:Barium fluoride
{{Short description|Chemical compound}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 413666960
| Name = Barium fluoride
| ImageFile1 =Barium fluoride crystal sample.jpg
| ImageFile2 =Fluorite-unit-cell-3D-ionic.png
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 56421
| SMILES = F[Ba]F
| SMILES2 = [Ba+2].[F-].[F-]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Ba.2FH/h;2*1H/q+2;;/p-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = OYLGJCQECKOTOL-UHFFFAOYSA-L
| CASNo = 7787-32-8
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = H96A02I53Y
| RTECS = CQ9100000
| PubChem = 62670
}}
|Section2={{Chembox Properties
| Formula = {{chem2|BaF2}}
| MolarMass = 175.324 g/molHaynes, p. 4.49
| Appearance = white cubic crystals
| Solubility = 1.58 g/L (10 °C)
1.61 g/L (25 °C)Haynes, p. 5.167
| SolubleOther = soluble in methanol, ethanol
| SolubilityProduct = 1.84·10−7{{cite book |author1=John Rumble |title=CRC Handbook of Chemistry and Physics |date=June 18, 2018 |publisher=CRC Press |isbn=978-1138561632 |pages=4–47|edition=99th |language=English}}
| MeltingPtC = 1368
| BoilingPtC = 2260
| RefractIndex = {{ubl|1.557 (200 nm)|1.4744 (589 nm)|1.4014 (10 μm)}}Haynes, p. 10.248
| ThermalConductivity = 10.9 W/(m·K)Haynes, p. 12.222
| MagSus = −51·10−6 cm3/molHaynes, p. 4.126
}}
|Section3={{Chembox Structure
| CrystalStruct = Fluorite (cubic), cF12
| SpaceGroup = Fm{{overline|3}}m, No. 225
| LattConst_a = 0.62 nm
| UnitCellFormulas = 4
}}
| Section4 = {{Chembox Thermochemistry
| Thermochemistry_ref =Haynes, p. 5.5
| HeatCapacity = 71.2 J/(mol·K)
| Entropy = 96.4 J/(mol·K)
| DeltaHform = −1207.1 kJ/mol
| DeltaGfree = −1156.8 kJ/mol
| DeltaHcombust =
| DeltaHfus =
| DeltaHvap =
| DeltaHsublim =
| HHV =
| LHV =
}}
|Section7={{Chembox Hazards
| ExternalSDS = [https://pubchem.ncbi.nlm.nih.gov/compound/62670 PubChem]
| MainHazards = Toxic
| GHSPictograms = {{GHS07}}
| FlashPt = Non-flammable
| NFPA-H =
| NFPA-F =
| NFPA-R =
| LD50 = 250 mg/kg, oral (rat)
}}
|Section8={{Chembox Related
| OtherAnions = {{ubl|Barium chloride|Barium bromide|Barium iodide}}
| OtherCations = {{ubl|Beryllium fluoride|Magnesium fluoride|Calcium fluoride|Strontium fluoride|Radium fluoride}}
}}
}}
Barium fluoride is an inorganic compound with the formula {{chem2|BaF2|auto=1}}. It is a colorless solid that occurs in nature as the rare mineral frankdicksonite.{{cite journal|url=http://www.minsocam.org/ammin/AM59/AM59_885.pdf|title = Frankdicksonite, BaF2, a New Mineral from Nevada | author = Radtke A.S., Brown G.E.|journal = American Mineralogist|year = 1974|volume = 59|pages = 885–888}} Under standard conditions it adopts the fluorite structure and at high pressure the lead(II) chloride structure.{{cite book| author = Wells, A.F. | year = 1984| title = Structural inorganic chemistry −5th Edition |location = Oxford | isbn = 0-19-855370-6| publisher = Clarendon Press}} Like Calcium fluoride, it is resilient to and insoluble in water.
Above ca. 500 °C, {{chem2|BaF2}} is corroded by moisture, but in dry environments 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 it is the most resistant of all the optical fluorides to high-energy radiation, though its far ultraviolet transmittance is lower than that of the other fluorides. It is quite hard, very sensitive to thermal shock and fractures quite easily.
Optical properties
Barium fluoride is transparent from the ultraviolet to the infrared, from 150 to 200 nm to 11–11.5 μm. It is used 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). The refractive index is about 1.46 from 700 nm to 5 μm.{{cite web | url=http://www.crystran.co.uk/barium-fluoride-baf2.htm | title=Crystran Ltd. Optical Component Materials | access-date=29 December 2009 | archive-date=11 June 2010 | archive-url=https://web.archive.org/web/20100611112530/http://www.crystran.co.uk/barium-fluoride-baf2.htm | url-status=dead }}
Barium fluoride is also a common, very fast (one of the fastest) scintillators 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. It responds also to alpha and beta particles, but, unlike most scintillators, it does not emit ultraviolet light.{{cite journal| doi = 10.1016/0167-5087(83)91254-1| title = Barium fluoride – Inorganic scintillator for subnanosecond timing| year = 1983| author = Laval, M| journal = Nuclear Instruments and Methods in Physics Research| volume = 206| issue = 1–2| pages = 169–176| last2 = Moszyński| first2 = M.| last3 = Allemand| first3 = R.| last4 = Cormoreche| first4 = E.| last5 = Guinet| first5 = P.| last6 = Odru| first6 = R.| last7 = Vacher| first7 = J.| bibcode = 1983NIMPR.206..169L}} It can be also used for detection of high-energy (10–150 MeV) neutrons, using pulse shape discrimination techniques to separate them from simultaneously occurring gamma photons.
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.
Gas phase structure
In the vapor phase the {{chem2|BaF2}} molecule is non-linear with an F-Ba-F angle of approximately 108°.{{Greenwood&Earnshaw}} Its nonlinearity violates VSEPR theory. Ab initio calculations indicate that contributions from d orbitals in the shell below the valence shell are responsible.{{cite journal | doi = 10.1063/1.459748 | title = Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I) | year = 1991 | author = Seijo, Luis | journal = The Journal of Chemical Physics | volume = 94 | pages = 3762 | last2 = Barandiarán | first2 = Zoila | last3 = Huzinaga | first3 = Sigeru | issue = 5| url = https://repositorio.uam.es/bitstream/10486/7315/1/41581_jchemphysseijo_91_jcp_94_3762.pdf |bibcode = 1991JChPh..94.3762S|hdl = 10486/7315| hdl-access = free }} 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.{{cite journal| doi =10.1021/ic00113a023| title =Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba| year =1995| author =Bytheway, Ian| journal =Inorganic Chemistry| volume =34| pages =2407| last2 =Gillespie| first2 =Ronald J.| last3 =Tang| first3 =Ting-Hua| last4 =Bader| first4 =Richard F. W.| issue =9}}
References
{{Reflist}}
Cited sources
- {{cite book | editor= Haynes, William M. | date = 2016| title = CRC Handbook of Chemistry and Physics | edition = 97th | publisher = CRC Press | isbn = 9781498754293|page=4.49| title-link = CRC Handbook of Chemistry and Physics}}
External links
- [http://physchem.ox.ac.uk/MSDS/BA/barium_fluoride.html MSDS at Oxford University] {{Webarchive|url=https://web.archive.org/web/20060517175535/http://physchem.ox.ac.uk/MSDS/BA/barium_fluoride.html |date=2006-05-17 }}
{{Barium compounds}}
{{fluorine compounds}}
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{{DEFAULTSORT:Barium Fluoride}}
Category:Phosphors and scintillators