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Cryolite and Ceramics

Etymology: From the Greek words "kryos", cold, and "lithos", stone.

An allusion to its glare close to that of ice

Year of discovery : 1799

Cryolite : Sodium Hexafluoaluminate (Molecular formula ALF6NA3, contains 32.9% Na, 12.8% Al, 54.3% F) can also contain traces of Fe and Ca.

Main deposits : Cryolite of the Ivitgut complex (Greenland)

This mineral is associated with large pegmatite deposits.

CAS# : 15096-52-3

European N° (and/or) EINECS: 2391488 (EINECS: European Inventory of Existing Commercial Substances)

HAZARD SENTENCES
20/22	Harmful by inhalation and ingestion
48/23/25	Toxic: risk of serious health effects in the event of prolonged exposure by inhalation and ingestion
CAUTION SENTENCES
22	Do not to breathe dust
37	Wear suitable gloves
45	In the event of an accident or feeling of sickness, see a doctor immediately
46	(if possible show him the label)

Because of its scarcity, this mineral has been replaced in industrial processes by artificially produced sodium and aluminium fluorides.

The production of aluminum fluoride(AlF3) and cryolite (AlF3,3NaF) on a world level represents more than 400,000 tons/year. They are used, mainly, in the electrometallurgy of aluminium.

In general :

Refined cryolite is a very fine white powder.

1 kg of cryolite gives 0.443 kg of Na2O and 0.243 kg of Al2O3 in glazes or glass.

Slightly soluble in water : 0.4 g/liter at 20°C

Molecular weight: 210 g

Density: 2.97

Linear dilation coefficient in glass: 2.2 X 10-7 °K-1 (very weak)

Fusion point : 1000-1020°C

Uses in glass and ceramics :

Cryolite is a powerful flux rather low in iron, used especially in glass for its strong solvent action on oxides such as SiO2, Al2O3 and CaO with which it forms eutectics at low melting temperatures. It is also an opacifier used in opal glasses in which it favours opalescence.

The melting and opacifying action of cryolite contributes to the homogeneity and fining of glass, it is also an easily fusible alumina source. Cryolite is used to accelerate fusion. The action of fluorine in small proportion strongly lowers viscosity and facilitates fining (elimination of bubbles present in glass in fusion).

Glazes : the addition of fluorides in glazes opacified by tin improves opacity, but fluorine release can cause pinholes and small bubbles if the glaze solidifies too early.

In white glazes cryolite can be used as a component at the level of 5 to 15 % by weight.

Cryolite is sometimes used as an auxiliary flux in white clays.

Cryolite is the most stable form for supplying fluoride in glass and glazes because of its high alumina content.

Cryolite is used in some Shino glazes in which the role of fluorine allows to intensify colors and facilitate the migration of iron to the surface while it escapes as a gas through the glaze in fusion.

Link to Hank Murrow's article on Shino glazes in order to learn more : http://perso.wanadoo.fr/smart2000/shinos.htm#formules

Use in metallurgy :

In metallurgy, it is mainly used as a slovent of alumina in the metallurgy of aluminium by electrolysis. Cryolite has the following properties: it dissolves fluorides and oxides of aluminium but not the metal. Melted at 1000°C, it becomes a conductor of electrical current.

Its density weaker than that of aluminium facilitates phase separation during electrolysis.

Production of aluminium: The process most often used consists in dissolving alumina in molten cryolite then to separate aluminium by electrolysis. The aluminium obtained is 99%, pure, after elimination of impurities by refining (iron, silicon, zinc, titanium, copper...), its purity reaches 99.99%.

Presence of fluorine in our environment :

Excerpt from Haguenau's site on fluorides in water:

9, way of Gases - 67500 Haguenau - Tel.. 03.88.73.71.71

http://www.ville-haguenau.fr/site_eau_vers2/pages/qualite/fluorure.asp

The earth's crust contains approximately 0,3 g/kg of fluorine. This element is more abundant than copper, for instance.One always finds it in a combined state as fluorides in association with other elements. Fluorine is concentrated in the ores containing cryolite and fluorite.

Fluorides are naturally present at concentrations generally lower than 1 mg/l in surface waters, but can reach several tens of mg/l in certain deep waters.

Fluorine is also present in plants, and mainly in the graminaceous ones. It plays a significant role in the animal kingdom, where it is found primarily in bones and teeth. Almost all foodstuffs contain fluorine but exotic tea, fish and some fruits are particularly rich in it. It should be noted that certain mineral waters are very rich in fluorides (up to 8 mg/l).

  

© Smart.Conseil / July 2003

  

 

CAS Number :

This number is allotted by Chemical Abstracts Services to each chemical entity, be it a quite precise molecule, a mixture of isomers or a product resulting from a well defined industrial process. Considering the complexity of chemical nomenclature and the possibility of indicating a substance by several names, the CAS Number makes it possible to identify chemical species without any ambiguity

 

CRYOLITE Toxicology by Edouard Bastarache

 

 

Molecular Formula : ALF6NA3

 

Main synonyms :

 

I-English :

Sodium hexafluoroaluminate.

CRYOLITE.

II-French :

Hexafluoroaluminate de sodium.

CRYOLITE.

Uses and sources of emission :

I-Aluminium Smelting :

Aluminium is produced from bauxite, a mineral containing aluminium oxide, ferrous oxide and silica. By a chemical process, bauxite is refined to aluminium oxide.

Pure aluminium is then produced by using an electrothermal process, where electrolysis takes place in a carbonlined steel container with molten cryolite.

Carbon anodes are dipped into the liquid molten cryolite. A direct current generates molten aluminium in the bottom of the cell.

II- Glaze Chemistry

III-Pesticide (Raticide)

Hygiene and Safety :

I-Appearance :

Crystalline, solid powdery material, colourless to dark, odourless.

II- Immediately dangerous to life or health (IDLH) : 250 mg/m3 as F.

III-Inflammability :

This product is non flammable.

IV-Techniques and Means of Extinguishing :

Special techniques :

Wear an autonomous respiratory apparatus provided with a complete facial mask and suitable protective clothing. Move containers away from the zone of fire if that does not present any risk.

V-Products of Combustion :

Highly toxic and irritating fumes of hydrofluoric acid.

Prevention :

I-Reactivity :

A-Stability :

This product is stable.

B-Incompatibility :

This product is incompatible with the following substances: Calcium oxide; at high temperature, strong acids, water or moisture breaks it up. It breaks up upon heating with aqueous solutions of calcium hydroxide or aqueous solution of alkali hydroxides.

C-Products of Decomposition :

It breaks up at the point of boiling. Thermal decomposition gives off toxic and irritating hydrofluoric acid fumes. Hydrolytic decomposition gives off hydrofluoric acid (normally at high temperature).

II-Handling :

Avoid prolonged and repeated skin contacts.

Ventilate adequately if not, wear a suitable breathing apparatus. Do not smoke, drink or eat during use.

Remove contaminated clothes and wash them before re-using them.

III-Storage :

Store away from incompatible materials. Preserve in an airtight container placed in a dry and well ventilated place.

IV-Leaks :

Avoid accumulation of dust. Collect it. Put in a container.

Collect waste materials and put them in a hermetic container.

V-Waste Disposal :

Check with the regional office of the Department of the Environment.

Toxicology :

I-Absorbtion :

This material is absorbed by the respiratory and digestive tracts.

II-Acute Effects :

The insoluble derivatives of fluorine (spathfluor, cryolite) have a very low acute toxicity. It causes irritation of the eyes and the respiratory system but, no irritation of the skin during tests carried out on animals.

III-Chronic Effects :

Loss of weight, anorexia, anemia, dental effects, eosinophilia, disorders of growth in young individuals.Gastro-intestinal, circulatory, respiratory and neurological disorders, itching. Possibility of constipation and pain located with the area of the liver. Possible fluorosis: brittleness of the bones, rigidity of the joints and decalcification of the bones.

When ingested, this product releases fluoride ions.

IV-Effects on Development :

No data concerning the antenatal development was found in the consulted documentary sources.

V-Cancerogenic Effects :

Evaluation by the ACGIH : Substance not classifiable as cancerogenic for man (A4 group).

The data do not make it possible to make an adequate evaluation of the cancerogenic effect.

VI-Mutagenic Effects :

No data concerning a mutagenic effect in vivo or in vitro on the cells of mammals were found in the consulted documentary sources.

 

Biological surveillance :

I-Biological parameter, biological index of exposure and time of sampling :

Urinary fluorides:

18 µmol/mmol of creatinine measured at the beginning of the first workshift of the week,

60 µmol/mmol of creatinine measured at the end of the workshift.

II-Factors to be considered at the time of interpretation :

The measurement of urinary fluorides is not a specific indicator of professional exposure.

Possible external contamination of the sample at the time of sampling can distort the evaluation due to exposure.

Absorption by the digestive tract may be considerable if there is a risk of contamination of the hands or food;

Biological indices of exposure apply only to exposures to metallic fluorides, hydrofluoric acid and fluorine.

An exposure to fluorides at levels equivalent to the standard may cause a urinary excretion of fluorides higher than the values suggested ACGIH; biological indices of exposure suggested by this organization aim at preventing any effect to the health of workers.

 

First aid :

Rinse abundantly the eyes with water, wash the skin and see a doctor.

In the event of ingestion, make the person vomit if he is conscious. Call a doctor.

In the event of inhalation of vapors or dusts, bring the person in a ventilated place.

See a doctor.

Quebec's Exposure limit :

Valeur d'exposition moyenne pondérée (VEMP) : 2,5 mg/m³, expressed as F (Fluorides)

 

References :

1-CSST-Quebec, Répertoire Toxicologique, 2003

2-Toxicologie Industrielle et Intoxications Professionnelles, Lauwerys R. last edition.

3-Sax's Dangerous Properties of Industrial Materials, Lewis C., last edition.

4-Clinical Environmental Health and Toxic Exposures, Sullivan J.B and Krieger G.R., last dition.

5-Occupational Medicine, Zenz C arl, last edition.

Out Bound Links

• (Typecodes) 12: EBA - Article by Edouard Bastarache

In Bound Links

• (Materials - General) Cryolite - Na3AlF6

  Cryloite, Sodium Fluoaluminate, Kryolith

---

Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, Québec, CANADA
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/