Thermal properties of silica aerogels between 1.4 and 330 K

Scheuerpflug, P.; Hauck, Maximilian; Fricke, J.

doi:10.1016/s0022-3093(05)80455-7

“…Scheuerpflug et al [27] measured the thermal conductivity and heat capacity between 1.4 and 300 K of several base catalyzed aerogels with densities from 71 to 262 kg/m 3 . Einarsrud et al [12] reported the thermal conductivity at 45 • C of bulk silica aerogels and xerogels obtained by measuring the surface temperature of a heated sample using an infrared camera.…”

Section: Current State Of Knowledgementioning

confidence: 99%

Thermal conductivity of cubic and hexagonal mesoporous silica thin films

Coquil¹,

Richman²,

Hutchinson³

et al. 2009

Journal of Applied Physics

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This paper reports the cross-plane thermal conductivity of highly ordered cubic and hexagonal templated mesoporous amorphous silica thin films synthesized by evaporation-induced self-assembly process. Cubic and hexagonal films featured spherical and cylindrical pores and average porosity of 25% and 45%, respectively. The pore diameters ranged from 3 to 18 nm and film thickness from 80 to 540 nm while the average wall thickness varied from 3 to 12 nm. The thermal conductivity was measured at room temperature using the 3ω method. The experimental setup and the associated analysis were validated by comparing the thermal conductivity measurements with data reported in the literature for the silicon substrate and for high quality thermal oxide thin films with thicknesses ranging from 100 to 500 nm. The cross-plane thermal conductivity of the synthesized mesoporous silica thin films does not show strong dependence on pore size, wall thickness, or film thickness. This is due to the fact that heat is mainly carried by very localized non propagating vibrational modes. The average thermal conductivity for the cubic mesoporous silica films was 0.30 ± 0.02 W/m.K, while it was 0.20 ± 0.01 W/m.K for the hexagonal films. This corresponds to a reduction of 79% and 86% from bulk fused silica at room temperature.

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“…Scheuerpflug et al [27] measured the thermal conductivity and heat capacity between 1.4 and 300 K of several base catalyzed aerogels with densities from 71 to 262 kg/m 3 . Einarsrud et al [12] reported the thermal conductivity at 45…”

Section: Current State Of Knowledgementioning

confidence: 99%

Thermal Conductivity of Cubic and Hexagonal Mesoporous Silica Thin Films

Coquil

¹

,

Hutchinson

²

,

Pilon

³

et al. 2009

Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer

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This paper reports the cross-plane thermal conductivity of highly ordered cubic and hexagonal templated mesoporous amorphous silica thin films synthesized by evaporation-induced self-assembly process. Cubic and hexagonal films featured spherical and cylindrical pores and average porosity of 25% and 45%, respectively. The pore diameters ranged from 3 to 18 nm and film thickness from 80 to 540 nm while the average wall thickness varied from 3 to 12 nm. The thermal conductivity was measured at room temperature using the 3ω method. The experimental setup and the associated analysis were validated by comparing the thermal conductivity measurements with data reported in the literature for the silicon substrate and for high quality thermal oxide thin films with thicknesses ranging from 100 to 500 nm. The cross-plane thermal conductivity of the synthesized mesoporous silica thin films does not show strong dependence on pore size, wall thickness, or film thickness. This is due to the fact that heat is mainly carried by very localized non propagating vibrational modes. The average thermal conductivity for the cubic mesoporous silica films was 0.30 ± 0.02 W/m.K, while it was 0.20 ± 0.01 W/m.K for the hexagonal films. This corresponds to a reduction of 79% and 86% from bulk fused silica at room temperature.

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“…The dynamics of fractal networks was described theoretically [3] and in the case of aerogels the vibrational density of states (DOS) was examined by neutron, Raman and Brillouin scattering [4][5][6][7][8][9]. Thermal properties of aerogels were investigated either using steady-state methods [10][11][12] or dynamical techniques [13]. The conductive heat transport for temperatures above 100 K was described as a diffusion process, since a proportionality between specific heat and thermal conductivity could be established if contributions of phonons and localized modes are negligible or can be corrected for [12,13].…”

Section: Introductionmentioning

confidence: 99%

Scaling properties and structure of aerogels

Emmerling

¹

,

Fricke

²

1997

J Sol-Gel Sci Technol

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Abstract. Young's modulus as well as solid thermal and electrical conductivitiy of aerogels have been observed to scale with density. No quantitative explanations were available up to now for these experimental findings. To establish a quantitive relationship between morphological and topological features of fractal gel networks, a simulation procedure is introduced that allows to produce three-dimensional gel structures, from which two important parameters can be extracted: i) the fraction o~ of interconnected mass of the gel network and ii) the ratio y of Pythagorean distance to minimum path length on the gel backbone. Surprisingly the product o~),, which enters important macroscopic parameters such as elasticity or solid thermal (and electrical) conductivity, was found to scale with an exponent that is only a function of the mass fractal dimension D. Also, an analytical relation between modulus and conductivity can be derived.

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Thermal properties of silica aerogels between 1.4 and 330 K

Cited by 56 publications

References 7 publications

Thermal conductivity of cubic and hexagonal mesoporous silica thin films

Thermal conductivity of cubic and hexagonal mesoporous silica thin films

Thermal Conductivity of Cubic and Hexagonal Mesoporous Silica Thin Films

Scaling properties and structure of aerogels

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