cryolite


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cryolite

or

kryolite

(both: krī`əlīt') [Gr.,=frost stone], mineral usually pure white or colorless but sometimes tinted in shades of pink, brown, or even black and having a luster like that of wax. Chemically, it is a double fluoride of sodium and aluminum, Na3AlF6. Its principal use is as a flux in the smelting of aluminum. It is used also as a source of soda, aluminum salts, fluorides, and hydrofluoric acid (by the action of sulfuric acid). It was discovered in Greenland in 1794 and occurs almost nowhere else. Cryolite has been produced synthetically.

Cryolite

 

a mineral from the group of natural fluorides, with chemical composition Na2NaAlF6.

In cryolite’s structure, the Al and one-third of the Na are located in the center of the AlF6 and NaF6 octahedrons, while two-thirds of the Na is in the center of the NaF12 polyhedrons. The mineral crystallizes in the monoclinic system; cubic crystals are rare. Ordinarily, colorless, white, or gray crystal aggregates with a vitreous luster form. Cryolite has a hardness of 2.5–3.0 on the mineralogical scale and a density of 2,960–2,970 kg/m3. It is found in metasomatically displaced pegmatites and is formed from fluoride-enriched hot water solutions associated with alkaline granites. Industrial deposits are rare (Ivigtut in western Greenland).

Cryolite is used extensively in aluminum metallurgy; it is also used to obtain enamels and for other purposes. Most of the cryolite used in industry is obtained synthetically [by the interaction of the sulfates of Al and NaF; by neutralization of gaseous fluosilicic acid (H2SiF6) with aluminum hydroxide and NaOH].

The mineral is called cryolite because of its resemblance in luster and refractive index to ice. Some scientists use the term “cryolite” for all varieties of ice (ice, snow, hail); but others, only for ice, as a monomineral rock.

cryolite

[′krī·ə‚līt]
(mineralogy)
Na3 AlF6 A white or colorless mineral that crystallizes in the monoclinic system but has a pseudocubic aspect; found in masses of waxy luster; hardness is 2.5 on Mohs scale, and specific gravity is 2.95-3.0; used chiefly as a flux in producing aluminum from bauxite and for making salts of sodium and aluminum and porcelaneous glass. Also known as Greenland spar; ice stone.
References in periodicals archive ?
Construction of plants for production of cryolite and aluminum fluoride was started in 2008, but the financial crisis has not allowed the aluminum company to complete it.
Belonging to another than typical form morphologic and ecological group is has the possibility to inhabit the same biotopes [8], but in conditions of cryolite zone of Yakutia both forms are being observed only in flood land cenosis and rarely in watersheds [11].
The cryolite video experiments followed a similar setup to the gelatin experiments.
Cryolite has many properties which make it an ideal cryogenic insulation: It is free flowing which eliminates voids in cold box applications, is heat resistant, has good availability, is chemically inert and K value stable and does not change with time.
Asmund, and T Trond, "Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis," Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, vol.
Though SCML from CBP of synthetic cryolite possesses complicated composition as shown in Table 1, [F.sup.-], [Cl.sup.-], [H.sup.+], and [Na.sup.+] are four main kinds of ions in it.
Natural sources that contain the fluoride ion are fluorite, cryolite, and fluorapatite [4].
To arrive at his figures, Hodge cited a classic study of the effects of fluoride among cryolite workers by a European researcher, Kaj Roholm, and published in 1937.
Rich cryolite mines, necessary for the production of aluminum, required protection.
Chief among the native Brazilians who made major contributions was Jose Bonifacio de Andrada e Silva (1726-1789), who, after graduating from the Freiberg Mining Academy, went on to write prolifically of Brazil's "natural history." Andrada was the first to describe petalite, seapolite and cryolite; the mineral species andradite was named for him.
The Company also has three aluminium powder metallurgy plants, and produces cryolite, aluminium fluoride and cathodes.
Also, was added cryolite ([Na.sub.3]Al[F.sub.6]) which has the role to eliminate aluminum oxide in dros.