Selenium

Selenium shows photovoltaic action (light is converted directly to electricity) and photoconductive action (electrical conductance increases with increased illumination).   These properties make selenium useful in the production of photocells and exposure meters for photography, and solar cells.   Selenium converts a.c. (alternating current) to d.c. (direct current), which makes it useful in rectifiers (devices that change a.c. to d.c.).   It is a p-type semiconductor, so it is used in solid-state devices, e.g., transistors.   It is used in Xerography toner, glassmaking, and an additive to stainless steel. ^{Lide 4-26}

Selenium is essential to animal life and beneficial to plant life.   It promotes healthy immune functioning, reduces the incidence of viral hepatitis in selenium-deficient populations, presumably by enhancing immune system, improves the motility of sperm cells to increase conception.   Sources: brewer's yeast, organ meats, egg yolks, dairy products, fish, shellfish, whole grains, onions.^{Netzer 803}   Selenium compounds (e.g., hydrogen selenide) are extremely toxic.   Concentrated amounts of these compounds in soil can harm animals feeding on grasses.

Selenium was discovered in 1817 by Jöns Jakob Berzelius.   Selenium is found in a few rare minerals, viz., crooksite and clausthalite.   It is obtained from the anode muds from copper electrolytic refining.   The muds are roasted with soda and sulfuric acid or they are smelted with soda and niter.   Selenium can be prepared with either an amorphous or crystalline structure. ^{Lide 4-26}