Pore-structure determinations of silica aerogels by {sup 129}Xe NMR spectroscopy and imaging.

Journal Article · Wed Apr 01 04:00:00 EST 1998 · J. Magn. Resonance

DOI:https://doi.org/10.1006/jmre.1998.1358· OSTI ID:938144

Gregory, D M; Gerald, II, R E; Botto, R E

Silica aerogels represent a new class of open-pore materials with pore dimensions on a scale of tens of nanometers, and are thus classified as mesoporous materials. In this work, we show that the combination of NMR spectroscopy and chemical-shift selective magnetic resonance imaging (MRI) can resolve some of the important aspects of the structure of silica aerogels. The use of xenon as a gaseous probe in combination with spatially resolved NMR techniques is demonstrated to be a powerful, new approach for characterizing the average pore structure and steady-state spatial distributions of xenon atoms in different physicochemical environments. Furthermore, dynamic NMR magnetization transfer experiments and pulsed-field gradient (PFG) measurements have been used to characterize exchange processes and diffusive motion of xenon in samples at equilibrium. In particular, this new NMR approach offers unique information and insights into the nanoscopic pore structure and microscopic morphology of aerogels and the dynamical behavior of occluded adsorbates. MRI provides spatially resolved information on the nature of the flaw regions found in these materials. Pseudo-first-order rate constants for magnetization transfer among the bulk and occluded xenon phases indicate xenon-exchange rate constants on the order of 1 s-1 for specimens having volumes of 0.03 cm3. PFG diffusion measurements show evidence of anisotropic diffusion for xenon occluded within aerogels, with nominal self-diffusivity coefficients on the order of D= 10-3cm2/s.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: ER
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 938144
• Report Number(s): ANL/CHM/JA-27544
• Journal Information: J. Magn. Resonance, Journal Name: J. Magn. Resonance Journal Issue: 2 ; Apr. 1998 Vol. 131; ISSN 1090-7807; ISSN JMARF3
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
77 NANOSCIENCE AND NANOTECHNOLOGY
GELS
NANOSTRUCTURES
NUCLEAR MAGNETIC RESONANCE
PORE STRUCTURE
SELF-DIFFUSION
SILICA
SPATIAL DISTRIBUTION