ZR

Zirconium, chemical symbol Zr, is a transition metal in group 4 of the periodic table. It has atomic number 40 and an atomic weight of approximately 91.22. In its natural state it is a silvery-gray, lustrous metal with a high melting point of about 1,855°C and a density around 6.49 g/cm³. A defining property is its tendency to form a protective oxide layer that renders most zirconium alloys highly resistant to corrosion, even at high temperatures.

Zirconium occurs naturally in the minerals zircon (ZrSiO4) and baddeleyite (ZrO2). Often found together with hafnium, zirconium must be separated from hafnium for many applications because the two elements have very similar chemical properties. Commercial production typically starts with zircon, converting it to zirconium tetrachloride (ZrCl4) and then reducing it with magnesium in the Kroll process to metal, followed by purification to remove hafnium and other impurities.

Chemically, zirconium most commonly exhibits the +4 oxidation state. It forms stable oxides such as zirconium dioxide (ZrO2) and various halides and organometallic compounds. The protective ZrO2 layer accounts for its corrosion resistance in aggressive environments and its usefulness in high-temperature alloys. Zirconium alloys, notably Zircaloy, are designed to minimize neutron absorption in nuclear reactors.

Major applications include nuclear fuel cladding and structural components, chemical processing equipment, and ceramic materials where zirconia is used for its mechanical properties and corrosion resistance. Zirconium and its alloys also find use in high-performance dental and biomedical ceramics and coatings. The element is relatively non-toxic, but fine zirconium compounds can be irritants; handling of zirconium metal powder requires appropriate safety measures due to fire hazards in small particles.