Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a metal of Group 4 of the periodic table, It used as a structural material for nuclear reactors. It is a lustrous, grey-white, strong transition metal that closely resembles hafnium and, to a lesser extent, titanium. It is mainly used as a refractory and opacifier, although small amounts are used as an alloying agent for its strong resistance to corrosion. It forms a variety of inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. Five isotopes occur naturally, three of which are stable. It compounds have no known biological role.
- It is a lustrous, greyish-white, soft, ductile, malleable metal that is solid at room temperature, though it is hard and brittle at lesser purities.
- In powder form, It is highly flammable, but the solid form is much less prone to ignition. Zirconium is highly resistant to corrosion by alkalis, acids, salt water and other agents. However, it will dissolve in hydrochloric and sulfuric acid, especially when fluorine is present. Alloys with zinc are magnetic at less than 35 K.
- The melting point of zirconium is 1855 °C (3371 °F), and the boiling point is 4371 °C (7900 °F).
- It has an electronegativity of 1.33 on the Pauling scale. Of the elements within the d-block with known electronegativities, zirconium has the fifth lowest electronegativity after hafnium, yttrium, lanthanum, and actinium.
- At room temperature zirconium exhibits a hexagonally close-packed crystal structure, α-Zr, which changes to β-Zr, a body-centered cubic crystal structure, at 863 °C. It exists in the β-phase until the melting point.
Uses of Zirconium
It is used in nuclear reactors for cladding fuel rods, for alloying with uranium, and for reactor-core structures because of its unique combination of properties. Zirconium has good strength at elevated temperatures, resists corrosion from the rapidly circulating coolants, does not form highly radioactive isotopes, and withstands mechanical damage from neutron bombardment. Hafnium, present in all zirconium ores, must be scrupulously removed from the metal intended for reactor uses because hafnium strongly absorbs thermal neutrons.