Cesium as a Raw Material: Occurrence and Uses
Occurrence on the Moon
Cesium is a minor element on the Moon. It is sometimes found in
concentrations in excess of 0.1%, although usually between 100 and
1000 ppm. It is possible that, in some rock types, the same geochemical
processes that highly enrich phosphates could produce ores of
incompatible trace elements such as cesium. Part per million
concentrations, however, can be enriched by as much as two orders of
magnitude when other minerals of interest are removed for processing.
Elements like cesium, barium, phosphorous, and other incompatible
trace elements show strong inverse correlations with grain size, in
some soils (the Luna 24 Mare Crisium sample in particular) being
enriched by a factor of two or mare at grain sizes undur 10 microns.
Concentrations are also highest in polyminct breccias.
Cesium concentrations correlate strongly with samarium and other
incompatable trace elements. Barium, for example, consistently exists
in about three times the concentration of cesium, and most
incompatible trace elements occur in a nearly fixed ratio with highly
incompatible elements such as lanthanum.
Cesium can be used for plenty of nifty things around a moonbase.
Cesium makes a great fuel for electrostatic and electromagnetic
propulsion, which is likely to propel a large segment of cargo
traffic, especially on long-duration Mars or asteroid flights. Cesium
is used in a number of low-temperature alloys with sodium and
potassium, which have potential as heat-transfer fluids. The element's
highly electropositive nature has been exploited in the production of
photoelectric cells and vacuum tubes, as visible light has enough
energy to ionize cesium.
Several low-melting eutectics can be made using cesium. The ternary
system of 12% sodium, 47% potassium and 41% cesium has a freezing
point of -78 C, the lowest of any known metal system. Much like the
familiar NaK alloy of 22.3% sodium and 76.7% potassium (-12.5 C), the
key cesium alloys include 5.5% sodium and 94.5% cesium at -29 C, 22%
potassium and 78% cesium at -45 C, and 13% rubidium and 87% cesium
with a freezing point of -39 C.
Information about processing cesium oxide ore can be found in
section 2.2.3 of the Artemis Data Book.
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