Bunsen and Kirchhoff discovered cesium/caesium spectroscopically in 1860 in mineral water from Durkheim. It is obtain from the minerals Lepidolite and Pollucite (2Cs2O.2Al2O3.9SiO2.H2O), a hydrated silicate of aluminium and caesium. It can be isolated by electrolysis of the fused cyanide and by a number of other methods. Very pure gas free caesium can be prepared by thermal decomposition of cesium/caesium azide.
Caesium (Cs) metal resembles rubidium and potassium. It is silvery white in appearance and is very soft and ductile.
It is the most electropositive and most alkaline element. It oxidises easily in the air and ignites at ordinary temperatures. Caesium reacts explosively with cold, and reacts with ice at temperatures above (–116°C). Due to its high propensity to oxidise it should be stored in vacuum, inert gas, or anhydrous liquid hydrocarbons protected from oxygen and air. It is one of three metals that are liquid at room temperature. Cesium/caesium metal has an excellent affinity for oxygen.
Caesium has 32 isotopes, more than any element with masses ranging from 114 to 145 g/mol.
Caesium metal is used in the following applications:
- As a “getter” in low-voltage electron tubes, to scavenge trace amounts of oxygen.
- Caesium 137, recovered from waste of atomic plants is used as a gamma-ray emitter; it has a half-life of 33 years.
- It finds use also in teletherapy.
- Caesium is used in atomic clocks, where a loss of 5s over 300 years is achievable.
- Caesium may also be used as a catalyst for hydrogenation of certain organic compounds.
- It has also been considered for in ion propulsion systems, for outer space uses.
- In photoelectric cells as a photosensitive deposit on the cathode. The caesium metal in this application is also used in the infrared signalling lamp (known as a photophone) in this application it gives infrared waves without visible light.
Caesium compounds have been implemented on filaments of radio tubes to increase sensitivity.