Cerium Ce

Discovery

In 1803 Jöns Jacob Berzelius and Wilhelm Hisinger in Sweden analysed a heavy mineral from the Bastnäs mine, now called cerite, and found a new oxide. In the same year the German chemist Martin Heinrich Klaproth independently discovered the same oxide.

Ceria was then thought to be the oxide of one element, but from 1839 onward Carl Gustaf Mosander separated lanthanum and didymium from it, revealing that it was a mixture of several rare earths.

The metal was first prepared in 1875 by William Hillebrand and Thomas Norton in the United States, who electrolysed molten cerium chloride. In 1903 the Austrian chemist Carl Auer von Welsbach patented ferrocerium, an alloy of cerium and iron that throws sparks when scratched and is still used as lighter flint.

Origin of the name

The element is named after Ceres, discovered in 1801 and now classed as a dwarf planet, which in turn was named after the Roman goddess of agriculture. The symbol is Ce.

Main uses

• Glass polishing: cerium oxide reacts chemically with glass surfaces as it grinds, giving a smooth finish to lenses, mirrors, phone screens and silicon wafers.
• Catalytic converters: cerium oxide can store and release oxygen, helping three-way catalysts work efficiently under changing conditions.
• Flints: ferrocerium produces the sparks in lighters and camping fire steels.
• Glass additives: it decolourises glass and blocks ultraviolet light.
• Phosphors: cerium-doped YAG phosphor converts blue light into yellow in white LEDs.
• Chemistry: ceric ammonium nitrate is a common oxidising agent in organic synthesis.

Isotopes

Natural cerium has four isotopes, cerium-136, -138, -140 and -142, with cerium-140 making up about 88%. Cerium-142 could in theory decay very slowly, but no decay has been observed. Radioactive cerium-144 (half-life about 285 days) and cerium-141 (about 33 days) are fission products measured in environmental monitoring after nuclear accidents.

In everyday life

Cerium is extracted with other rare earths from bastnäsite and monazite. It is about as abundant in the crust as copper, so despite the term "rare earth" it is not rare at all.

The spark from a lighter is a tiny shaving of cerium alloy that burns as it flies through the air. Cerium oxide was once part of the gas mantles that made gas lamps glow brightly. Cerium compounds have fairly low toxicity, but the metal powder ignites easily and must be handled with care.