The thermodynamics and vaporization of thorium, hafnium, and zirconium

• Published in: The Journal of chemical thermodynamics 1972-01, Vol.4 (4), p.521-532
• Main Authors: Ackermann, R.J., Rauh, E.G.
• Format: Article
• Language: English
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/0021-9614(72)90074-2

The vapor pressures of liquid thorium, solid and liquid hafnium, and liquid zirconium have been determined by a combination of mass-effusion and mass-spectrometric techniques. Single crystal tungsten cups were used as containers. The substantial solubility of tungsten in both liquid hafnium and zirconium markedly extends the liquid range as a result of eutectic behavior. The measured partial pressures corrected for the respective solubilities via Raoult's law therefore yield the vapor pressures of the pure metals over ranges of temperature in which the liquids are in part supercooled. The results derived for the pure metals are given by the linear equations in terms of the enthalpies and entropies of vaporization: −(RT/ ca th mol −1) In {p°(Th, l)/atm} = (136 200±1000)−(27.57±0.45)T/K, (2020 to 2500 K −(RT/ cal th mol −1) In {p°(Hƒ, l)/atm} = (139 300±1100)−(28.85±0.39)T/K, (2020 to 2500 K) (2020 to 2500 K −(RT/ cal th mol −1) In {p°(Hƒ, s)/atm} = (145 500±700)−(31.37±0.33)T/K, (1940 to 2464 K −(RT/ cal th mol −1) In {p°(Zr, l)/atm} = (137 000±1100)−(29.93±0.37)T/K, (2134 to 2550 K The measured vapor pressures and enthalpies are consistent with the thermodynamic properties of the vapor and condensed phases and yield the following average values for the enthalpies of sublimation at 298.15 K: ΔH o(Th) = (142.8 ± 1.1) kcal th mol -1, ΔH o(Hf) = (148.4 ± 1.2) kcal th mol −1, and ΔH o(Zr) = (143.4 ± 1.2) kcal th mol −1.