Barium fluoride

Barium fluoride (BaF2) is an inorganic compound with the formula BaF2. It is a colorless solid that occurs in nature as the rare mineral frankdicksonite.[8] Under standard conditions it adopts the fluorite structure and at high pressure the PbCl2 structure.[9] Like CaF2, it is resilient to and insoluble in water.

Barium fluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.189
RTECS number
  • CQ9100000
UNII
Properties
BaF2
Molar mass 175.324 g/mol[1]
Appearance white cubic crystals[1]
Density 4.893 g/cm3[1]
Melting point 1,368 °C (2,494 °F; 1,641 K) [1]
Boiling point 2,260 °C (4,100 °F; 2,530 K) [1]
1.58 g/L (10 °C)
1.61 g/L (25 °C)[2]
Solubility soluble in methanol, ethanol
-51·10−6 cm3/mol[3]
Thermal conductivity 10.9 W/(m·K)[4]
1.557 (200 nm)
1.4744 (589 nm)
1.4014 (10 µm)[5]
Structure[6]
Fluorite (cubic), cF12
Fm3m, No. 225
a = 0.62 nm
4
Thermochemistry[7]
71.2 J/(mol·K)
96.4 J/(mol·K)
Std enthalpy of
formation (ΔfH⦵298)
 -1207.1 kJ/mol
-1156.8 kJ/mol
Hazards
Main hazards Toxic
Safety data sheet PubChem
GHS pictograms
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Above ca. 500 °C, 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 150–200 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.[10]

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.[11] 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 BaF2 molecule is non-linear with an F-Ba-F angle of approximately 108°.[12] Its nonlinearity violates VSEPR theory. Ab initio calculations indicate that contributions from d orbitals in the shell below the valence shell are responsible.[13] 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.[14]

References
  1. Haynes, p. 4.49
  2. Haynes, p. 5.167
  3. Haynes, p. 4.126
  4. Haynes, p. 12.222
  5. Haynes, p. 10.248
  6. Hohnke, D. K.; Kaiser, S. W. (1974). "Epitaxial PbSe and Pb1−xSxSe: Growth and electrical properties". Journal of Applied Physics. 45 (2): 892–897. Bibcode:1974JAP....45..892H. doi:10.1063/1.1663334.
  7. Haynes, p. 5.5
  8. Radtke A.S., Brown G.E. (1974). "Frankdicksonite, BaF2, a New Mineral from Nevada" (PDF). American Mineralogist. 59: 885–888.
  9. Wells, A.F (1984). Structural inorganic chemistry −5th Edition. Oxford: Clarendon Press. ISBN 0-19-855370-6.
  10. "Crystran Ltd. Optical Component Materials". Retrieved 29 December 2009.
  11. 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 (1–2): 169–176. Bibcode:1983NIMPR.206..169L. doi:10.1016/0167-5087(83)91254-1.
  12. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  13. 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)" (PDF). The Journal of Chemical Physics. 94 (5): 3762. Bibcode:1991JChPh..94.3762S. doi:10.1063/1.459748. hdl:10486/7315.
  14. 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.

Cited sources
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