Cerium - Ce
Cerium is a malleable, soft, ductile, iron-grey metal, slightly harder than lead. It is very reactive: it tarnishes readily in the air, it oxidizes slowly in cold water and rapidly in hot water. It dissolves in acids. It can burn when heated or scratched with a knife.
The metal is used as a core for the carbon electrodes of arc lamps, for incandescent mantles for gas lighting. Cerium is used in aluminium and iron alloys, in stainless steel as a precipitation hardening agent, to make permanent magnets. Cerium oxide is part of the catalyst of catalytic converters used to clean up exhaust vehicles, it also catalyzes the reduction of nitrogen oxides (NOx) to nitrogen gas. All new cars are now equipped with catalytic conveter which consist in a ceramic or metal substrate, a coating of aluminium and cerium oxides and a layer of finely dispersed metal such as platinum or rhodium, which is the active surface.
Cerium in the environment
Cerium is the most abundant of the rare earth elements. It makes up about 0.0046 % of the Earth's crust by weight. Cerium comes mainly from the major lanthanide ores but some is obtained from perovskite, a titanium mineral and allanite, both of which can have enough cerium to make them viable sources. Production amounts to 23.000 tonnes a year, but this amount is likely to increase since more and more cerium is used nowadays.
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