Metal of the month

Se Selenium

Selenium

Berzelius discovered selenium in 1817 in the dusts formed in the lead chambers of a sulphuric acid plant. He found the element associated with tellurium (after the Latin tellus, earth) and called it selenium (after the Greek σελενη, moon).

In 1873, Willoughby Smith, an English electrical engineer, discovered that selenium’s electrical resistance decreased when illuminated - a property that paved the way for its use in photoelectric cells.

Properties

  • Exists in two forms: a silvery metal or a red powder.
  • Red selenium is an amorphous, glass-like solid, whereas grey selenium is a soft, bluish-grey metal.
  • Grey selenium is a semi-conductor. Its electrical conductivity increases on exposure to light, reverting to its normal value in darkness.

 

Applications

  • Selenium is used in glass making. When added in small amounts to silicate glasses, it decolours them by neutralising the green colour due to the presence of iron. At higher concentrations selenium may give the glass a bronze, anti-glare colour. Added as cadmium sulphoselenide, selenium gives glass a dark red colour (like traffic signals for roads and railways).
  • Together with cadmium and sulphur, selenium is a component of pigments used in plastic colouring.
  • Zinc selenide is also used in windows for infrared optical devices.
  • Selenium can be found in new CIGS photovoltaic technologies (cadmium indium gallium selenide)
  • Solid state memory in electronic applications.
  • Selenium is an essential micronutrient for animals.

Recycling

Selenium is most commonly produced from selenide in many sulfide ores and can be particularly found in the residues from copper refining. Other sources of recycling include spent targets used in chemical or physical vapour deposition or scrap from the production processes for CIGS photovoltaics.

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