Sorption of noble gases by solids, with reference to meteorites

A report is presented on the trapping of noble-gases by chromite and carbon. Nineteen samples were synthesized in a Ne-Ar-Kr-Xe atmosphere at 440 K to 720 K. The reactant metal films were prepared either by vacuum evaporation of alloy or by thermal decomposition of Fe- and Cr-carbonyls. The products - including Fe3O4, Cr2O3, carbides, and unreacted metal - were partially separated by selective solvents, such as HCl, H2SO4-H3PO4, or HClO4. Samples were characterized by XRD, SEM, and atomic absorption; noble gases were measured by mass spectrometry. Surface areas, as measured by the BET method, were 2 to 100 m2/g. All samples are dominated by an adsorbed noble gas component that is largely released upon heating at =< 4000C or slight etching. Elemental abundance patterns show that this component is derived from the highest-pressure noble gas reservoir seen by the sample -atmosphere or synthesis vessel - indicating that desorption or exchange rates at room T are slow on the time scale of our experiments. Adsorptive capacity is reduced by up to 2 orders of magnitude upon light etching with HClO4 and, less drastically, by heating. Apparently some active adsorption sites are destroyed by these treatments. The results are discussed. (author)