Silica Aerogel Composite

A special issue of Gels (ISSN 2310-2861).

Deadline for manuscript submissions: closed (15 April 2022) | Viewed by 11080

Special Issue Editor

State Key Laboratory of Strength and Vibration of Mechanical Structures, School of Arerospace Engineering, Xi'an Jiaotong University, Xi'an 710049, Shaanxi, China
Interests: silica aerogel composite; thermal property; thermal insulation; thermal–fluid–solid coupling

Special Issue Information

Dear Colleagues,

Aerogels are the lightest solids on earth. Due to their low density, high porosity, extremely large specific area and random nano-porous structure, they have a wide range of applications in the fields of catalysts, absorbents, supercapacitors and thermal insulation, etc. Silica aerogel has many exceptional properties; in particular, its thermal conductivity can be lower than that of stilled air. Thus, silica aerogel is an ideal thermal insulation material. However, pure silica aerogel is too fragile and nearly transparent to the thermal radiation within the spectrum range of 3–8 μm, which will lead to a significant increase in radiative thermal conductivity at high temperatures. In order to improve the mechanical strength and thermal insulation performance at elevated temperatures, additives such as reinforced fibers and opacifiers are usually composited with silica aerogel. At present, there are still many challenges in synthesizing low-cost and high-performance silica aerogel composites. Numerical prediction and experimental measurement for revealing the thermal insulation mechanism and optimizing both the mechanical and thermal insulation performances are also insufficient.       

This Special Issue focuses on recent research and advances in silica aerogel composite. The topics include but are not limited to synthesizing silica aerogel composite, numerical predicting and experiment studies of the properties of silica aerogel composite, and research relating to the corresponding applications is also welcomed.

Dr. Hu Zhang
Guest Editor

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Keywords

  • silica aerogel composite
  • thermal property
  • mechanical property
  • material synthesis
  • numerical simulation
  • experimental test
  • application

Published Papers (4 papers)

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Research

12 pages, 3597 KiB  
Article
Thermal Insulation Performance of SiC-Doped Silica Aerogels under Large Temperature and Air Pressure Differences
by Sheng-Nan Zhang, Hao-Qiang Pang, Ting-Hui Fan, Qing Ye, Qi-Lin Cai and Xi Wu
Gels 2022, 8(5), 320; https://doi.org/10.3390/gels8050320 - 20 May 2022
Cited by 8 | Viewed by 1923
Abstract
Silica aerogel composite is an excellent thermal insulator for spacecraft under high-temperature and complex air environments. This study intends to evaluate SiC-doped silica aerogel’s thermal insulation performance under large temperature and air pressure differences. In this paper, the hot surface’s temperature response of [...] Read more.
Silica aerogel composite is an excellent thermal insulator for spacecraft under high-temperature and complex air environments. This study intends to evaluate SiC-doped silica aerogel’s thermal insulation performance under large temperature and air pressure differences. In this paper, the hot surface’s temperature response of SiC-doped silica aerogel with different content was studied at significant temperature differences (ΔT) when pressure changes instantaneously. Their thermal insulation performance was evaluated by analyzing the influence of pressure gradients on the unsteady-state heat transfer. When the cold surface’s temperature of the specimen keeps constant at 15 °C and ΔT = 171~912 K, the results demonstrate that the correlative thermal conductivities of silica aerogel with 1% and 5.84% SiC are 0.02223~0.04077 W·m−1·K−1 at P ≈ 10 Pa and 0.03165~0.04665 W·m−1·K−1 at P = 1 atm, respectively. The aerogel composite with 0% SiC showed the best thermal insulation performance at ΔT < 200 K and P ≈ 10 Pa, while the aerogel with 5.84% SiC became the best at ΔT > 700 K and P = 1 atm. In addition, the transient pressure decreases will significantly impair the heat transfer of the gas inside the aerogel, thereby weakening the gaseous thermal conductivity and improving the thermal insulation performance. Full article
(This article belongs to the Special Issue Silica Aerogel Composite)
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14 pages, 4899 KiB  
Article
Thermal Insulation Performance of Silica Aerogel Composites Doped with Hollow Opacifiers: Theoretical Approach
by He Liu, Jia’ao Liu, You Tian, Junhua Jiao and Xuehong Wu
Gels 2022, 8(5), 295; https://doi.org/10.3390/gels8050295 - 10 May 2022
Cited by 11 | Viewed by 2738
Abstract
Silica aerogels demonstrate great promise in thermal insulation applications, such as energy-efficient buildings, cold-chain transportation, and aerospace engineering. However, the application of pure silica aerogels is limited in high temperature applications (>500 K) due to their transparency in the wavelength of 2–8 µm. [...] Read more.
Silica aerogels demonstrate great promise in thermal insulation applications, such as energy-efficient buildings, cold-chain transportation, and aerospace engineering. However, the application of pure silica aerogels is limited in high temperature applications (>500 K) due to their transparency in the wavelength of 2–8 µm. The conventional strategy is to dope silica aerogel with solid spherical opacifiers (e.g., SiC, TiO2, and ZrO2) to increase their extinction coefficient; however, incorporating solid opacifiers into silica aerogel matrix improves the structural density of silica aerogel composites. Herein, we propose to improve the extinction coefficient of the silica aerogel by using hollow opacifiers. A theoretical model was developed to investigate the parameters including the outer diameter, shell thickness, and mass fraction on both the radiative thermal conductivity and total thermal conductivity of the silica aerogel composite doped with hollow opacifiers. Our results indicate that doping hollow opacifiers can enable the silica aerogel matrix to achieve lower radiative thermal conductivity when compared to matrices doped with optimally sized solid opacifiers. The total thermal conductivity of silica aerogel doped with hollow opacifiers could be lower than that of the silica aerogel doped with optimally sized solid opacifiers. This work contributes to the understanding of heat transfer within porous materials and guides the structural design of high-temperature thermally insulating materials. Full article
(This article belongs to the Special Issue Silica Aerogel Composite)
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13 pages, 4142 KiB  
Article
Silica-Bacterial Cellulose Composite Aerogel Fibers with Excellent Mechanical Properties from Sodium Silicate Precursor
by Qiqi Song, Changqing Miao, Huazheng Sai, Jie Gu, Meijuan Wang, Pengjie Jiang, Yutong Wang, Rui Fu and Yaxiong Wang
Gels 2022, 8(1), 17; https://doi.org/10.3390/gels8010017 - 26 Dec 2021
Cited by 11 | Viewed by 3506
Abstract
Forming fibers for fabric insulation is difficult using aerogels, which have excellent thermal insulation performance but poor mechanical properties. A previous study proposed a novel method that could effectively improve the mechanical properties of aerogels and make them into fibers for use in [...] Read more.
Forming fibers for fabric insulation is difficult using aerogels, which have excellent thermal insulation performance but poor mechanical properties. A previous study proposed a novel method that could effectively improve the mechanical properties of aerogels and make them into fibers for use in fabric insulation. In this study, composite aerogel fibers (CAFs) with excellent mechanical properties and thermal insulation performance were prepared using a streamlined method. The wet bacterial cellulose (BC) matrix without freeze-drying directly was immersed in an inorganic precursor (silicate) solution, followed by initiating in situ sol-gel reaction under the action of acidic catalyst after secondary shaping. Finally, after surface modification and ambient drying of the wet composite gel, CAFs were obtained. The CAFs prepared by the simplified method still had favorable mechanical properties (tensile strength of 4.5 MPa) and excellent thermal insulation properties under extreme conditions (220 °C and −60 °C). In particular, compared with previous work, the presented CAFs preparation process is simpler and more environmentally friendly. In addition, the experimental costs were reduced. Furthermore, the obtained CAFs had high specific surface area (671.3 m²/g), excellent hydrophobicity, and low density (≤0.154 g/cm3). This streamlined method was proposed to prepare aerogel fibers with excellent performance to meet the requirements of wearable applications. Full article
(This article belongs to the Special Issue Silica Aerogel Composite)
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20 pages, 7555 KiB  
Article
Numerical Study of the Influence of Coupling Interface Emissivity on Aerogel Metal Thermal Protection Performance
by Fengfei Lou, Sujun Dong, Yinwei Ma, Bin Qi and Keyong Zhu
Gels 2021, 7(4), 250; https://doi.org/10.3390/gels7040250 - 03 Dec 2021
Cited by 4 | Viewed by 2066
Abstract
For aerogels in metal thermal protection system (MTPS), radiative heat transfer will participate in the thermal transport process. Therefore, the influence of the emissivity of the coupling interface between metal and aerogels on thermal insulation performance is considered an important research focus. In [...] Read more.
For aerogels in metal thermal protection system (MTPS), radiative heat transfer will participate in the thermal transport process. Therefore, the influence of the emissivity of the coupling interface between metal and aerogels on thermal insulation performance is considered an important research focus. In this paper, CFD numerical simulation is performed to study the influence of emissivity on the performance with different extinction coefficients at different boundary temperatures. The finite volume method and the discrete ordinate method are used to solve the govern equations. The results show that when the boundary temperatures are 600 K and 2100 K, the extinction coefficient is 50 m−1, and the reduction percentage of the effective thermal conductivity with an emissivity of 0.2 can be up to 47.5% and 69.8%, compared to the system with an emissivity of 1. Thus, the reduction in emissivity has a good effect on the thermal insulation performance of the MTPS at a higher boundary temperature for materials with small extinction coefficients. Full article
(This article belongs to the Special Issue Silica Aerogel Composite)
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