Barium fluoride
4525764
217989377
2008-06-08T17:30:54Z
Vishnava
6847159
Reverted edits by [[Special:Contributions/24.63.157.208|24.63.157.208]] to last version by Axiosaurus (using [[WP:HG|Huggle]])
{{Chembox new
| Name = Barium fluoride
| ImageFile = Barium fluoride.jpg
<!-- | ImageSize = 200px -->
| ImageName = Barium fluoride
| Section1 = {{Chembox Identifiers
| CASNo = 7787-32-8
}}
| Section2 = {{Chembox Properties
| Formula = BaF<sub>2</sub>
| MolarMass = 175.324 g.mol<sup>-1</sup>
| Appearance = white cubic crystals
| Density = 4.893 g.cm<sup>-3</sup>, solid
| Solubility = 1.7 g/kg (26°C)
| Solvent = [[methanol]]
| SolubleOther =
| Solvent = [[ethanol]]
| SolubleOther =
| MeltingPt = 1368 °C
| BoilingPt = 2260 °C
}}
| Section3 = {{Chembox Structure
| Coordination =
| CrystalStruct = [[Cubic crystal system|cubic]]
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −???? kJ/mol
| Entropy = ??? J·K<sup>−1</sup>·mol<sup>−1</sup>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| EUClass = Toxic ('''T''')
| RPhrases = {{R20}}, {{R22}}
| SPhrases = {{S28}}
| FlashPt = Non-flammable
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Barium chloride]]<br />[[Barium bromide]]<br />[[Barium iodide]]
| OtherCations = [[Calcium fluoride]]<br />[[Strontium fluoride]]}}
}}
'''Barium fluoride''' (BaF<sub>2</sub>) is a chemical compound of [[barium]] and [[fluorine]], also known as Barium(II) fluoride. It is a solid which can be a transparent crystal. It occurs in nature as the mineral [[frankdicksonite]] .<ref> Frankdicksonite, BaF2, a New Mineral from Nevada Radtke A.S., Brown G.E. American Mineralogist (1974) 59, 885-888</ref>
==Structure==
The solid adopts the [[calcium fluoride|fluorite]] structure and at high pressure the [[lead(II) chloride|PbCl<sub>2</sub>]] structure.<ref name = "Wells"> A.F Wells (1984) Structural inorganic chemistry -5th Edition Oxford ISBN 0-19-855370-6</ref> In the vapour phase the BaF<sub>2</sub> molecule is non-linear with an F-Ba-F angle of approximately 108°. <ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref> This is an exception to [[VSEPR theory]] which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible.<ref>Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX<sub>2</sub> (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)Seijo L.,Barandiarán Z J. Chem. Phys. 94, 3762 (1991) {{doi||10.1063/1.459748 }}</ref> Another proposal is that polarisation of the electron core of the barium atom creates an approximately tetrahedral distribution of charge that interacts with the Ba-F bonds.<ref>Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba Bytheway I, Gillespie RJ, Tang TH, Bader RF Inorganic Chemistry, Vol.34, No.9, 2407-2414, 1995 {{doi|10.1021/ic00113a023}}</ref>
==Applications==
Barium Fluoride is transparent from the [[ultraviolet]] to the [[infrared]], from 150-200 [[nanometer|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-ray]]s, [[gamma ray]]s or other high energy particles. One of its applications is the detection of 511 [[electronvolt|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 <ref>M. Laval, Barium Fluoride - inorganic scintillator for subnanoseconds timing, Nuclear Instruments and Methods, 206 :169-176, 1983 </ref>. It can be also used for detection of high-energy (10-150 MeV) [[neutron]]s, 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 [[opacifier|preopacifying]] agent and in [[Vitreous enamel|enamel]] and glazing frits production. Its other use is in the production of [[welding]] agents (an additive to some [[flux (metallurgy)|fluxes]], a component of coatings for [[welding rod]]s and in welding powders). It is also used in [[metallurgy]], as a molten bath for refining [[aluminium]].
==References==
<references/>
==External links==
* [http://physchem.ox.ac.uk/MSDS/BA/barium_fluoride.html MSDS at Oxford University]
[[Category:Barium compounds]]
[[Category:Fluorides]]
[[Category:Optical materials]]
[[Category:Phosphors and scintillators]]
[[Category:Crystals]]
[[Category:Metal halides]]
[[ar:فلوريد باريوم]]
[[it:Fluoruro di bario]]
[[pl:Fluorek baru]]