Zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr, atomic number 40 and atomic mass of 91.224. The name of zirconium is taken from the mineral zircon, the most important source of zirconium. It is a lustrous, grey-white, strong transition metal that resembles titanium. Zirconium is mainly used as a refractory and opacifier, although it is used in small amounts as an alloying agent for its strong resistance to corrosion. Zirconium 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. Zirconium compounds have no known biological role.

Occurrence

Zirconium has a concentration of about 130 mg/kg within the Earth's crust and about 0.026 μg/L in sea water. It is not found in nature as a native metal, reflecting its intrinsic instability with respect to water. The principal commercial source of zirconium is the silicate mineral, zircon (ZrSiO4), which is found primarily in Australia, Brazil, India, Russia, South Africa and the United States, as well as in smaller deposits around the world. 80% of zircon mining occurs in Australia and South Africa. Zircon resources exceed 60 million metric tons worldwide and annual worldwide zirconium production is approximately 900,000 metric tons.Zirconium also occurs in more than 140 other minerals, including the commercially useful ores baddeleyite and kosnarite.

Zr is relatively abundant in S-type stars, and it has been detected in the sun and in meteorites. Lunar rock samples brought back from several Apollo program missions to the moon have a quite high zirconium oxide content relative to terrestrial rocks.

Symbol		Zr
Atomic Number		40
Atomic Weight		91.224
Oxidation States		+4
Electronegativity, Pauling		1.33
State at RT		Solid, Metal
Melting Point, K		2125
Boiling Point, K		4650

Appearance and Characteristics

Harmful effects:

Zirconium is considered to be non-toxic.

Characteristics:

• Zirconium is a strong, malleable, ductile, lustrous, grayish-white metal.
• When present in compounds, zirconium exists mostly in the oxidation state IV.
• Its oxide (ZrO2) is white, like many of its compounds.
• Zirconium is generally exceptionally resistant to corrosion. It is however rapidly attacked by hydrofluoric acid, even at low concentrations.
• In an oxygen atmosphere, finely divided Zirconium burns with the highest known temperature for a metal flame: 4460 oC.(4) Powdered zirconium can spontaneously ignite in air.
• Exposed surfaces of zirconium form a protective oxide layer.
• Zirconium tungstate (ZrW2O8) is an unusual substance: it shrinks when heated from near absolute zero to 780 oC(5).

Uses of Zirconium

• Zirconium is very poor at absorbing neutrons. It is therefore useful in nuclear energy applications such as in the cladding (outer layer) of fuel rods through which it is important that neutrons can travel easily.
• Zirconium is used as to make surgical instruments and is used in steel alloys as a hardening agent.
• As a result of its exceptional corrosion resistance, zirconium is used extensively in the chemical industry in corrosive environments where zirconium’s alloys can be found in pipes, fittings and heat exchangers.
• Zirconium is also used to make superconductive magnets.
• Zircon (zirconium silicate, ZrSiO4) is a natural gemstone and synthetic cubic zirconia (zirconium dioxide, ZrO2) is produced as a low-cost substitute for diamond.
• Zirconium based catalysts are used in amination, hydrogenation, isomerization and oxidation reactions.
• Lithium zirconate can be used to absorb carbon dioxide. The reaction is reversible so the carbon dioxide can be released in a location of choice and the lithium zirconate used again. This application may be useful in addressing environmental concerns about the release of carbon dioxide into the atmosphere.