(So named (Modern Latin Hafnia, "Copenhagen") in 1923 by D. Coster, Dutch chemist, and G. C. de Hevesy, Hungarian chemist after where it was discovered) A metallic chemical element found with, and similar to, zirconium. It is used in the manufacture of light-bulb filaments and in reactor control rods.

Symbol: Hf
Atomic number: 72
Atomic weight: 178.49
Density (at room temperature and pressure): 13.31 g/cc
Melting point: 2,230°C
Boiling point: 4,603°C
Valence: +4
Ground state electron configuration: [Xe]4f145d26s2

Symbol: Hf
Atomic Number: 72
Atomic Weight: 178.49
Boiling Point: 4875 K
Melting Point: 2504
Density at 300 K: 13.31 g/cm3
Covalent radius: 1.44
Atomic radius: 2.16
Atomic volume: 13.6 m3/mol
First ionization potental: 6.65 V
Specific heat capacity: 0.14 J g-1 K-1
Thermal conductivity: 23.0 W m-1 K-1
Electrical conductivity: 3.4*106 Ω-1 m-1
Heat of fusion: 21.76 kJ/mol
Heat of vaporization: 661.07 kJ/mol
Electronegativity: 1.3 (Pauling's)

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Solid hafnium does not burn. However, particles of 10 microns or less can spontaneously combust at room temperature. This can happen even though the particles are wet. Spraying burning hafnium with water is not a good idea. A CO2 fire extiguisher is also not effective on Hafnium fires. If a fire starts in a mass of wet metal fines, such as a barrel of damp machining chips, the initial fire may be followed by an explosion and a very high temperature flash radiation due to the evolution of hydrogen and steam.

Hafnium metal is rapidly dissolved by hydrofluoric acid or hydrofluoric-nitric acid mixtures. Above 200°C, hafnium reacts exothermically with fluorine, chlorine, bromine, iodine and with halocarbons, including carbon tetrachloride, carbon tetrafluoride and Freons. Nitryl fluoride, FNO, will initiate a reaction with hafnium metal at room temperature to produce a glowing or white incandescence.

Pure hafnium is not known to be toxic or carcinogenic, and is not soluble in water, saline, or other fluids found in the body.

Info paraphrased from http://www.thermadyne.com/tdc/literature/pdfs/msds/TR702.pdf

thanks to C-Dawg, eliserth and montecarlo

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