Study of Liquid Metals by Electrostatic Levitation

Citation

Li, John Jian-Zhong (2009) Study of Liquid Metals by Electrostatic Levitation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JY7J-Q837. https://resolver.caltech.edu/CaltechETD:etd-06012009-162039

Abstract

With the development of bulk metallic glasses (BMG) in recent years, more and more scientists in solid state physics are trying to understand the mechanism of glass-formation in terms of thermodynamics and kinetics, while engineers in metallurgy are trying different compositions and processes to improve the mechanical properties of BMGs and their composites.

Glasses are nothing but frozen liquids. So far most of the studies of metallic glasses have been below the glass transition temperature because molten metallic liquids are chemically reactive with the container walls. For this reason, we used the Electrostatic Levitation (ESL) method that was developed by Dr. Won-Kyu Rhim.

In this thesis, the instrumentation of the ESL is described. Discussion on the advantages and disadvantages of ESL is given by comparing with the other levitation methods. Because of the advantage in sample position stability over all the other levitation methods, the ESL facility at Caltech is uniquely capable of measuring the viscosity and thermophysical properties of liquid metals in the undercooled temperature range. The ESL was further improved at Caltech to reduce temperature gradients on a sample and increase the stability of the sample positioning with a tetrahedral laser heating system.

Using such an improved ESL, thermophysical properties of some evaporative metallic liquids such as Ti and silicon-germanium alloys have been successfully studied and mass loss as well as composition changes could be accounted for.

Several BMGs developed at Johnson group at Caltech have been studied using ESL. Among the liquid thermodynamics and kinetic properties of interest, special attention has been paid on to measurements of the TTT curve, viscosity, and volume changes with temperature. These data give useful insight on the glass-forming mechanism. Through these studies, guidelines in the search for good ductile metallic glass-formers have emerged. Discussing these guidelines is an important part of this thesis.

Finally, we discuss an investigation to understand observed hysteresis in the viscosity and the so-called threshold temperature that has been observed in some of the best glass-forming metallic liquids. We conclude this investigation with a hypothesis of a liquid-to-liquid phase transition that occurs above liquidus temperatures in several systems that we have studied.

Thesis Files