Isotopic exchange techniques

Fig. 1. Rate constants, for the exchange of water molecules from the first coordination sphere of a given metal ion and the corresponding mean life times, tm = l//zex, of a particular water molecule measured by " 0 NMR. The gray bars indicate values determined by NMR isotope exchange technique (except Cr + ).

Payne, T.E. Waite, T.D. (1991) Surface com-plexation modeling of uranium sorption data obtained by isotopic exchange techniques. Radiochim. Acta 52-53 (Pt 2) 487-493 Peacock, M.A. (1942) On goethite and lepidocro-cite. Trans. Roy. Soc. Ca. 36 107-119 Peacock, S. Rimmer, D.L. (2000) The suitability of an iron oxide-rich gypsum by-product as a soil amendment. J. Environ. Qual. 29 1969-1975... 

Payne, T. E. Waite, T. D. 1991. Surface complexation modeling of uranium sorption data obtained by isotope exchange techniques. Radiochimica Acta, 52/53, 487-493. 

Recently Midelfort and Rose (4) introduced a positional isotope exchange technique that is also suitable for study by the chemical shift technique. Briefly, this technique follows the exchange of label from one part of a substrate to another due to rotational equivalence of some intermediate. The method was first applied to glutamine synthetase in the reaction ... 

For predominant electronic conductors like, for example, the perovskites Lai xSrxCoi.yFey03 is determined by the ratio of the oxygen self diffusivity and surface exchange coefficient. Both parameters can be measured simultaneously by using isotopic exchange techniques. Calculations show that... 

Rynders, R.M. Rao, M.B., and Sircar, S. (1997). Isotope exchange technique for measurement of pure and multi-component adsorption equiUbria and kinetics. 

The isotope-exchange technique is essentially different. The isotope-incorporation method can lead to valuable deductions about reaction mechanisms and reaction intermediates, but much more direct information of this kind is provided by isotope-exchange studies. In these, a labeled substance is introduced into a reacting mixture and from the extent to which the isotope undergoes exchange, conclusions can be drawn about the nature of the reaction intermediates, and hence about the overall mechanism. 

The present review deals with recently developed techniques to measure surface mobility in supported metal catalysts. Special attention will be paid to isotopic exchange techniques, well-adapted to diffusion measurements on metal/support catalj ts, and to complementary techniques such as IR spectroscopy, having given a comprehensive view of both the nature and the rate of diffusing species. Kinetic equations of isotopic exchange developed in Sec. 2 of this review will be restricted to the measurements conducted in a closed reactor. 

Gla] Kinetics of absorption, isotopic exchange technique 1600°C, < 20 mass% Cr... 

Microscopic, such as NMR spectroscopy, pulsed field gradient NMR (PFG-NMR), quasielastic neutron scattering (QENS), or isotope exchange technique... 

Among isotope exchange techniques direct deuteration with gaseous or liquid D2O in combination with IR spectroscopic investigations has been widely applied in studies of polymeric structure... 

The cationic forms of Cd, Pb Cr, and Ni were shown to be immobilized in clinoptilolite structure by two mechanisms ion exchange and chemisorption [05M1]. In case of lead and chromium, chemisorption predominates. The contributions of both mechanisms in case of Cd and Ni were equal. The long term kinetics of Cd sorption and desorption by Ca-exchanged clinoptilohte was studied by using isotope exchange technique while maintaining pH at circumneutral values [lOAl]. 

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 ... 

The self-diffusion of O in undoped alumina monocrystals was investigated by using the gas-solid isotope exchange technique. After diffusion annealing, the profiles of O were determined by means of secondary ion mass spectrometry. This revealed 2 parts, in which the behavior close to the initial surface was attributed to bulk self-diffusion while the diffusion tails were attributed to migration in dislocation walls. At 1500 to 1720C, the bulk self-diffusivity of O could be described by ... 

The self-diffusion coefficient of oxygen in polished slices of Vemeuil single-crystals was determined at 1500 to 1770C by using the gas-solid isotope exchange technique. The results were represented by ... 

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 ... 

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 ... 

The O self-diffusion coefficients were determined for polycrystalline microspheres by using an isotope exchange technique with 1 0 as the tracer. The diffusion coefficients for 1099 to 1644C could be described by ... 

The O self-diffusion coefficient for samples which contained between 12 and 16mol%MgO was determined by using the isotope exchange technique and an 1 0 tracer. The results for single-phase cubic material containing 12mol%MgO could be described by ... 

Using the heterogeneous isotope exchange technique, a study was made of the diffusion of 22]sfa in type-A synthetic zeolite at 21C. The exchange rate did not fit the classical function for the time-independence of an ideal diffusion process. For the initial exchange, the diffiisivity at 21C was about 3 x lO cm /s. Over the range of 0 to 30C, the diffusivity was described by ... 

Using isotope-exchange techniques, it was found that the self-diffusion of Sr ions in type-A zeolite at 21 to lOOC could be described by ... 

Oxygen isotopic exchange techniques are used to measure the oxygen exchange rate, which is usually decomposed into two parts the surface exchange rate and the rate of oxygen diffusion in the bulk. Different techniques are used. 

Bouwmeester, H.J.M., Song, C., Zhu, J., Yi, J., van Sint Annaland, M., and Boukamp, BA. (2009) A novel pulse isotopic exchange technique for rapid determination of the oxygen surface exchange rate of oxide ion conductors. Phys. Chem. Chem. Phys., 11 (42), 9641U9643. 

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