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  • Author: A. Ott x
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The diffusion of Ag110m in lithium has been measured, using a thin film plating and sectioning method, between 67° and 160 °C. The data fit the Arrhenius relation

D=D0·exp(—Q/R T),

where

D0=0.37±0.13 cm2 sec-1 and Q=12.83 ±0.25 kcal·mol—1.

There are reasons to believe that diffusion takes place by a highly relaxed or cooperative mechanism. The difference in activation energy between Ag tracer diffusion in Li and Li self-diffusion is very small.

The inter-diffusion coefficient of 6Li and 7Li in liquid Li metal has been measured by a capillaryreservoir vacuum lock technique and by mass spectrometric analysis. For the temperature interval 195—450 °C and near-normal isotopic composition, the results can be represented by

D= (1.41 ±0.12) ·10-3 exp[— (2825 ± 90)/ (R T)].

Theoretical relations connecting diffusion and viscosity are well obeyed. Fair agreement is obtained with the COHEN-TURNBULL free volume theory, if Li* is the diffusing species.

Abstract

The diffusion of 22Na and 195Au has been investigated in solid, isotopically pure 8Li and 7Li metal. The Na tracer has been found to diffuse by about 4 % faster in 8Li than in 7Li. For Au the corresponding difference was 4% at the melting point, but as much as about 15% at 2 3 Tm (°K). A formalism is given for the interpretation of diffusion experiments where the matrix isotope mass is varied. The present results for Na in Li can be plausibly explained in terms of the vacancy mechanism. For Au diffusion in Li, the interpretation appears incompatible with a simple vacancy mechanism, and the anomalous departure from the inverse root mass relationship can be connected with recently detected quantum effects in 6Li - 7Li mutual diffusion

The mobilities of foreign metal tracers in isotopically pure lithium matrices have been studied. Differential diffusivities have been obtained for Na, Ag, Au, Zn and Ga in Li. The behaviour of impurities whose diffusion is not of a regular vacancy character (Au, Ag, Zn) appears connected with the quantum effects in Li self-diffusion.

Temperature differences ranging from 100°C to 500°C were maintained between the top and bottom ends of vertical capillaries containing liquid metal. The light isotope was found to be enriched at the hot end. The steady-sate isotope separation for different temperature ranges were between 1 and 3 per cent, corresponding to the thermal diffusion factors αK=3.1×10-2, αRb=3.1 × 10-2 and αGa=3.8 × 10 -2. According to a theoretical model, the results imply that the diffusing species is a “cluster” of several cooperating atoms, the mean diffusive displacement of which is considerably less than the effective cluster diameter. The clusters drift into voids given by the statistical fluctuations of free volume.

The solid and solution IR spectra of the yellow formazans (1) show in most cases a strong J'(NH) or ν (ND) band. The ν (NH) absorption of the red formazans (2) is so weak (ε ≈ 1 [liter mole-1 cm-1]), that it is only observed in solutions and with long path length. In the case of C-ethoxycarbonyl-N.N′-diphenylformazan opening of the intramolecular N — H - - - N hydrogen bridge by light gives rise to a new intramolecular N — H - - - O hydrogen bridge. The nuclear N — H resonance of the red formazans is shifted far to low field (14 p. p.m.).

The isotope effect due to temperature gradient has been investigated in liquid K and Rb, using new type steel capillary cells, convenient for the study of the variation of the effect with temperature. The physical parameters, deduced from the experimentally determined steady state gradient of the isotope separation factor versus reciprocal temperature, agree with earlier results obtained within restricted temperature ranges, and were found to be nearly independent of temperature.