Effect of aging on thermal conductivity of fiber-reinforced aerogel composites: An X-ray tomography study

Iswara, Subramaniam; Griffa, Michele; Kaufmann, Rolf; Beltran, Mario; Huber, Lukas; Brunner, Samuel; Lattuada, Marco; Koebel, Matthias M.; Malfait, Wim J.

doi:10.1016/j.micromeso.2018.12.006

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Effect of aging on thermal conductivity of fiber-reinforced aerogel composites: An X-ray tomography study

Iswara, Subramaniam University of Fribourg, Department of Chemistry, Switzerland
Griffa, Michele Concrete/Construction Chemistry Laboratory, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland - Center for X-ray Analytics, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
Kaufmann, Rolf Center for X-ray Analytics, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
Beltran, Mario Center for X-ray Analytics, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
Huber, Lukas Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
Brunner, Samuel Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
Lattuada, Marco University of Fribourg, Department of Chemistry, Switzerland
Koebel, Matthias M. Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
Malfait, Wim J. Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland

01.04.2019

Published in:

Microporous and Mesoporous Materials. - 2019, vol. 278, p. 289–296

English Silica aerogels display an ultra-low thermal conductivity (λ) and are used as thermal superinsulators. Here, we study the influence of aging and drying processes on the microstructure and thermal conductivity of fiber-reinforced silica aerogel composites. Glass wool-silica gel composites were aged for variable times, hydrophobized, and dried either at ambient pressure or from supercritical CO2 (scCO2). The X-ray micro- tomographic data display three distinct phases: silica aerogel, glass fibers, and macroscopic pores and cracks. The silica aerogel appears as a continuous medium in the tomograms because the spatial resolution (6–11 μm) is insufficient to resolve the aerogel mesopores (∼0.02–0.10 μm). For the composites prepared by ambient pressure drying, insufficient aging led to prominent drying shrinkage and cracking, and a high macro-porosity, as quantified by 3D image analysis. Insufficient aging also led to an increase in λ from 15.7 to 21.5 mW m−1 K−1. On the contrary, composites that were nearly free of cracks and displayed a constant λ of 16.3 ± 0.8 mW m−1 K−1 could be prepared by scCO2, independent of aging time. The thermal conductivity was reproduced from the macro-porosity to within 0.7 mW m−1 K−1 using simple thermal transport models consisting of thermal elements connected in series or parallel. Our results illustrate the usefulness of X-ray micro-tomography to quantify the 3D microstructure and its effects on the bulk composite properties and the data highlight the importance of aging for the production of low λ aerogel-fiber composites by ambient pressure drying.

Faculty

Faculté des sciences et de médecine

Department

Département de Chimie

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