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Chemical element, symbol Hf and atomic number 72 / From Wikipedia, the free encyclopedia

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Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, by Dirk Coster and George de Hevesy,[6][7] making it the penultimate stable element to be discovered (the last being rhenium in 1925). Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.[8][9]

Quick facts: Hafnium, Pronunciation, Appearance, Standard ...
Hafnium, 72Hf
Pronunciation/ˈhæfniəm/ (HAF-nee-əm)
Appearancesteel gray
Standard atomic weight Ar°(Hf)
  • 178.486±0.006
  • 178.49±0.01 (abridged)[1]
Hafnium in the periodic table


Atomic number (Z)72
Groupgroup 4
Periodperiod 6
Block  d-block
Electron configuration[Xe] 4f14 5d2 6s2
Electrons per shell2, 8, 18, 32, 10, 2
Physical properties
Phase at STPsolid
Melting point2506 K (2233 °C, 4051 °F)
Boiling point4876 K (4603 °C, 8317 °F)
Density (near r.t.)13.31 g/cm3
when liquid (at m.p.)12 g/cm3
Heat of fusion27.2 kJ/mol
Heat of vaporization648 kJ/mol
Molar heat capacity25.73 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2689 2954 3277 3679 4194 4876
Atomic properties
Oxidation states−2, 0, +1, +2, +3, +4 (an amphoteric oxide)
ElectronegativityPauling scale: 1.3
Ionization energies
  • 1st: 658.5 kJ/mol
  • 2nd: 1440 kJ/mol
  • 3rd: 2250 kJ/mol
Atomic radiusempirical: 159 pm
Covalent radius175±10 pm
Color lines in a spectral range
Spectral lines of hafnium
Other properties
Natural occurrenceprimordial
Crystal structure hexagonal close-packed (hcp)
Hexagonal close packed crystal structure for hafnium
Speed of sound thin rod3010 m/s (at 20 °C)
Thermal expansion5.9 µm/(m⋅K) (at 25 °C)
Thermal conductivity23.0 W/(m⋅K)
Electrical resistivity331 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[2]
Molar magnetic susceptibility+75.0×10−6 cm3/mol (at 298 K)[3]
Young's modulus78 GPa
Shear modulus30 GPa
Bulk modulus110 GPa
Poisson ratio0.37
Mohs hardness5.5
Vickers hardness1520–2060 MPa
Brinell hardness1450–2100 MPa
CAS Number7440-58-6
Namingafter Hafnia. Latin for: Copenhagen, where it was discovered
PredictionDmitri Mendeleev (1869)
Discovery and first isolationDirk Coster and George de Hevesy (1922)
Isotopes of hafnium
Main isotopes[4] Decay
abun­dance half-life (t1/2) mode pro­duct
172Hf synth 1.87 y ε 172Lu
174Hf 0.16% 7.0×1016 y[5] α 170Yb
176Hf 5.26% stable
177Hf 18.6% stable
178Hf 27.3% stable
178m2Hf synth 31 y IT 178Hf
179Hf 13.6% stable
180Hf 35.1% stable
182Hf synth 8.9×106 y β 182Ta
Symbol_category_class.svg Category: Hafnium
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Hafnium is used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nanometers and smaller feature lengths. Some superalloys used for special applications contain hafnium in combination with niobium, titanium, or tungsten.

Hafnium's large neutron capture cross section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.

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