Physical Properties of Liquid Terbium Measured by Levitation Techniques

To understand the nature and behavior of rare earth metals in their liquid phases, accurate values of their physical properties are essential. However, to measure their physical properties, the samples should be maintained in liquid phases for prolonged time, and this raises a formidable challenge. This is mainly explained by their high melting temperatures (e.g., 1629 K for Tb), high vapor pressure, and the risk of melt contamination with a crucible or support. An electrostatic levitation furnace alleviated these difficulties and allowed the determination of density, surface tension, and viscosity of several metals above their melting temperature. Here, first, the levitation furnace facility and the noncontact diagnostic procedures were briefly discussed, followed by the explanation of their thermophysical property measurements over wide temperature ranges. The density was obtained using an ultraviolet-based imaging technique that allowed excellent illumination, even at elevated temperatures. Over the 1615 to 1880 K temperature span, the density measurements could be expressed as p(T) = 7.84 × 103 - 0.47 (T - Tm) (kg · m−3) with Tm = 1629 K, yielding a volume expansion coefficient α(T) = 6.0 x 10−5(K−1). In addition, the surface tension and the viscosity could be determined by inducing a drop oscillation to a molten sample. Using this technique, the surface tension data could be expressed as σ(T) = 8.93 x 102 - 0.10 (T - Tm)(mN · m−1) and those for viscosity as η(T) = 0.583 exp [4.1 x 104/(RT)] (MPa · s) over the 1690 to 1980 K temperature range.