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| ==Structure== | ==Structure== | ||
| BeO adopts the hexagonal ] structure form.<ref name = "Greenwood"/> In contrast, other group 2 oxides, ], ], ], ], crystallize in the cubic rock salt motif.<ref name = "Greenwood"/> At high temperature the structure transforms to a tetragonal form.<ref>{{cite book|author=A.F. Wells|year=1984|title=Structural Inorganic Chemistry|edition=5|publisher=Oxford Science Publications|isbn=0-19-855370-6}}</ref> In the vapor phase, beryllium oxide is present as discrete diatomic covalent molecules. The electronic structure of the beryllium oxide monomer is unusual, the orbital overlap only allows for one strong covalent bond to form, the other two orbitals do not overlap strongly enough to form a covalent bond, neither does it form an ionic bond. The result is a triplet diradical species, this is commonly simplified to a double bond. |
BeO adopts the hexagonal ] structure form.<ref name = "Greenwood"/> In contrast, other group 2 oxides, ], ], ], ], crystallize in the cubic rock salt motif.<ref name = "Greenwood"/> At high temperature the structure transforms to a tetragonal form.<ref>{{cite book|author=A.F. Wells|year=1984|title=Structural Inorganic Chemistry|edition=5|publisher=Oxford Science Publications|isbn=0-19-855370-6}}</ref> In the vapor phase, beryllium oxide is present as discrete diatomic covalent molecules. The electronic structure of the beryllium oxide monomer is unusual, the orbital overlap only allows for one strong covalent bond to form, the other two orbitals do not overlap strongly enough to form a covalent bond, neither does it form an ionic bond. The result is a triplet diradical species, this is commonly simplified to a double bond.{{fact}} | ||
| ==Applications== | ==Applications== | ||
Revision as of 22:56, 7 November 2011
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| Names | |
|---|---|
| IUPAC name Beryllium oxide | |
| Other names
Berlox Beryllia | |
| Identifiers | |
| CAS Number | |
| 3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.013.758 
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| EC Number |
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| MeSH | Beryllium+oxide |
| PubChem CID | |
| RTECS number |
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| UN number | 1566 |
| CompTox Dashboard (EPA) | |
InChI
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SMILES
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| Properties | |
| Chemical formula | BeO |
| Molar mass | 25.011 g·mol |
| Appearance | White crystals |
| Odor | Odourless |
| Density | 3.02 g cm |
| Melting point | 2,507 °C (4,545 °F; 2,780 K) |
| Boiling point | 3,900 °C (7,050 °F; 4,170 K) |
| Band gap | 10.6 eV |
| Thermal conductivity | 330 W/(m·K) |
| Refractive index (nD) | 1.7 |
| Structure | |
| Crystal structure | hexagonal, hP4 |
| Space group | P63/mc, No. 186 |
| Thermochemistry | |
| Std molar entropy (S298) |
13.77(4) J K mol |
| Std enthalpy of formation (ΔfH298) |
–609.4(25) kJ mol |
| Hazards | |
| GHS labelling: | |
| Pictograms |  
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| Signal word | Danger |
| Hazard statements | H301, H315, H317, H319, H330, H335, H350, H372 |
| NFPA 704 (fire diamond) |
 |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
| LD50 (median dose) | 2062 mg/kg (mouse, oral) |
| Related compounds | |
| Other anions | Beryllium sulfide Beryllium selenide Beryllium telluride |
| Other cations | Magnesium oxide Calcium oxide |
| Supplementary data page | |
| Beryllium oxide (data page) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa).
 Y verify (what is ?)
Infobox references
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Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This white crystalline solid is notable as it is an electrical insulator with a thermal conductivity higher than any other non-metal except diamond, and actually exceeds that of some metals. Its high melting point leads to its use as a refractory. It occurs in nature as the mineral bromellite. Historically beryllium oxide was called glucina or glucinium oxide.
Preparation and chemical properties
Beryllium oxide can be prepared by calcining (roasting) beryllium carbonate, dehydrating beryllium hydroxide or igniting the metal:
- BeCO3→ BeO + CO2
- Be(OH)2 → BeO + H2O
- 2 Be + O2 → 2 BeO
Igniting beryllium in air gives a mixture of BeO and the nitride Be3N2. Unlike oxides formed by the other group 2 (alkaline earth metals), beryllium oxide is amphoteric rather than basic.
Beryllium oxide formed at high temperatures (>800°C) is inert, but dissolves easily in hot aqueous ammonium bifluoride (NH4HF2) or a hot solution of concentrated sulfuric acid (H2SO4) and ammonium sulfate ((NH4)2SO4).
Structure
BeO adopts the hexagonal wurtzite structure form. In contrast, other group 2 oxides, MgO, CaO, SrO, BaO, crystallize in the cubic rock salt motif. At high temperature the structure transforms to a tetragonal form. In the vapor phase, beryllium oxide is present as discrete diatomic covalent molecules. The electronic structure of the beryllium oxide monomer is unusual, the orbital overlap only allows for one strong covalent bond to form, the other two orbitals do not overlap strongly enough to form a covalent bond, neither does it form an ionic bond. The result is a triplet diradical species, this is commonly simplified to a double bond.
Applications
Sintered beryllium oxide, which is very stable, has ceramic characteristics. Beryllium oxide is used in rocket engines.
Beryllium oxide is used in many high-performance semiconductor parts for applications such as radio equipment because it has good thermal conductivity while also being a good electrical insulator. It is used as a filler in some thermal interface materials such as thermal grease. Some power semiconductor devices have used beryllium oxide ceramic between the silicon chip and the metal mounting base of the package in order to achieve a lower value of thermal resistance than for a similar construction made with aluminium oxide. It is also used as a structural ceramic for high-performance microwave devices, vacuum tubes, magnetrons, and gas lasers.
Safety
Like all beryllium compounds, BeO is carcinogenic and may cause chronic beryllium disease. Once fired into solid form, it is safe to handle as long as it is not subjected to any machining that generates dust. Beryllium oxide ceramic is not a hazardous waste under Federal law in the USA.
References
- Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0487-3.
- Cox, J. D.; Wagman, D. D.; Medvedev, V. A. (1989), CODATA Key Values for Thermodynamics, New York: Hemisphere, ISBN 0891167587.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- Raymond Aurelius Higgins (2006). Materials for Engineers and Technicians. Newnes. p. 301. ISBN 0750668504.
- A.F. Wells (1984). Structural Inorganic Chemistry (5 ed.). Oxford Science Publications. ISBN 0-19-855370-6.
- Günter Petzow, Fritz Aldinger, Sigurd Jönsson, Peter Welge, Vera van Kampen, Thomas Mensing, Thomas Brüning"Beryllium and Beryllium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a04_011.pub2
- Greg Becker, Chris Lee, and Zuchen Lin (2005). "Thermal conductivity in advanced chips — Emerging generation of thermal greases offers advantages". Advanced Packaging: 2–4. Retrieved 2008-03-04.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - Beryllium Oxide Safety
External links
- Beryllium Oxide MSDS from American Beryllia
- Beryllium Oxide Properties (solid form)
- IARC Monograph "Beryllium and Beryllium Compounds"
- International Chemical Safety Card 1325
- National Pollutant Inventory - Beryllium and compounds
- NIOSH Pocket guide to Chemical Hazards
| Beryllium compounds | |
|---|---|
| Beryllium(I) | |
| Beryllium(II) |
|