72HfHafnium

Hafnium is a chemical element with the 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, 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. 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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Atomic properties

Standard atomic weight178.486 ±0.006
Atomic mass178.492 u

Atomic radii

Radius (empirical)159 pm
Radius (calculated)208 pm
Covalent radius175 ±10 pm

Atomic shell

Electron configurationXe 4f14 5d2 6s2
Ionization energy(1st) 6.82507 eV
(2nd) 114.61 eV
(3rd) 22.55 eV
(4th) 33.37 eV
(5th) 68.37 eV
Shell model
Electrons
k-shell:2
l-shell:8
m-shell:18
n-shell:32
o-shell:10
p-shell:2

Physical properties

Phasesolid
Density13.28 g·cm−3 (298.1 K)
Molar volume1.344·10-5 m3·mol−1
Speed of sound3,010 m·s−1 (293.1 K)

Temperatures

Melting point2,506 K
Boiling point4,876 K
Liquid range2,370 K
Transition temperature0.38 K

Enthalpies

Melting enthalpy25.5 kJ·mol-1
Enthalpy of vaporization630 kJ·mol-1
Binding energy621 kJ·mol-1

Heat and conductivity

Specific heat capacity140 J·kg−1·K−1
Thermal conductivity23 W·m-1·K-1
Expansion coefficient5.9·10-6 K-1

Hardnesses

Mohs hardness5.5
Brinell hardness1,700 NM·m-2
Vickers hardness1,760 NM·m-2

Elastic properties

Young’s modulus78 GPa
Shear modulus30 GPa
Bulk modulus110 GPa
Poisson’s ratio0.37

Electrical properties

Electrical conductivity3.12·106 S·m-1
Resistance3.4·10-7 Ωm

Magnetism

Magnetismparamagnetic
Magnetic susceptibility7.5·10-5 cm3·mol−1 (298 K)

Chemical properties

Basicityamphoteric
Oxidation state2, 4
Standard potential-1.505 V (HfO2 + 4H+ + 4e- → Hf + 2H2O)

Electronegativity

Pauling scale1.3
Allred-Rochow scale1.23
Nagle scale1.2
Pearson absolute negativity3.8 eV

Other properties

Natural occurrenceprimordial
Crystal structureHexagonal close-packed
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature (solid body, normal pressure)
Price/kg900 USD

Natural abundances

satellite_alt
Universe
0.7 ppb ≈ 7.03·109 M☉
sunny
Sun
1 ppb ≈ 1.98·109 Mt
destruction
Meteorite
170 ppb ≈ 170 mg
public
Earth’s crust
3,300 ppb ≈ 91,400 Mt
water_drop
Oceans
0.008 ppb ≈ 10.9 kt
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