Noncontact technique for measuring surface tension and viscosity of molten materials using high temperature electrostatic levitation

A new, noncontact technique is described which entails simultaneous measurements of the surface tension and the dynamic viscosity of molten materials. In this technique, four steps were performed to achieve the results: (1) a small sample of material was levitated and melted in a high vacuum using a high temperature electrostatic levitator, (2) the resonant oscillation of the drop was induced by applying a low level ac electric field pulse at the drop of resonance frequency, (3) the transient signals which followed the pulses were recorded, and (4) both the surface tension and the viscosity were extracted from the signal. The validity of this technique was demonstrated using a molten tin and a zirconium sample. In zirconium, the measurements could be extended to undercooled states by as much as 300 K. This technique may be used for both molten metallic alloys and semiconductors

Thermocapillary Flow Induced by Laser Heating of an Acoustically Levitated and Flattened Glycerin Drop

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Non-intrusive thermophysical property measurement by acoustic and electrostatic levitation of liquids

There has been a great deal of current interest in understanding the thermodynamic behaviour of liquids in the undercooled state. In industrial systems as well as in nature, liquid states are found to exist below the freezing point, especially if a pure liquid remains in a relatively undisturbed state. For undercooled liquids, the measurement of thermophysical properties such as viscosity, surface tension and thermal diffusivity present challenges because any physical interference with a probe could lead to solidification. The undercooled state is sustainable in a containerless environment that may be provided for by acoustic or electrostatic levitation. Among the methods used, the relaxation history of deformed drops as they revert back towards spherical shape is recorded and used to obtain viscosity. Similarly, the thermal relaxation of an initially heated drop is thermographically recorded and the history is used to evaluate the thermal diffusivity. Another technique involving the stimulation of thermocapillary flow on a levitated liquid sample with a laser has also been developed. Thermal measurements include additional challenges because of buoyant convection which dominates over thermocapillary flow masks the desired measurements. Therefore, drops horizontally flattened by the acoustic field are used. This procedure reduces the hydrostatic head to 0.5 mm and significantly reduces the presence of buoyant convection. In this review, some techniques involving physical and thermal manipulation of highly viscous liquids in the levitated state are discussed and the feasibility of some new methods is discussed and evaluated.info:eu-repo/semantics/publishe