Diffusion and demixing in liquid Al-In

Kurzfassung

Thermodiffusion designates a diffusive motion of particles, driven by a temperature gradient. In liquid alloys, this effect can influence the concentration distribution and change the homogeneity of grown crystals. The effect has been shown to be particularly strong in mixtures with a miscibility gap, but this has, until now, not been observed outside of organic mixtures. We measured thermodiffusion as well as interdiffusion in aluminum-rich liquid Al-In as a function of temperature and composition. The experimental setup consists of a specialized furnace in combination with X-ray radiography, which allows an in-situ observation of the diffusion process [1]. The time- and space-resolved information from X-ray radiography makes it possible to detect free surfaces in the melt, which would cause Marangoni convection. Additionally, it is also possible to detect the onset of demixing, helping to refine the position of the miscibility gap in the phase diagram. Al-In was chosen as the sample system because it offers excellent contrast in X-ray absorption and exhibits monotectic liquid-liquid segregation behavior. Close to the miscibility gap, the interdiffusion coefficient in liquid Al-In is found to decrease, while the thermodiffusion coefficient remains virtually unchanged, thus 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. References [1] A. T. Krüger, E. Sondermann, and A. Meyer, Phys. Rev. B 107, 064301 (2023).