Cerium

Cerium

Cerium is a chemical element with symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet Ceres (itself named for the Roman goddess of agriculture). Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is found in a number of minerals, the most important being monazite and bastnasite. Commercial applications of cerium are numerous. They include catalysts, additives to fuel to reduce emissions and to glass and enamels to change their color. Cerium oxide is an important component of glass polishing powders and phosphors used in screens and fluorescent lamps. It is also used in the "flint" (actually ferrocerium) of lighters.

Occurrence

Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is found in a number of minerals including allanite (also known as orthite)—(Ca,Ce,La,Y)2(Al,Fe)3(SiO4)3(OH), monazite (Ce,La,Th,Nd,Y)PO4, bastnasite (Ce,La,Y)CO3F, hydroxylbastnasite (Ce,La,Nd)CO3(OH,F), rhabdophane (Ce,La,Nd)PO4-H2O, zircon (ZrSiO4), and synchysite Ca(Ce,La,Nd,Y)(CO3)2F. Monazite and bastnasite are presently the two most important sources of cerium. Large deposits of monazite, allanite, and bastnasite will supply cerium, thorium, and other rare-earth metals for many years to come.

Cerium content in the soil varies between 2 and 150 parts per million (ppm), with an average of 50 ppm. Seawater contains 1.5 parts per trillion of cerium. There is almost no cerium in the atmosphere.

Symbol		Ce
Atomic Number		58
Atomic Weight		140.115
Oxidation States		+3, +4
Electronegativity, Pauling		1.12
State at RT		Solid, Metal
Melting Point, K		1072
Boiling Point, K		3699

Appearance and Characteristics

Harmful effects:

Cerium is considered to be moderately toxic.

Characteristics:

• Cerium is a reactive, soft, gray, lustrous metal that is malleable and ductile.
• When present in compounds, cerium exists in both the trivalent state (Ce3+, cerous, usually orange-red) and the tetravalent state (Ce4+, ceric , usually colorless).
• The metal tarnishes in moist air and reacts with water to form cerium hydroxide plus hydrogen gas.
• Small particles of the metal may ignite if a knife scratches the pure metal surface.
• It is attacked by alkali solutions and all acids.
• Cerium has a variable electronic structure: the energy of the inner 4f level is nearly the same as that of the 6s level, allowing variable occupancy of these two levels.

Uses of Cerium

• An alloy of cerium and lanthanum, with small amounts of neodymium and praseodymium (misch metal) combined with iron oxide and magnesium oxide is used as the flint in cigarette and gas lighters.
• Cerium is used in carbon-arc lighting, especially in the motion picture industry. It is also used in phosphors for color television screens and fluorescent lighting.
• Cerium oxide is used as a catalytic converter to reduce carbon monoxide emissions in the exhaust fumes from automobiles. Cerium oxide, as a nanopowder, is added to diesel fuel to reduce sooty fumes and improve engine performance. It is used in the walls of self-cleaning ovens and is also used to polish glass surfaces.
• Flammacerium (cerium nitrate-silver sulphadiazine) is a cream to treat and prevent infections in extensive burn wounds. The cerium nitrate component reduces the occurrence of immunosuppression.