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| Atomic Number: | 34 | Atomic Symbol: | Se | | Atomic Weight: | 78.96 | Electron Configuration: | 2-8-18-6 | | Shells: | 2,8,18,6 | Filling Orbital: | 4p4 | | Melting Point: | 217oC | Boiling Point: | 384.9oC | | Uses: | copy machines, photoelectric cells, TV cameras, semiconductor in
solar batteries and rectifiers, colors glass red |
History(Gr. Selene, moon) Discovered by Berzelius in 1817, who found it
associated with tellurium, named for the earth.
SourcesSelenium is found in a few rare minerals such as crooksite and
clausthalite.
In years past it has been obtained from flue dusts remaining
from processing copper sulfide ores, but the anode metal from electrolytic
copper refineries now provide the source of mostof the world's
selenium.
Selenium is recoverd by roasting the muds with soda or sulfuric
acid, or by smelting them with soda and niter.
Properties- Selenium exists in several allotropic forms.
- Three are generally recognized, but as many as that have been claimed.
- Selenium can be prepared with either an amorphous or crystalline structure.
- The color of amorphous selenium is either red, in powder form, or black, in
vitreous form.
- Crystalline monoclinic slenium is a deep red; crystalline hexagonal
selenium, the most stalbe variety, is a metallic gray.
- Naturaly selenium contains six stable isotopes.
- Fifteen other isotopes have been characterized.
CompoundsThe element is a member of the sulfur family and resembles
sulfur both in its various forms and in its compounds.
UsesSelenium exhibits both photovoltaic action, where light is
converted directly into electricity, and photoconductive action, where the
electrical resistance decreases with increased illumination.
These properties
make selenium useful in the production of photocells and exposure meters for
photographic use, as well as solar cells.
Selenium is also able to convert
a.c. electricity to d.c., and is extensively used in rectifiers.
Below its
melting point selenium is a p-type semiconductor and is finding many uses in
electronic and solid-state applications.
It is used in Xerography for
reproducing and copying documents, letters, etc.
It is used by the glass
industry to decolorize glass and to make ruby-colored glasses and enamels.
It
is also used as a photographic toner, and as an additive to stainless steel.
HandlingElemental selenium has been said to be practially nontoxic and
is considered to be an essential trace element; however, hydrogen selenide and
other selenium compounds are extremely toxic, and resemble arsenic in their
physiological reactions.
Hydrogen selenide in a concentration of 1.5 ppm is
intolerable to man.
Selenium occurs in some soild in amounts sufficient to
produce serious effects on animals feeding on plants, such as locoweed, grown in
such soils.
Exposure to selenium compounds (as Se) in air should not exceed
0.2 mg/m^3 (8-hour time-weighted average - 40-hour week).
CostsSelenium is priced at about $300/lb.
It is also available in
high-purity form at a higher cost
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