Lithium fluoride
 |
|
 |
|
| Names | |
|---|---|
| IUPAC name
Lithium fluoride
|
|
| Identifiers | |
7789-24-4  |
|
| ChemSpider | 23007 |
| EC Number | 232-152-0 |
| Jmol 3D model | Interactive image |
| PubChem | 224478 |
| RTECS number | OJ6125000 |
|
|
|
|
| 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 |
|
Other cations
|
Sodium fluoride Potassium fluoride Rubidium fluoride Caesium fluoride |
|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
|
 verify (what is  ?) |
|
| 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.
Contents
Manufacturing[edit]
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[edit]
In molten salts[edit]
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[edit]
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[edit]
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[edit]
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[edit]
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[edit]
Naturally occurring lithium fluoride is known as the mineral griceite. It is extremely rare.[6]
References[edit]
- ^ "Lithium fluoride". Retrieved 2006-02-26.
- ^ http://chem.sis.nlm.nih.gov/chemidplus/rn/7789-24-4
- ^ a b 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
