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40 Zr 91.224(2)

Zirconium

Transition metal
Symbol Zr
Atomic Number 40
Atomic Weight 91.224(2)
CAS Registry ID 7440-67-7
Group Name (none)
Period Number 5
Block d-block
State at STP Solid

Description

Sample of Zirconium ⌕ Enlarge Image

Zirconium is a transition metal that is a silvery white color in its natural solid state. Zirconium is resistant to corrosion, but it will ignite when exposed to air if it is in small, fine, amounts. Zirconium has an atomic weight of 91.224, a melting point of 3371 °F, and a boiling point of 7968 °F. The most common use of zirconium is as a component in fuel rods used in nuclear reactors; zirconium is also used as a component in some gems.

Isolation

Zirconium is never found free in nature, and isolation procedures are needed to extract zirconium from its mineral sources.

Zirconium ⌕ Enlarge Image

Zirconium occurs in over 30 different types of minerals, but the mineral that is used most often for isolating zirconium is zircon. Zircon can also be collected as a by product of titanium, tin, ilmenite, and rutile processing. The isolation procedure that is most often used to isolate zirconium from other minerals and elements is the Kroll process; during this process, zirconium chloride is reduced using magnesium metal.

The Kroll process is an industrial process that is mainly used to produce titanium through pyrometallurgical methods. During the zirconium isolation process, zirconium oxide is reacted with chlorine and carbon and heated to approximately 1652 °F. The result of this reaction is the formation of zirconium tetrachloride, iron trichloride, and carbon monoxide. The zirconium tetrachloride is separated from this mixture using fractional distillation producing zirconium chloride. The last step in the reaction involves combining zirconium chloride with magnesium and heating the mixture to 2012 °F. The end result is pure zirconium and magnesium chloride.

General

NameZirconium
SymbolZr
Number40
Chemical seriesTransition metal
Group4
Period5
Blockd
Appearancesilvery white
Standard atomic weight91.224(2) g·mol⁻¹
Electron configuration[Kr] 4d2 5s2
Electrons per shell2, 8, 18, 10, 2

Atomic Properties

Crystal structurehexagonal
Oxidation states4 (amphoteric oxide)
Electronegativity1.33 (scale Pauling)
Ionization energies1st:  640.1  kJ·mol−1
2nd:  1270  kJ·mol−1
3rd:  2218  kJ·mol−1
Atomic radius155  pm
Atomic radius (calc.)206 pm
Covalent radius148 pm
Van der Waals radius

Physical Properties

Phasesolid
Density (near r.t.)6.52  g·cm−3
Liquid density at m.p.5.8  g·cm−3
Melting point2128 K (1855 °C, 3371 °F)
Boiling point4682 K (4409 °C, 7968 °F)
Critical point
Heat of fusion14  kJ·mol−1
Heat of vaporization573  kJ·mol−1
Heat capacity(25 °C) 25.36  J·mol−1·K−1

Miscellaneous

Magnetic ordering
Electrical resistivity(20 °C) 421 n Ω·m
Thermal conductivity(300 K) 22.6  W·m−1·K−1
Thermal expansion(25 °C) 5.7  µm·m−1·K−1
Speed of sound (thin rod)(20 °C) 3800 m/s
Young's modulus68  GPa
Shear modulus33  GPa
Bulk modulus
Poisson ratio0.34
Mohs hardness5.0
Vickers hardness903  MPa
Brinell hardness650  MPa