NMR mit thermischpolarisiertem und hyperpolarisiertem Xenon

In this dissertation NMR experiments with thermally polarized as well as hyperpolarized xenon have been performed.Several porous samples like catalysts and natural rubber have been investigated by thermally polarized xenon. Due to the fact, that the xenon chemical shift is correlated with the pore size of a porous material, changes in the pore size and the pore geometry of a naptha-reforming catalyst during the deactivation and regeneration process could be observed by using 129Xe-NMR spectroscopy. The measurement of the longitudinal and the transversal relaxation times of xenon atoms in mineral oil containing natural-rubber elastomers (NR) obtained more characteristic results compared to 1H relaxometry measurements, which have been performed with an analytic device which is widespread in the industry already. Natural-rubber elastomers with different degrees of cross-linking have been investigated with 129Xe NMR. In the case of a lower degree of cross-linking, NR samples with a different content and sort of fillers provided different chemical shifts and full widths at half maximum (FWHM) of the Xe-NMR signals. The influence of a filler on a polymer network could be shown with 129Xe NMR. Unfilled NR samples with different degrees of cross-linking could be identified via the chemical shift and the line width of the Xe signals. The NR samples filled with a highly active carbon black provided nearly constant chemical-shift values. Therefore it was assumed that the xenon atoms dissolved in the filled polymer are close to the filler particles. Furthermore 129Xe-NMR measurements on NR samples with different degrees of strain have been performed. In the case of the unfilled NR samples the longitudinal xenon relaxation time (Xe-T1) could be correlated to the degree of strain whereas for NR samples filled with carbon black no correlation could be observed.NMR measurements with hyperpolarized 129xenon on water, ethanol, and several mixtures of water and ethanol have been performed. The experiments with hyperpolarized xenon have been performed in the batch mode. The formation and degradation of imperfect clathrate- hydrates structures type I could be observed in the case of pure water, and in mixtures of ethanol and water with volume ratios of 80/20, 70/30, and 50/50, but not in the case of pure ethanol and in mixtures with a volume ratio of 90/10. During the formation and degradation of the clathrate hydrates the bigger 5(12)6(2) cage was observed to be more stable than the smaller 5(12) cage. Pure ethanol was proven to be an appropriate storage and transport medium for hyperpolarized xenon. The investigation of natural rubber samples and of a polyamide-6,12 membrane is in principle possible with hyperpolarized xenon in the batch mode, but the intensity of the signals was very low. In low-field SPINOE experiments on toluene high enhancement factors could be achieved temporarily by spin polarization transfer from hyperpolarized Xe atoms to the protons of the toluene molecule.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2004

Author dc:creator

• Kühn, Holger D.

Contributors dc:contributor

• Blümich, Bernhard

• info:eu-repo/classification/ddc/540
• Chemie
• NMR-Spektroskopie
• Xenon-129
• Katalysator
• Naturkautschuk
• Hyperpolarisation
• Clathrathydrate
• NMR spectroscopy
• catalyst
• natural rubber
• hyperpolarization
• clathrate hydrate

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122180%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:60472