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Lecture

Containerless processing in the study of undercooled melts: on Earth and in Space

Thursday (27.09.2018)
18:00 - 18:15 S1/01 - A01
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Most materials in daily human life are produced from the liquid state as their parent phase. The entire solidification and production process of materials takes often a long pathway. Efforts are directed towards to shortening the production process to save energy and costs. In order to realize this challenging task it is mandatory to have detailed knowledge of all properties of the liquid and all processes involved in solidification. All of these figures provide a solid basis to use computer aided materials design to discover new materials and to develop advanced production routes of higher efficiency.

In the present paper the power of containerless processing is demonstrated in order to approach the goal of virtual design of metastable materials. Using alternating electromagnetic fields and stationary electrostatic fields small drops of metals and alloys are freely suspended. Solidification takes place from a metastable liquid deeply undercooled below its melting temperature without any influence by container walls. The enhanced Gibb's free energy of the undercooled liquid opens up a great variety of solidification pathways into different metastable solids. Furthermore, the freely suspended drop is directly accessible both to measure physical properties of the melt important for modelling and to investigate in situ processes involved in the solidification process. The levitation techniques can be combined with proper diagnostic means at external laboratories in order to make use of a huge spectrum of materials investigation techniques. The application of levitation on Earth needs large forces to compensate the gravitational force that limits their applicability. These limitations are overcome when using the reduced gravity in Space. Here, the forces to compensate disturbing accelerations are about three orders of magnitude smaller than on Earth. We present examples to measure thermo-physical properties of liquids even in the undercooled melt regime. Also, studies of crystal nucleation and crystal growth investigations are presented using levitation both on Earth and in Space. The comparison of both sets of experiments allow for the discrimination of the influence of forced convection on transport processes in liquids and on solidification kinetics as well.

Experiments in reduced gravity are conducted at present on board the International Space Station ISS by several international research teams.

Speaker:
Prof. Dr. Dieter M. Herlach
Ruhr-Universität Bochum