Beryllium oxide

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 exceeds that of most metals.[4] As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a refractory material.[5] It occurs in nature as the mineral bromellite. Historically and in materials science, beryllium oxide was called glucina or glucinium oxide.

Beryllium oxide
Names
Preferred IUPAC name
Beryllium(II) monoxide
Systematic IUPAC name
Oxoberyllium
Other names
Beryllia, Thermalox, Bromellite, Thermalox 995.[1]
Identifiers
3D model (JSmol)
3902801
ChEBI
ChemSpider
ECHA InfoCard 100.013.758
EC Number
  • 215-133-1
MeSH beryllium+oxide
RTECS number
  • DS4025000
UNII
UN number 1566
Properties
BeO
Molar mass 25.011 g·mol−1
Appearance Colourless, vitreous crystals
Odor Odourless
Density 3.01 g/cm3
Melting point 2,507 °C (4,545 °F; 2,780 K)
Boiling point 3,900 °C (7,050 °F; 4,170 K)
0.00002 g/100 mL
Band gap 10.6 eV
Thermal conductivity 330 W/(K·m)
1.719
Structure
Hexagonal
P63mc
C6v
Tetragonal
Linear
Thermochemistry
25.5 J/(K·mol)
13.73–13.81 J/(K·mol)
Std enthalpy of
formation (ΔfH⦵298)
 −599 kJ/mol[2]
−582 kJ/mol
Hazards
Main hazards Very toxic, carcinogen
Safety data sheet See: data page
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H301, H315, H317, H319, H330, H335, H350, H372
P201, P260, P280, P284, P301+310, P305+351+338
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 4: Very short exposure could cause death or major residual injury. E.g. VX gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
4
0
Lethal dose or concentration (LD, LC):
2062 mg/kg (mouse, oral)
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 0.002 mg/m3
C 0.005 mg/m3 (30 minutes), with a maximum peak of 0.025 mg/m3 (as Be)[3]
REL (Recommended)
 Ca C 0.0005 mg/m3 (as Be)[3]
IDLH (Immediate danger)
 Ca [4 mg/m3 (as Be)][3]
Related compounds
Other anions
 Beryllium telluride
Other cations
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Preparation and chemical properties

Beryllium oxide can be prepared by calcining (roasting) beryllium carbonate, dehydrating beryllium hydroxide, or igniting metallic beryllium:

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.[4] Unlike the oxides formed by the other Group 2 elements (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 solution of hot concentrated sulfuric acid (H2SO4) and ammonium sulfate ((NH4)2SO4).

Structure

BeO crystallizes in the hexagonal wurtzite structure, featuring tetrahedral Be2+ and O2− centres, like lonsdaleite and w-BN (with both of which it is isoelectronic). 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.[4] At high temperature the structure transforms to a tetragonal form.[6]

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 on both atoms, featuring one σ (between one sp orbital on each atom) and one π bond (between aligned p orbitals on each atom oriented perpendicular to the molecular axis). Molecular orbital theory provides a slightly different picture with no net sigma bonding (because the 2s orbitals of the two atoms combine to form a filled sigma bonding orbital and a filled sigma* anti-bonding orbital) and two pi bonds formed between both pairs of p orbitals oriented perpendicular to the molecular axis. The sigma orbital formed by the p orbitals aligned along the molecular axis is unfilled. The corresponding ground state is ...(2sσ)2(2sσ*)2(2pπ)4 (as in the isoelectronic C2 molecule), where both bonds can be considered as dative bonds from oxygen towards beryllium.[7]

Applications

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, can give a variety of colours to the otherwise colourless host crystals.

Sintered beryllium oxide is a very stable ceramic.[8] Beryllium oxide is used in rocket engines[9] and as a transparent protective over-coating on aluminised telescope mirrors.

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.[10] Some power semiconductor devices have used beryllium oxide ceramic between the silicon chip and the metal mounting base of the package to achieve a lower value of thermal resistance than a similar construction of aluminium oxide. It is also used as a structural ceramic for high-performance microwave devices, vacuum tubes, magnetrons, and gas lasers. BeO has been proposed as a neutron moderator for naval marine high-temperature gas-cooled reactors (MGCR), as well as NASA's Kilopower nuclear reactor for space applications.[11]

Safety

BeO is carcinogenic in powdered form [12] and may cause a chronic allergic-type lung disease berylliosis. Once fired into solid form, it is safe to handle if not subjected to machining that generates dust, clean breakage releases little dust but crushing or grinding actions can pose a risk.[13] Beryllium oxide ceramic is not a hazardous waste under federal law in the USA.

References
  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. NIOSH Pocket Guide to Chemical Hazards. "#0054". National Institute for Occupational Safety and Health (NIOSH).
  4. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  5. Raymond Aurelius Higgins (2006). Materials for Engineers and Technicians. Newnes. p. 301. ISBN 0-7506-6850-4.
  6. A. F. Wells (1984). Structural Inorganic Chemistry (5 ed.). Oxford Science Publications. ISBN 0-19-855370-6.
  7. Fundamentals of Spectroscopy. Allied Publishers. p. 234. ISBN 978-81-7023-911-6. Retrieved 29 November 2011.
  8. 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
  9. Ropp, Richard C. (2012-12-31). Encyclopedia of the Alkaline Earth Compounds. Newnes. ISBN 9780444595539.
  10. Greg Becker; Chris Lee; Zuchen Lin (2005). "Thermal conductivity in advanced chips — Emerging generation of thermal greases offers advantages". Advanced Packaging: 2–4. Archived from the original on June 21, 2000. Retrieved 2008-03-04.
  11. McClure, Patrick; Poston, David; Gibson, Marc; Bowman, Cheryl; Creasy, John (14 May 2014). "KiloPower Space Reactor Concept – Reactor Materials Study". Retrieved 21 November 2017. Cite journal requires |journal= (help)
  12. "Hazardous Substance Fact Sheet" (PDF). New Jersey Department of Health and Senior Services. Retrieved August 17, 2018.
  13. "Beryllium Oxide Safety". American Beryllia. Retrieved 2018-03-29.
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