The cryolite , or cryolite , is a Minéral composed of double Fluor RUE of Sodium and Aluminum, of formula NaAlF also noted 3NaF, AlF.

Cryolite is mainly used for the production of Aluminum and in the industry of ceramics. She was discovered on the west coast of the Greenland. It is a mineral rare  ; also, to face the needs for industry, cryolite is produced artificially.

Discovered

At the end of the 18th century a cargo liner of the royal Compagnie of the Greenlandic trade brings back Greenland of the samples of various ores to Copenhagen. The first cryolite sample is studied and described by Heinrich Christian Friedrich Schumacher in 1795 (professor of medicine, botanist and mineralogist with the royal academy of surgery).

He was studied by brésilo-Portuguese Jozé Bonifacius de Andrada and Danish Peter Christian Abildgaard . De Andrada reported that cryolite had a transparent aspect and brilliance and that it had the property to melt under the action of a flame as the ice. He called it cryolite what means “  hone gelée  ” in Greek (κρύος “  froid  ”, λίθος “  pierre  ”). The inhabitants of Greenland called it orsukksiksæt . Abildgaard made a communication with the Danish academy of sciences in 1800.

The chemical analysis of cryolite was made in an independent way by Martin Heinrich Klaproth with Berlin and Nicolas Louis Vauquelin with Paris.

After having explored Greenland, German Karl Ludwig Giesecke employed by royal Compagnie of the Greenlandic trade , in 1820 showed that cryolite was only not very present. The only known layer is located in bay of Arsuk meadows of the city called Ivigtut .

The single cryolite mine is worked in the town of Ivitgut.

Characteristics

• Number CASE  : 15096-52-3
• Number EINECS  : 239-148-8

Use

Aluminum

Cryolite is mainly used as flux in the production of Aluminum. It is mixed with the Alumine extracted the Bauxite. The mixture molten around 950 °C and then is electrolyzed.

It was selected because it dissolves fluorides and the oxides (of which alumina) but not aluminum, it leads the electric current and it melts with 1000 °C.

Glass and ceramics

For the manufacture of glasses, cryolite is used like flux and darkening agent. In the same way, it lowers the viscosity of glass in fusion, thus facilitating the removal of the bubbles.

As in the case of alumina, it is thanks to its capacity of dissolution of the Oxyde S (SiO, CAD for example) which it lowers the melting point of these oxides by forming Eutectique S. Its capacity opacifying is used to increase the opalescence (color of the opal, hones semi-precious pearly white color with mother-of-pearl reflection) of certain glasses.

It enters the composition of certain white enamels in proportions going from 5 to 15% in mass. It helps has to give an aspect frozen by the fluoride contribution.

Artificial cryolite

The single cryolite layer cannot provide the industrial needs.

It is manufactured by various techniques resting on the de  mixture;: Acid hydrofluoric (HF), Fluoride of sodium (NaF), Fluoride of ammonium, Fluosilicic acid, Fluoboric acid, Hydroxide of aluminum, Sulfate of aluminum, Aluminate of sodium, Soda (NaOH), Sodium carbonate, Sodium chloride (NaCl), Sulfate of sodium.

In the industrial application, it is generally presented in the form of white powder.

The worldwide production (with the Fluoride of aluminum AlF) is of more than 400  000 tons per annum.

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