Hafnium (Hf)

Stable isotopes of hafnium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Hf-174  72  102  173.940042 0.162%  13.46% Oxide
Hf-176 72 104 175.941406 5.260% 84.60% Oxide
Hf-177  72  105  176.943220 18.606%  85.40% Oxide
Hf-178  72  106  177.943698 27.297%  92.40% Oxide
Hf-179  72  107  178.945815 13.629%  75.00% Oxide
Hf-180  72  108  179.946549 35.100%  ≥94.60% Oxide

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Hafnium was discovered in 1923 by Dirk Coster and George Charles von Hevesy. Its name derives from the Latin name Hafnia, meaning “Copenhagen.”

Hafnium is generally similar to zirconium. It has gray crystals, good corrosion resistance and high strength. It occurs as a close-packed hexagonal alpha form and as a body-centered cubic beta modification. It has a magnetic susceptibility of 0.42 x 10-6 emu/g at 25 ºC. It is insoluble in water, dilute mineral acids and nitric acid at all concentrations, and is soluble in hydrofluoric acid, concentrated sulfuric acid and aqua regia. The metal in bulk form does not react with most reagents at ordinary temperatures; however, the powdered metal or hafnium sponge may readily burn in air after being ignited with a spark. When heated to 360 ºC under water pressure, the metal is oxidized to hafnium oxide, forming a thin, protective surface oxide layer. Reaction with hydrofluoric acid at ordinary temperatures yields hafnium tetrafluoride. In finely divided form, hafnium is pyrophoric, igniting in air spontaneously; however, bulk metal reacts slowly in oxygen or air above 400 ºC. Reaction with hydrogen occurs around 700 ºC.

Hafnium is used in control rods for nuclear reactors. It has high resistance to radiation, as well as very high corrosion resistance. Another major application is in alloys with other refractory metals, such as tungsten, niobium and tantalum.

Properties of Hafnium

Name Hafnium 
Symbol Hf 
Atomic number 72 
Atomic weight 178.49 
Standard state Solid at 298 ºK 
CAS Registry ID 7440-58-6 
Group in periodic table
Group name None 
Period in periodic table
Block in periodic table d-block 
Color Gray steel 
Classification Metallic 
Melting point 2233 °C
Boiling point 4602 °C
Vaporization point 2233 ºC
Thermal conductivity 23.0 W/(m·K) at 298.2 ºK
Electrical resistivity 35.1 µΩ·cm at 25 ºC 
Electronegativity 1.3 
Specific heat 0.14 kJ/kg K
Heat of vaporization 630 kJ·mol-1 at 4602 ºC
Heat of fusion 25.5 kJ·mol-1 mole
Density of liquid 12 g/cm3 at 2233 °C 
Density of solid 13.31 g/cm3 
Electron configuration [Xe]4f145d26s2 
Atomic radius 1.442 Å
Common oxidation state  +4 (also exhibits oxidation states +2 and +3) 

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