Single tracer exchange measurement

First tracer ZLC measurements [113], however, are in contrast to this finding. In these studies, tracer exchange is found to be rather fast, so that there is no indication of single-file behavior. Moreover, it appears that the (transport) diffusivities resulting from ZLC measurements are in complete agreement with the concentration dependence of the (self-) diffusivities resulting from... 

The tracer diffusion coefficient of oxide ions in single crystals was measured by using the gas-solid isotopic exchange technique with 1 0 tracer. Least-squares analysis of tracer diffusion coefficients under an oxygen pressure of 4.5 x lO Pa gave ... 

The expression given above for R indicates that the exchange process is first order, and it will remain so provided tracer quantities are employed. It is also possible to roughly measure R by single-point determinations, but it is preferable to use several sampling times and to confirm the first-order nature of the measured exchange... 

For reactions which are completely at equilibrium, tracer experiments are often the only method whereby rate data can be obtained. Although there is no net production or consumption of molecular species, movement of atoms from one species to another can be followed using radioactively labelled molecules. Measuring the rate of [14-C] isotope redistribution Parravano has studied a number of reaction systems.TTie success of the method depends upon the availability of exchange reactions, characterized by the transfer of a single atom (or atomic group), similar to that involved in the gas surface reaction step under study. Taking >CH2 transfer as an example, the key step in catalytic alkylation is ... 

Self-diffusion coefficients of nitrogen in polycrystalline alpha- and beta-silicon nitride were measured by using a gas-solid isotope exchange technique with as a tracer at 1200 to 14IOC. The diffusion coefficients for single-crystal grains could be expressed as ... 

Self-diffusion of 0 ions in polycrystalline and single-crystal magnesioferrites was measured by using a gas-solid isotopic exchange technique, with as a tracer, at 975 to 1465C. The bulk diffusion coefficients of polycrystalline magnesio-ferrite (MgO/Fe203 mole ratio = 0.95) could be expressed by ... 

Hancock and Martin (1991) modified the above procedure to measure all four Ra isotopes in a single sample. They used 2 Ra as a tracer and separated Ra from the sample by coprecipitation with PbS04. The precipitate was dissolved in a few mL of alkaline (pH = 10) 0.1 mol/L EDTA solution, mixed with a few drops of a slurry of anion-exchange resin (Bio-... 

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