The chemistry of cesium with oxygen is unique: no other metal offers such a colorful abundance of binary compounds, whereby the simple oxide Cs of all things₂O is particularly rare to see. The suboxides [3] Cs₇O (bronze colored), Cs₄O (metallic red violet), Cs₁₁O₃ (metallic blue-violet) and “Cs₃O “(black with a blue-green sheen) are hermaphrodites made of metals and ion crystals. The orange oxide Cs₂O is produced by using the suboxide Cs₃O thermal to Cs + Cs₂O decomposes and the excess cesium is distilled off. The colorless peroxide Cs₂O₂ can be obtained from the hyperoxide by controlled thermal decomposition or by reaction from the elements in liquid ammonia. If cesium metal is reacted with an excess of oxygen, a black, heterogeneous product mixture is initially obtained. Long-term annealing in an oxygen atmosphere finally gives the canary-yellow hyperoxide CsO₂.

Only the stable isotope occurs in nature ¹³³Cs before. However, since the Chernobyl nuclear disaster in 1986, large parts of the population have found the element cesium in the form of the radioactive fission product ¹³⁷Cs became known, which came to a large extent in the environment. The isotope has a half-life of 30,17 years and, since cesium is readily water-soluble, it reaches the food chain from the soil above all via fungi and plants and is still responsible for a large proportion of the background radioactivity. The rare metal is physiologically irrelevant. In the body it is similar to potassium and can replace it. This means that when it is incorporated, it is involved in essential physiological processes, but is also excreted very quickly.

The uses of the expensive metal are limited. In the vast majority of cases (reducing agent, cooling medium, ...) it can be replaced by cheaper alkali metals. Larger amounts of cesium chloride are used as drilling lubricants in oil production, otherwise small amounts are used as getter metal in vacuum tubes, as an ultracentrifuge medium or in camouflage ammunition. A few atoms are sufficient for the most famous application in the cesium atomic clock. ¹³⁷Cs has found a niche existence as a tracer element in geophysics and radiation therapy, and some thermionic batteries and food irradiation systems are also based on this isotope. The binding energy of the 6s electron in cesium is so low that infrared light of 910 nm is sufficient to produce the photoelectric effect. [5] The work functions are even lower for the metal-rich oxygen compounds, the suboxides of cesium. And these are unique to cesium. Therefore, the first night vision devices had a silver layer as a photo cathode, which is so thin that it shines through in blue. This was coated with cesium and cesium oxide, which resulted in the formation of cesium suboxides. Modern residual light amplifiers use semiconductor materials, cesium has been completely displaced from this area.

The high price of cesium is an obstacle for many chemists to use this element to a greater extent in syntheses. The price for cesium is currently around 40 euros per gram, roughly on the level of the gold price, with larger quantities showing significantly lower prices than small quantities. The actual price depends more on the ampoule size than on the purity. If you want, you can even do isotope-pure ¹³³Buy Cs for 1.000 euros per gram, which is particularly interesting when you consider that natural cesium is inherently isotope-pure. The easiest way, however, is to buy cesium cheaply from customs or the criminal police. For some time now, there has been constant smuggling of excellently prepared material from Eastern Europe and Russia. The material was produced in the 1970s and 1980s, probably in connection with Soviet projects on magnetohydrodynamic (MHD) generators. A plasma is shot through between two conductive electrodes. A magnetic field is applied perpendicular to the electrodes, which spatially separates the differently charged ions. The resulting voltage difference can therefore directly convert kinetic energy into electrical energy. The first MHD generator with 11,5 kW was built in the USA in 1959, an MHD pilot power plant with 25 MW output went into operation in the Soviet Union in 1971, a 1985 MW power plant was planned in Ryazan for 500, and other large power plants were to be used nationwide consequences. The first systems used the hot combustion gases from conventional power plants as operating plasma, but a plasma circuit could be used in so-called closed MHD generators. [6] Cesium is ideally suited as an operating medium: it can be easily ionized, already has a high vapor pressure at moderate temperatures and transports a lot of kinetic energy due to its high atomic weight. In addition, the refractive index in gaseous cesium is <1, which is advantageous for the plasma dynamics. The large-scale projects were abandoned in the course of the collapse of the Eastern Bloc, the cesium that was available became unemployed and finally began its way west. Either the cesium is confiscated during transport to the inner-European borders, or it is seized in "bunker finds". [7] It is not surprising that, after briefly studying the relevant substance data and safety data sheets, the responsible authorities are generally happy to find competent buyers for the often several kilograms of cesium. A number of German research groups are therefore grateful to organized smuggling for the constant and selfless support of their work.

Text with slight changes taken from:

 https://faszinatio nchemie.de/wissen-und-ffekten/news/caesium-das-unedle-gold/

Source:

Many thanks to Dr. High.

Priv. Lecturer Dr. Constantin Hoch

LMU Munich, Department of Chemistry

constantin.hoch [at] cup.lmu.de