Measurements of thermodiffusion near the miscibility gap of liquid Al–In alloys

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. The effect has been shown to be very strong in mixtures with a miscibility gap, due to the halting of mixing, so that the concentration separation is not held back by interdiffusion anymore, but this has until now not been observed outside of organic mixtures. Here, using x-ray radiography, thermodiffusion at the miscibility gap of liquid Al-In has been measured, with compositions ranging from Al₉₇In₃to Al_70.5In_29.5. Closer to the miscibility gap the interdiffusion coefficient diminishes, while the thermodiffusion coefficient remains virtually unchanged, leading the ratio of the two coefficients (the so-called Soret coefficient) to diverge. This result is similar to previous investigations on liquid organic mixtures with miscibility gaps.