Cerium is the most abundant of the rare earth elements. It is a reactive, grey metal and a member of the Lanthanoid Group of the Periodic Table; it is the 25th most abundant element within the Earth's crust. When exposed to air, it tarnishes, will burn if scratched with a knife, it reacts rapidly with water and dissolves in acids. Due to its reactivity, it is stored in light mineral oil to protect it against oxidation.
Cerium was discovered in 1804 by Jons Jacob Berzelius and Wilhelm Hisinger in Sweden. They found it as an impurity in the mineral bastnasite. Simultaneously yet independently, cerium was also discovered by Martin Klaproth. The name cerium was derived from the asteroid 'Ceres', which had been discovered a few years previously and named after the Roman goddess of agriculture. Several attempts at obtaining a pure sample were made, but the usual techniques all failed. It was not until 1875 that the American chemists, William Hillebrand and Thomas Norton, finally obtained a pure sample by passing an electric current through molten cerium chloride.
Cerium is extracted from the ores Bastnäsite and Monazite, and its annual world production is in the region of 24,000 mt. The main mining areas are the same as other rare earths: USA, Brazil, India, Sri Lanka, Australia and China. The characteristics and uses of cerium are also very similar to all lanthanides, however cerium is one of the most reactive. Cerium is sold as metal, various oxides and as other cerium compounds.
Cerium oxide is probably the most important outlet for cerium, and has many applications centred on glass and ceramics production. For example, it is used as an addition to glass melts and ceramic glasses, catalysts, refractory ceramics and glass polishing. Cerium metal in a highly pure form is used in casting alloys, for example, as an additive to aluminium, magnesium, iron, battery and vacuum alloys. It is also used to add resistance to stainless steel, tool steel and lamps, and can refine the grain in some alloys. Cerium mischmetal, which is an alloy of other rare earths, primarily Ce, La, Nd and Pr, is very reactive and therefore forms compounds with a large number of elements. This general quality of cerium makes it particularly useful in catalytic converters for the reduction of carbon monoxide (CO) emissions, as it stores and releases oxygen atoms converting CO to CO2.
- Emsley, John. Nature's Building Blocks, An A-Z Guide to the Elements, New Edition, Oxford University Press, 2011
- Gray, Theodore. The Elements, A Visual Exploration of Every Known Atom in the Universe, Black Dog & Leventhal Publishers, Inc, NY, 2009
- Stwertka, Albert. A Guide to the Elements, 3rd Edition, Oxford University Press, 2012