Electron Configuration: [Ar] 4s2 3d10 4p4
Name of Element: Selenium
Element Classification: Non-Metal
Atomic Number: 34
Atomic Mass: 78.96 amu
Melting Point (°K): 490.15
Boiling Point (°K): 958.05
Crystal Structure: Hexagonal
Density (g/cm3): 4.79
Specific Heat (@20°C J/g mol): 0.321 (Se-Se)
Fusion Heat (kJ/mol): 5.23
Evaporation Heat (kJ/mol): 59.7
Pauling Negativity Number: 2.55
First Ionizing Energy (kJ/mol): 940.4
Oxidation States: 6, 4, -2
Lattice Structure: Hexagonal
Lattice Constant (Å): 4.360
Description: Selenium can be prepared with either an amorphous or crystalline structure. Crystalline monoclinic selenium is deep red; crystalline hexagonal selenium, the most stable variety, is a metallic grey.
Separation: Most selenium is made as a byproduct of copper refining. It also accumulates in the residues from sulphuric acid production. Extraction of Selenium is a complex process and the specific technique employed varies depending on the other compounds and elements that are present. Typically, the first step involves an oxidation in the presence of sodium carbonate (soda ash):
Cu2Se + Na2CO3 + 2O2 → 2CuO + Na2SeO3 + CO2
The selenite Na2SeO3 is acidified with sulphuric acid. Any tellurites precipitateout leaving selenous acid, H2SeO3, in solution. Selenium is liberated from selenous acid by SO2 addition:
H2SeO3 + 2SO2 + H2O → Se + 2H2SO4
"Mineral Yearbook 2007: Selenium and Tellurium". United States geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/selenium/myb1-2007-selen.pdf.
"Selenium", Los Alamos National Laboratory, 2003-12-15, http://periodic.lanl.gov/elements/34.html
Coutts, T.J. ; Kazmerski, L.L. ; Wagner, S., "Copper indium diselenide for photovoltaic applications", http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5189733
Noufi, Rommel; Ken Zweibel. "HIGH-EFFICIENCY CDTE AND CIGS THIN-FILM SOLAR CELLS: HIGHLIGHTS AND CHALLENGES". National Renewable Energy Laboratory. http://www.nrel.gov/pv/thin_film/docs/wc4papernoufi__.doc.
- Glass and Ceramics: Selenium is used extensively in glass and ceramic manufacturing, where it is used to impart red-bronze color to glasses, enamels and glazes as well as to remove color from glass by counteracting the green tint imparted by ferrous impurities.
- Catalysts: Selenium is a catalyst in many chemical reactions and is widely used in various industrial and laboratory syntheses, particularly organoselenium chemistry. It is also widely used in structure determination of proteins and nucleic acids by X-ray crystallography.
- Metallurgical Applications: Selenium is used with bismuth in brasses to reduce the toxicity of lead.
- Rubber Industry: Selenium can improve the abrasion resistance (wear properties) of vulcanized rubber.
- Electronics: due to its photoconductive properties, Selenium is used in photocopying, photocells, x-ray imaging, light meters and photovoltaic solar cells.
- Photography: Selenium is used as a toner in photographic prints.
- Biological Applications:
- Medical use: Selenium disulfide is used as an active ingredient in some dandruff shampoos, and in body lotions as an anti-fungal aid.
- Nutrition: Selenium is used widely in multi-vitamins and dietary supplements (typically 50 to 200 micrograms per day for adult humans). The role of Selenium in preventing various types of cancer is being widely studied and reported; Selenium is also being studied as a key additive in anti-HIV drugs.
- Livestock feeds: Selenium is used in carefully prescribed quantities to improve the nutritional value of animal feeds.
- Cosmetics: an evolving application for Selenium includes orthodontic materials with improved antibacterial properties.
- Coatings: Selenium is used as an antimicrobial/antifouling additive in industrial, architectural and marine coatings and sealants.