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Hafnium (group) .
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 1922, by Dirk Coster and George de Hevesy ,[8] [9] making it one of the last two stable elements to be discovered. (The element rhenium was found in 1908 by Masataka Ogawa , though its atomic number was misidentified at the time, and it was not generally recognised by the scientific community until its rediscovery by Walter Noddack , Ida Noddack , and Otto Berg in 1925. This makes it somewhat difficult to say if hafnium or rhenium was discovered last.)[10] Hafnium is named after Hafnia , the Latin name for Copenhagen , where it was discovered.[11] [12]
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Hafnium, 72 Hf Pronunciation (HAF -nee-əm ) Appearance steel gray
Atomic number (Z ) 72 Group group 4 Period period 6 Block d-block Electron configuration [ Xe ] 4f14 5d2 6s2 Electrons per shell 2, 8, 18, 32, 10, 2 Phase at STP solid Melting point 2506 K (2233 °C, 4051 °F) Boiling point 4876 K (4603 °C, 8317 °F) Density (at 20° C) 13.281 g/cm3 [3] when liquid (at m.p. ) 12 g/cm3 Heat of fusion 27.2 kJ/mol Heat of vaporization 648 kJ/mol Molar heat capacity 25.73 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
Oxidation states −2, 0, +1, +2, +3, +4 (an amphoteric oxide) Electronegativity Pauling scale: 1.3 Ionization energies 1st: 658.5 kJ/mol 2nd: 1440 kJ/mol 3rd: 2250 kJ/mol Atomic radius empirical: 159 pm Covalent radius 175±10 pm Spectral lines of hafniumNatural occurrence primordial Crystal structure hexagonal close-packed (hcp) (hP2 )Lattice constants a = 319.42 pmc = 505.12 pm (at 20 °C)[3] Thermal expansion 5.9 µm/(m⋅K) (at 25 °C) Thermal conductivity 23.0 W/(m⋅K) Electrical resistivity 331 nΩ⋅m (at 20 °C) Magnetic ordering paramagnetic [4] Molar magnetic susceptibility +75.0× 10−6 cm3 /mol (at 298 K)[5] Young's modulus 78 GPa Shear modulus 30 GPa Bulk modulus 110 GPa Speed of sound thin rod 3010 m/s (at 20 °C) Poisson ratio 0.37 Mohs hardness 5.5 Vickers hardness 1520–2060 MPa Brinell hardness 1450–2100 MPa CAS Number 7440-58-6 Naming after Hafnia . Latin for: Copenhagen , where it was discovered Prediction Dmitri Mendeleev (1869)Discovery and first isolationDirk Coster and George de Hevesy (1922)
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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 .