Speaker
Description
Ultra pure metals have various applications in biology or electronics. Crystallization from the melt, e. g. via zone melting, accompanied with segregation of impurities at the solidification front is the basic mechanism behind many different processes for the refining of metals and semi-metals. In this presentation, we focus on a crystallization methodology with a gas cooled (cooling finger)
dipped into a metallic melt in a rotating crucible [1]. The basic requirement for purification in a solidification process is a morphologically stable, solidification front. This is the only way to achieve macroscopic separation of the impurities. For cellular or dendritic solidification morphologies, the segregated impurities will be only pushed into the interdendritic melt, remaining as so-called micro-segregation in the solidified metal. The morphological stability [2] depends on the process parameters temperature gradient G at the solidification front, the solidification front velocity v and thermodynamic properties of the alloy.
To quantify the impact of varying cooling rates and temperature gradients on the morphological evolution especially on the planar/cells/dendrites transition and thus on microsegregation profiles, phase field simulations coupled to thermodynamic database are performed for an aluminium melt with three impurities, Si, Mn and Fe. The simulations provide the process window for an energy efficient purification process, i. e. low thermal gradients and elucidate the benefit of melt convection. We have investigated the dynamic evolution of the temperature field by using the homoenthalpic approach together with a 1D temperature field approximation to solve the transient long range temperature evolution to mimic realistic experimental conditions [3].
[1] D. Curtilo, G. Shankar Nayak, B. Friedrich, Metals – Open Access Metallurgy Journal, (2017)
[2] Danzig, J.; Rappaz, M.: Solidification, 1. Edition, EPFL Press, (2009)
[3] B. Böttger, J. Eiken, M.Apel, Journal of Computational Physics, vol. 228 (2209)
| Speaker Country | Germany |
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