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Grain boundaries in Ni3Ga as paths of rapid diffusion
Čermák, Jiří ; Růžičková, Jana ; Konecny, M. ; Ipser, H.
Grain boundary diffusivity P (P is a triple product of diffusion coefficient in grain boundary D, grain boundary width .delta. and segregation coefficient s) of nickel was measured by serial sectioning and residual activity methods in temperature interval 973-1373 K. Measurements are compared with our previous results on Ni grain boundary diffusivity in Ni3Al. It was obtained that the values of P for nickel in Ni3Ga are slightly higher than those for nickel in Ni3Al. The observed relation between Ps was interpreted by different affinity of diffusing Ni to different components X in the two Ni3X alloys.
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Teoretické studium difúze iontů dúležitých pro analýzu dechu metodou SIFT-MS
Dryahina, K. ; Španěl, Patrik
Accuracy of quantitative Selected Ion Flow Tube Mass Spectrometry SIFT-MS is ultimately determined by the proper accounting in the data analysis for the effect of differential diffusion. Diffusion loss of the product ions can be typically lower by a factor of up to 3 in comparison with the precursor ions. Hard sphere model of diffusion of polyatomic ions in helium has been used to calculate diffusion coefficients of the precursor and product ions involved in SIFT-MS quantification of common breath metabolites ammonia, acetone, isoprene, acetaldehyde and ethanol. Calculation involves semiempirical PM3 method for determination of the geometries of the ions, numerical averaging of the geometrical cross section for collisions with helium atoms and construction of a model interaction (12, 4) model potential followed by the analytical calculation of ionic mobility using momentum-transfer collision integral. Finally the values of diffusion enhancement factors have been calculated.
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Určení transportních charakteristik z protiproudé difuze plynů
Soukup, Karel ; Šolcová, Olga ; Schneider, Petr
Two types of a diffusion cell commonly used for studying of isobaric counter-current diffusion in porous solids are compared. Both cells enable determination of diffusion coefficients and transport characteristics of porous materials. Transport parameters are material constants of the porous solids and can be evaluated through application of a suitable model of porous solids to results of measurements of transport processes withing the porous structure
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