Viscometer
Viscosity of a melt is an important materials parameter which, on the one hand, provides information about collective atomic dynamics and is required as a materials property, on the other hand, in order to design technical casting- and flow processes.
Currently, the most accurate method for measuring the viscosity of liquid metals at elevated temperatures is the oscillating cup viscometry. In this technique, the melt is inside a crucible suspended on a thin wire. The torsion pendulum, formed this way, carries out rotational oscillations which are damped by the inner friction of the melt. Measuring the damping constant yields the viscosity with an absolute expanded uncertainty of better than 20 %.
The oscillating cup viscometer available at the institute allows to measure over a temperature range of 400 – 2100 °C. Thus, it is in society with the best devices worldwide. Such high temperatures require certain demands on the materials used inside.
The setup is located inside a vacuum chamber that can be evacuated down to the pre-vacuum regime. This serves the removal of residual gas impurities. The actual measurements are finally carried out under protective gas atmosphere. As the working temperature is slowly varied over the range, highly precise continuous curves are obtained.
Results achieved with this viscometer were included into the definitions of standard reference materials.