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.

Potential Applications

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.