Nomenclature
CAS number: 7631-86-9
Silica; silicic anhydride.
O
2Si; mol wt 60.08.
O 53.26%, Si 46.75%.
SiO
2.
Description and references
Occurs in nature as agate, amethyst, chalcedony, cristobalite, flint, quartz, sand, tridymite. Reviews: Kirk-Othmer
Encyclopedia of Chemical Technology vol. 18 (Interscience, New York, 2nd ed., 1969) pp 46-111; Rochow in Comprehensive Inorganic Chemistry vol.
1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press,
Oxford, 1973) pp 1388-1402. Toxicology: L. T. Fairhall, Industrial Toxicology (Hafner, New York,
1969) pp 105-107.
Properties
Transparent, tasteless crystals, or amorphous
powder. d (amorphous) 2.2. d
0 (quartz) 2.65. Melts to a glass. Silica has the lowest coefficient
of expansion by heat of any known substance. It is practically insol
in water or acids, except hydrofluoric acid in which it readily dissolves
forming the gas silicon tetrafluoride; it is also slowly attacked
by heating with concd phosphoric acid. The crystallized forms of
silica are scarcely attacked by alkalies, while the amorphous is sol,
especially when finely divided.
See also Infusorial Earth.
Caution
Potential symptom of overexposure
to amorphous silica are eye irritation and pneumoconiosis. Potential
symptoms of overexposure to crystalline silica as respirable dust
are cough, dyspnea, wheezing; decreased pulmonary function, progressive
respiratory symptoms (silicosis). See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140,
1997) p 276-279. Crystalline silica (respirable size), primarily
quartz dusts occurring in industrial and occupational settings, is
listed as a known human carcinogen: Report
on Carcinogens, Eleventh Edition (PB2005-104914, 2004)
p III-231.Use
Manuf glass, water glass, refractories, abrasives,
ceramics, enamels; decolorizing and purifying oils, petroleum products,
etc.; in scouring- and grinding-compounds, ferrosilicon, molds for
castings; as anticaking and defoaming agent.