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Cerium(IV) oxide

|Section2={{Chembox Properties | Formula = CeO2 | MolarMass = 172.115 g/mol | Appearance = white or pale yellow solid,slightly hygroscopic | Density = 7.215 g/cm3 | Solubility = insoluble | MeltingPtC = 2400 | BoilingPtC = 3500 | pKa = | pKb = | MagSus = +26.0·10−6 cm3/mol }} |Section3={{Chembox Structure | MolShape = | Coordination = | CrystalStruct = cubic ( fluorite)Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, | Dipole = }} |Section7={{Chembox Hazards | ExternalSDS = | MainHazards = | NFPA-H = 1 | NFPA-F = 0 | NFPA-R = 0 | NFPA-S = }} |Section8={{Chembox Related | OtherAnions = | OtherCations = | OtherCompounds = Cerium(III) oxide }} }} Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores. The distinctive property of this material is its reversible conversion to a nonstoichiometric oxide.Klaus Reinhardt and Herwig Winkler in "Cerium Mischmetal, Cerium Alloys, and Cerium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim. .

Production

Cerium occurs naturally as a mixture with other rare-earth elements in its principal ores bastnaesite and monazite. After extraction of the metal ions into aqueous base, Ce is separated from that mixture by addition of an oxidant followed by adjustment of the pH. This step exploits the low solubility of CeO2 and the fact that other rare-earth elements resist oxidation. Cerium(IV) oxide is formed by the calcination of cerium oxalate or cerium hydroxide. Cerium also forms cerium(III) oxide, , which is unstable and will oxidize to cerium(IV) oxide. Thermodynamic data

Structure and defect behavior

Cerium oxide adopts the fluorite structure, space group Fm3m, #225 containing 8-coordinate Ce4+ and 4-coordinate O2−. At high temperatures it releases oxygen to give a non-stoichiometric, anion deficient form that retains the fluorite lattice. This material has the formula CeO(2−x), where 0 < x < 0.28.Defects and Defect Processes in Nonmetallic Solids By William Hayes, A. M. Stoneham Courier Dover Publications, 2004. The value of x depends on both the temperature and the oxygen partial pressure. The equation \frac{x}{0.35 - x} = \left(\frac{106\,000\text{ Pa}}{P_{\mathrm{O}_2}}\right)^{0.217} \exp\left( \frac{-195.6\text{ kJ/mol}}{RT} \right) has been shown to predict the equilibrium non stoichiometry x over a wide range of oxygen partial pressures (103–10−4 Pa) and temperatures (1000–1900 °C). The non stoichiometric form has a blue to black color, and exhibits both ionic and electronic conduction with ionic being the most significant at temperatures > 500 °C.
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This article based upon the http://en.wikipedia.org/wiki/Cerium(IV)_oxide, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Cerium(IV)_oxide&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany