Challenges of Handling, Processing, and Studying Liquid and Supercooled Materials at Temperatures above 3000 K with Electrostatic Levitation

Takehiko Ishikawa,Paul-François Paradis

doi:10.3390/cryst7100309

Abstract

Over the last 20 years, great progress has been made in techniques for electrostatic levitation, with innovations such as containerless thermophysical property measurements and combination of levitators with synchrotron radiation source and neutron beams, to name but a few. This review focuses on the technological developments necessary for handling materials whose melting temperatures are above 3000 K. Although the original electrostatic levitator designed by Rhim et al. allowed the handling, processing, and study of most metals with melting points below 2500 K, several issues appeared, in addition to the risk of contamination, when metals such as Os, Re, and W were processed. This paper describes the procedures and the innovations that made successful levitation and the study of refractory metals at extreme temperatures (>3000 K) possible; namely, sample handling, electrode design (shape and material), levitation initiation, laser heating configuration, and UV range imaging. Typical results are also presented, putting emphasis on the measurements of density, surface tension, and viscosity of refractory materials in their liquid and supercooled phases. The data obtained are exemplified by tungsten, which has the highest melting temperature among metals (and is second only to carbon in the periodic table), rhenium and osmium. The remaining technical difficulties such as temperature measurement and evaporation are discussed.

Highlights

Containerless techniques offer many technological and scientific advantages for material processing
Due to their high melting temperature and the risk of contamination at elevated temperatures, is very challenging to determine the thermophysical properties of refractory metals in their liquid phaseit phase using levitation techniques, and extremely difficult conventional methods
The new procedures and technological innovations implemented by Japan Aerospace Exploration Agency (JAXA) in their electrostatic levitation made possible the processing of refractory metals at temperatures above 3000 K, and permitted the measurements of the density, surface tension, and viscosity

Summary

Introduction

Containerless techniques offer many technological and scientific advantages for material processing. The absence of a crucible allows the handling of chemically reactive materials, such as molten refractory metals, alloys, or semiconductors. It eliminates the risk of sample contamination in their liquid phase above or under their melting temperature (overheated and supercooled regions). This offers excellent opportunities to characterize the structure of materials and to determine accurately their thermophysical properties. Developments include thermophysical property measurements (density [2], surface tension [3], viscosity [3], heat capacity [4], electrical resistivity [5,6]) of high-temperature melts, and the combination of levitation with either synchrotron radiation sources [7] or neutron sources [8,9] to unveil the structure of high

Methods

Results

Conclusion