Viscous flow and self-diffusion in densely and loosely packed metallic melts

The Ni self-diffusion, density, and viscosity of the densely packed liquid Ni66.7B33.3 and the more loosely packed liquid Ge66.7Ni33.3 were measured with high accuracy using different experimental methods. The viscosity eta was obtained using the oscillating-drop method combined with electrostatic levitation and the oscillating-cup technique in a rheometer. The Ni self-diffusion coefficient D-Ni was obtained from quasielastic neutron scattering experiments. For Ni66.7B33.3, it was found that the activation energies for self-diffusion and viscous flow, E-D and E-eta, respectively, are almost equal. Hence, the product of the viscosity. and self-diffusion coefficient D is fairly constant over the entire temperature range measured, spanning almost 800 K. In contrast, for Ge66.7Ni33.3, D eta increases with increasing temperature, indicating that the dynamics in liquid Ge66.7Ni33.3 shows better agreement with an activated process. This temperature dependence is in line with the StokesEinstein relation.