Barium fluoride

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Barium fluoride
Barium fluoride
Identifiers
CAS number 7787-32-8 YesY
PubChem 62670
ChemSpider 56421 YesY
RTECS number CQ9100000
Jmol-3D images Image 1
Properties
Molecular formula BaF2
Molar mass 175.34 g/mol
Appearance white cubic crystals
Density 4.893 g/cm3
Melting point 1368 °C
Boiling point 2260 °C
Solubility in water 0.16 g/100 mL (20 °C)
Solubility soluble in methanol, ethanol
Refractive index (nD) 1.455
Structure
Crystal structure Fluorite (cubic), cF12
Space group Fm3m, No. 225
Hazards
EU Index 056-002-00-7
EU classification Harmful (Xn)
R-phrases R20/22
S-phrases (S2), S28
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
LD50 250 mg/kg, oral (rat)
Related compounds
Other anions Barium chloride
Barium bromide
Barium iodide
Other cations Beryllium fluoride
Magnesium fluoride
Calcium fluoride
Strontium fluoride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Barium fluoride (BaF2) is a chemical compound of barium and fluorine. It is a solid which can be a transparent crystal. It occurs in nature as the mineral frankdicksonite.[1]

Structure[edit]

The solid adopts the fluorite structure and at high pressure the PbCl2 structure.[2] In the vapor phase the BaF2 molecule is non-linear with an F-Ba-F angle of approximately 108°.[3] 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.[4] 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.[5]

Applications[edit]

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 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 [6]

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. It responds also to alpha and beta particles, but, unlike most scintillators, it does not glow in ultraviolet light.[7] 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, very sensitive to thermal shock and fractures quite easily.

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[edit]

  1. ^ Radtke A.S., Brown G.E. (1974). "Frankdicksonite, BaF2, a New Mineral from Nevada". American Mineralogist 59: 885–888. 
  2. ^ A.F Wells (1984). Structural inorganic chemistry -5th Edition. Oxford: Clarendon Press. ISBN 0-19-855370-6. 
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  4. ^ Seijo, Luis; Barandiarán, Zoila; Huzinaga, Sigeru (1991). "Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)". The Journal of Chemical Physics 94 (5): 3762. doi:10.1063/1.459748. 
  5. ^ Bytheway, Ian; Gillespie, Ronald J.; Tang, Ting-Hua; Bader, Richard F. W. (1995). "Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba". Inorganic Chemistry 34 (9): 2407. doi:10.1021/ic00113a023. 
  6. ^ "Crystran Ltd. Optical Component Materials". Retrieved 29 December 2009. 
  7. ^ Laval, M; Moszyński, M.; Allemand, R.; Cormoreche, E.; Guinet, P.; Odru, R.; Vacher, J. (1983). "Barium fluoride – Inorganic scintillator for subnanosecond timing". Nuclear Instruments and Methods in Physics Research 206: 169. doi:10.1016/0167-5087(83)91254-1. 

External links[edit]