LITHIUM FLUORIDES

Benzyne may also be generated by treating o bromofluorobenzene with lithium In this case o fluorophenylhthmm is formed which then loses lithium fluoride to form benzyne... 

Lithium fluoride is the optimum crystal for all wavelengths less than 3 A. Pentaerythritol (PET) and potassium hydrogen phthalate (KAP) are usually the crystals of choice for wavelengths from 3 to 20 A. Two crystals suppress even-ordered reflections silicon (111) and calcium fluoride (111). 

Lithium fluoride is transparent down to about 105 nm, below which windowless systems must be used with differential pumping. 

Figure 8.28 shows how the X-rays fall on the solid or liquid sample which then emits X-ray fluorescence in the region 0.2-20 A. The fluorescence is dispersed by a flat crystal, often of lithium fluoride, which acts as a diffraction grating (rather like the quartz crystal in the X-ray monochromator in Figure 8.3). The fluorescence may be detected by a scintillation counter, a semiconductor detector or a gas flow proportional detector in which the X-rays ionize a gas such as argon and the resulting ions are counted.

The use of CIF and BrF as ionizing solvents has been studied (102,103). At 100°C and elevated pressures, significant yields of KCIF [19195-69-8] CsClF [15321-04-7], RbClF [15321-10-5], I-CBrF [32312-224], RbBrF [32312-224], and CsBrF [26222-924]obtained. Chlorine trifluoride showed no reaction with lithium fluoride or sodium fluoride. 

Properties. Lithium fluoride [7789-24-4] LiF, is a white nonhygroscopic crystaUine material that does not form a hydrate. The properties of lithium fluoride are similar to the aLkaline-earth fluorides. The solubility in water is quite low and chemical reactivity is low, similar to that of calcium fluoride and magnesium fluoride. Several chemical and physical properties of lithium fluoride are listed in Table 1. At high temperatures, lithium fluoride hydroly2es to hydrogen fluoride when heated in the presence of moisture. A bifluoride [12159-92-17, LiF HF, which forms on reaction of LiF with hydrofluoric acid, is unstable to loss of HF in the solid form. 

Manufacture. Lithium fluoride is manufactured by the reaction of lithium carbonate or lithium hydroxide with dilute hydrofluoric acid. If the lithium carbonate is converted to the soluble bicarbonate, insolubles can be removed by filtration and a purer lithium fluoride can be made on addition of hydrofluoric acid (12). High purity material can also be made from other soluble lithium salts such as the chloride or nitrate with hydrofluoric acid or ammonium bifluoride (13). 

Optical crystals of high purity lithium fluoride are grown by use of the Stockbarger process (10) in sizes to 25 cm dia x 25 cm high (14). Typical commercial material contains 99.2% LiF typical impurities include Li CO and Fe202 at <0.1% levels, and and heavy metals as Pb at <0.01%... 

Uses. Lithium fluoride is used primarily in the ceramic industry to reduce firing temperatures and improve resistance to thermal shock, abrasion, and acid attack (see Ceramics). Another use of LiF is in flux compositions with other fluorides, chlorides, and borates for metal joining (17) (see Solders). 

Lithium fluoride is an essential component of the fluorine cell electrolyte 1% LiF in the KF 2HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cells to depolarize (18). Thermoluminescent radiation dosimeters used in personnel and environmental monitoring and in radiation therapy contain lithium fluoride powder, extmded ribbons, or rods (19). 

Molten lithium fluoride is used in salt mixtures for an electrolyte in high temperature batteries (qv) (FLINAK) (20), and as a carrier in breeder reactors (FLIBE) (21) (see Nuclear reactors). 

Beryllium. Beryllium [7440-41-7], Be, metal is produced by electrolysis of KCl—NaCl—BeCl2 melts. Temperatures up to 900°C are required. CeU voltages are 6 to 9 V (115). Electrolysis of mixtures of beryUium oxide [1304-56-9], BeO, ia lithium fluoride [7789-24-4], LiF, and beryUium fluoride [7787-49-7], BeF2, has produced beryUium metal at about 700°C and 2.6 V (116). DetaUs of fused salt metal winning processes are given ia Table 7. 

Figure 3.11. VISAR fringe record and the velocity profile at the calcite/lithium fluoride interface at about 18 GPa. The excellent time resolution of the interferometer allows an unambiguous determination of the rarefaction shock (d) in calcite (Grady, 1986).

J.E. Flinn, G.E. Duvall, G.R. Fowles, and R.F. Tinder, Initiation of Dislocation Multiplication in Lithium Fluoride Monocrystals Under Impact Loading, J. Appl. Phys. 46, 3752-3759 (1975). 

K.S. Tunison and Y.M. Gupta, Effects of Surface Preparation on Elastic Precursor Decay in Shocked Pure Lithium Fluoride, Appl. Phys. Lett. 48, 1351-1353 (1986). 

S.E. Arione and G.E. Duvall, Temperature Dependence of the Precursor Amplitude in <111 > Lithium Fluoride, in Shock Waves in Condensed Matter (edited by Y.M. Gupta), Plenum, New York, 1986, pp. 299-302. 

Figure 9.20 shows the setup for a symmetric plate impact test. The projectile here has a facing plate of ceramic and is backed with a low-density foam, for support of the ceramic during launch. The facing plate of the target is also made of ceramic. The lithium fluoride slab, which backs the target sample, serves as a window for the laser velocity interferometer (VISAR) that measures the time-resolved particle velocity at the sample/window interface. 

The ionic bond is the most obvious sort of electrostatic attraction between positive and negative charges. It is typified by cohesion in sodium chloride. Other alkali halides (such as lithium fluoride), oxides (magnesia, alumina) and components of cement (hydrated carbonates and oxides) are wholly or partly held together by ionic bonds. 

Heptafluoro-2-naphthyllithiuni prepared by metalation reaction can thermally decompose to a hexafluoro-l,2-naphlhalyne by elimination of lithium fluoride [36, 37] In this organolithium compound, fluorine elimination can occur from either position 1 or 3, however, no evidence for fluorine elimination from position 3 IS observed... 

In this case, o-fluorophenyllithium is fonned, which then loses lithium fluoride to fonn... 

Fluor-jod, n. iodine fluoride, -kalium, n. potassium fluoride, -kalzium, n. calcium fluoride, -kiesel, m. silicon fluoride, -kie-selsaure,/. fluosilicic acid, -kohlenstoff, m. carbon fluoride, -lithium, n. lithium fluoride. -metall, n. metallic fluoride, -natrium, n. sodium fluoride, -phosphat, n. fluophosphate. -phosphor, m. phosphorus fluoride, -salz, n. fluoride, -schwefel, m. sulfur fluoride, -selen, n. selenium fluoride, -silber, n. silver fluoride, -silikat, n. fluo-silicate. -silizium, n. silicon fluoride, -sili-ziumverbindung, /. fluosilicate. -tantal-sMure, /. fluotantalic acid, -tellur, n. tellurium fluoride, -titan, n. titanium fluoride, -toluol, n. fluorotoluene, fluotoluene. 

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