Self diffusion in liquid titanium was measured at 2000K by quasi-elastic neutron scattering combined with container-less processing via electromagnetic levitation. At small wave-numbers, q, the quasi-elastic signal was dominated by incoherent scattering. Up to about 1.2/Å the width of the quasi-elastic line exhibited a q2 dependence, as expected for long-range atomic transport, thus permitting measurement of the self diffusion coefficient DTi. As a result, a DTi value of 5.3 x 10-9m2/s was obtained. Via a molecular dynamics computer simulation, using an embedded atom model for Ti, the self-diffusion coefficient was determined from the mean square displacement as well as from the decay of the incoherent intermediate scattering function at various q values. By comparing both methods, it was shown that the hydrodynamic prediction of a q2 dependence indeed extended up to about 1.2/Å. Since this result did not depend significantly upon the details of the interatomic potential, the findings showed that accurate values of self diffusion coefficients in liquid metals could be measured by quasi-elastic neutron scattering on an absolute scale.

Self Diffusion in Liquid Titanium: Quasi-Elastic Neutron Scattering and Molecular Dynamics Simulation. Meyer, A., Horbach, J., Heinen, O., Holland-Moritz, D., Unruh, T.: Defect and Diffusion Forum, 2009, 289-292, 609-14