The Hg-Pa (Mercury-Protactinium) System
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Section II: Phase Diagram Evaluations
The Hg-Pa (Mercury-Protactinium) System C. Gumin´ski
The Hg-Pa phase diagram is not available, and no experimental material on this system is known. Hg melts at −38.8290 °C, and Pa melts at 1572 °C [Massalski2]. The allotropic phase transformation ␣Pa ↔ Pa occurs at 1170 °C. By similarity to the neighboring elements (Th and U) in the periodic table, Pa should react with Hg to form stable intermetallics that probably decompose at temperatures higher than the boiling point of Hg (356.623 °C) at normal pressure. The expected stoichiometries of the Hg-Pa compounds are 45 to 11, 3 to 1, 2 to 1, and 1 to 1. The solubility
of Pa in liquid Hg was predicted by [1989Gum] and should be on the order of 10−3 at.% Pa at 25 °C as the mean value of the solubilities measured for Th and U. The crystal structures of pure components of the system are listed in Table 1.
Reference 1989Gum: C. Gumin´ski, Selected Properties of Simple Amalgams, J. Mater. Sci., Vol 24, 1989, p 2661-2676 (Review)
Table 1
Hg-Pa crystal structure and lattice parameter data
Phase
Pearson symbol
Space group
Strukturbericht designation
Prototype
a
c
Temperature, °C
Reference
hR1 tI2 cI2
R3¯m I4/mmm Im3¯m
A10 Aa A2
␣Hg ␣Pa W
0.3005 0.3921 0.381
␣ ⳱ 70.53° 0.3235 …
−48 25 >1170
[Massalski2] [Massalski2] [Massalski2]
Hg ␣Pa Pa
Lattice parameters, nm
Hg-Pa evaluation contributed by C. Gumin´ski, Department of Chemistry, University of Warsaw, Pasteura 1, 02093 Warszawa Poland. This work was supported by ASM International. Literature was searched through 2002. Dr. Gumin´ski is the Alloy Phase Diagram Program Category Editor for binary mercury alloys.
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Journal of Phase Equilibria and Diffusion Vol. 26 No. 1 2005
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