Sub-Micron Anisotropy in Super Insulation Nano-Fumed Silicas
34 Pages Posted: 14 Dec 2018 Publication Status: Accepted
Abstract
It is well accepted that global energy transition will be strongly dependent on energy saving. Here, we focus on describing the multi-scale structure of a fumed silica characterized by remarkably low thermal conductivity (ca. 2-5 mW.m-1.K-1) when used as a core material in vacuum insulating panels. While such powders are known to be highly polydisperse at different lengthscales (hardly quantifiable), we propose an original methodology based on small-angle X-ray scattering experiments with the aim of providing simple criteria for characterizing the morphology of these nanostructured silicas. Combining this technique with transmission electron microscopy, electron-tomography and mercury intrusion porosimetry also allow assigning the origin of the super-insulation to the pronounced and graduated anisotropy of the silica aggregates at lengthscales smaller than 500 nm. This result shows the need for nanometric structure tailoring and provides the basis for designing new synthesis routes scalable at the industrial level.
Keywords: silica, small angle X-ray scattering, insulator, electron tomography, fractal aggregate
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