Physics – Condensed Matter – Materials Science
Scientific paper
2005-09-13
Journal of Chemical Physics 123 (2005) 064506
Physics
Condensed Matter
Materials Science
Scientific paper
10.1063/1.1997130
Hyperpolarized 3He is used to nondestructively probe by NMR the structure of custom-made and commercial silica aerogels (97% and 98.5% porous). Large spin-echo signals are obtained at room temperature and very low magnetic field (2mT) even with small mounts of gas. Attenuation induced by applied field gradients results from the combined effects of gas diffusion and confinement by the porous medium on atomic motion. Nitrogen is used as a buffer gas to reach equivalent 3He pressures ranging from 5 mbars to 3.5 bars. The observed pressure dependence suggests a non-uniform structure of the aerogels on length scales up to tens of micrometers. A description by broad phenomenological distributions of mean free paths is proposed, and quantitatively discussed by comparison to numerical calculations. The investigated aerogel samples exhibit different effective diffusion characteristics despite comparable nominal porosities.
Nacher Pierre-Jean
Tastevin Geneviève
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