Lithium fluoride
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| Names | |
|---|---|
| IUPAC name
Lithium fluoride | |
| Identifiers | |
7789-24-4  | |
| 3D model (Jmol) | Interactive image |
| ChemSpider | 23007 |
| ECHA InfoCard | 100.029.229 |
| EC Number | 232-152-0 |
| PubChem | 224478 |
| RTECS number | OJ6125000 |
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| Properties | |
| LiF | |
| Molar mass | 25.939(2) g/mol |
| Appearance | white powder or transparent crystals, non-hygroscopic |
| Density | 2.635 g/cm3 |
| Melting point | 845 °C (1,553 °F; 1,118 K) |
| Boiling point | 1,676 °C (3,049 °F; 1,949 K) |
| 0.27 g/100 mL (18 °C)[1] 0.134 g/100 mL (25 °C) | |
| Solubility | soluble in HF insoluble in alcohol |
| Refractive index (nD) |
1.3915 |
| Structure | |
| Cubic | |
| a = 403.51 pm | |
| Linear | |
| Thermochemistry | |
| 1.604 J/(g K) | |
| Std molar entropy (S |
1.376 J/(g K) |
| Std enthalpy of formation (ΔfH |
-616 kJ/mol |
| Hazards | |
| NFPA 704 | |
| Lethal dose or concentration (LD, LC): | |
| LD50 (median dose) |
143 mg/kg (oral, rat)[2] |
| Related compounds | |
| Other anions |
Lithium chloride Lithium bromide Lithium iodide Lithium astatide |
| Other cations |
Sodium fluoride Potassium fluoride Rubidium fluoride Caesium fluoride Francium fluoride |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
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| Infobox references | |
Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid, that transitions to white with decreasing crystal size. Although odorless, lithium fluoride has a bitter-saline taste. Its structure is analogous to that of sodium chloride, but it is much less soluble in water. It is mainly used as a component of molten salts.[3] Formation of LiF releases one of the highest energy per mass of reactants, only second to that of BeO.
Manufacturing
LiF is prepared from lithium hydroxide and hydrogen fluoride or by dissolving lithium carbonate in excess hydrogen fluoride, evaporating to dryness and heating to red hot.
Applications
In molten salts
Fluorine is produced by the electrolysis of molten potassium bifluoride. This electrolysis proceeds more efficiently when the electrolyte contains a few percent of LiF, possibly because it facilitates formation of Li-C-F interface on the carbon electrodes.[3] A useful molten salt, FLiNaK, consists of a mixture of LiF, together with sodium fluoride and potassium fluoride. The primary coolant for the Molten-Salt Reactor Experiment was FLiBe; LiF-BeF2 (66-33 mol%).
Optics
Because of its large band gap, LiF crystals are transparent to short wavelength ultraviolet radiation, more so than any other material. LiF is therefore used in specialized UV optics,[4] (See also magnesium fluoride). Lithium fluoride is used also as a diffracting crystal in X-ray spectrometry.
Radiation detectors
It is also used as a means to record ionizing radiation exposure from gamma rays, beta particles, and neutrons (indirectly, using the 6
3Li
(n,alpha) nuclear reaction) in thermoluminescent dosimeters.
Nuclear reactors
Lithium fluoride (highly enriched in the common isotope lithium-7) forms the basic constituent of the preferred fluoride salt mixture used in liquid-fluoride nuclear reactors. Typically lithium fluoride is mixed with beryllium fluoride to form a base solvent (FLiBe), into which fluorides of uranium and thorium are introduced. Lithium fluoride is exceptionally chemically stable and LiF/BeF2 mixtures (FLiBe) have low melting points (360 C - 459 C) and the best neutronic properties of fluoride salt combinations appropriate for reactor use. MSRE used two different mixtures in the two cooling circuits.
Cathode for PLED and OLEDs
Lithium fluoride is widely used in PLED and OLED as a coupling layer to enhance electron injection. The thickness of LiF layer is usually around 1 nm. The dielectric constant (or relative permittivity) of LiF is 9.0[5]
Natural occurrence
Naturally occurring lithium fluoride is known as the mineral griceite. It is extremely rare.[6]
References
- ↑ "Lithium fluoride". Retrieved 2006-02-26.
- ↑ http://chem.sis.nlm.nih.gov/chemidplus/rn/7789-24-4
- 1 2 J. Aigueperse, P. Mollard, D. Devilliers, M. Chemla, R. Faron, R. Romano, J. P. Cuer, "Fluorine Compounds, Inorganic" in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a11_307.
- ↑ "Crystran Ltd., a manufacturer of infrared and ultraviolet optics". Retrieved 2010-12-28.
- ↑ C. Andeen, J. Fontanella,D. Schuel, "Low-Frequency Dielectric Constant of LiF, NaF, NaC1, NaBr, KC1, and KBr by the Method of Substitution", Physical Review B, 2, 5068-5073 (1970) doi:10.1103/PhysRevB.2.5068.
- ↑ Mindat http://www.mindat.org/min-1749.html