也谈生命 联系站长

浏览量

National Pollutant Inventory

作者:ihpa.net 发布时间:2017-10-13

Industry uses selenium to manufacture photocells, photographic exposure meters, solar cells, and rectifiers for home entertainment equipment. Further uses are in metal alloys, xerography, red or black glass, anti-dandruff shampoos, pigments in plastics, paints, dyes, enamels, inks, textiles, rubber (accelerator and vulcanising agent), photographic emulsions, and petroleum. It is also used in veterinary medicine, in medical therapeutic agents, as a nutritional feed additive for poultry and livestock, and as a fungicide and insecticide. Uses in electronics and photography account for the majority of selenium use, followed by the glass industry, then pigments. Some applications for specific selenium compounds follow. Selenium dioxide is the most widely used selenium compound in industry. It is used as an oxidising agent in drug and other chemical manufacture, a catalyst in organic syntheses, and an anti-oxidant in lubricating oils. Selenium sulfide is used in anti-dandruff shampoo. Selenous acid can be found in gun blueing solution which is used to clean the metal parts of a gun.

Substance details

Substance name: Selenium & compounds

CASR number: 7782-49-2

Molecular formula: Se

Synonyms: No synonyms.

Selenium compounds include selenium (IV) oxide or selenium dioxide (CAS# 7446-08-4), selenium (VI) fluoride or selenium hexafluoride (CAS# 7783-79-1), selenium (II) hydride or hydrogen selenide (CAS# 7783-07-5), selenium (IV) oxychloride (CAS# 7791-23-3), selenium (IV) sulfide or selenium disulfide (CAS# 7488-56-4), selenic acid (CAS# 7783-08-6), and selenous acid (CAS# 7783-00-8).

Physical properties

Selenium is an odourless metalloid (an element which has both metallic and non-metallic properties). It can be a grey (the 'metallic' and most stable form), red or black solid.

Atomic Number: 34

Atomic Mass: 79.0

Melting Point: 221°C (grey selenium)

Boiling Point: 685°C

Specific Gravity: 4.4-4.8

Properties vary widely depending on the particular compound. Some physical properties for selected selenium compounds follow.

Selenium disulfide is a light orange to red powder. Its melting point is less than 100°C and it decomposes when heated.

Selenium hydride is an extremely poisonous gas with revolting odour. Its melting point is -66°C, its boiling point is -41°C, and the compound is thermodynamically stable to 280°C.

Selenium dioxide is hygroscopic and melts at 315°C. It has a specific gravity of 3.95.

Selenous acid forms hygroscopic, colourless crystals that melt at 70°C. Its boiling point is 315°C, with a specific gravity 3.0.

Selenic acid forms white crystals that melt at 58°C. Its boiling point is 260°C.

Selenium hexafluoride is a very toxic colourless gas (melting point -39°C, boiling point -35°C).

Selenium oxychloride has a vapour density 5.7 and a melting point of 9°C.

Chemical properties

Selenium can exist in four different oxidation states, (II-), (0), (IV) and (VI), forming various salts. In aquatic environments, the (IV) and (VI) oxidation states are predominant. Selenium (IV) is known as selenite and selenium (VI) is known as selenate. Various chemical properties for selenium and selected selenium compounds follow.

Selenium burns in air when heated to give selenium dioxide. It reacts when heated with halogens, most metals and non-metals. Non-oxidising acids do not affect selenium.

Selenium dioxide can be obtained by treating selenium with hot nitric acid. It dissolves in water to give solutions of selenous acid.

Selenic acid evolves oxygen when heated above 200°C. It is a strong oxidising agent. Selenous acid and selenic acid are both water soluble.

Selenium dioxide is slightly water soluble.

Selenium disulfide and selenium hexafluoride are both insoluble in water.

Selenium hydride has a water solubility of 0.70 g/100 mL.

Further information

The National Pollutant Inventory (NPI) holds data for all sources of selenium and compounds in Australia.

Description

The severity of health effects will depend on how much selenium a person has been exposed to, for how long, the nature of the selenium compound(s), and current state of health. Trace amounts of selenium are essential for humans and most diets usually provide enough selenium to meet the daily requirement. Diets lacking selenium have resulted in heart problems and muscle pain. Diets with too much selenium can be harmful at levels 5 to 10 times higher than the daily requirement. Accidentally swallowing a large quantity of selenium supplement pills could be life-threatening without immediate medical treatment. Eating too much selenium over long periods of time can result in excessive tooth decay, discolouration of the skin and teeth, brittle hair, deformed nails, fatigue, irritability, depression and pallor. Feeling and control in the arms and legs may also be lost. People exposed to very high levels of selenium in the workplace have reported headaches, dizziness, fatigue, irritation (eye, nose, throat and bronchial tubes), collection of fluid in the lungs, and severe bronchitis. The exact levels at which these effects occur are not known. Upon contact with skin, selenium compounds have caused rashes, swelling, and pain. It may also protect against the toxicity of heavy metals such as cadmium, mercury and silver.

More details about two selenium compounds follow.

网友吐槽

推荐阅读

创业故事

  • Nigeria Natural Resources

    Nigeria Natural Resources

    Nigeria Natural Resources Category: About Nigeria Nigeria Natural Resources Nigeria is one of those countries in Africa ..

  • Mine Closures Deal A Blow To Illino

    Mine Closures Deal A Blow To Illino

    On the last day of January, Ozark-Mahoning will halt its mining operations in deep southern Illinois, where fluorspar, o..

  • Eureka Mine, Death Valley National

    Eureka Mine, Death Valley National

    Eureka Mine, Death Valley National Park Larry Seith exploring the Eureka Mine Did you know that Death Valley has more ab..

  • Vietnamese Dong (VND)

    Vietnamese Dong (VND)

    Wikinvest 2006, 2007, 2008, 2009, 2010, 2011, 2012. Use of this site is subject to express Terms of Service, Privacy Pol..

友情链接

前沿科技 高新技术 一路同行 技术动态 也谈生命

纳米材料,纳米技术,纳米科技,纳米论坛,中国纳米技术,新材料