Hafnium

Hafnium - Hf

CAS:7440-58-6
Description: Ductile metal with a brilliant silver luster
Classification: Transition Metal
Date of Discovery: 1923
Discoverer: Dirk Coster
Name Origin: Latin Hafnia, "Copenhagen"

Atomic Number: 72
Number of Neutrons: 106
Atomic Mass: 178.49(2) amu
Melting Point: 2233 ± 20 °C
Boiling Point: 4603 °C
Density (293 K): 13.31 g/cm³
Atomic volume: 13.6 cm³/mol
Electrical resistivity: 0.0312 10^-6/cm

Thermal conductivity: 0.230 W/cmK
Enthalpy of atomization: 703 kJ/mol (est.)
Enthalpy of vaporization: 575.0 kJ/mol
Enthalpy of fusion: 24.060 kJ/mol
Specific heat capacity: 0.14 J/gK

Energy levels: 2-8-18-32-10-2
Electron configuration: [Xe]4f¹⁴5d²6s²
Crystal Structure: Hexagonal
Atomic radius: 2.16 Å
Covalent radius: 1.44 Å
Oxidation States: +4
Electronegativity, Pauling: 1.5
Electron affinity:

0 eV
First ionization energy: 6.65 eV
2nd ionization energy: 14.925 eV
3rd ionization energy: 23.32 eV
Polarizability: 16.2 10^-24cm³

Isotope	Natural Abundance	Atomic Mass	Half-life	Decay Mode	Spin
¹⁵⁴Hf	153.964	2 s	EC, ⁺
¹⁵⁵Hf	154.963	0.9 s	EC, ⁺
¹⁵⁶Hf	155.9593	25 ms
¹⁵⁷Hf	156.9581	0.11 s
¹⁵⁸Hf	157.9539	2.9 s	EC;	0+
¹⁵⁹Hf	158.9538	5.6 s	⁺;
¹⁶⁰Hf	159.95063	12 s	⁺;	0+
¹⁶¹Hf	160.9503	17 s
¹⁶²Hf	161.94720	38 s	⁺, EC	0+
¹⁶³Hf	162.9471	40 s	⁺, EC
¹⁶⁴Hf	163.9536	2.8 m	EC, ⁺
¹⁶⁵Hf	164.9445	1.7 m	EC	11/2-
¹⁶⁶Hf	165.9423	6.8 m	EC; ⁺
¹⁶⁷Hf	166.9426	2.0 m	⁺; EC	(5/2-)
¹⁶⁸Hf	167.9406	25.9 m	⁺, EC	0+
¹⁶⁹Hf	168.9412	3.25 m	EC; ⁺	(5/2-)
¹⁷⁰Hf	169.9397	16.0 h	EC	0+
¹⁷¹Hf	170.9405	12.2 h	EC, ⁺	7/2+
¹⁷²Hf	171.93946	1.87 y	EC	0+
¹⁷³Hf	172.9407	23.6 h	EC	1/2-
¹⁷⁴Hf	0.162(3)	173.940042	2.0 x 10¹⁵ y	0+
¹⁷⁵Hf	174.941504	70 d	EC	5/2-
¹⁷⁶Hf	5.206(5)	175.941403	Stable	0+
^177m2Hf	51.4 m	IT	37/2-
^177m1Hf	1.1 s	IT	23/2+
¹⁷⁷Hf	18.606(4)	176.943220	Stable	7/2-
^178m2Hf	31 y	IT	16+
^178m1Hf	4.0 s	IT	8-
¹⁷⁸Hf	27.297(4)	177.943698	Stable	0+
^179m2Hf	25.1 d	IT	25/2-
^179m1Hf	18.7 s	IT	1/2-
¹⁷⁹Hf	13.629(6)	178.945815	Stable	9/2+
^180mHf	5.52 h	IT	8-
¹⁸⁰Hf	35.100(7)	179.946549	Stable	0+
¹⁸¹Hf	180.949099	42.4 d	^-	1/2+
^182mHf	62 m	^-; IT	8-
¹⁸²Hf	181.95055	9 x 10⁶ y	^-	0+
¹⁸³Hf	182.95353	1.07 h	^-	3/2-
¹⁸⁴Hf	183.95545	4.1 h	^-	0+
¹⁸⁵Hf	3.5 m	^-
Hafnium was thought to be present in various minerals and concentrations many years prior to its discovery, in 1923, credited to D. Coster and G. von Hevesey. On the basis of the Bohr theory, the new element was expected to be associated with zirconium. It was finally identified in zircon from Norway, by means of X-ray spectroscopic analysis. It was named in honor of the city in which the discovery was made. Most zirconium minerals contain 1 to 5% hafnium. It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides bv von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tunasten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). Hafnium is a ductile metal with a brilliant silver luster. Its properties are considerably influenced by the impurities of zirconium present. Of all the elements, zirconium and hafnium are two of the most difficult to separate. Their chemistry is almost identical, however, the density of zirconium is about half that of hafnium. Very pure hafnium has been produced, with zirconium being the major impurity. Natural hafnium contains six isotopes, one of which is slightly radioactive. Hafnium has a total of 40 recognized isotopes and isomers. Because hafnium has a good absorption cross section for thermal neutrons (almost 600 times that of zirconium). has excellent mechanical properties, and is extremely corrosion resistant, it is used for reactor control rods. Such rods are used in nuclear submarines. Hafnium has been successfully alloyed with iron, titanium, niobium, tantalum, and other metals. Hafnium carbide is the most refractory binary composition known, and the nitride is the most refractory of all known metal nitrides (m.p. 3310 °C). Hafnium is used in gas-filled and incandescent lamps, and is an efficient "getter" for scavenging oxygen and nitrogen. Finely divided hafnium is pyrophoric and can ionite spontaneously in air. Care should be taken when machining the metal or when handling hot sponge hafnium. At 700 °C hafnium rapidly absorbs hydrogen to form the composition HfH_1.86. Hafnium is resistant to concentrated alkalis, but at elevated temperature reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Halogens react directly to form tetrahalides. LINKS: Development of Hafnium based STJs Halide Structure Database: Hafnium-Halide Frameworks Information, data sheet and standard forms OSHA Chemical Sampling Information USGS Minerals Information: Zirconium and Hafnium Return Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998.

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