Cerium
Cerium is a rare earth element denoted by the atomic symbol Ce. The most abundant of this type of element, cerium has an atomic number of 58, and an atomic weight of 140.12. It is an iron-gray metal with a melting point of 1,463°F (795°C) and a boiling point of 5,895°F (3,257°C). Cerium is a highly reactive element that will decompose in cold water slowly but hot water rapidly. In fact, it may catch fire if cut with a knife or ignite spontaneously if finely divided.
The first allusion to cerium appears in 1751, when Axel Crönstedt (1722-1765) described a new mineral found in the Bastnäs Mineat Riddarhyttan, Sweden. At first, chemists thought the mineral might be a form of tungsten since it was so heavy.
A correct description of the mineral appeared from two sources at almost the same time. One source was the great discoverer of elements, Martin Heinrich Klaproth. The other source was the Swedish chemist Jöns Berzelius and his partner, Wilhelm Hisinger (1766-1852). Hisinger was a wealthy nobleman who owned the Bastnäs Mine. Klaproth, Berzelius, and Hisinger all realized that the "heavy stone of Bastnäs" must contain a new element. The name that was eventually chosen for this element, cerium, was chosen in honor of the recently discovered asteroid, Ceres. The element was not actually extracted from an ore until 1875 when T. H. Norton (1851-1941) and W. F. Hillebrand electrolyzed molten cerium(III) chloride, CeCl 3.
Cerium is found naturally in many minerals such as allanite, monazite and bastnasite. High purity metallic cerium can be produced by a variety of metallothermic reduction techniques. For example, it can be obtained by reducing cerous fluoride to its component elements with calcium. It can also be derived by electrolysis of molten cerous chloride.
Perhaps the best known alloy of cerium is misch metal. Misch metal is prepared by fusing the chlorides of cerium, lanthanum, neodymium, and praseodymium. The product is a pyrophoricalloy, a substance that will ignite at or below room temperatures. Misch metal is used in pocket cigarette lighters because it sparks when friction of a metal wheel is applied. Another alloy of cerium is used to make heat-resistant parts in jet engines. The element is also employed as a catalyst in the manufacture of ammonia.
The greatest quantity of cerium, in the form of cerium(IV) oxide (CeO 2), is used to decolorize glass. The same compound has also found application in enamel and ceramic coatings, electronic components, and high temperature resistant materials. It is also used as a catalyst in self cleaning ovens. Certain compounds of cerium are now being studied as possible anti-knock agents in gasoline.
This is the complete article, containing 435 words
(approx. 1 page at 300 words per page).
