- Zirconium (Zr) is a transition metal with atomic number 40, located in Group 4 of the periodic table alongside titanium and hafnium.
- It is a strong, lustrous, grayish-white metal that is highly resistant to corrosion, due in part to the formation of a stable, adherent oxide layer (ZrO₂) on its surface.
- Zirconium has four valence electrons—two in the 5s subshell and two in the 4d subshell—and it typically exhibits the +4 oxidation state, although +3 and +2 states can occur in certain compounds. Its atomic structure consists of forty protons, typically fifty-one neutrons, and forty electrons arranged in five shells.
- Naturally occurring zirconium consists of five stable isotopes: zirconium-90 (⁹⁰Zr, 51.45%), zirconium-91 (⁹¹Zr, 11.22%), zirconium-92 (⁹²Zr, 17.15%), zirconium-94 (⁹⁴Zr, 17.38%), and zirconium-96 (⁹⁶Zr, 2.80%), the last of which is very slightly radioactive.
- Zirconium is relatively abundant in the Earth’s crust at about 165 parts per million, making it more common than copper. It does not occur in native metallic form, but is found primarily in the mineral zircon (ZrSiO₄), which is the main commercial source, and in baddeleyite (ZrO₂). Large deposits are found in Australia, South Africa, India, Brazil, and the United States. Zirconium is extracted through mineral concentration, chemical processing, and reduction, often via the Kroll process, which involves the reduction of zirconium tetrachloride (ZrCl₄) with magnesium.
- The element was first identified in 1789 by German chemist Martin Heinrich Klaproth, who discovered zirconium oxide in zircon gemstones. Metallic zirconium was first isolated in 1824 by Swedish chemist Jöns Jacob Berzelius. The name comes from zargun, a Persian word meaning “gold-colored,” referring to certain zircon gemstones.
- Zirconium’s remarkable corrosion resistance makes it valuable in chemical processing equipment, especially in environments involving strong acids and alkalis. It is also a key material in the nuclear industry, where zirconium alloys (notably Zircaloy) are used for cladding nuclear reactor fuel rods because zirconium has a very low thermal neutron absorption cross-section and excellent mechanical properties at high temperatures.
- Zirconium compounds have numerous uses. Zirconium dioxide (zirconia, ZrO₂) is an extremely hard, high-melting material used in ceramics, refractory linings, abrasives, and as a gemstone simulant (cubic zirconia). It is also used in dental crowns and oxygen sensors. Zirconium carbonate and zirconium salts find applications in antiperspirants, catalysts, and specialty coatings.
- Chemically, zirconium is relatively inert to most acids and alkalis but reacts with hydrofluoric acid and concentrated sulfuric acid. It forms stable halides, nitrides, carbides, and borides. Finely divided zirconium can ignite spontaneously in air, producing zirconium oxide and nitride.
- Biologically, zirconium has no known essential role in living organisms, and it is generally considered non-toxic in its stable forms. However, zirconium dust and powder can be a fire and inhalation hazard.
- From an environmental standpoint, zirconium is not a major pollutant and is relatively benign, although mining of zircon-bearing sands can disturb ecosystems and require significant environmental management.
