NOBLE-GAS IMMOBILIZATION IN ZEOLITES

It was discovered that the noble gases Ar, Kr and Xe can be trapped firmly in type A zeolites as well as in mordenites and chabazites when the molecular sieves are hydrothermally vitrified at temperatures between 340 and 650 degree C in the presence of pressurized gas. The occurence of trapping in an amorphous nonzeolitic species was demonstrated by X-ray diffraction, neutron scattering and electron scattering. The change in structure of loaded zeolites is also manifested by a substantial loss in sorption capacity for water as well as an almost complete disappearance of the specific surface area. The gas release rates at temperatures below 550 degree C were found to be extremely low. The activation energies for the diffusion of Kr through amorphous Ca and Mg exchanged 5 A zeolite were determined to be 209 plus or minus 15 and 187 plus or minus 16 kj/mol respectively.