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Impact of convective flow on long-capillary chemical diffusion studies of liquid binary alloys
Florian Kargl, Elke Sondermann, Henning Weis and Andreas Meyer

Chemical diffusion in binary liquid Al-Cu alloys is studied in-situ using X-ray radiography in combination with long-capillary experiments on ground. It is shown that even in the presence of a stabilizing density layering and in small diameter capillaries Marangoni flow caused by surface tension gradients on free surfaces between sample and capillary wall in Al-Cu leads to an increase in the effective diffusion coefficients by up to a factor of two whereas a small radial temperature gradient in the absence of free surfaces leads to a 50% increase. It is further shown that unstable density layering in the absence of free surfaces and temperature gradients leads to a helical flow pattern causing complete mixing on timescales of a few seconds, which is orders of magnitude faster than purely diffusive transport.

Keywords: Chemical diffusion, al-based alloys, long-capillary, shearcell, x-ray radiography

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