Cerium

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Cerium is a chemical element with symbol Ce and atomic number 58. It is one of the most abundant rare earth metals, one of the easiest to separate, and one of the easiest to purchase. It is notable by its high propensity for sparking when struck, making it an ideal material for firestarters in the alloys ferrocerium and mischmetal.

Properties

Chemical

Cerium metal tarnishes slowly in air and burns readily at 150 °C to form cerium(IV) oxide:

Ce + O2 → CeO2

Cerium reacts with all halogens to form trihalides. Cerium will slowly react with water.

Cerium is notable among the lanthanides due to the existence of a cerium(III) (cerous) state and cerium(IV) (ceric) state. While cerous compounds are usually colorless or white, and form colorless complexes as well, cerric salts usually present a yellow, orange, or red coloration. Cerium(IV) sulfate is a strong oxidizing agent which can oxidize hydrogen peroxide to oxygen and water. Ceric ammonium sulfate is a commonly available from lab suppliers.

Physical

Cerium is a grey silvery metal, soft, and both malleable and ductile. Cerium has the third-longest liquid range of any element, after thorium and uranium: 2648 °C (795 °C to 3443 °C). It sparks readily when cut, ground, or struck.

Availability

Cerium can be purchased from GalliumSource. 30 g costs US$55. It can also be found in ferrocerium firestarters, though due to its high reactivity, the extraction process is complex and required reduction with a more reactive metal, such as calcium.

Preparation

Cerium can be prepared by reducing its oxide with lithium or calcium, but this is impractical compared to simply purchasing a sample of the metal.

Projects

  • Ferrocerium
  • Use as an oxidizer

Safety and storage

Safety

Cerium metal is not known to be toxic, but it is a relatively large fire hazard due to its tendency to spark. Even sanding or filing a sample by hand can cause a significant amount of sparking and ignite flammable objects. These sparks are quite large and may include small globs of burning metal. Cerium fires should never be put out with water as it may cause a hydrogen explosion. Cerium and mischmetal fires have a distinct smell that has both a metallic and smoky quality.

Storage

Cerium corrodes relatively easily and should be stored in an airtight container under mineral oil or argon.

Disposal

Cerium compounds present little toxicity and can be safely disposed of. However, due to the high price of lanthanides, it's better to try to recycle them.

References

Relevant Sciencemadness threads