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.
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Later, the United States began to import cryolite from the Ivittuut deposit.
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Production and marketing of various alumina-based chemicals including specialty calcined aluminas, alumina hydrate, aluminum sulphate (solid and liquid) and the marketing of electrolytes including aluminum fluoride and cryolite is administered by our Alcan Chemicals division.
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He used aluminum oxide dissolved in a molten mineral named cryolite, and into it he stuck carbon electrodes.
Lopac (1975), polyacrylate (1975), nitrile barrier resins (1975), polybutylene (1975), Cryolite (1977), styrenic terpolymers (1977), high clarity PVC (1978), HMW-PE, acrylic-modified nylon 6, ethylene-vinyl chloride copolymer.
In smelting pots where aluminum is made, carbon anodes are held partially submerged in molten cryolite, and their precise elevation is critical to efficiency.
In addition, some of its profitable new projects were put into production, like the 30,000t/a cryolite.
Last week the President of Tajikistan made a working visit to Beijing, where a package of documents was signed, including the agreement between the Export-Import Bank of China and Finance Ministry of Tajikistan on concessional loan for construction of the section of the Dushanbe-Kurgan-Tube railway, construction of the second unit of the Dushanbe-2 combined heat and power plant, construction of the plants manufacturing cryolite, aluminum fluoride, sulphate acid as part of modernization of the Tajik Aluminum Company (TALCO).