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Home , Hydrogen selenide, Isotopes of selenium, Selenic acid, Selenide, Selenium, Selenium dioxide

SELENIUM 217

4. CHEMICAL AND PHYSICAL INFORMATION

4.1 CHEMICAL IDENTITY

Information regarding the chemical identity of and selenium compounds is presented in Table 4-1.

4.2 PHYSICAL AND CHEMICAL PROPERTIES

Selenium is a non- element with 34 and an of 78.96 (Lide 2000). Selenium belongs to 6 (Group VIA) of the , located between and , and resembles sulfur both in its various forms and in its compounds. The six stable of selenium are 74Se, 76Se, 77Se, 78Se, 80Se, and 82Se. These isotopes occur naturally with approximate abundances of 0.87, 9.02, 7.58, 23.52, 49.82, and 9.19%, respectively (Hoffmann and King 1997). Artificial radioactive have also been created by neutron activation. The gamma-emitting 75Se has been used in diagnostic applications of medicine (Hoffmann and King 1997). Selenium exists in several allotropic forms. Three are generally recognized, but as many as six have been claimed (Lide 2000). The stable form at ordinary room temperatures is the grey or hexagonal form with a of 220.5 EC (Lide 2000). The other two important forms are red (monoclinic) with a melting point of 221 EC and amorphous selenium, which exists in black and red forms. Black amorphous selenium is vitreous and is formed by the rapid cooling of liquid selenium. Red amorphous selenium is colloidal and is formed in reduction reactions (Hoffmann and King 1997). Important selenium oxidation states are -2, 0, +4, and +6.

The chemical properties of selenium are similar to sulfur. Selenium combines with and many directly or in aqueous solution. The resemble in appearance, composition, and properties (Hoffmann and King 1997). Selenium may form halides by reacting vigorously with and , but the reactions with and are not as rapid. Selenium does not react directly with fluoride or hydrogen , but decomposes to liberate and yield hydrogen (Hoffmann and King 1997). Selenium reacts with to form a number of , the most stable of which is .

Information regarding the physical and chemical properties of selenium and selenium compounds is located in Table 4-2.

SELENIUM 218

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-1. Chemical Identity of Selenium and Selected Compoundsa

Hydrogen Selenious Characteristic Selenium selenide Selenic acid

Synonyms Elemental Dihydrogen , Monohydrated selenium; selenide; liquidDOT,b selenium selenium base; hydrogen dioxide; selenium dust; selenide [H2Se]; selenous colloidal selenium; selenium selenium anhydride; homopolymerb; selenium selenium alloy dihydride; selenium ; selane

Registered trade C.I. 77805; name(s) VANDEXb

Chemical formula Se H2Se H2SeO4 H2SeO3

Wisewesser line SE H2 SE H2.SE-04 H2SE-03 notation

Identification numbers: CAS 7782-49-2 7783-07-5 7783-08-6 7783-00-8 NIOSH RTECS VS7700000 MX1050000 VS6575000 VS7175000 EPA hazardous No data No data No data U204c waste OHM/TADS 7216880 No data No data No data DOT/UN/NA/IMCO UN 2658b UN 2202; UN 1905; IMCO 8.0 No data shipping Hydrogen

selenide;

anhydrous HSDB 4493 548 675 6065 NCI No data No data No data No data

SELENIUM 219

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-1. Chemical Identity of Selenium and Selected Compoundsa

Potassium Characteristic selenate

Synonyms Disodium selenate Selenic acid, Disodium Disodium dipotassium saltb monoselenideb selenite; disodium ; selenious acid disodium ; sodium selenium

Registered trade P-40b; Sel-Tox No data No data name(s) SS02 and SS-20c

d b d Na2SeO4 K2SeO4 Na2Se Na2SeO3

Wisewesser line NA2 SE-04b KA2 SE-04 NA2 SE NAS SE-03 notation

Identification numbers: CAS 13410-01-0 7790-59-2 1313-85-5b 10102-18-8 NIOSH RTECS No data VS6600000 WE0350000b VS7350000 EPA hazardous No data No data No data No data waste OHM/TADS No data No data No data 7217299 b DOT/UN/NA/IMCO No data No data No data UN 2630 shipping HSDB No data No data No data 768 NCI No data No data No data No data

SELENIUM 220

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-1. Chemical Identity of Selenium and Selected Compoundsa

Selenium Characteristic Selenium dioxide trioxide Selenocystine

Synonyms Selenious No data Selenium Methionine, selenob; anhydride; selenium cystineb; 2-amino-4- oxide; selenium 3,3-diselenodi- (methylselenyl) b oxide [SeO2]; DL-alanine ; butyric acid; seleno-DL- 2-amino-4-(methylsel anhydride cystineb; DL- eno) selenocystineb

Registered trade No data No data name(s)

e Chemical formula SeO2 SeO3 C2H4NO2(CH2)Se (CH3)Se(CH2)2C2H4 2(CH2)C2 NO2 H4NO2

Identification numbers: CAS 7446-08-04 13768-86-0f 1464-43-3b 1464-42-2 NIOSH RTECS VS8575000 No data AY6030000b ES100000 EPA hazardous V204c No data No data No data waste OHM/TADS 7800105 No data No data No data DOT/UN/NA/IMCO No data No data No data No data shipping HSDB 677 No data No data No data NCI No data No data No data No data

SELENIUM 221

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-1. Chemical Identity of Selenium and Selected Compoundsa

Characteristic Selenium Selenium

Synonyms Selenium monosulfide; Selenium disulphide; selenium selenium sulfide [SeS]; sulfideb; sulfur selenide selensulfid (German); sulfur selenide (SSe)

Registered trade name(s) No data Exsel; Selsun Blue; Selsumb; Seleen

b Chemical formula SeS SeS2

Wisewesser line notation SE S SE S2b

Identification numbers: CAS 744-34-6 7488-56-4 NIOSH RTECS VTO525OOO VS8925000 EPA hazard waste V205b V205 OHM/TADS 8400272 8400272 DOT/UN/NA/IMCO shipping No data UN 2657 HSDB 679 No data NCI NCI-C50033 No data

aAll information obtained from HSDB 2001, except where noted bRTECS 2001 cEPA 1980a, 1980b (40 CFR 261.33) dBudavari et al. 1996 eLide 2000 fChemIDplus 3003

CAS = Chemical Abstracts Service; DOT/UN/NA/IMCO = Department of Transportation/United Nations/North America/International Maritime Dangerous Goods Code; EPA = Environmental Protection Agency; HSDB = Hazardous Substances Data Bank; NCI = National Cancer Institute; NIOSH = National Institute for Occupational Safety and Health; OHM/TADS = Oil and Hazardous Materials/Technical Assistance Data System; RTECS = Registry of Toxic Effects of Chemical Substances

SELENIUM 222

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Selenium and Selenium Compoundsa

Hydrogen Property Selenium selenide Selenic acid Selenious acid Molecular weight 78.96 80.98 144.97 128.97

Color/form Red, grey, or black Colorlessb White White hygroscopic hexagonal prismsb prisms; hygroscopicb Physical state Gas Solid Solid

Melting point 221 EC(red); -65.73 EC 58 EC 70 EC 220.5 EC (grey); (decomposes)b 180 EC (black)b 685 EC -41.3 EC 260 EC None, loses water upon heating (g/cm3) 4.39 (red); 4.81 2.12 (-42 EC) 2.9508 (15 EC) 3.004 (15 EC) (grey); 4.28 (black)b Odor Unknown; upon Disagreeable odor No data No data combustion, smells like rotten Odor threshold: Water (mg/m3) No data No data No data No data Air No data No data No data No data : Insoluble 377 mL/100 mL at Very soluble in 90 parts dissolve Water 4 EC; hot water in 100 parts of 270 mL/100 mL at water at 0 EC; 400 22.5 EC; parts in 100 parts 0.73 mL/100 mL at at 90 EC 20 ECc Organic solvent(s) Insoluble in , Soluble in Decomposes in Very soluble in slightly soluble in disulfide, carbonyl alcoholb alcohol chloride (2 mg/100 mL, room temperature), soluble in ether Partion coefficients: Log Kow No data No data No data No data Log Koc No data No data No data No data 1 mmHg at 356 EC 1,330 mmHg at - No data 2 mmHg at 15 EC; (grey) 30 EC; 3,420 mmHg 4.5 mmHg at at 0.2 EC; 9,120 33 EC; 7mmHg at mmHg at 30.8 EC 40.3 EC Henry’s Law Not applicable No data Not applicable Not applicable constant Autoignition No data No data No data No data temperature

SELENIUM 223

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Selenium and Selenium Compoundsa

Hydrogen Property Selenium selenide Selenic acid Selenious acid Flashpoint No data Not applicable No data No data

Flammability limits No data No data No data No data

Conversion factors No data ppm selenium to mg No data No data Selenium/m3 in air (20 EC): ppm selenium x 3.23=mg selenium/m3 to ppm selenium in air (20 EC): mg selenium/m3 x 0.31=ppm selenium (v/v) Explosive limits Unknownd No data No data No data

SELENIUM 224

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Selenium and Selenium Compoundsa

Potassium Sodium Property Sodium selenate selenate selenide Molecular weight 188.94 221.15 124.94 172.94

Color/form White crystals Colorless crystals or Crystalline; White tetragonal white powder turns red on crystalsb exposure to air and deliquesces Physical state Solid Solid Solid Solid

Melting point No data No data >875 EC No data

Boiling point No data No data No data No data

Density (g/cm3) 1.61b 3.07 2.625 (10 EC) No data

Odor No data No data No data No data

Odor threshold: Water (mg/m3) No data No data No data No data Air No data No data No data No data Solubility: Water Very soluble in Soluble in about 1 Decomposes in Freely soluble in water part of water water water Organic solvent(s) No data No data No data No data Partition coefficients: Log Kow No data No data No data No data Log Koc No data No data No data No data Vapor pressure No data No data No data No data

Henry’s Law No data No data No data No data constant Autoignition No data No data Not flammablee Not flammablee temperature Flashpoint No data No data Not flammablee Not flammablee

Flammability limits No data No data Not flammablee Not flammablee

Conversion factors No data No data No data No data

Explosive limits No data No data No data No data

SELENIUM 225

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Selenium and Selenium Compoundsa

Selenium Property Selenium dioxide trioxide Selenocystine Selenomethionine Molecular weight 110.96 126.96b 334.12c 196.11

Color/form Lustrous, White crystalsb No data Transparent, tetragonal needles; hexagonal sheets or yellowish-green plates; metallic luster vapor or crystals Physical state Solid Solid No data Solid

Melting point 340 EC; sublimes at 118 ECb No data DL form: 265 EC 315 ECb (decomposes); L form: 266–268 EC Boiling point Noneb Sublimesb No data Not applicable

Density (g/cm3) 3.954 (15 EC) 3.44 b No data No data

Odor Pungent sour smell No data No data No data

Odor threshold: Water (mg/m3) 0.0002e No data No data No data Air No data No data No data No data Solubility: Water (g/100 mL) 38.4 at 14 EC; Soluble in water No data No data Organic solvent(s) in : 10.16 No data No data No data (parts/100 parts at 11.8 EC; in 93% solvent) : 6.67 at 14 EC; in : 4.35 at 15.3 EC; in : 1.11 at 13.9 EC; soluble in Partition coefficients: Log Kow No data No data No data No data Log Koc No data No data No data No data Vapor pressure 12.5 mm Hg at No data No data No data 70 EC; 20.2 mm Hg No data No data at 94 EC; 39.0 mm Hg at 181 EC; 760 mm Hg at 315 EC; 848 mm Hg at 320 EC Henry’s Law Not applicable Not applicable No data No data constant Autoignition Not flammablee Not flammablee No data No data temperature Flashpoint Not flammablee Not flammablee No data No data

SELENIUM 226

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Selenium and Selenium Compoundsa

Selenium Property Selenium dioxide trioxide Selenocystine Selenomethionine Flammability limits Not flammablee Not flammablee No data No data

Conversion factors ppm (v/v) to mg/m3 No data No data No data in air (20 EC): ppm (v/v) x 4.53=mg/m3; mg/m3 to ppm (v/v) in air (20 EC): mg/m3 x 0.22=ppm (v/v) Explosive limits No data No data No data No data

SELENIUM 227

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Selenium and Selenium Compoundsa

Property Selenium sulfide Molecular weight 111.02f 143.08f

Color/form -yellow tablets or powderf Bright red-yellow powderf Physical state Solidf Solidf

Melting point 118–119 EC (decomposes)f <100 ECf

Boiling point No data No data

Density (g/cm3) 3.056 (0 EC)f No data

Odor No data No data

Odor threshold: Water (mg/m3) No data No data Air No data No data Solubility: Water Insoluble Insoluble Organic solvent(s) Insoluble in ether; decomposes in alcoholf No data Partition coefficients: Log Kow Not applicable No data Log Koc Not applicable No data Vapor pressure Not applicable Not applicable

Henry’s Law constant Not applicable Not applicable

Autoignition temperature No data No data

Flashpoint No data No data

Flammability limits No data No data

Conversion factors No data No data

Explosive limits No data No data

aAll information obtained from Budavari et al. 1996, unless otherwise noted. bLide 2000 cRTECS 2001 dNIOSH/OSHA 1981 eWeiss 1986 fLide 1993

Note: The gray metallic form is the most stable form of selenium (Budavari et al. 1996).