The diffusivities of 23Na and 39K in the eutectic melt, K0.68Na0.32, were measured by means of pulsed field-gradient nuclear magnetic resonance techniques between the melting point (about 260K) and 640K. Very high accuracy could be achieved, without having to make corrections for systematic errors which were caused by gravity-induced convection. Within the above temperature ranges, the diffusivities of both Na and K were well-described by single Arrhenius laws:

K:     D (m2/s) = 4.1 x 10-8 exp[-0.079(eV)/kT]

Na:     D (m2/s) = 8.6 x 10-8 exp[-0.089(eV)/kT]

The Na/K ratio of the diffusivities was 1.34, and this was explained in terms of classical and quantum-mechanical diffusion mechanisms. It was noted that, in general, the diffusivity decreased with increasing average mass of the matrix atoms; thus reflecting the collective nature of diffusion in liquid alkali metals.

Diffusion of 23Na and 39K in the Eutectic Melt Na0.32K0.68. A.Feinauer, G.Majer: Physical Review B, 2001, 64[13], 134302 (4pp)