At A Glance: Ce
|Atomic Radius:||235 pm (Van der Waals)|
|Melting Point:||798 °C|
|Boiling Point:||3,443 °C|
|Sources: Cerium is the most abundant rare earth element. Monazite and bastnasite ores are presently the more important sources of cerium.Uses:Pollution control technologies such as catalytic converters and fuel additives, glass polishing and UV shielding, water filtration, fluorescent lighting.Content provided by Los Alamos National Laboratory. Used with permission.|
Cerium, the second element in the Lanthanide series, is the most abundantly prevalent Rare Earth element and is chemically characterized by having two stable, readily accessible valence states (III and IV) which make it perfect for many different uses.
Cerium is an environmentally critical component in the manufacture of all kinds of environmental protection and pollution-control systems, from automobiles to oil refineries. One of the crucial chemical components in catalytic converters is Cerium oxide (or other Cerium compounds). Other Cerium-based pollution control catalysts help to significantly reduce the sulfur oxide emissions from oil refineries.
A new application of cerium is in our product called SorbX, which is a water purification technology based on the properties of cerium oxide. Since SORBX removes a wide variety of undesirable impurities from water, e.g. industrial chemicals, oxyanions, a wide variety of organic molecules, pharmaceuticals, viruses, and bacteria, we expect this technology will find wide application.
Cerium also is used as a diesel fuel additive for micro-filtration of pollutants and will also promote more complete fuel combustion thus reducing un-combusted smoky particulate and provide for a more energy efficient engine. Cerium is also used as a recycled oxidant for performing low temperature, energy efficient waste treatment on many pollutants.
Cerium oxide slurried in water is the active ingredient in polishing compounds for glass, television faceplates, mirrors, optical glass, silicon microprocessors and disk drives. Cerium is also used to de-colorize glass for applications such as containers or tableware. The glass is initially colored by the metal contaminates present in the raw materials used to produce glass. Cerium oxide is strong enough to oxidize these metals to different states thereby eliminating the unwanted color. TV glass contains cerium to shield us from harmful UV radiation emitted within the tube. The fact that the TV screen remains clear after prolonged use is also due to Cerium. Photographic filters can contain Cerium for the shielding properties.
Computers contain cerium polished disk drives and silicon micro-processors as well as Cerium treated glass in the monitor screens. Certain Cerium compounds are used in thin surface coatings applied to optical components to improve performance. The compounds have a refractive index suitable for building up the multiple layers deposited on lenses, sensors, mirrors, etc.
Cerium, typically doped with Terbium, is an essential component in several of the new generation of phosphors used in tricolor lamps that have made possible more efficient and more compact fluorescent lighting.
The addition of Cerium oxide to zirconia produces a high temperature engineering ceramic having exceptional toughness and good strength. The US Space Shuttle program is dependent on engineering ceramics containing Cerium which is also incorporated into other shuttle components. The oxide has a high refractive index and is an opacifying agent in enamel compositions used as protective coatings on metals.
Cerium improves the physical properties of high-strength, low-alloy steels due to its affinity to scavenge oxygen and sulfur. Cerium is added primarily to provide sulfide shape control.
Chromium plating quality is improved with the addition of cerium fluoride to the electroplating bath. The solubility of the cerous fluoride is virtually independent of the temperature of the plating solution thereby stabilizing the active chromium intermediate necessary for quality plating. Cerium is also used in the reduction and co-precipitation removal of waste chromium generated during the plating process.
Cerium was named for the asteroid Ceres, which was discovered in 1801. The element was discovered two years later in 1803 by Klaproth and by Berzelius and Hisinger. In 1875 Hillebrand and Norton prepared the metal.
Cerium is the most abundant so-called rare-earth metals. It is found in a number of minerals including allanite (also known as orthite), monazite, bastnasite, cerite, and samarskite. Monazite and bastnasite are presently the more important sources of cerium.
Large deposits of monazite (found on the beaches of Travancore, India and in river sands in Brazil), allanite (in the western United States), and bastnasite (in Southern California) will supply cerium, thorium, and the other rare-earth metals for many years to come.
Metallic cerium is prepared by metallothermic reduction techniques, such as reducing cerous fluoride with calcium, or using electrolysis of molten cerous chloride or others processes. The metallothermic technique produces high-purity cerium.
Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer (valence) electrons, and only small amounts of energy are required to change the relative occupancy of these electronic levels. This gives rise to dual valency states.
For example, a volume change of about 10 percent occurs when cerium is subjected to high pressures or low temperatures. Cesium’s valence appears to change from about 3 to 4 when it is cooled or compressed. The low temperature behavior of cerium is complex.
Cerium is an iron-gray lustrous metal. It is malleable, and oxidizes very readily at room temperature, especially in moist air. Except for europium, cerium is the most reactive of the rare-earth metals. It decomposes slowly in cold water and rapidly in hot water.
Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife.
Ceric slats are orange red or yellowish; cerous salts are usually white.
Source: Los Alamos National Laboratory; Molycorp