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Dense and strong, but superinsulating silica aerogel

Iswar, Subramaniam and Galmarini, Sandra and Bonanomi, Luca and Wernery, Jannis and Roumeli, Eleftheria and Nimalshantha, Sudheera and Ben Ishai, Avner M. and Lattuada, Marco and Koebel, Matthias M. and Malfait, Wim J. (2021) Dense and strong, but superinsulating silica aerogel. Acta Materialia, 213 . Art. No. 116959. ISSN 1359-6454. doi:10.1016/j.actamat.2021.116959.

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Silica aerogel is the ultimate thermal insulator thanks to its record-breaking low thermal conductivity (λ), open porosity and hydrophobicity. Silica aerogel's thermal conductivity is lowest at intermediate densities (ρ ≈ 0.11 g/cm³) and, because of the strong, power-law dependence of the E modulus on density, this rather low density so far led to low E moduli. Even with polymer reinforcement, increasing stiffness is only possible at higher density, thus higher conductivity. This paper explores the synthesis of silica aerogel granules using ambient pressure drying to provide enhanced mechanical stiffness whilst maintaining thermal conductivities well below 20 mW m⁻¹ K⁻¹. The aging and drying conditions affect the interplay between mechanical and thermal properties, and are varied to optimize the physical properties. The dense (ρ≤0.29 g/cm³), but superinsulating (λ≈15 mW m⁻¹ K⁻¹) silica aerogels presented in this paper challenge the community's understanding of heat transport in aerogels, and do not rely on polymer reinforcement. The underlying microscopic structural parameters affecting the mechanical and thermal transport properties are investigated by modelling and simulation of the aerogel back-bone. Short aging times reduce the cross-section of, and heat transport through, inter-particle necks, leading to an overall decrease in thermal conductivity through the solid skeleton (λ_s). In addition, short-aged gels undergo a partial pore collapse during ambient pressure drying of the pore fluid due to less aged, hence weaker network structures. The resulting denser structure contains additional point contacts that increase stiffness, by up to an order of magnitude. However, heat transport through these newly formed point-contacts is limited and the gas phase conduction (λ_s) is further suppressed due to the even smaller pore sizes. Strong and superinsulating particles are ideal fillers for aerogel composites, concrete and renders. The optimized APD aerogels, available as granules, are finally compiled in a composite thermal insulation board with an effective thermal conductivity down to 20 mW m⁻¹ K⁻¹ with improved strength: a 2-fold increase for E, compared to a board produced from classical silica aerogel granulate. The possibility to improve mechanical properties of pure silica aerogels can help aerogels to break into new high-strength, superinsulating structural applications needed to reduce carbon emissions of the built environment.

Item Type:Article
Related URLs:
URLURL TypeDescription
Galmarini, Sandra0000-0003-2183-3100
Wernery, Jannis0000-0001-6819-9683
Roumeli, Eleftheria0000-0002-2828-1428
Ben Ishai, Avner M.0000-0001-6869-1627
Lattuada, Marco0000-0001-7058-9509
Malfait, Wim J.0000-0002-1668-8749
Additional Information:© 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. Under an Attribution 4.0 International (CC BY 4.0). Received 19 January 2021, Revised 21 April 2021, Accepted 30 April 2021, Available online 9 May 2021. We thank Dr. Geert Snellings (Recticel N.V.) for his suggestions and input. We are also grateful to Shanyu Zhao for discussions, Beatrice Fischer for providing access to the Zwick press and Yucheng Zhang for TEM analysis. We thank the Flemish agency ‘Agentschap Innoveren en Ondernemen’ for financial support. Declaration of Competing Interest: Empa owns equity in patent application EP3498672A1 about the use of high ρ, low λ silica aerogel for insulation applications.
Funding AgencyGrant Number
Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium)UNSPECIFIED
Subject Keywords:Silica aerogel; Evaporative drying; Shrinkage; Thermal conductivity; Uniaxial compression
Record Number:CaltechAUTHORS:20210514-102010066
Persistent URL:
Official Citation:Subramaniam Iswar, Sandra Galmarini, Luca Bonanomi, Jannis Wernery, Eleftheria Roumeli, Sudheera Nimalshantha, Avner M. Ben Ishai, Marco Lattuada, Matthias M. Koebel, Wim J. Malfait, Dense and strong, but superinsulating silica aerogel, Acta Materialia, Volume 213, 2021, 116959, ISSN 1359-6454, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109130
Deposited By: Tony Diaz
Deposited On:14 May 2021 17:29
Last Modified:26 May 2021 18:01

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