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| 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 |
|
| MeSH | beryllium+oxide |
| RTECS number |
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| UNII | |
| UN number | 1566 |
| |
| |
| Properties | |
| BeO | |
| Molar mass | 25.011 g·mol−1 |
| Appearance | Colourless, vitreous crystals |
| Odor | Odourless |
| Density | 3.01 g/cm3[2] |
| Melting point | 2,578 °C (4,672 °F; 2,851 K)[2] |
| Band gap | 10.6 eV[3] |
| −11.9·10−6 cm3/mol[4] | |
| Thermal conductivity | 210 W/(m·K)[5] |
Refractive index (nD) | n11.7184, n2=1.733[6][7] |
| Structure[8] | |
| Hexagonal,zincite | |
| P63mc | |
| C6v | |
a = 2.6979 Å,c = 4.3772 Å | |
Formula units (Z) | 2 |
| Linear | |
| Thermochemistry[9] | |
| 25.6 J/(K·mol) | |
Std molar entropy(S⦵298) | 13.77±0.04 J/(K·mol) |
Std enthalpy of formation(ΔfH⦵298) | −609.4±2.5 kJ/mol |
Gibbs free energy(ΔfG⦵) | −580.1 kJ/mol |
Enthalpy of fusion(ΔfH⦵fus) | 86 kJ/mol |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Very toxic, Group 1B carcinogen |
| GHS labelling: | |
   | |
| Danger | |
| H301,H315,H317,H319,H330,H335,H350,H372 | |
| P201,P260,P280,P284,P301+P310,P305+P351+P338 | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 15 mg/kg (mouse, oral)[11] |
| 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)[10] |
REL (Recommended) | Ca C 0.0005 mg/m3 (as Be)[10] |
IDLH (Immediate danger) | Ca [4 mg/m3 (as Be)][10] |
| Related compounds | |
Otheranions | Beryllium telluride |
Othercations | |
| Supplementary data page | |
| Beryllium oxide (data page) | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Beryllium oxide (BeO), also known asberyllia, is aninorganic compound with theformula BeO. This colourless solid is anelectrical insulator with a higherthermal conductivity than any other non-metal exceptdiamond, and exceeds that of most metals.[12] As anamorphous solid, beryllium oxide is white. Its high melting point leads to its use as arefractory material.[13] It occurs in nature as the mineralbromellite. Historically and inmaterials science, beryllium oxide was calledglucina orglucinium oxide, owing to its sweet taste.
Beryllium oxide can be prepared bycalcining (roasting)beryllium carbonate, dehydratingberyllium hydroxide, or igniting metallicberyllium:
Igniting beryllium in air gives a mixture of BeO and the nitrideBe3N2.[12] Unlike the oxides formed by the other Group 2 elements (alkaline earth metals), beryllium oxide isamphoteric rather than basic.
Beryllium oxide formed at high temperatures (>800 °C) is inert, but dissolves easily in hot aqueousammonium bifluoride (NH4HF2) or a solution of hot concentratedsulfuric acid (H2SO4) andammonium sulfate ((NH4)2SO4).
BeO crystallizes in the hexagonalwurtzite structure, featuring tetrahedral Be2+ and O2− centres, likelonsdaleite and w-BN (with both of which it isisoelectronic). In contrast, the oxides of the larger group-2 metals, i.e.,MgO,CaO,SrO,BaO, crystallize in the cubicrock salt motif with octahedral geometry about the dications and dianions.[12] At high temperature the structure transforms to a tetragonal form.[14]
In the vapour phase, beryllium oxide is present as discretediatomic molecules. In the language ofvalence bond theory, these molecules can be described as adoptingsporbital hybridisation on both atoms, featuring oneσ bond (between onesp orbital on each atom) and oneπ bond (between alignedp orbitals on each atom oriented perpendicular to the molecular axis).Molecular orbital theory provides a slightly different picture with nonet σ 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 π bonds formed between both pairs ofp orbitals oriented perpendicular to the molecular axis. The sigma orbital formed by thep orbitals aligned along the molecular axis is unfilled. The corresponding ground state is ...(2sσ)2(2sσ*)2(2pπ)4 (as in the isoelectronicC2 molecule), where both bonds can be considered asdative bonds from oxygen towards beryllium.[15]
High-quality crystals may be grownhydrothermally, or otherwise by theVerneuil method. For the most part, beryllium oxide is produced as a white amorphous powder,sintered into larger shapes. Impurities, like carbon, can give rise to a variety of colours to the otherwise colourless host crystals.
Sintered beryllium oxide is a very stableceramic.[16] Beryllium oxide is used in rocket engines[citation needed] and as a transparentprotective over-coating onaluminisedtelescope mirrors. Metal-coated beryllium oxide (BeO) plates are used in the control systems of aircraft drive devices.[17]
Beryllium oxide is used in many high-performancesemiconductor 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 asthermal grease.[18] It is also employed inheat sinks and spreaders that cool electronic devices, such asCPUs, lasers, and power amplifiers.[19] Somepower semiconductor devices have used beryllium oxide ceramic between thesilicon chip and the metal mounting base of the package to achieve a lower value ofthermal resistance than a similar construction ofaluminium oxide. It is also used as a structuralceramic for high-performance microwave devices,vacuum tubes,cavity magnetrons[citation needed], andgas lasers. BeO has been proposed as aneutron moderator for naval marine high-temperaturegas-cooled reactors (MGCR), as well asNASA'sKilopowernuclear reactor for space applications.[20]
BeO iscarcinogenic in powdered form[21] and may cause a chronic allergic-type lung diseaseberylliosis. 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.[22]
