Density determination of liquid metals by means of fast resistive pulse-heating and electromagnetic levitation
Alexander Schmon
Institute of Experimental Physics, TU Graz
10:20 - 11:00 Friday 22 May 2015 HS P3 PH02112

Thermophysical properties of metals in the liquid phase have become increasingly important as input data for modern numerical simulations. Especially density is a relevant parameter for e.g. casting modelling.

Investigations of metals at high temperatures have to deal with difficulties such as chemical reactions, evaporation, loss of mechanical stability ect. One way to minimize interactions with the environment is to reduce the experimental duration. Applying a fast resistive pulse-heating technique, wire shaped specimens were resistively volume heated as part of an electrical discharge circuit. The passage of an electrical current of about 10.000 A leads to heating rates up to 10^8 K/s. The specimen is heated from room temperature to the end of its liquid phase in about 60 µs. During this process the sample’s thermal expansion is monitored by an adapted CCD camera system. Temperature is determined by measuring the surface radiance emitted from the sample by a pyrometer.
In addition an electromagnetic levitation apparatus was built up to perform containerless thermal expansion measurements in a much longer time regime. An inhomogeneous high-frequency electromagnetic field is generated by a water-cooled coil to heat and levitate the specimen. Temperature again is determined by a pyrometer. For thermal expansion determination shadowgraph-images are recorded with a high-speed CCD camera and evaluated with an edge detection algorithm. Density is calculated by averaging several 1000 frames for each temperature point.
Investigations of pure metals as well as application-relevant alloys were performed with both techniques and are compared to each other and to literature values.