Measurement of the Soret coefficient in liquid Al-Ag alloys using x-ray radiography

Thermodiffusion designates a diffusive motion of particles driven by a temperature gradient. In liquid alloys, this effect can influence the concentration distribution during directional solidification and change the homogeneity of grown crystals. Using x-ray radiography (XRR), thermodiffusion in liquid Al--Ag has been measured, with compositions ranging from ${\mathrm{Al}}₈₀{\mathrm{Ag}}₂₀$ to ${\mathrm{Al}}₅₀{\mathrm{Ag}}₅₀$. The Soret coefficient is determined to be $(0.9\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, where the silver atoms diffuse to the cold end of the sample. Thanks to the time-resolved information from in situ XRR, the interdiffusion coefficient could simultaneously be measured and is in good agreement with previous interdiffusion measurements in this concentration range. The measured Soret coefficient is compared with the values predicted by the current theoretical models, which are found to be off by at least a factor of two.