XE-129 NUCLEAR-MAGNETIC-RESONANCE OF AL2O3 FIBERS

Xe-129 Nuclear magnetic resonance (NMR) is used to study the adsorption of xenon in amorphous Al2O3 and Al2O3-ZrO2 fibres. Sintering affects the intensity of the NMR line of adsorbed Xe, and qualitatively this intensity is proportional to the degree of sintering. It definitely shows that the xenon adsorption sites have to be found in the pores which are affected by the sintering. Further, the chemical shift of adsorbed Xe is determined as a function of both temperature and pressure. In the temperature dependence two regions can be discerned. In the low temperature region the curves for different pressures have the same curved shape and at the lowest temperature the chemical shifts become independent of the pressure. Above the transition temperature, the chemical shifts become linearly dependent on the temperature, while the pressure dependence follows a typical Langmuir-type pattern. A simple theoretical model is proposed to explain the temperature and pressure dependence. For the low temperature region it is assumed that the Xe atom can move in a potential well due to interaction with an oxygen atom. For the high temperature region the temperature and pressure dependence of the chemical shift are described by the Langmuir model. This combination of two models can qualitatively describe the observed temperature and pressure dependences.