|
|||||||
|
|
|
|||||
|
|
|||||||
Ce
Ce at. wt. 140.12
at. no. 58
m.p. 798±3°C
b.p. 3257°C
sp. gr. 6.771 (25°C)
valence 3 or 4.
| SHELL | K | L | M | N | O | P | Q |
| SUB SHELL | He | Neon | Argon | Krypton | Xenon | Radon | Eka-radon |
| 1s | 2s 2p | 3s 3p | 3d 4s 4p | 4d 5s 5p | 4f 5d 6s 6p | 5f 6d 7s 7p | |
| Cerium | 1s22s22p63s23p63d104s24p64d105s25p6 | 4f15d16s2 | |||||
| Symbol | 3H4 | ||||||
Cerium was discovered in 1803 by Klaproth and by Berzelius and Hisinger; metal prepared by Hillebrand and Norton in 1875. Cerium is the most abundant of the metals of the so-called rare earths; it is found in a number of minerals including allanite (also known as orthite), monazite, bastirasite, cerite, and samarskite. Monazite and basnasite are presently the two most important sources of cerium. Large deposits of monazite found on the beaches of Travancore, India, in river sands in Brazil, and deposits of 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 by reducing cerous fluoride with calcium, or by electrolysis of molten cerous chloride or other cerous halides. The metallothermic technique is used to produce 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 thit bf the outer or 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% occurs when cerium is subjected to high pressures or low temperatures. It appears that the valence changes from about 3 to 4 when it is cooled or compressed. The low tem- perature behavior of cerium is complex. Four allotropic modifications are thought to exist: cerium at room tempera- ture and at atmospheric pressure is known as y cerium. Upon cooling to - 23°C, y cerium changes to fi cerium. The remaining y cerium starts to change to a cerium when cooled to - I 580C, and the transformation is complete at 196°C. a cerium has a density of 8.24 d cerium exists above 726°C. At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point. 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 slowly decomposes 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 salts are orange-red or yellowish; cerous salts are usually white. Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters, etc. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incan- descent gas mantles and it is emerging as a hydrocarbon catalyst in "self-cleaning" ovens. In this application it can be incbrporated into oven walls to prevent the collection of cooking residues. As ceric sulfate it finds extensive use as a volumetric oxidizing agent in quantitative analysis. Cerium compounds are used in the manufacture of glass, both as a component and as a decolorizer. The oxide is finding increased use as a glass polishing agent instead of rouge, for it is much faster than rouge in polishing glass surfaces. Cerium, with other rare earths, is used in carbon-arc lighting, especially in the motion picture industry. It is also finding use as an important catalyst in petroleum refining and in metallurgical and nuclear applications. Commercial cerium metal costs about $75/lb. In small lots, 99.9% cerium costs about 65¢/gm.
© 1999 F. Davies
Delphi O.E.M. Co.
All rights reserved
