Measurements of Density of Liquid Oxides with an Aero-Acoustic Levitator

Densities of liquid oxide melts with melting temperatures above 2000 °C are required to establish mixing models in the liquid state for thermodynamic modeling and advanced additive manufacturing and laser welding of ceramics. Accurate measurements of molten rare earth oxide density were recently reported from experiments with an electrostatic levitator on board the International Space Station. In this work, we present an approach to terrestrial measurements of density and thermal expansion of liquid oxides from high-speed videography using an aero-acoustic levitator with laser heating and machine vision algorithms. The following density values for liquid oxides at melting temperature were obtained: Y2O3 4.6 ± 0.15; Yb2O3 8.4 ± 0.2; Zr0.9Y0.1O1.95 4.7 ± 0.2; Zr0.95Y0.05O1.975 4.9 ± 0.2; HfO2 8.2 ± 0.3 g/cm3. The accuracy of density and thermal expansion measurements can be improved by employing backlight illumination, spectropyrometry and a multi-emitter acoustic levitator.

Using an acoustic levitator to investigate the drying kinetics and solids forming process of individual droplets during spray drying

Spray drying is a widely used process to turn slurries into dry powders and is especially important for thermally-sensitive materials, that are often found in the food or pharmaceutical industry. However, detailed insight into the drying kinetics during spray drying is difficult to investigate due to the boundary conditions in a spray drying tower. As a result, there is a lack of important information on the drying process and subsequent solidification of individual droplets. In this context, an experimental setup for a droplet positioned in a stationary ultrasonic field of an acoustic levitator is designed to enable a non-contacting measurement of the drying kinetics and the subsequent solidification process. To generate a comparable situation like in a real spray drying process, the droplet is positioned in an airflow, where air temperature, humidity, and velocity can be adjusted over wide range. Using an infrared camera to measure the surface temperature and a Complementary Metal Oxide Semiconductor (CMOS) camera for object recognition, the droplet can be observed continuously and drying kinetics of the droplet can be determined from the measured surface temperature and decreasing droplet size. Result of a 10 wt.% aqueous micro particle TiO2 suspension are reported and show that the investigated method is a very valuable and fast tool to safely scale-up spray drying systems very close to real process conditions. Especially when only small sample amounts are available in an early development stage.