Aerogels

Reichenauer, Gudrun

doi:10.1002/0471238961.010518151115.a01.pub2

Cited by 11 publications

(9 citation statements)

References 187 publications

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“…This is mainly because their solid fraction is low and, thus, the contribution of λ solid to λ total is low. The bulk density of the xerogels in the present study was approximately 0.3 g cm –3 , which was higher than those of porous structures such as flexible polymer foams (0.02–0.1 g cm –3 ) and typical silica aerogels , (0.01–0.2 g cm –3 ). The thermal conductivity of 0.06–0.07 W m –1 K –1 was thus realized to be relatively low for a high-bulk-density material.…”

Section: Results and Discussioncontrasting

confidence: 58%

“…This value was within the conductivity range that flexible polymer foams cover, which was higher than those of aerogels ,,, but lower than those of woods . The thermal conductivity, λ total , of porous structures is expressed as follows: where λ solid and λ gas are the conductivities of the solid and gas phases in the porous structure, respectively, and λ rad is the contribution from radiation. In general, porous structures demonstrate lower conductivities compared to their nonporous counterparts.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Aerogels are porous structures that combine a high specific surface area (SSA) and high porosity. , Their structural profiles enable them to be utilized as catalyst supports, , air filters, , and adsorbents . Well-designed aerogels also exhibit low thermal conductivity and high optical transparency, making them potential candidates for transparent window insulators. − Many kinds of aerogels have been reported in the field of inorganic chemistry since their report by Kistler in 1931 .…”

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confidence: 99%

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Mechanically Strong, Scalable, Mesoporous Xerogels of Nanocellulose Featuring Light Permeability, Thermal Insulation, and Flame Self-Extinction

et al. 2021

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Scalability is a common challenge in the structuring of nanoscale particle dispersions, particularly in the drying of these dispersions for producing functional, porous structures such as aerogels. Aerogel production relies on supercritical drying, which exhibits poor scalability. A solution to this scalability limitation is the use of evaporative drying under ambient pressure. However, the evaporative drying of wet gels comprising nanoscale particles is accompanied by a strong capillary force. Therefore, it is challenging to produce evaporative-dried gels or "xerogels" that possess the specific structural profiles of aerogels such as mesoscale pores, high porosity, and high specific surface area (SSA). Herein, we demonstrate a structure of mesoporous xerogels with high porosity (∼80%) and high SSA (>400 m 2 g −1 ) achieved by exploiting cellulose nanofibers (CNFs) as the building blocks with tunable interparticle interactions. CNFs are sustainable, wood-derived materials with high strength. In this study, the few-nanometer-wide CNFs bearing carboxy groups were structured into a stable network via ionic inter-CNF interaction. The outline of the resulting xerogels was then tailored into a regular, millimeter-thick, board-like structure. Several characterization techniques highlighted the multifunctionality of the CNF xerogels combining outstanding strength (compression E = 170 MPa, σ = 10 MPa; tension E = 290 MPa, σ = 8 MPa), moderate light permeability, thermal insulation (0.06−0.07 W m −1 K −1 ), and flame self-extinction. As a potential application of the xerogels, daylighting yet insulating, load-bearing wall members can be thus proposed.

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Section: Results and Discussioncontrasting

confidence: 58%

Section: Results and Discussionmentioning

confidence: 99%

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confidence: 99%

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Mechanically Strong, Scalable, Mesoporous Xerogels of Nanocellulose Featuring Light Permeability, Thermal Insulation, and Flame Self-Extinction

et al. 2021

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“…In general, conduction, radiation, and convection contribute to the thermal conductivity of an aerogel, with the latter two being negligible for isotropic porous materials at room temperature [12,26,31,52,53]. Hence, conduction, including gas conduction and solid conduction, is the main contributor to the overall thermal conductivity.…”

Section: Thermal Insulation and Moisture Resistance Applicationsmentioning

confidence: 99%

Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

Zhou

Apostolopoulou‐Kalkavoura

Costa

et al. 2019

Nano-Micro Lett.

140

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HIGHLIGHTS • The study reveals the great potential of metal-organic framework (MOF)-based nanocomposites in thermal insulation and fire retardancy applications. • A nanoengineering approach was developed to process MOFs into freestanding, mechanically strong, and elastic aerogels, which may boost the fundamental research and practical applications of MOFs in these areas. ABSTRACT Metal-organic frameworks (MOFs) with high microporosity and relatively high thermal stability are potential thermal insulation and flame-retardant materials. However, the difficulties in processing and shaping MOFs have largely hampered their applications in these areas. This study outlines the fabrication of hybrid CNF@MOF aerogels by a stepwise assembly approach involving the coating and cross-linking of cellulose nanofibers (CNFs) with continuous nanolayers of MOFs. The cross-linking gives the aerogels high mechanical strength but superelasticity (80% maximum recoverable strain, high specific compression modulus of ~ 200 MPa cm 3 g −1 , and specific stress of ~ 100 MPa cm 3 g −1).

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“…Via a drying step the liquid phase is removed from the gel thus leaving a porous solid, the so called aerogel, behind [3].…”

Section: Contribution Of the Pore Gas To The Total Effective Heat Tramentioning

confidence: 99%

Thermal Transport Properties of Functionally Graded Carbon Aerogels

et al. 2009

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Novel graded carbon aerogels were synthesized to study the impact of different synthesis parameters on the material properties on a single sample and to test a new, locally resolved thermal conductivity measurement technique. Two identical cylindrical aerogels with a graded structure along the main cylindrical axis were synthesized. Along the gradient with an extension of about 20 mm the densities range from 240 to 370 kg·m -3 and the effective pore diameter determined via small angle X-ray scattering and SEM increase systematically from 70 up to 11000 nm. One specimen was cut perpendicular to the cylinder axis into disc shaped samples; their thermal conductivities in argon atmosphere as determined via standard laser flash range from 0.06 to 0.12 W·m -1 ·K -1 at 600°C. The second specimen, cut to obtain a sample with the gradient in plane, was investigated with a spatially resolved laser flash technique at ambient conditions. The results of the two different techniques are compared and discussed in detail.

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Aerogels

Cited by 11 publications

References 187 publications

Mechanically Strong, Scalable, Mesoporous Xerogels of Nanocellulose Featuring Light Permeability, Thermal Insulation, and Flame Self-Extinction

Mechanically Strong, Scalable, Mesoporous Xerogels of Nanocellulose Featuring Light Permeability, Thermal Insulation, and Flame Self-Extinction

Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

Thermal Transport Properties of Functionally Graded Carbon Aerogels

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