Ever since selenium was found to possess photoconductive properties, it has been used for many diverse applications in industry. Photoconductivity was discovered by William Adams and Richard Day in 1876.

They found that selenium produced an electric current when light was allowed to fall on it. The importance of this phenomenon was recognized by electrical scientists, in that it proved that light could be converted into electricity without the need for heat or machinery. This eventually led to the development of photovoltaic or solar cells.  

Selenium compounds and their uses

The most important current non-biologic uses of selenium are:

• In the form of sodium selenate, it is used in the glass industry, where small amounts act to decolorize glass. For example, adding a little selenium removes the green tint imparted by the presence of iron impurities in soda-lime silica glass.  
• Larger amounts of ammonium selenite are used to make ruby red glass, as in traffic lights, or for art glass, as well as black glass. The presence of selenium in plate glass is important to architects in reducing the amount of solar radiation that is transmitted through the glass.
• Cadmium selenide is used for its photoconductive and photoelectric properties, in the electronics industry. This includes security equipment such as “electric eyes”, and photoreceptors for photocopy machines, as well as rectifiers and light exposure meters for the photographic industry. Selenium compounds are now largely replaced by organic photoreceptors, which are safer, and more cost-effective as well as offering higher performance, when operating at lower speeds.  
• Elemental selenium is used in the manufacture of stainless steel and some other alloys, such as with bismuth as a safer substitute for lead in plumbing applications.
• In photography, selenium is used to coat metal cylinders in order to produce a transferable photographic image by the process of xerography.
• Selenium is used to produce heat-stable pigments in the red spectrum, such as those used to manufacture plastics, paints, enamels, inks and rubber.  These pigments resist dampness, and withstand chemicals as well as solar radiation. However, the toxicity of cadmium and the higher cost has restricted their widespread use.  
• Selenium acts as a catalyst in the production of medicinal drugs such as cortisone.
• Selenium sulfide is the effective ingredient in antidandruff shampoos, and in some veterinary medications; selenium disulfide is also an ingredient in several veterinary formulations.
• Selenium diethyldithiocarbamate is used in other fungicidal preparations and in the vulcanization process of rubber.
• Selenium is used as feed enrichment for livestock and poultry and also as a component in the preparation of pesticides.
• Selenium-containing dietary supplements are usually tablets containing 10-25 µg of available selenium.
• Sodium selenite is an inorganic compound used to enrich soil in selenium-deficient areas.
• Selenium dioxide is a catalyst used in several processes such as oxidation, hydrogenation and dehydrogenation of organic compounds.
• Selenium hexafluoride is an electrical insulator gas.
• Selenium oxychloride is an industrial solvent used in the processing of sulfur, selenium, tellurium, rubber, resins, bakelite, gums, glues, and asphalt.
• Aluminium selenite is used in the production of hydrogen selenide for use as semiconductors.
• Cupric selenate is used to impart color to copper and copper alloys.
• Tungsten diselenide is used in lubricants.

References

• http://www3.epa.gov/airtoxics/hlthef/selenium.html
• http://www.atsdr.cdc.gov/toxprofiles/tp92-c5.pdf
• http://minerals.usgs.gov/minerals/pubs/commodity/selenium/selemyb02.pdf

Further Reading

• Selenium - What is Selenium?
• Sources of Selenium
• Selenium Biologic Applications
• Selenium Controversial Health Effects
• Selenium Toxicity