Beryllium oxide

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Beryllium oxide
Unit cell, ball and stick model of beryllium oxide
Identifiers
CAS number 1304-56-9 YesY
PubChem 14775
ChemSpider 14092 YesY
EC number 215-133-1
UN number 1566
MeSH beryllium+oxide
ChEBI CHEBI:62842 N
RTECS number DS4025000
Beilstein Reference 3902801
Jmol-3D images Image 1
Image 2
Properties
Molecular formula BeO
Molar mass 25.01 g mol−1
Appearance Colourless, vitreous crystals
Odor Odourless
Density 3.01 g cm−3
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 K−1 m−1
Refractive index (nD) 1.7
Structure
Crystal structure Hexagonal
Space group P63mc
Point group C6v
Coordination
geometry
Tetragonal
Molecular shape Linear
Thermochemistry
Std molar
entropy
So298
13.73–13.81 J K−1 mol−1
Std enthalpy of
formation
ΔfHo298
–599 kJ mol−1[2]
Hazards
MSDS External MSDS
GHS pictograms The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
GHS hazard statements H301, H315, H317, H319, H330, H335, H350, H372
GHS precautionary statements P201, P260, P280, P284, P301+310, P305+351+338
EU Index 004-003-00-8
EU classification Very Toxic T+
R-phrases R49, R25, R26, R36/37/38, R43, R48/23
S-phrases S53, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
LD50 2.062 mg kg−1 (mouse, oral)
Related compounds
Other anions Beryllium telluride
Other cations Magnesium oxide

Calcium oxide

Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and actually exceeds that of most metals.[3] As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a refractory.[4] It occurs in nature as the mineral bromellite. Historically and in materials science, beryllium oxide was called glucina or glucinium oxide. Formation of BeO from beryllium and oxygen releases the highest energy per mass of reactants for any chemical reaction, close to 24MJ/kg.[citation needed]

Preparation and chemical properties[edit]

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.[3] 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[edit]

BeO crystallizes in the hexagonal wurtzite structure, featuring tetrahedral Be2+ and O2- centres, like lonsdaleite and w-BN (both of which it is isoelectronic with). In contrast, the oxides of the larger group 2 metals, i.e., MgO, CaO, SrO, BaO, crystallize in the cubic rock salt motif with octahedral geometry about the dications and dianions.[3] At high temperature the structure transforms to a tetragonal form.[5]

In the vapour phase, beryllium oxide is present as discrete diatomic molecules. In the language of valence bond theory, these molecules can be described as adopting sp orbital hybridisation, featuring two sigma and two pi bonds. The corresponding ground state is .. (2sσ)2(2sσ*)2(2pπ)4, where both degenerate π orbitals can be considered as dative bonds from oxygen towards beryllium.[6]

Applications[edit]

High quality crystals may be grown hydrothermally, or otherwise by the Verneuil method. For the most part, beryllium oxide is produced as a white amorphous powder, sintered into larger shapes. Impurities like carbon, trapped with the crystals can give a variety of colours to the otherwise colourless host crystals.

Sintered beryllium oxide, is a very stable ceramic.[7] 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.[8] 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[edit]

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.[9] Beryllium oxide ceramic is not a hazardous waste under Federal law in the USA.

References[edit]

  1. ^ "beryllium oxide – Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 27 March 2005. Identification and Related records. Retrieved 8 November 2011. 
  2. ^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 0-618-94690-X. 
  3. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  4. ^ Raymond Aurelius Higgins (2006). Materials for Engineers and Technicians. Newnes. p. 301. ISBN 0-7506-6850-4. 
  5. ^ A.F. Wells (1984). Structural Inorganic Chemistry (5 ed.). Oxford Science Publications. ISBN 0-19-855370-6. 
  6. ^ Fundamentals of Spectroscopy. Allied Publishers. pp. 234–. ISBN 978-81-7023-911-6. Retrieved 29 November 2011. 
  7. ^ 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
  8. ^ 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. [dead link]
  9. ^ Beryllium Oxide Safety

External links[edit]