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Element Fact
Americium is one of the few radioactive elements that find its use in homes as a smoke detector.

Zirconium, Zr

zirconium sample

Atomic number: 40
Atomic mass: 91.224(2)
Natural abundance: 162 ppm
90Zr (89.904704) - 51.45%
91Zr (90.905645) - 11.22%
92Zr (91.905040) - 17.15%
94Zr (93.906316) - 17.38%
96Zr (95.908276) - 2.80%

History and Production

From Arabic zargon or Syraic zargun, meaning gold color. Its mineral may have known since ancient. However, its oxide was first isolated by M.H. Klaproth from zircon (ZrSiO4). The impure metal was prepared by J.J. Berzelius in 1824 by heating a mixture of potassium and potassium zirconium fluoride. Nowadays it is produced by reduction of the chloride with with magnesium. Very pure form can be obtained by the iodide-decomposition process, a method invented by A.E. van Arkel and J.H. de Boer in 1925. Basically, the process involves heating impure zirconium with a little iodine when ZrI4 evaporates. It is then decomposed immediately by tungsten or zirconium filament heated to about 1300C and pure zirconium subsequently deposited on the filament. The metal has low neutron adsorption as is used in nuclear energy industry. Due to its unusual resistance to most chemical attacks, it is also used by the chemical industry where corrosive chemicals are employed. The metal is also used in photoflash bulbs, lamp filaments and rayon spinerets. It is also used in applications to withstand heat such as laboratory crucibles and refractory materials.

Physical Data

It is silvery lustrous metal with a high melting point. Its mechanical properties can be markedly affected by traces of impurities such as oxygen, nitrogen and carbon which have an embrittling effect on the metal. Baddeleyite (ZrO2) and zircon are the principle ores. The compound zirconium tungstate has an unusual properties that actually shrinks when heated over a wide range of temperature.

Interatomic distance: 318 pm
Melting point: 1855C
Boiling point: 4409C
Thermal conductivity/Wm-1K-1: 22.7 (27C)
Density/kgm-3: 6506 (20C), 5800 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 608.8 kJ/mol
Gibbs free energy of formation: 566.5 kJ/mol
Entropy: 181.4 J/mol K
Heat capacity: 26.7 J/mol K

Electronic data

Electronic configuration: [Kr] 4d2 5s2
Term symbol: 3F2
Electron affinity: 41.1028 kJ/mol   Electronegativity (Pauline): 1.33
Ionization energy (first, second, third): 640.074, 1266.85, 2218.20 kJ/mol

Chemical properties

The finely devided metal is pyrophoric and when heated to high temperature, zirconium reacts directly with most non-metals. However, zirconium in massive form is resistant to corrosion, due to the presence of a protective oxide film. For this reason, zirconium only reacts slowly with strong mineral acids when cold. On the other hand, aqueous alkalis, even when hot, do not react with the metal.

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