Hafnium
Symbol: Hf
Atomic Number: 72
Atomic Mass: 178.49 amu (atomic mass units)
Melting Point: 2233 C (2506 K, 4051 F)
Boiling Point: 4603 C (4876 K, 8317 F)
Number of Protons: 72
Number of Electrons: 72
Number of Neutrons: 106
Classification: Transition Metal
Crystal Structure: Hexagonal
Density @ 293 K: 13.3 grams per cubic centimeter
Color: Silver
The element hafnium was discovered by the Danish chemist Dirk Coster and the Hungarian chemist Charles de Hevesy in 1923. It was discovered using X-ray spectroscopy on a sample of zirconium ore. Using this method the scientists could study the outer electrons of the atoms in the ore. The Nobel Prize winning scientist Niels Bohr had predicated the outer electron arrangement of element 72 and the two scientists found a match for this prediction. It is name after the Latin name for the Danish city Copenhagen – “Hafnia”.
Hafnium is a ductile metal. It is always found with zirconium and the two elements are very difficult to separate. Even the purest sample of hafnium metal yet produced contains small amounts of zirconium contamination. The oxidation state of hafnium is +4 and its ionization energy is 6.825 eV. Some hafnium compounds have very high melting points. Hafnium chloride (HfC) has the highest melting point of any two element compound at 3890 C (4163 K, 7034 F). The melting point of hafnium nitride (HfN) is 3305 C (3578 K, 5981 F); this is the highest melting point of any known nitride.
There are six naturally occurring isotopes of hafnium. Five of these isotopes are stable and the sixth, hafnium-174 has a half-life of 2,000,000,000,000,000 years. The most common isotope is hafnium-180 at 35.08% in order of abundance the rest are: hafnium-178 (27.28%), hafnium-177 (18.60%), hafnium-179 (13.62%), hafnium-176 (5.26%) and hafnium-174 (0.16%). A number of unstable isotopes of hafnium have been discovered with mass numbers that range from 154 to 188.
Hafnium is extracted commercially from zirconium ores. Zirconium ores can contain between one and five percent hafnium. Hafnium metal is produced by the reduction of hafnium tetrachloride with either sodium or potassium this is known as the Kroll process.
Industrially hafnium has a number of uses.
* It is very good at absorbing neutrons and is used to manufacture control rods for nuclear generators. Such control rods are used on nuclear submarines.
* In vacuum tube technology hafnium is used as a getter. A getter removes trace gases from the vacuum tubes.
* A number of metals are alloyed to hafnium including iron, titanium, niobium and tantalum.
