Vapor Pressures of the Rare-Earth Metals

Abstract

Vapor-pressure measurements on the rare-earth metals were made by the Knudsen effusion technique using a quartz-fiber microbalance over a pressure range of 10—1 to 10—4 mm of Hg. The material used was specially prepared in order to minimize impurity effects. Ytterbium is the most volatile of the rare-earth metals, while lanthanum and cerium are the least volatile. The data were fitted to a straight line by the least-squares method and the heats of vaporization or sublimation were calculated from the slope of the line. The heats of sublimation at 298°K were then calculated using the best available data for the enthalpies of the condensed and vapor states. For nine of the elements, measured heat content and entropy data for the condensed state as well as calculated free energy functions for the gaseous state were available, permitting a third law calculation of ΔH298°. The second- and third-law methods were generally in good agreement, but a comparison of the present work and previous investigations revealed several differences, amounting to as much as 15 kcal/mole in the case of gadolinium. A possible explanation for the variations in the room temperature heats of sublimation of the different rare-earth metals, based on the differences in the electronic structures of the gaseous atoms and the number of d electrons present in the condensed phase is presented.

Measurements of vapor pressure of Y and activity of Y in Y–O alloy by multi-Knudsen cell mass spectrometry

“…The ionization cross-sections of Y, Cu, and Ni [21] listed in Table 2 were also used for the calculation: Fig. 6 depicts the vapor pressures of Y obtained in this study, and compares them with those reported by Ackermann et al [10,12] and Habermann and Danne [11], and those calculated from the data of Barin and Knacke [9]. This figure indicates that the vapor pressures of Y measured by the four experimental runs showed almost the same value irrespective of the reference material and orifice size, providing evidence for the validity of our experimental method.…”

“…As for yttrium (Y), a few data on vaporization of elemental Y from 1336 to 2185 K [10][11][12] and activity of Y in the Y-O system at 2000 K were reported [12]. These were examined by using Knudsen effusion technique [11] and single Knudsen mass spectrometry [10,12].…”

“…These were examined by using Knudsen effusion technique [11] and single Knudsen mass spectrometry [10,12]. Although the Gibbs energy of formation of gaseous Y below the melting point (1795 K) is also shown in the data book edited by Barin and Knacke [9], the data is an estimation based on a research in the late 1950s, and thus, revalidation of the data is desirable.…”

Measurements of Vapor Pressures of Sc, La, and Ce by Multi-Knudsen Cell Mass Spectrometry

“…The determined vapor pressures of La and Ce could be expressed as functions of temperature by the least-squares method as follows: ln ðP La =PaÞ ¼ 27:2 AE 1:7 À ð54; 000 AE 2; 500Þ 1 T ½6 ln ðP Ce =PaÞ ¼ 27:2 AE 0:8 À ð53; 600 AE 1; 300Þ 1 T ½7 Figure 7 compares the vapor pressures of Sc, La, and Ce determined in this study with those reported by Ackermann and Rauth [8] and Habermann and Danne. [9] As shown in the figure, the previous measurements were limited to a higher pressure range, whereas lower pressures were measured in this study. Our results are basically in agreement with the extrapolation value of their data for each substance, indicating that low vapor pressures on the order of 10 À4 to 10 À3 Pa could be accurately measured.…”

“…The Gibbs energies of formation of gaseous elements were derived from the vapor pressures. Ackermann and Rauth [8] and Habermann and Danne [9] reported on the vapor pressure measurements of these metals at high temperature (more than 1520 K for Sc and more than 1874 K for La and Ce). The thermodynamic properties of these metals in a wide range of temperature are listed in a book edited by Barin and Knaeke.…”