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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
- This mineral is associated with large
- CAS# : 15096-52-3
- European N° (and/or) EINECS:
2391488 (EINECS: European Inventory of Existing Commercial
Harmful by inhalation and
Toxic: risk of serious health
effects in the event of prolonged exposure by inhalation
Do not to breathe dust
Wear suitable gloves
In the event of an accident or
feeling of sickness, see a doctor immediately
(if possible show him the
- 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
- 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
- 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
- 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
- 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..
- 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
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
by Edouard Bastarache
- Molecular Formula :
- Main synonyms
- I-English :
- Sodium hexafluoroaluminate.
- II-French :
- Hexafluoroaluminate de sodium.
- Uses and sources of
- 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
- 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
- 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
- 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
- Ventilate adequately if not, wear a
suitable breathing apparatus. Do not smoke, drink or eat during
- 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
- 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.
- 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
- 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
- Absorption by the digestive tract may be
considerable if there is a risk of contamination of the hands or
- Biological indices of exposure apply
only to exposures to metallic fluorides, hydrofluoric acid and
- 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
- 2-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R. last
- 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
- 5-Occupational Medicine, Zenz C arl,
Out Bound Links
In Bound Links
Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, QuÃ©bec, CANADA