Thermophysical Properties of Molten Yttrium Measured by Non-contact Techniques

Abstract

Understanding the nature and behavior of liquid metals requires accurate values of their physical properties (e.g., density, surface tension, viscosity). However, maintaining samples of matter in their liquid phases, in particular under supercooled conditions, is a great challenge when dealing with refractory metals. This is due mainly to their high melting temperatures (e.g., 3,695 K for W), their high vapor pressure, and the risk of melt contamination with a support or crucibles. Electrostatic levitation, laser heating in vacuum, and non-contact characterization techniques circumvented these difficulties and allowed the determination of the properties of several metals in their liquid state, above their melting temperature as well as in their supercooled phase. In this work, several thermophysical properties were successfully measured with an electrostatic levitation furnace under vacuum conditions. For the first time, density and viscosity data of yttrium were reported over large temperature intervals in the liquid phase. Over the 1,560 to 2,100 K temperature span, the density can be expressed as $\rho (T)=4.15\times 10^3-0.21\, (T - T_{\rm m})$ (kg·m^− 3) with T _m = 1,796 K, yielding a volume expansion coefficient of 5.1 × 10^− 5 K^− 1. In addition, the surface tension can be expressed as $\sigma \left( T \right)=8.04\times 10^2-0.05\,(T - T_{\rm m})$ (mN·m^− 1) and the viscosity as $\eta \left( T \right)=0.00287\,\exp \left[ {{1.1\times 10^5} \mathord{\left/ {\vphantom {{1.1\times 10^5} {\left( {\mbox{RT}} \right)}}} \right. \kern-\nulldelimiterspace} {\left( {\mbox{RT}} \right)}} \right]$ mPa·s over the 1,830 to 2,070 K interval. The results, in particular those for viscosity, suggest that performing similar experiments in microgravity could improve the accuracy of the measurements.