Calcium fluoride synthetic

The usual method for the synthesis of the w-fluoro aldoses is based on the displacement of a methylsulfonyloxy group by fluorine (supplied by either potassium fluoride or calcium fluoride). The reaction may be accomplished in aqueous methanol, ethylene glycol," or JV,JV-dimethyl-formamide, employing carbohydrate derivatives that have all the hydroxyl groups, except that to be replaced, blocked by groups stable to bases. The following example illustrates the synthetic method. ... 

Cryolite, which is so called on account of its high fusibility, is a double fluoride of aluminium and sodium of the formula Al2Fe.6NaF. It is obtained from Western Greenland, where it occurs in beds up to one metre thick, but the high price of this material has led to the manufacture of synthetic cryolite, using calcium fluoride (fluor-spar), which is found in considerable quantities. 

Concerning synthetic fluoridated calcium phosphate biomaterials (i.e. fluorapa-tites, fluorhydroxyapatites, carbonated fluorhydroxyapatites and other calcium... 

Fig. 8. Evolution of synthetic and biological apatites in the presence of fluoride ions. The increase of pH and/or phosphate concentration in solution favours the formation of fluoridated apatite, whereas the increase of fluoride and/or calcium concentration favours CaF2 formation. At physiologic pH and mineral ions concentrations (in all body fluids), the formation of fluoridated apatite is favoured.

Both lyotropic and thermotropic liquid-crystalline synthetic polymers have been widely studied. Aromatic polyamides constitute the most important class forming liquid-crystalline solutions the solvents are either powerfully protonating acids such as 100% sulphuric acid, chloro-, fluoro- or methane-sulphonic acid, and anhydrous hydrogen fluoride, or aprotic dipolar solvents such as dimethyl acetamide containing a small percentage, usually 2-5 %, of a salt such as lithium chloride or calcium chloride. Such solutions constitute a nematic phase within certain limits. Some criteria for formation of a nematic instead of an isotropic phase are ... 

Bone ash, and synthetic apatite, which are essentially calcium phosphate (Ca3(P04)2), or a synthetic apatite, calcium hydroxide mixture, are also effective methods for fluoride removal because of their affinity for these phosphate salts. 

Nriagu JO (1984) Formation and stability of base metal phosphates in soils and sediments. In Phosphate Minerals. Nriagu JO, Moore PB (eds) Springer-Verlag, New York, p. 318-329 Oberti R, Ottolini L, Della Ventura G, Pardon GC (2001) On the symmetiy and crystal chemistiy of britholite New stmctural and microanalytical data. Am Mineral 86 1066-1075 Ohkubo Y (1968) EPR spectra of manganese(II) ions in synthetic calcium chloride fluoride phosphates. J Appl Phys 39 5344-5345... 

These techniques are bas not only on the principle that lead-containing phosphates with the apatite structure are highly insoluble, but also that rapid reactions occur with apatite and lead ions at the sohd/aqueous solution interface [12, 13, 15, 20, 29, 48, 53, 56]. Removal of lead from aqueous solutions using synthetic hydroxyapatite gives aqueous lead concentrations below the maximum contamination level after Ih [12, 53]. Other workers [9] observed the formation of calcium-lead apatite solid-solutions after 3 mins contact between synthetic hydroxyapatite and aqueous solutions containing lead, and no lead was detected in the aqueous solution after 24 h contact. However, the efficiency of lead removal depends on the characteristics of the phosphate rock employed [15]. It has been shown that the composition and crystallinity of the phosphate influence the speed of the surface reactions [4, 44]. More highly crystalline solids have lower solubilities and dissolution rates, making the apatite less reactive [4]. The presence of fluoride in the hydroxyapatite structure decreases its solubility and dissolution rate, while the presence of carbonate decreases structural stability, and increases solubility and the dissolution rate [4, 35]. 

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