Though they are key data for physics of liquids and for the modelisation of solidification, diffusion coefficients in liquids are still badly known. A strong scattering is observed in the experimental data of the literature. Diffusive fluxes are indeed so small that even very weak convective levels significantly affect the transport during diffusion experiments. Under normal gravity, the origin of convection is mainly thermosolutal, especially at high temperatures where it is difficult to perform good isothermal conditions. This convection artificially increases the mixing and often leads to an overestimate of the diffusivity. Space experiments are, till now, the best way to get rid of this effect. We propose here a new ground based method. Its principle is to create a well define velocity field and to tale its transport into account by an analytical model. A steady magnetic field is used to control the convective motion. Successful experiments have been conducted on impurity diffusion of In and Bi in Sn.
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