Calcium fluoride, properties

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. 

Calcium fluoride is insoluble in water and is transparent to light. Because of these properties, calcium fluoride is sometimes used to make windows for optical devices. Design a synthesis of 1.0 kg of CaF2. ... 

In his first paper3 , Stokes called the observed phenomenon dispersive reflexion, but in a footnote, he wrote I confess I do not like this term. I am almost inclined to coin a word, and call the appearance fluorescence, from fluorspar, as the analogous term opalescence is derived from the name of a mineral. Most of the varieties of fluorspar or fluorspath (minerals containing calcium fluoride (fluorite)) indeed exhibit the property described above. In his second paper7, Stokes definitely resolved to use the word fluorescence (Scheme 1.2). 

For more than the last half century experiments have been carried out to obtain electrodes with solid membranes containing inorganic insoluble compounds which the authors expect (consciously or not) to have ion-exchange properties (for a review, see [57]). These substances, for example insoluble cyanoferrates(II), phosphomolybdates, calcium fluoride, etc., are not, however, promising materials and probably only generate problems for the editors of specialized journals. 

Plasma-sprayed, flame-plated, or electrolytically deposited coatings of powders of Al O Ci O TiN, WC, and Ti02 can be applied as wear-resistant ceramics on metal substrates with or without Co, Ni, or Cr incorporated to improve mechanical properties. Silver, barium fluoride—calcium fluoride, and other modifying materials have also been found useful in ceramic coatings for improved friction and wear properties (35). Diamond coatings are also being developed (36). 

Regarding the two-dimensional systems, the optoelectronic properties of Si nanoslabs embedded in calcium fluoride and in silicon dioxide have been experimentally studied [44-52], confirming the role of quantum confinement, even if the discussion is still alive. 

Mix 0.5 gram of the precipitated silica with 1 gram of powdered calcium fluoride. Place the mixture in a test tube, moisten it with 36 N H2S04, and warm it gently under the hood. Dip a stirring rod in water and lower it, with a drop adhering, into the gas in the test tube. Note the precipitate that forms in the drop of water. Write equations for all the reactions, and state what rather unusual properties are shown by this experiment to be possessed by hydrofluoric acid and by silicon tetrafluoride. 

In 1961 Hayes and Twidell (8) found that if calcium fluoride crystals containing trivalent thulium were irradiated with x-rays, some of the thulium was converted to the divalent state. This discovery was the first of many in the study of dilute solutions of divalent rare earth ions. Most workers prefer to study the alkaline earth fluorides since these materials are stable with respect to air and have more attractive mechanical properties than the alkaline earth chlorides, bromides, and iodides. Enough work has been carried out in these softer materials to show that reactions similar to those in the fluorides do occur. 

What makes the sodium-sulfur cell possible is a remarkable property of a compound called beta-alumina, which has the composition NaAlnOiy. Beta-alumina allows sodium ions to migrate through its structure very easily, but it blocks the passage of polysulfide ions. Therefore, it can function as a semipermeable medium like the membranes used in osmosis (see Section 11.5). Such an ion-conducting solid electrolyte is essential to prevent direct chemical reaction between sulfur and sodium. The lithium-sulfur battery operates on similar principles, and other solid electrolytes such as calcium fluoride, which permits ionic transport of fluoride ion, may find use in cells based on those elements. 

Furthermore the electrolyte usually contains additives (AIF3 can be so regarded) that are intended to reduce the vapor pressure of the electrolyte, and therefore vapor losses/emissions of fluorides, or to improve such properties as electrical conductivity, liquidus temperature, or density. A representative additive is calcium fluoride. For example cryolite plus 5 wt%... 

In the foregoing examples the spectral data indicated a Lewis acid-base reaction on the surface where the alkali and alkaline earth cations acted as the electron acceptors while the adsorbates were the electron donors. It is quite natural that the reverse situation might be possible that is, the adsorbent be basic while the adsorbate show acidic properties so that in the chemisorption electron transfer will occur in the reverse direction. Several examples of such adsorption have already been discussed in this chapter. Kortiim (22) found another example in the adsorption of symmetrical trinitrobenzene on magnesia and on alumina. Whereas trinitrobenzene adsorbed on calcium fluoride or silica was colorless, on magnesia it was red with an absorption maximum at 4650 A (Fig. 26) and the spectrum of the adsorbed species was very... 

Samarium is used to dope calcium fluoride crystals for use in optical masers or lasers. Compounds of the metal act as sensitizers for phosphors excited in the infrared the oxide exhibits catalytic properties in the dehydration and dehydrogenation of ethyl alcohol. It is used in infrared absorbing glass and as a neutron absorber in nuclear reactors. The metal is priced at about 3.50/g (99.9%). Little is known of the toxicity of samarium therefore, it should be handled carefully. 

CHEMICAL PROPERTIES generally stable under ordinary conditions of use and storage calcium fluoride can react with hot concentrated sulfuric acid to liberate hydrogen fluoride fluorocarbons are chemically inert to most materials fluoroamides can react with lithium tetrahydroaluminate and with sodium at very high temperatures some fluorinated cyclopropenyl methyl ethers react with water or methanol FP(NA) LFL/UFL (NA) AT (NA) HC(NA). 

Raj] Rajagopalan, K.V., Kalyanaraman, R., Sundaresan, M., Thermodynamic Properties of Dicalcium Ferrite by Calcium Fluoride Galvanic Cells , J. Electrochem. Soc. India, 36(3), 157-159 (1987) (Thermodyn., Exsperimental, 7)... 

One of the most important properties of solutions is their ability to allow chemical species to come into close contact so that they can react For example, if perfectly dry crystals of calcium chloride, CaClj, were mixed with dry crystals of sodium fluoride, NaF, a chemical reaction would not occur. However, if each is dissolved in separate solutions which are then nuxed, a precipitation reaction occurs in which calcium chloride and sodium fluoride in aqueous solution (aq) react to produce calcium fluoride solid (s) and a solution of sodium chloride ... 

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