Hafnium is a tetravalent transition element recognized with the symbol Hf. This element has an atomic number 72. It is a lustrous, silvery gray metal. Naturally, it is found in zirconium minerals. Its existence was predicted by Russian chemist Dmitri Mendeleev in 1869. The term "Hafnium" was derived from "Hafnia", the Latin name for "Copenhagen", where it was discovered. About 5 ppm of the Earth's crust is Hafnium. It is extensively used to manufacture filaments, semiconductors, and electrodes. Due to its excellent neutron capturing capability, Hafnium is used in control rods implemented in nuclear power plants. Moreover, it is fused with niobium, titanium, or tungsten to produce some superalloys.
In 1923, renowned Dutch physicist Dirk Coster (1889-1950), and Hungarian chemist George Charles de Hevesy (1889-1966) discovered presence of element 72 in a Norwegian zircon (ZrSiO4) sample. Since Zirconium and Hafnium had similar chemical and physical properties, hence it was difficult to differentiate the new element. With the help of high energy X-ray, they found out the differences of the two elements.
The metal Hafnium is a very shiny, silvery, ductile element. It is corrosion-resistant metal. Its melting point is 2,150 degree Celsius and the boiling point is 5,400 degree Celsius. The density of Hafnium is 13.1gm/cm3 at 20°C. This element belongs to the group 4B and has an atomic weight of 178.49. The electronic configuration is [Xe]4f14 5d2 6s2
Hafnium is not a very reactive element. It does not combine readily oxygen in the air. It does not react with water or cold acids and concentrated alkalis. The metal is insoluble in water, or any saline solutions. However, it may be reacting with hot acids. Hafnium has 6 naturally occurring isotopes: hafnium-174, hafnium-176, hafnium-177, hafnium-178, hafnium-179, and hafnium-180. Most of these isotopes are radioactive in nature. Besides, their half-lives range from only 400 ms to 2.0 petayears.
Hafnium is always contaminated with zirconium minerals. Specifically, solvent extraction methods are used to separate metals. However, the process is not easy. Different solubilities of the metal thiocyantes in methyl isobutyl ketone are utilized in the extraction process.
Hafnium finds use in nuclear reactors, tungsten lamps, microprocessors and alloy making.
Hafnium metal has no known toxicity. However, it has been proved to be most dangerous when inhaled. Powdered hafnium metal can ignite and explode very easily. Over-exposure to this element can cause eye, skin, and mucous membrane irritation, and liver damage. Hafnium poses no threat to plants. They absorb small amounts of Hafnium from the soil in which they grow.