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Barium fluoride

Barium fluoride

Identifiers
CAS number	7787-32-8
Properties
Molecular formula	BaF₂
Molar mass	175.324 g.mol^-1
Appearance	white cubic crystals
Density	4.893 g.cm^-3, solid
Melting point	1368 °C
Boiling point	2260 °C
Solubility in water	1.7 g/kg (26°C)
Structure
Crystal structure	cubic
Thermochemistry
Std enthalpy of formation Δ_fH^o₂₉₈	−???? kJ/mol
Standard molar entropy S^o₂₉₈	??? J·K⁻¹·mol⁻¹
Hazards
EU classification	Toxic (T)
R-phrases	R20, R22
S-phrases	S28
Flash point	Non-flammable
Related Compounds
Other anions	Barium chloride Barium bromide Barium iodide
Other cations	Calcium fluoride Strontium fluoride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Barium fluoride (BaF₂) is a chemical compound of barium and fluorine, also known as Barium(II) fluoride. It is a solid which can be a transparent crystal.

Additional recommended knowledge

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Applications

Barium Fluoride is transparent from the ultraviolet to the infrared, from 150-200 nm to 11-11.5 µm, and can be used as a material to make optical components such as lenses. It is used eg. in windows for infrared spectroscopy, in particular in the field of fuel oil analysis. Its transmittance at 200 nm is relatively low (0.60), but at 500 nm it goes up to 0.96-0.97 and stays at that level until 9 µm, then it starts falling off (0.85 for 10 µm and 0.42 for 12 µm).

Barium fluoride is also a common, very fast (one of the fastest) scintillator for the detection of X-rays, gamma rays or other high energy particles. One of its applications is the detection of 511 keV gamma photons in positron emission tomography; other material used in this application is eg. bismuth germanate. It responds also to alpha and beta particles, but, unlike most scintillators, it glows in ultraviolet light ^[1]. It can be also used for detection of high-energy (10-150 MeV) neutrons, and use pulse shape discrimination techniques to separate them from simultaneously occurring gamma photons.

When heated to 500 °C, it gets corroded by water, but in dry environment it can be used up to 800 °C. Prolonged exposure to moisture degrades transmission in the vacuum UV range. It is less resistant to water than calcium fluoride, but is the most resistant of all the optical fluorides to high-energy radiation, though its far ultraviolet transmittance is lower than theirs. It is quite hard, and very sensitive to thermal shock.

Barium fluoride is used as a preopacifying agent and in enamel and glazing frits production. Its other use is in the production of welding agents (an additive to some fluxes, a component of coatings for welding rods and in welding powders). It is also used in metallurgy, as a molten bath for refining aluminium.

References

^ M. Laval, Barium Fluoride - inorganic scintillator for subnanoseconds timing, Nuclear Instruments and Methods, 206 :169-176, 1983

Categories: Barium compounds | Fluorides | Phosphors and scintillators | Crystals | Metal halides

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Barium_fluoride". A list of authors is available in Wikipedia.