Cerium(IV) oxide
1723722
220430237
2008-06-19T20:41:38Z
Harold f
1040921
Tightened specificity: powder, not bulk
{{Chembox new
| Name = Cerium(IV) oxide
| ImageFile = Cerium(IV) oxide.jpg
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| ImageName = Cerium(IV) oxide
| ImageFile1 = Ceria-3D-ionic.png
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| IUPACName = Cerium(IV) oxide
| OtherNames = ceric oxide, ceria,<br />cerium oxide, cerium dioxide
| Section1 = {{Chembox Identifiers
| CASNo = 1306-38-3
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| Section2 = {{Chembox Properties
| Formula = CeO<sub>2</sub>
| MolarMass = 172.115 g/mol
| Appearance = white or pale yellow solid,<br />slightly [[hygroscopic]]
| Density = 7.65 g/cm<sup>3</sup>, solid<br />7.215 g/cm<sup>3</sup>, fluorite phase
| Solubility = not soluble — ? g/100 ml (? °C)
| MeltingPt = Approximately 2400 K (2100 °C)
| BoilingPt = 3500 °C (? K)
| pKa =
| pKb =
| Viscosity =
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| Section3 = {{Chembox Structure
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| Section7 = {{Chembox Hazards
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| Section8 = {{Chembox Related
| OtherAnions =
| OtherCations =
| OtherCpds = Ce<sub>2</sub>O<sub>3</sub>
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'''Cerium(IV) oxide''', '''ceric oxide''', '''ceria''', or sometimes simply '''cerium oxide''' or '''cerium dioxide''', is a pale yellow-white powder, CeO<sub>2</sub>. It is used in [[ceramic]]s, to [[Polishing|polish]] glass, and to sensitize [[photosensitive glass]]. It is also used in [[lapidary]] as "[[Jeweller%27s_rouge#Polishing|jeweller's rouge]]"; it is also known as "optician's rouge".<ref>[http://home.thezone.net/~dbourgeo/feb/feb-2001-talk.html Grinding and Testing a Telescope Mirror<!-- Bot generated title -->]</ref> Ceria is used in the walls of [[self-cleaning ovens]] as a hydrocarbon catalyst during the high-temperature cleaning process. It has high absorption of [[ultraviolet]] radiation while it is transparent for visible light, so it is a prospective replacement of [[zinc oxide]] and [[titanium dioxide]] in [[sunscreen]]s, as it has lower [[photocatalysis|photocatalytic]] activity. However its thermal catalytic properties have to be decreased by coating the particles with [[amorphous silica]] or [[boron nitride]].
Powdered ceria is slightly [[hygroscopic]] and will also absorb a small amount of [[carbon dioxide]] from the [[Earth's atmosphere|atmosphere]].
Note that [[cerium]] also forms [[cerium(III) oxide]], Ce<sub>2</sub>O<sub>3</sub>.
==As a fuel cell electrolyte==
In the doped form, ceria has seen interest as a material for [[Solid-oxide fuel cells|solid oxide fuel cell]]s or SOFCs because of its relatively high oxygen [[ion conductivity]] (i.e. oxygen atoms readily move through it) at intermediate temperatures (500-800 °C). Undoped and doped ceria also exhibit high electronic conductivity at low partial pressures of oxygen due to the formation of small [[polaron]]s. However, doped ceria has an extended electrolytic region (area of predominant ionic conductivity), over that of ceria, that allows its use as an [[electrolyte]] in SOFCs. Substituting a fraction of the ceria with [[gadolinium]] or [[samarium]] will introduce oxygen [[vacancy|vacancies]] in the crystal without adding electronic charge carriers. This increases the ionic conductivity and results in a better electrolyte.
Under [[Redox|reducing]] conditions, those experienced on the [[anode]] side of the [[fuel cell]], a large amount of [[vacancy|oxygen vacancies]] within the ceria electrolyte can be formed. This results in the normally pale yellow ceria to turn black or grey as the result of [[color center]] formation. Some of the cerium(IV) oxide is also [[Redox|reduced]] to [[cerium(III) oxide]] under these conditions which consequently increases the electronic conductivity of the material. Finally, ceria undergoes what is described as a chemical expansion under [[Redox|reducing]] conditions as a result of reduction of the cerium cation from a 4+ to a 3+ state in order to charge compensate for oxygen vacancy formation.
==As a catalyst==
Ceria has been used in [[catalytic converter]]s in automotive applications. Since ceria can become non-stoichioimetric in oxygen content (i.e. it can give up oxygen without decomposing) depending on its ambient [[partial pressure]] of oxygen, it can release or take in oxygen in the exhaust stream of a combustion engine. In association with other catalysts, ceria can effectively reduce [[NOx]] emissions as well as convert harmful [[carbon monoxide]] to the less harmful [[carbon dioxide]].
==Defects==
In the [[fluorite]] structure, ceria exhibits several defects depending on partial pressure of oxygen. The primary defects of concern are oxygen vacancies and small polarons (electrons localized on cerium cations) because these two are located in the "useful" range of ceria.
==References==
<references />
*[http://www.webelements.com/webelements/compounds/text/Ce/Ce1O2-1306383.html Webelements at University of Sheffield]
*[http://www.camd.lsu.edu/msds/c/cerium_iv_oxide_powder.htm Center for Advanced Microstructures and Devices at Louisiana State University]
==External Links==
* [http://www.nano-oxides.com/pdf/CeO2_Brochure.pdf Information from Nano-Oxides, Inc. on CeO<sub>2</sub>.]
[[Category:Oxides]]
[[Category:Cerium compounds]]
[[Category:Catalysts]]
[[Category:Sunscreening agents]]
[[ar:أكسيد سيريوم رباعي]]
[[cs:Oxid ceričitý]]
[[de:Cer(IV)-oxid]]
[[it:Ossido di cerio]]