Other Interesting Cesium Compounds

Cesium Auride
Formula: CsAu
MW: 329.87
Melting point: Approximately 480 C
Toxicity: Unknown, but probably not good to eat.
Properties: Reacts violently with water, producing Cesium hydroxide and metallic gold; also with oxygen.

Uses: Curiousity, production of Auriferous Cesium soaps, gold-plated, Cesium-reduced rodents, self-destructing military electronic components.

Comments: Cesium auride (CsAu), is an ionic intermetallic compound with the composition Cs+ Au-. Evidence for the ionic nature of the compound appears in the behavior of the binary alloy, which exhibits a sharp drop in conductivity of several orders of magnitude at the stoichiometric composition. The resultant solid has semiconductor properties, thus straddling the gap between typical ionic solids, which are insulators, and typical intermetallic compounds, which tend to be good conductors. This anomolous behavior is attributable to the extreme electropositivity of Cesium.

Cesium uranate
Formula: Cesium uranate is actually a system of compounds of Cesium, uranium, and Oxygen. A number of these compounds belong to the pseudo-binary system Cs2O - UO3, where Cesium is in the +1 oxidation state, and uranium in the +6. Identified members of this group include Cs2-U-O4, Cs2-U2-O7, Cs2-U4-O13, Cs2-U5-O16, Cs2-U7-O22, Cs2-U15-O46, and Cs4-U5-O17. A number of compounds with uranium in a lower valence have also been identified. These include Cs2-U4-O12, Cs2-U6-O18, and Cs2-U9-O27. All these involve mixed oxides of uranium where one of the atoms is in the +4 oxidation state. There is also a stoichiometric mixed oxide Cs2-U-O3.56. This is the compound that exists in equilbrium with liquid Cesium and UO2.

Uses: Source of Cs137 during fuel rod reprocessing. Glowing blue light source. Body paint

Comments: The Cesium urananate compounds are important in modeling the aging of fuel rods in nuclear reactors. Cesium 137 is a major fission product, and accumulates in the fuel rods during operation. The Cesium produced undergoes a reaction with the Uranium dioxide fuel producing various Cesium uranates. Because these compounds are, in general, much less dense than UO2, The fuel expands, and can eventually cause cracking and rupture of the cladding, with consequent loss of highly radioactive fission products into the primary coolant loop.

Cesium Graphite
Formula: Cesium Graphite is one of a series of interlamellar alkali metal compounds, where the metal atoms position themselves between the planes of carbon atoms in the graphite crystal structure. The placement is not arbitrary, however, and the coumpounds form a stoichiometric series C(n)Cs. Compounds with n = 8, 16, 24, 36, 48 and 60 have been produced.

Heat of formation: (C8CS) -83.2 kJ/mol.

Properties: Highly reactive; ignites spontaneously on contact with air; explodes in water. Electrical conductivity is increased above that of pure graphite due to the mixing of the valence electron into the graphite conduction band. Cesium essentially acts as an N type semiconductor dopant.

Uses: The relatively high heat of formation has allowed the Cesium graphite compounds to be used as a method of removing trace amounts of radioactive Cesium from the hot loop of sodium-cooled reactors. This is accomplished simply, by immersing graphite in the liquid sodium of the primary circuit.

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