Barium

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Barium is a silver-white, somewhat malleable metal used in various alloys, for the production of evaporation getters (gas absorbers) in cathode ray tubes, in sodium vapor lamps, and in spark plugs. Barium is relatively abundant in nature and is found in plants and animal tissue. Barium is an alkaline earth metal, so-called because the alchemists referred to any nonmetallic substance insoluble in water and unchanged by fire as an “earth” and because the “earths” of this group give decidedly alkaline reactions. It quickly oxidizes in air and therefore has to be strictly kept under a protective inert medium like paraffin oil or argon gas. Barium is flammable at room temperature in powder form, and reacts violently with water, acids or alcohols, developing hydrogen and forming alkaline caustic decomposition products.

The toxicity of barium compounds depends upon their solubility. Soluble compounds are absorbed and small amounts are accumulated in the skeleton. The lung has an average concentration of 1 ppm (dry weight). The kidney, spleen, muscle, heart, brain and liver concentrations are all less than <0.11 ppm. Although barium is excreted in urine, it is reabsorbed by the renal tubules. The major route of excretion is the feces. Occupational poisoning from barium is uncommon. Accidental poisoning from ingestion of soluble barium salts has resulted in gastroenteritis, muscular paralysis, decreased pulse rate, and ventricular fibrillation and extrasystoles.

Typical Properties

  • Atomic Weight: 137.34
  • Specific Gravity: 3.6 gm/cc @ 20 oC
  • Melting Point Range: ~710 oC
  • Boiling Point Range: ~1500 oC
  • Electronic Coefficient (γ): 19 + 3 mJ/Kg ⋅ K2
  • Latent Heat of Fusion: 56.4 + 7.6 kJ/Kg
  • Latent Heat of Vaporization: 1290 kJ/Kg
  • Thermal Conductivity: 18.4 W/m ⋅ K
  • Temperature of Superconductivity: Ba II, ~1.3 K @ 5.5 GPa; Ba III, 3.05 K from 8.5-8.8, ~5.2 K for pressures >14.0 GPa
  • Coefficient of Expansion: (0-100 Oc) 18 x 10-6/K
  • Electrical Resistivity: 60 µΩ ⋅ cm @ oC. 133 µΩ ⋅ cm for liquid Ba
  • Magnetic Susceptibility: Molar: 1.254 mks @ oC
  • Thermal Neutron Cross Section (0.025 eV): Absorption, 1.3 b; Scattering, 8 b
  • Modulus: Bulk, 10.30 GPa; rigidity, 4.86 GPa
  • Poisson’s Ratio: 0.28