Title: Barium
CAS Registry Number: 7440-39-3
Literature References: Ba; at. wt. 137.327; at. no. 56; valence 2. Group IIA (2). Alkaline earth metal. Abundance in earth's crust 0.05% by wt. Naturally occurring isotopes: 138 (71.70%); 137 (11.23%); 136 (7.85%); 135 (6.593%); 134 (2.42%); 132 (0.101%); 130 (0.106%). Known radioactive isotopes: 117, 119-129, 131, 133, 139-149. Does not occur free in nature as metal. Compds occur in minerals barite and witherite. Commercial production by thermal reduction of barium oxide with aluminum. First prepared as a mercury amalgam by Davy in 1808. Toxicity studies of barium compds: Syed, Hosain, Toxicol. Appl. Pharmacol. 22, 150 (1972). Reviews: Gmelins, Barium (8th ed.) 30, (1960); Goodenough, Stenger, "Magnesium, Calcium, Strontium, Barium and Radium" in Comprehensive Inorganic Chemistry Vol. 1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 591-664; Chemistry of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 117-154; C. Boffito in Kirk-Othmer Encyclopedia of Chemical Technology vol. 3 (Wiley-Interscience, New York, 4th ed., 1992) pp 902-908. Review of toxicology and human exposure: Toxicological Profile for Barium and Compounds (PB93-110658, 1992) 163 pp.
Properties: Silvery-white, slightly lustrous metal when pure; yellowish-white when contaminated with nitrogen. Body-centered cubic structure at atm pressure. Soft, ductile. Fairly volatile; extremely reactive, very easily oxidizable; must be kept under petroleum or other oxygen-free liquid to exclude air. Reacts vigorously with water, liberating hydrogen and creating an explosion hazard. Keep dry and tightly sealed. Pyrophoric when finely divided; store powder under dry argon or helium. d 3.6. mp ~710°. bp ~1600°. E0 (aq) Ba2+/Ba -2.91 V. Emits characteristic yellow-green color in flame. Dissolves in liq NH3 to give deep blue-black solns. Solns of sol barium salts give a white ppt with H2SO4 or sol sulfates.
Melting point: mp ~710°
Boiling point: bp ~1600°
Density: d 3.6
CAUTION: Potential symptoms of overexposure to soluble barium compounds are excessive salivation, vomiting, colic, diarrhea, convulsive tremors, slow, hard pulse, elevated blood pressure, confusion; hemorrhages in stomach, intestines, kidneys; respiratory failure, cardiac arrest. See: Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams & Wilkins, Baltimore, 5th ed., 1984) Section III, pp 61-63; Patty's Industrial Hygiene and Toxicology vol. 2C, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York, 4th ed., 1994) pp 1925-1930.
Use: Alloys with Al or Mg as "getters" to remove residual gases from vacuum systems and electronic tubes. Deoxidizer for steel and other metals. Carrier for radium. The b- and g-radiation emitted by 140Ba + 140La makes a large contribution to the activity of the fission products of uranium rods during the first few weeks after their withdrawal from the reactor. The emissions from 133Ba and 137mBa as standards in g-spectrometry: Haissinsky, Adloff, Radiochemical Survey of the Elements (Elsevier, 1965) pp 12-14. |