437696
• Journal Information: Journal of Materials Research; (United States), Journal Name: Journal of Materials Research; (United States) Vol. 8:7; ISSN JMREEE; ISSN 0884-2914
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360606* -- Other Materials-- Physical Properties-- (1992-)
CHALCOGENIDES
COLLOIDS
DIELECTRIC PROPERTIES
DISPERSIONS
ELECTRICAL PROPERTIES
ENERGY LOSSES
FREQUENCY RANGE
GELS
GHZ RANGE
GHZ RANGE 01-100
LOSSES
MATERIALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PERMITTIVITY
PHYSICAL PROPERTIES
POROSITY
POROUS MATERIALS
SILICON COMPOUNDS
SILICON OXIDES