Ammonium tetrafluoroberyllate

August 30, 2021
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Diammonium tetrafluoroberyllate is one of several salts of the tetrafluoroberyllate anion, in which four fluorine atoms are covalently bonded to a beryllium atom in a tetrahedral arrangement. The anion has also been prepared as salts of alkali metals, alkaline earths, transition metals, and many organic amines, some with varying degrees of hydration.

Also called ammonium beryllium fluoride, the salt is formed by dissolving beryllium hydroxide [Be(OH)2] in an aqueous solution of ammonium hydrogen fluoride [(NH4)HF2]. The aqueous solution is concentrated in an evaporative crystallizer to form the diammonium tetrafluoroberyllate salt. Its crystals are orthorhombic (shown) with a density of 1.71 g/mL. Like all beryllium-containing compounds, it is extremely toxic.

Diammonium tetrafluoroberyllate is used to produce beryllium fluoride (BeF2) glass by heating the salt to ≈1000 °C. BeF2, in turn, can be used to make beryllium metal by reducing it with elemental magnesium at 1300 °C. In the past several years, beryllium has been in short supply; in 2016, L. N. Malyutin and co-workers at Tomsk Polytechnic University (Russia) developed improved methods to purify diammonium tetrafluoroberyllate on its way to making the metal.

Advanced materials manufacturers, such as Materion (Mayfield Heights, OH), use ammonium tetrafluoroberyllate to make their beryllium-containing products. Materion uses the synthetic route described above to make BeF2 and the metal.

In addition to being the precursor to the metal, BeF2 has applications in the nuclear energy industry. Beryllium metal produced from ammonium tetrafluoroberyllate was used to make the mirrors of the James Webb Space Telescope, which is  scheduled to be launched later this year.

Ammonium tetrafluoroberyllate hazard information*

Hazard class**GHS code and hazard statement
Acute toxicity, oral, category 3H301—Toxic if swallowedChemical Safety Warning
Skin corrosion/irritation, category 2H315—Causes skin irritationChemical Safety Warning
Sensitization, skin, category 1H317—May cause an allergic skin reactionChemical Safety Warning
Serious eye damage/eye irritation, category 2AH319—Causes serious eye irritation Chemical Safety Warning
Acute toxicity, inhalation, category 1H330—Fatal if inhaled Chemical Safety Warning
Specific target organ toxicity, single exposure, respiratory tract irritation, category 3H335—May cause respiratory irritationChemical Safety Warning
Carcinogenicity, category 1AH350—May cause cancer by inhalation Chemical Safety Warning
Specific target organ toxicity, repeated exposure, category 1H372—Causes damage to organs through prolonged or repeated exposureChemical Safety Warning
Hazardous to the aquatic environment, long-term hazardH411—Toxic to aquatic life with long-lasting effectsChemical Safety Warning

*Information acquired from online sources, not a specific safety data sheet.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals.  

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Ammonium tetrafluoroberyllate 
fast facts

CAS Reg. No.14874-86-3
Beryllate(2–), tetrafluoro-, ammonium (1:2)
Empirical formulaH8BeF4N2
Molar mass121.08 g/mol
AppearanceWhite crystals
Melting point280 °C (dec.)
Water solubility323 g/L

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