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Gels
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Recent Advances in Silica Aerogel Composites for Thermal Superinsulation
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Recent Advances in Silica Aerogel Composites for Thermal Superinsulation

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Applications".

Deadline for manuscript submissions: closed (31 March 2023) | Viewed by 9230

Special Issue Editors

Dr. Jannis Wernery

E-Mail Website
Guest Editor
Laboratory for Building Energy Materials and Components, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
Interests: superinsulation; silica aerogel insulation materials & products; nature-based thermal insulation; building user behavior; decision making in buildings
Dr. Samuel Brunner

E-Mail Website
Guest Editor
Laboratory for Building Energy Materials and Components, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
Interests: aerogel; VIP; vacuum insulation panels; superinsulation; thermal insulation; nature-based thermal insulation

Special Issue Information

Dear Colleagues,

Silica aerogels are high-performance insulation materials with thermal conductivities reaching as low as approximately 12 mW/(m·K) in their monolithic form. With such a low thermal conductivity, these materials are ideal in scenarios where space is scarce and/or a high insulation performance is needed. However, due to their brittle nature, silica aerogels are typically reinforced with other materials such as fibres, or included in composite materials such as renders, concrete, or a polymer matrix. Thus, most commercially available materials are in fact composites.

In this Special Issue, we invite contributions focusing on the synthesis and characterisation of new silica aerogel composite materials, the characterisation of existing materials, e.g., quality control and durability, and the applications of both new and existing silica aerogel composites as thermal superinsulation. Of special interest are new composites with improved material properties, such as mechanical strength, thermal conductivity, and acoustic properties, but also with reduced manufacturing costs and a lower embodied CO2-equivalent for higher sustainability.

The focus concerning the designated application is on its use as a thermal insulator, for example in the building sector, in industrial applications, transport, or in electric vehicles. Articles examining applications that make use not only of the insulating but also other properties, e.g., optical/translucent, are also welcome.

Dr. Jannis Wernery
Dr. Samuel Brunner
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • synthesis of silica aerogel composites
  • characterisation of silica aerogel composites
  • applications of silica aerogel composites
  • silica aerogel composites for thermal superinsulation
  • manufacturing cost and greenhouse gas footprint

Published Papers (5 papers)

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19 pages, 3542 KiB  
Article
Comparison of Different Aerogel Granules for Use as Aggregate in Concrete
by Torsten Welsch, Yannick Vievers, Martina Schnellenbach-Held, Danny Bialuschewski and Barbara Milow
Gels 2023, 9(5), 406; https://doi.org/10.3390/gels9050406 - 12 May 2023
Cited by 3 | Viewed by 1621
Abstract
In previous work of this group, a structural lightweight concrete was developed by embedding silica aerogel granules in a high-strength cement matrix. This concrete, called high-performance aerogel concrete (HPAC), is a lightweight building material characterized by its simultaneous high compressive strength and very [...] Read more.
In previous work of this group, a structural lightweight concrete was developed by embedding silica aerogel granules in a high-strength cement matrix. This concrete, called high-performance aerogel concrete (HPAC), is a lightweight building material characterized by its simultaneous high compressive strength and very low thermal conductivity. Besides these features, high sound absorption, diffusion permeability, water repellence and fire resistance qualify HPAC as an interesting material for the construction of single-leaf exterior walls without any further insulation. During the development of HPAC, the type of silica aerogel was found to majorly influence both fresh and hardened concrete properties. To clarify these effects, a systematic comparison of SiO2 aerogel granules with different levels of hydrophobicity as well as different synthesis methods was conducted in the present study. The granules were analyzed for their chemical and physical properties as well as their compatibility in HPAC mixtures. These experiments included determinations of pore size distribution, thermal stability, porosity, specific surface and hydrophobicity, as well as fresh/hardened concrete experiments such as measurements of compressive strength, flexural bending strength, thermal conductivity and shrinking behavior. It was found that the type of aerogel has a major influence on the fresh and hardened concrete properties of HPAC, particularly compressive strength and shrinkage behavior, whereas the effect on thermal conductivity is not very pronounced. Full article
(This article belongs to the Special Issue Recent Advances in Silica Aerogel Composites for Thermal Superinsulation)
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23 pages, 8122 KiB  
Article
Increasing Water Absorptivity of an Aerogel-Based Coating Mortar in Subsequent Wetting and Drying
by Ali Naman Karim, Pär Johansson and Angela Sasic Kalagasidis
Gels 2022, 8(12), 764; https://doi.org/10.3390/gels8120764 - 24 Nov 2022
Cited by 4 | Viewed by 1285
Abstract
Aerogel-based coating mortars are energy-efficient composites with thermal conductivities of 30–50 mW/(m·K). They are useful when retrofitting uninsulated building envelopes, particularly in listed masonry buildings, as shown in studies. Meanwhile, the long-term reliability of their hygrothermal properties, typically declared after a single laboratory [...] Read more.
Aerogel-based coating mortars are energy-efficient composites with thermal conductivities of 30–50 mW/(m·K). They are useful when retrofitting uninsulated building envelopes, particularly in listed masonry buildings, as shown in studies. Meanwhile, the long-term reliability of their hygrothermal properties, typically declared after a single laboratory measurement, is not confirmed. To illustrate the latter and by combining experimental and numerical methods, this study shows that (1) the capillary water absorptivity of a commercially available aerogel-based coating mortar increases after repeated drying and wetting cycles, and (2) leads to a higher moisture content in a masonry wall. After the third cycle, the measured water absorption was more than five times higher than after the first one. Based on numerical simulations, the increasing capillary water absorptivity results in 36% higher relative humidity in the wall if the aerogel-based coating mortar is applied externally and exposed to driving rain. Future research should investigate the reasons behind the observed deviations in the capillary water absorptivity and whether it applies to other types of aerogel-based coating mortars. Full article
(This article belongs to the Special Issue Recent Advances in Silica Aerogel Composites for Thermal Superinsulation)
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20 pages, 5551 KiB  
Article
X-ray Tomography Coupled with Finite Elements, A Fast Method to Design Aerogel Composites and Prove Their Superinsulation Experimentally
by Genevieve Foray, Jaona Harifidy Randrianalisoa, Jerome Adrien and Eric Maire
Gels 2022, 8(11), 732; https://doi.org/10.3390/gels8110732 - 10 Nov 2022
Cited by 1 | Viewed by 1347
Abstract
Composite aerogels can include fibers, opacifiers and binders but are rarely designed and optimized to achieve the best thermal/mechanical efficiency. This paper proposes a three-dimensional X-ray tomography-based method for designing composites. Two types of models are considered: classical and inexpensive homogenization models and [...] Read more.
Composite aerogels can include fibers, opacifiers and binders but are rarely designed and optimized to achieve the best thermal/mechanical efficiency. This paper proposes a three-dimensional X-ray tomography-based method for designing composites. Two types of models are considered: classical and inexpensive homogenization models and more refined finite element models. XrFE is based on the material’s real three-dimensional microstructure and/or its twin numerical microstructure, and calculates the effective conductivity of the material. First, the three-dimensional sample is meshed and labeled. Then, a finite element method is used to calculate the heat flow in the samples. The entire three-dimensional microstructure of a real or fictitious sample is thus associated with a heat flow and an effective conductivity. Parametric studies were performed to understand the relationship between microstructure and thermal efficiency. They highlighted how quickly a low volume fraction addition can improve or ruin thermal conductivity. A reduced set of three formulations was developed and fully characterized. The mechanical behavior was higher than 50 KPa, with thermal efficiencies ranging from 14 to 15 mW·m·K−1. Full article
(This article belongs to the Special Issue Recent Advances in Silica Aerogel Composites for Thermal Superinsulation)
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15 pages, 3375 KiB  
Article
Robust Silica–Agarose Composite Aerogels with Interpenetrating Network Structure by In Situ Sol–Gel Process
by Xin Yang, Pengjie Jiang, Rui Xiao, Rui Fu, Yinghui Liu, Chao Ji, Qiqi Song, Changqing Miao, Hanqing Yu, Jie Gu, Yaxiong Wang and Huazheng Sai
Gels 2022, 8(5), 303; https://doi.org/10.3390/gels8050303 - 16 May 2022
Cited by 13 | Viewed by 2487
Abstract
Aerogels are three-dimensional nanoporous materials with outstanding properties, especially great thermal insulation. Nevertheless, their extremely high brittleness restricts their practical application. Recently, although the mechanical properties of silica aerogels have been improved by regulating the precursor or introducing a polymer reinforcer, these preparation [...] Read more.
Aerogels are three-dimensional nanoporous materials with outstanding properties, especially great thermal insulation. Nevertheless, their extremely high brittleness restricts their practical application. Recently, although the mechanical properties of silica aerogels have been improved by regulating the precursor or introducing a polymer reinforcer, these preparation processes are usually tedious and time-consuming. The purpose of this study was to simplify the preparation process of these composite aerogels. A silicic acid solution treated with cation exchange resin was mixed with agarose (AG) to gel in situ, and then composite aerogels (CAs) with an interpenetrating network (IPN) structure were obtained by aging and supercritical CO2 fluid (SCF) drying. Compared to previous works, the presented CAs preparation process is briefer and more environmentally friendly. Moreover, the CAs exhibit a high specific surface area (420.5 m2/g), low thermal conductivity (28.9 mW m−1 K−1), excellent thermal insulation properties, and thermal stability. These results show that these CAs can be better used in thermal insulation. Full article
(This article belongs to the Special Issue Recent Advances in Silica Aerogel Composites for Thermal Superinsulation)
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14 pages, 8926 KiB  
Case Report
Current Trends in Aerogel Use in Heritage Buildings: Case Studies from the Aerogel Architecture Award 2021
by Michal Ganobjak, Samuel Brunner, Jörg Hofmann, Verena Klar, Michael Ledermann, Volker Herzog, Beat Kämpfen, Ralf Kilian, Manfred Wehdorn and Jannis Wernery
Gels 2023, 9(10), 814; https://doi.org/10.3390/gels9100814 - 13 Oct 2023
Cited by 4 | Viewed by 1504
Abstract
Silica aerogels are high-performance thermal insulation materials that can be used to provide unique solutions in the envelopes of buildings when space is limited. They are most often applied in historic buildings due to thin insulation thicknesses and since they are compatible with [...] Read more.
Silica aerogels are high-performance thermal insulation materials that can be used to provide unique solutions in the envelopes of buildings when space is limited. They are most often applied in historic buildings due to thin insulation thicknesses and since they are compatible with historic structures. In 2021, the first Aerogel Architecture Award was held at Empa in Switzerland in order to collect, evaluate and award outstanding uses of this relatively new building material. From the submitted projects, three were selected for an award by an expert jury. They showcased applications in which heritage protection and the conservation of a building’s character and expression were reconciled with significant improvements in the energy efficiency of the building. The submissions also showed that a broader communication of these types of solutions is important in order to provide more information and security to planners and heritage offices and to facilitate the application of these materials in the future so that they can contribute to the protection of cultural heritage and reductions in the operational and embodied emissions of our building stock by extending the life expectancy and energy efficiency of existing buildings. Full article
(This article belongs to the Special Issue Recent Advances in Silica Aerogel Composites for Thermal Superinsulation)
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