Self-Diffusion Coefficient of Liquid Lithium

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The coefficient of self-diffusion of 7Li in liquid lithium has been measured with nuclear magnetic resonance. The diffusion coefficient was determined from observations of the dependence of the spin-echo signal upon the amplitude of a pulsed magnetic field gradient. It is found that at the melting point D = 6.8 ± 0.3 × 10−5cm2 / sec and (T / D) (dD / dT) = 2.8 ± 0.3. In terms of an activation model, D = 0.94 ± 0.4 × 10−3 exp [ − (2300 ± 300cal) / RT]cm2 / sec. Resultsare compared with the Cohen–Turnbull free-volume model and the Ascarelli–Paskin dense-gas model for liquid diffusion. From the free-volume model, the effective hardsphere diameter is determined for Li and, in addition, for Na and K as well. The results compare favorably with effective hard-sphere diameters determined from neutron-scattering data.