Hafnium

Hafnium, ₇₂Hf
Hafnium
Pronunciation	/ˈhæfniəm/ (HAF-nee-əm)
Appearance	steel gray
Standard atomic weight Ar°(Hf)
	178.486±0.006; 178.49±0.01 (abridged);
Hafnium in the periodic table
	lutetium ← hafnium → tantalum
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
Physical properties
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
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)
Atomic properties
Oxidation states	common: +4; −2, 0, +1, +2, +3
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 hafnium
Other properties
Natural occurrence	primordial
Crystal structure	hexagonal close-packed (hcp) (hP2)
Lattice constants	a = 319.42 pm; c = 505.12 pm (at 20 °C)
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
Molar magnetic susceptibility	+75.0×10−6 cm3/mol (at 298 K)
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
History
Naming	after Hafnia. Latin for: Copenhagen, where it was discovered
Prediction	Dmitri Mendeleev (1869)
Discovery and first isolation	Dirk Coster and George de Hevesy (1922)
Isotopes of hafnium v; e;
	Category: Hafnium; view; talk; edit; \| references

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. 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.

^ "Standard Atomic Weights: Hafnium". CIAAW. 2019.
^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^ ^a ^b Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^ Hf(–2) occurs in Hf(CO)_₆²⁻; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]₂^- to [Hf(CO)₆]₂^- and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.
^ Hf(0) occur in (η⁶-(1,3,5-^tBu)₃C₆H₃)₂Hf and [(η⁵-C₅R₅Hf(CO)₄]⁻, see Chirik, P. J.; Bradley, C. A. (2007). "4.06 - Complexes of Zirconium and Hafnium in Oxidation States 0 to ii". Comprehensive Organometallic Chemistry III. From Fundamentals to Applications. Vol. 4. Elsevier Ltd. pp. 697–739. doi:10.1016/B0-08-045047-4/00062-5. ISBN 9780080450476.
^ Hf(I) has been observed in hafnium monobromide (HfBr), see Marek, G.S.; Troyanov, S.I.; Tsirel'nikov, V.I. (1979). "Кристаллическое строение и термодинамические характеристики монобромидов циркония и гафния / Crystal structure and thermodynamic characteristics of monobromides of zirconium and hafnium". Журнал неорганической химии / Russian Journal of Inorganic Chemistry (in Russian). 24 (4): 890–893.
^ ^a ^b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.
^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ Caracciolo, V.; Nagorny, S.; Belli, P.; et al. (2020). "Search for α decay of naturally occurring Hf-nuclides using a Cs₂HfCl₆ scintillator". Nuclear Physics A. 1002 (121941): 121941. arXiv:2005.01373. Bibcode:2020NuPhA100221941C. doi:10.1016/j.nuclphysa.2020.121941. S2CID 218487451.

[1] "Standard Atomic Weights: Hafnium". CIAAW. 2019.

[CIAAW2021-2] Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.

[Arblaster_2018-3] Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.

[4] Hf(–2) occurs in Hf(CO)_₆²⁻; see John E. Ellis (2003). "Metal Carbonyl Anions: from [Fe(CO)₄]₂^- to [Hf(CO)₆]₂^- and Beyond†". Organometallics. 22 (17): 3322–3338. doi:10.1021/om030105l.

[5] Hf(0) occur in (η⁶-(1,3,5-^tBu)₃C₆H₃)₂Hf and [(η⁵-C₅R₅Hf(CO)₄]⁻, see Chirik, P. J.; Bradley, C. A. (2007). "4.06 - Complexes of Zirconium and Hafnium in Oxidation States 0 to ii". Comprehensive Organometallic Chemistry III. From Fundamentals to Applications. Vol. 4. Elsevier Ltd. pp. 697–739. doi:10.1016/B0-08-045047-4/00062-5. ISBN 9780080450476.

[6] Hf(I) has been observed in hafnium monobromide (HfBr), see Marek, G.S.; Troyanov, S.I.; Tsirel'nikov, V.I. (1979). "Кристаллическое строение и термодинамические характеристики монобромидов циркония и гафния / Crystal structure and thermodynamic characteristics of monobromides of zirconium and hafnium". Журнал неорганической химии / Russian Journal of Inorganic Chemistry (in Russian). 24 (4): 890–893.

[GE28-7] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.

[magnet-8] Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.

[9] Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.

[NUBASE2020-10] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[174Hf2020-11] Caracciolo, V.; Nagorny, S.; Belli, P.; et al. (2020). "Search for α decay of naturally occurring Hf-nuclides using a Cs₂HfCl₆ scintillator". Nuclear Physics A. 1002 (121941): 121941. arXiv:2005.01373. Bibcode:2020NuPhA100221941C. doi:10.1016/j.nuclphysa.2020.121941. S2CID 218487451.

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Hafnium

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