P h a s e D i a g r a m E v a l u a t i o n s : S e c t i o n 11

The At-Hg (Astatine-Mercury) System C. Guminski University o f Warsaw Due to its very unstable radioisotopes, At is regarded as the rarest, naturally-occurring terrestrial element. Very little is known about its bulk physical properties, and its chemical characteristics have only been outlined [89Gre]. Because of the scarcity of information, no At-Hg phase diagram is available. The melting points of At and Hg are -302 and -38.8290 ~ respectively [Melt]. In accord with phase diagram changes in the Hg-halogen series, phase relationships in At-Hg should be similar to those of the Hg-I system. It is likely that At has more metallic character

than I, so the immiscibility range on the Hg-rich side should be narrower with lower critical temperatures. Further, the compounds, At2Hg2 and At2Hg, should be thermodynamically less stable than corresponding iodides.

Cited Reference 89Gre: N.N. Gieenwood and A. Eamshaw, "Chemistry of Halogens," Chemistry of the Elements, Pergamon, Oxford, 1039-1041 (1989). (Review)

At-Hgevaluationcontributedby C. Guminski, Departmentof Chemistry,Universityof Warsaw,Pasteura 1,02093 Warsaw,Poland. This workwas supportedby ASM International.Literaturesearchedthrough 1990.Dr. Guminskiis the AlloyPhaseDiagramProgramCategoryEditorfor binary mercuryalloys.

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