Cerium(IV) oxide
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| Cerium(IV) oxide | |
|---|---|
 |
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| General | |
| Systematic name | Cerium(IV) oxide |
| Other names | ceric oxide, ceria, cerium oxide, cerium dioxide |
| Molecular formula | CeO2 |
| Molar mass | 172.115 g/mol |
| Appearance | white or pale yellow solid, slightly hygroscopic |
| CAS number | [1306-38-3] |
| Properties | |
| Density and phase | 7.65 g/cm3, solid 7.215 g/cm3, fluorite phase |
| Solubility in water | not soluble — ? g/100 ml (? °C) |
| Melting point | Approximately 2400 K (2100 °C) |
| Boiling point | ? °C (? K) |
| Acidity (pKa) | ? |
| Basicity (pKb) | ? |
| Viscosity | ? cP at ? °C |
| Structure | |
| Molecular shape | ? |
| Coordination geometry |
? |
| Crystal structure | ? |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | ? |
| NFPA 704 |
1
2
2
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| Flash point | None |
| R/S statement | R: ? S: ? |
| RTECS number | ? |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | ? |
| Other cations | ? |
| Related compounds | Ce2O3 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Cerium(IV) oxide, ceric oxide, ceria, or sometimes simply cerium oxide or cerium dioxide, is a pale yellow-white powder, CeO2. It is used in ceramics, to polish glass, and to sensitize photosensitive glass. It is also used in lapidary as "jeweller's rouge"; it is also known as "optician's rouge".[1] Ceria is used in the walls of self-cleaning ovens as a hydrocarbon catalyst during the high-temperature cleaning process.
It is slightly hygroscopic and will also absorb a small amount of carbon dioxide from the atmosphere.
Note that cerium also forms cerium(III) oxide, Ce2O3.
[edit] As a fuel cell electrolyte
Ceria has seen interest as a material for solid oxide fuel cells or SOFCs since it is an ionic conductor, i.e. oxygen atoms readily move through it. Ceria also exhibits electronic conduction so it is in fact a mixed ionic electronic conducting material. At sufficient temperatures, greater than 500°C, ceria becomes predominantly an ionic conductor and this is where its potential use as an electrolyte in SOFCs is. Another point of interest is that under reducing conditions, those experienced on the anode side of the fuel cell, a large amount of 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 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 reducing conditions as a result of oxygen vacancy formation. This occurs because as the oxygen atoms leave the ceria lattice vacancies are created that don't counteract the charge of the cerium atoms resulting in a repulsion of ceriums that leads to an expanion of the lattice. These vacancies are also responsible for the ionic conductivity of the ceria. Substituting a fraction of the ceria with for instance gadolinium or samarium will introduce vacancies without adding electronic charge carriers. This increases the ionic conductivity and results in a better electrolyte.
