3D multi-scale quantification of industrially relevant ultra-porous silicas by low-dose electron tomography combined with SANS

Chal, Bruno; Roiban, Lucian; Masenelli‐Varlot, Karine; Baeza, Guilhem P.; Yrieix, Bernard; Foray, Geneviève

doi:10.1016/j.jnoncrysol.2020.120577

Cited by 6 publications

(4 citation statements)

References 75 publications

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“…Inside the aerogel particles, the pores were close to 10 nm in size and their three-dimensional connectivity was known [ 44 ]. Between these aerogel particles (named SAP), some pores were defined and their overall volume content was equal to Intergranular Porosity, the IP.…”

Section: Resultsmentioning

confidence: 99%

X-ray Tomography Coupled with Finite Elements, A Fast Method to Design Aerogel Composites and Prove Their Superinsulation Experimentally

Foray

Randrianalisoa

Adrien

et al. 2022

Gels

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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.

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Section: Resultsmentioning

confidence: 99%

X-ray Tomography Coupled with Finite Elements, A Fast Method to Design Aerogel Composites and Prove Their Superinsulation Experimentally

Foray

Randrianalisoa

Adrien

et al. 2022

Gels

Self Cite

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“…To account for the scattering arising from different structures of different sizes, these terms were combined by the empirical equation used by Beaucage [ 56 ]. Another frequently employed approximation is the correlation length model, followed by us and used also in [ 57 ]. Here the characteristic size appearing in the scattering curves can be interpreted as polydisperse particles as well as interparticle holes, or dense interconnected particle chains in which scattering from particles or holes cannot be distinguished solely based on the scattering pattern.…”

Section: Resultsmentioning

confidence: 99%

Butyl-Methyl-Pyridinium Tetrafluoroborate Confined in Mesoporous Silica Xerogels: Thermal Behaviour and Matrix-Template Interaction

et al. 2021

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Organic-inorganic silica composites have been prepared via acid catalyzed sol-gel route using tetramethoxysilan (TMOS) and methyl-trimethoxysilane (MTMS) as silica precursors and n-butyl-3-methylpyridinium tetrafluoroborate ([bmPy][BF4]) as co-solvent and pore template, by varying the content of the ionic liquid (IL). Morphology of the xerogels prepared using the ionic liquid templating agent were investigated using scanning electron microscopy and small angle neutron scattering (SANS). Thermal analysis has been used in order to evaluate the thermal and structural stability of the materials, in both nitrogen and synthetic air atmosphere. In nitrogen atmosphere, the IL decomposition took place in one step starting above 150 °C and completed in the 150–460 °C temperature interval. In synthetic air atmosphere, the IL decomposition produced two-step mass loss, mainly in the 170–430 °C temperature interval. The decomposition mechanism of the IL inside the silica matrix was studied by mass spectrometric evolved gas analysis (MSEGA). The measurements showed that the degradation of the IL’s longer side chain (butyl) starts at low temperature (above 150 °C) through a C-N bond cleavage, initiated by the nucleophilic attack of a fluorine ion.

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“…Whilst simulations of aerogel thermal conductivity can provide valuable, qualitative insights into the mechanisms of heat transport in aerogels [36][37][38][39][40], they are not yet sufficiently advanced to serve as a quantitative tool. One main reason for this is our lack of accurate 3D structural data on aerogels, despite recent experimental [41][42][43] and numerical progress in this area [36].…”

Section: Experimental Techniques To Measure Thermal Conductivitymentioning

confidence: 99%

The poor reliability of thermal conductivity data in the aerogel literature: a call to action!

Malfait,

Ebert,

Brunner

et al. 2024

J Sol-Gel Sci Technol

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Aerogels are an exciting class of materials with record-breaking properties including, in some cases, ultra-low thermal conductivities. The last decade has seen a veritable explosion in aerogel research and industry R&D, leading to the synthesis of aerogels from a variety of materials for a rapidly expanding range of applications. However, both from the research side, and certainly from a market perspective, thermal insulation remains the dominant application. Unfortunately, continued progress in this area suffers from the proliferation of incorrect thermal conductivity data, with values that often are far outside of what is possible within the physical limitations. This loss of credibility in reported thermal conductivity data poses difficulties in comparing the thermal performance of different types of aerogels and other thermal superinsulators, may set back further scientific progress, and hinder technology transfer to industry and society. Here, we have compiled 519 thermal conductivity results from 87 research papers, encompassing silica, other inorganic, biopolymer and synthetic polymer aerogels, to highlight the extent of the problem. Thermal conductivity data outside of what is physically possible are common, even in high profile journals and from the world’s best universities and institutes. Both steady-state and transient methods can provide accurate thermal conductivity data with proper instrumentation, suitable sample materials and experienced users, but nearly all implausible data derive from transient methods, and hot disk measurements in particular, indicating that under unfavorable circumstances, and in the context of aerogel research, transient methods are more prone to return unreliable data. Guidelines on how to acquire reliable thermal conductivity data are provided. This paper is a call to authors, reviewers, editors and readers to exercise caution and skepticism when they report, publish or interpret thermal conductivity data. Graphical Abstract

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3D multi-scale quantification of industrially relevant ultra-porous silicas by low-dose electron tomography combined with SANS

Cited by 6 publications

References 75 publications

X-ray Tomography Coupled with Finite Elements, A Fast Method to Design Aerogel Composites and Prove Their Superinsulation Experimentally

X-ray Tomography Coupled with Finite Elements, A Fast Method to Design Aerogel Composites and Prove Their Superinsulation Experimentally

Butyl-Methyl-Pyridinium Tetrafluoroborate Confined in Mesoporous Silica Xerogels: Thermal Behaviour and Matrix-Template Interaction

The poor reliability of thermal conductivity data in the aerogel literature: a call to action!

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