CHEMISTRY : Metal Cation Identification

Information on CERIUM

1. General Information


2. Occurence Uses and Properties


3. History of the Metal


4. Compounds
5. Back to Main Metal List

In 1794, Johan Gadolin, a Finnish chemist, while investigating a rare Swedish mineral, discovered a new earth in impure form, which he believed to be a new element and to which he gave the name ytterbia, from Ytterby, the village where the ore was found. The name, however, was soon shortened to yttria. In 1803, from the same mineral, later named gadolinite in Gadolin's honour, another new earth was reported in the literature independently by several chemists. The new earth became known as ceria, from the asteroid Ceres, which had just been discovered (1801). Since yttria and ceria had been discovered in a rare mineral, and they closely resembled other known earths, they were referred to as the rare earths. Not until 1808 did Sir Humphry Davy demonstrate that the earths as a class were not elements themselves but were compounds of oxygen and metallic elements. Later, a number of chemists verified the existence of ceria and yttria in gadolinite and found that these oxides were also present in a wide variety of other rare minerals. The elements of which yttria and ceria were the oxides were then given the names yttrium and cerium, respectively.

Cerium and its compounds have a number of practical appliCATions. The dioxide is employed in the optics industry for fine polishing of glass (replacing rouge); it is also used as an opacifier in porcelain coatings and as a decolorizer in glass manufacturing. Cerium nitrate has been used in the manufacture of incandescent-gas mantles; other salts are employed in the ceramic, photographic, and textile industries. The metal serves as an ingredient in the carbon-impregnated arc lamps that have been used for illumination in the motion-picture, television, and related industries. Together with the other rare-earth metals, cerium is a constituent of numerous ferrous and nonferrous alloys; a superior high-temperature alloy for jet engines contains about 3 percent cerium with magnesium. Misch metal (50 percent cerium) is used for cigarette-lighter flints, in tracer bullets, and in electron-tube manufacture as a getter, which removes traces of oxygen.

Along with praseodymium and terbium, cerium is different from the other trivalent rare earths in that it forms compounds in which it is tetravalent; it is the only rare earth that exhibits a +4 oxidation state in solution. Tetravalent (ceric) salts, which are powerful but stable oxidizing agents, are used in analytical chemistry to determine oxidizable substances such as iron(II). Most cerium(IV) salts are orange to yellow in colour, as are solutions containing the Ce4+ ion. Cerium(III) behaves as a typical rare earth; its compounds are usually white.

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