Cerium is classified as a ‘light’ rare earth, heavier examples being Dysprosium, Terbium and Neodymium. Along with most of the lanthanides, it is non-toxic.
One of the commonly traded forms of Cerium is as Mischmetal. In this form it is what may be called a ‘rare earth alloy’, with a non-fixed mixture of REE content of which Ce is the majority with greater than 50%.
Today, in the market place, now that certain REEs have risen in price, elements such as Neodymium (Nd) which used to constitute up to 20% of mischmetal by mass will not be present at all, replaced by higher Lanthanum content at 30% min. (Praesodymium, which would have been present in the past, is also reduced in today’s product.)
The key use for Cerium mischmetal is for scavenging Oxygen and Sulphur in steel while in Aluminium and Magnesium products it adds strength. Cerium oxide powder is widely used for polishing glass.
It was discovered in 1803 by JJ Berzelius and W Hisinger in Vestmanland, Sweden and it was first isolated in 1875 by WF Hillebrand and TH Norton in Washington, USA.
Cerium is a member of the group of elements known as Rare Earths – though not as rare commercially as their name would suggest. However they were so called because of the difficulty of extracting them.
It is probably the most widely used of the rare metals. The metal is grey and very soft, being readily cut by a knife, oxidizes in air, but does not burn spontaneously. It reacts with water, releasing hydrogen.
It is mildly toxic by ingestion, but insoluble salts such as the oxalate are non toxic and doses of up to 500 mg were once prescribed to prevent travel sickness and morning sickness.
Cerium is used in glass, flints, ceramics and alloys.
Relative atomic mass