NMR diffusion of hyperpolarised 3He in aerogel: a systematic pressure study.
Diffusion of hyperpolarised 3He in a silica aerogel sample with 98% porosity was measured by NMR, and systematically studied as a function of pressure P in the range 20 mbar -1 bar. Spin-echo amplitudes, recorded with pulsed gradients in the usual CMPG sequence, follow a monoexponential decay, and the decay rate varies quadratically with the gradient intensity: thus the apparent diffusion coefficient of the gas D can be evaluated. Our results show a power-law (1/D proportional to P(0.55)), which could be consistent with a fairly broad mean free path distribution, implying some inhomogeneity in the aerogel structure. We have observed a spatial non-uniformity of D, and some deviation to the quadratic dependence of the decay rate with the gradient intensity, possibly related to sample structure inhomogeneity.
Guillot
G
G
U2R2M CNRS ESA 8081, Univ. Paris-Sud, Bât 220 91405, Orsay Cedex, France. guillot@u2r2m.u-psud.fr
Nacher
P J
PJ
Tastevin
G
G
D004058:Diffusion; D006371:Helium / Q000737:chemistry*; D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D016062:Porosity; D011312:Pressure; D058428:Silica Gel; D012822:Silicon Dioxide / Q000737:chemistry*
D007554:Isotopes; D006371:Helium; D058428:Silica Gel; D012822:Silicon Dioxide