BerylliumBeryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
oxide (
BeO), also known as
beryllia, is an
inorganic compoundInorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the
formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
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 some metals. As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a
refractoryA refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
. It occurs in nature as the mineral
bromelliteBromellite, whose name derives from the Swedish chemist Magnus von Bromell , is a white oxide mineral, found in complex pegmatitic manganese-iron deposits, but is more frequently made synthetically...
. Historically and in materials science, beryllium oxide was called
glucina or glucinium oxide.
Preparation and chemical properties
Beryllium oxide can be prepared by calcining (roasting) beryllium carbonate, dehydrating
beryllium hydroxideBeryllium hydroxide, Be2 is an amphoteric hydroxide, dissolving in both acids and alkalis. Industrially it is produced as a by-product in the extraction of beryllium metal from the ores, beryl and bertrandite. When alkali is added to beryllium salt solutions the α-form is formed. If this left to...
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 Be
3N
2.
Unlike oxides formed by the other group 2 (alkaline earth metals), beryllium oxide is
amphotericIn chemistry, an amphoteric species is a molecule or ion that can react as an acid as well as a base. The word is derived from the Greek word amphoteroi meaning "both"...
rather than basic.
Beryllium oxide formed at high temperatures (>800 °C) is inert, but dissolves easily in hot aqueous ammonium bifluoride (NH
4HF
2) or a hot solution of concentrated
sulfuric acidSulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
(H
2SO
4) and
ammonium sulfateAmmonium sulfate , 2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations, and 24% sulfur as sulfate anions...
((NH
4)
2SO
4).
Structure
BeO crystallizes in the hexagonal
wurtziteZinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...
structure, featuring tetrahedral Be
2+ and O
2- centres. In contrast, the oxides of the larger group 2 metals, i.e.,
MgOMagnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
,
CaOCalcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
,
SrOStrontium oxide or strontia, SrO, is formed when strontium reacts with oxygen. Burning strontium in air results in a mixture of strontium oxide and strontium nitride. It also forms from the decomposition of strontium carbonate SrCO3...
,
BaOBarium oxide, BaO, is a white hygroscopic compound formed by the burning of barium in oxygen, although it is often formed through the decomposition of other barium salts.It reacts with water to form barium hydroxide.-Uses:...
, crystallize in the cubic rock salt motif with octahedral geometry about the dications and dianions. At high temperature the structure transforms to a tetragonal form.
In the vapour phase, beryllium oxide is present as discrete diatomic molecules. In the language of
valence bond theoryIn chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...
, 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.
Applications
High quality crystals may be grown
hydrothermallyHydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mineralogists have studied hydrothermal phase...
, 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, which is very stable, has
ceramicA ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
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 conductivityIn physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
while also being a good electrical insulator. It is used as a filler in some thermal interface materials such as
thermal greaseThermal grease is a viscous fluid substance, originally with properties akin to grease, which increases the thermal conductivity of a thermal interface by filling...
. Some
power semiconductor devicePower semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits . They are also called power devices or when used in integrated circuits, called power ICs....
s have used beryllium oxide ceramic between the
siliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
chip and the metal mounting base of the package in order to achieve a lower value of
thermal resistanceThermal resistance is a heat property - and a measure of a temperature difference, by which an object - or material resist a heat flow...
than for a similar construction made with
aluminium oxideAluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
. It is also used as a structural
ceramicA ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
for high-performance microwave devices,
vacuum tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s, magnetrons, and
gas laserA gas laser is a laser in which an electric current is discharged through a gas to produce coherent light. The gas laser was the first continuous-light laser and the first laser to operate "on the principle of converting electrical energy to a laser light output...
s.
Safety
Like all beryllium compounds, BeO is
carcinogenA carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
ic and may cause chronic
beryllium diseaseBerylliosis, or chronic beryllium disease , is a chronic allergic-type lung response and chronic lung disease caused by exposure to beryllium and its compounds. As an occupational lung disease, it is most classically associated with beryllium mining or manufacturing of fluorescent light bulbs...
. 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.
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