Substance profile
Selenium
Selenium is a reddish colored powder that may become black upon exposure to air.
01 · Identification
What Selenium is
Selenium is a reddish colored powder that may become black upon exposure to air. Its molecular formula is Se and its molecular weight is 78.97 g/mol. It boils at 685 °C, melts at 221 °C, is practically insoluble in water.
Under the GHS it carries the signal word Danger. It is classed as hazardous Air Pollutants (HAPs).
02 · GHS classification
Hazards and label elements
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
| Code | Hazard statement |
|---|---|
| H331 | Toxic if inhaled. |
| H301 | Toxic if swallowed. |
| H373 | May cause damage to organs <or state all organs affected, if known> through prolonged or repeated exposure <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>. |
| H413 | May cause long lasting harmful effects to aquatic life. |
Precautionary statements: P260, P270, P271, P273, P301, P304, P310, P314, P330, P501
03 · Physical and chemical properties
Selenium properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 685 °C (1265 °F) | HSDB | |
| 685 °C (1265 °F) | at 760 mmHg | CAMEO | |
| Melting point | 220.8 °C (429.4 °F) | gray selenium | HSDB |
| 200 °C (392 °F) | NIOSH | ||
| Density | 4.39 g/cm³ | alpha form | HSDB |
| 4.28 g/cm³ | NIOSH | ||
| Solubility | Soluble in aq potassium cyanide soln, potassium sulfite soln, dilute aqueous caustic alkali soln | HSDB | |
| Insoluble in water and alcohol | HSDB | ||
| Soluble in concentrated nitric acid. | HSDB | ||
| Vapor pressure | 0 mmHg | approx | NIOSH |
| 0.0007501 mmHg | at 20 °C | ICSC | |
| Lower explosive limit (LEL) | Combustible Solid | NIOSH | |
| Critical temperature and pressure | 1493 °C (2719.1 °F) | HSDB | |
| Corrosivity | Strongly corrosive, especially at high temperature. | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
04 · Fire and explosion
Fire and explosion behaviour of Selenium
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Fire and explosion
During attempted conversion of recovered selenium metal to the dioxide by heating in oxygen, a vigorous explosion occurred. This was attributed to selenium-catalysed oxidation traces of organic impurities in the selenium. Oxidation of recovered selenium with nitric acid is rendered vigorous by presence of organic impurities, but is a safe procedure.
Source: HSDB
05 · Handling and storage
Storing and handling Selenium
Storage conditions
Usually stored at room temperature. Precautions must be taken to avoid contact with water or prolonged exposure to air and other materials with which it may react. Storage area construction must be such that rain water will not leak in or ground water will not enter. Used drums should be stored in this same dry area to avoid contamination /SRP: of the area/ and to minimize any hazard due to the residues.
Source: Hazardous Substances Data Bank (HSDB)
Incompatible materials
Selenium + Silver bromate: The reaction is violently explosive.
Source: Hazardous Substances Data Bank (HSDB)
Reactivity
SELENIUM, silicon, or sulfur ignites in fluorine gas at ordinary temperatures [Mellor 2:11-13 1946-47]. A mixture of barium carbide and selenium heated to 150 °C becomes incandescence [Mellor 5:862 1946-47]. Calcium carbide and selenium vapor react with incandescence [Mellor 5:862 1946-47]. A moist mixture of selenium and chlorates, except the alkali chlorates, becomes incandescent. Selenium reacts violently with chromium trioxide [Mellor 11:233 1946-47]. Reaction of selenium and silver bromate (also potassium bromate) is violently explosive [Mellor 2, Supp1:763 1956]. Freshly reduced selenium reacts vigorously with nitric acid. Trace amounts of organic matter probably influenced the reaction [J. Chem. Soc. 1938 p.391]. The reaction between zinc and selenium or tellurium is accompanied by incandescence [Mellor 4:476-480 1946-47].
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Selenium in the storage compatibility matrix →