Zirconium is a chemical element
with the symbol
Zr and atomic number
40. The name ''zirconium'' is taken from the name of the mineral zircon
(the word is related to Persian
'' (zircon; ''zar-gun'', "gold-like" or "as gold")), the most important source of zirconium. It is a lustrous
, grey-white, strong transition metal
that closely resembles hafnium
and, to a lesser extent, titanium
. Zirconium is mainly used as a refractory
, although small amounts are used 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 isotope
s occur naturally, three of which are stable. Zirconium compounds have no known biological role.
Zirconium is a lustrous
, greyish-white, soft, ductile
metal that is solid at room temperature, though it is hard and brittle
at lesser purities.
In powder form, zirconium 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
s with zinc
at less than 35 K.
The melting point
of zirconium is 1855 °C (3371 °F), and the boiling point
is 4371 °C (7900 °F).
Zirconium 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
, 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. Zirconium exists in the β-phase until the melting point.
Naturally occurring zirconium is composed of five isotopes. 90
Zr and 94
Zr are stable, although 94
Zr is predicted to undergo double beta decay
(not observed experimentally) with a half-life
of more than 1.10×1017
Zr has a half-life of 2.4×1019
years, and is the longest-lived radioisotope of zirconium. Of these natural isotopes, 90
Zr is the most common, making up 51.45% of all zirconium. 96
Zr is the least common, comprising only 2.80% of zirconium.
Twenty-eight artificial isotopes of zirconium have been synthesized, ranging in atomic mass from 78 to 110. 93Zr
is the longest-lived artificial isotope, with a half-life of 1.53×106
Zr, the heaviest isotope of zirconium, is the most radioactive, with an estimated half-life of 30 milliseconds. Radioactive isotopes at or above mass number 93 decay by electron emission
, whereas those at or below 89 decay by positron emission
. The only exception is 88
Zr, which decays by electron capture
Five isotopes of zirconium also exist as metastable isomers
Zr and 91m
Zr. Of these, 90m2
Zr has the shortest half-life at 131 nanoseconds. 89m
Zr is the longest lived with a half-life of 4.161 minutes.
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 zircon
), a silicate mineral
which is found primarily in Australia, Brazil, India, Russia, South Africa and the United States, as well as in smaller deposits around the world.
As of 2013, two-thirds of zircon mining occurs in Australia and South Africa.
Zircon resources exceed 60 million tonne
and annual worldwide zirconium production is approximately 900,000 tonnes.
Zirconium also occurs in more than 140 other minerals, including the commercially useful ores baddeleyite
Zirconium 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
missions to the moon have a high zirconium oxide content relative to terrestrial rocks.
EPR spectroscopy has been used in investigations of the unusual 3+ valence state of zirconium. The EPR spectrum of Zr3+, which has been initially observed as a parasitic signal in Fe‐doped single crystals of ScPO4, was definitively identified by preparing single crystals of ScPO4 doped with isotopically enriched (94.6%)91Zr. Single crystals of LuPO4 and YPO4 doped with both naturally abundant and isotopically enriched Zr have also been grown and investigated.
Zirconium is a by-product of the mining and processing of the titanium
, as well as tin
mining. From 2003 to 2007, while prices for the mineral zircon steadily increased from $360 to $840 per tonne, the price for unwrought zirconium metal decreased from $39,900 to $22,700 per ton. Zirconium metal is much more expensive than zircon because the reduction processes are costly.
Collected from coastal waters, zircon-bearing sand is purified by spiral concentrators
to remove lighter materials, which are then returned to the water because they are natural components of beach sand. Using magnetic separation
, the titanium ores ilmenite
Most zircon is used directly in commercial applications, but a small percentage is converted to the metal. Most Zr metal is produced by the reduction of the zirconium(IV) chloride
metal in the Kroll process
The resulting metal is sintered
until sufficiently ductile for metalworking.
Separation of zirconium and hafnium
Commercial zirconium metal typically contains 1–3% of hafnium
which is usually not problematic because the chemical properties of hafnium and zirconium are very similar. Their neutron-absorbing properties differ strongly, however, necessitating the separation of hafnium from zirconium for nuclear reactors.
Several separation schemes are in use.
[Nielsen, Ralph (2005) "Zirconium and Zirconium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. ]
The liquid-liquid extraction
of the thiocyanate
-oxide derivatives exploits the fact that the hafnium derivative is slightly more soluble in methyl isobutyl ketone
than in water. This method is used mainly in United States.
Zr and Hf can also be separated by fractional crystallization
of potassium hexafluorozirconate (K2
), which is less soluble in water than the analogous hafnium derivative.
of the tetrachlorides, also called extractive distillation
, is used primarily in Europe.
The product of a quadruple VAM (vacuum arc melting) process, combined with hot extruding and different rolling applications is cured using high-pressure, high-temperature gas autoclaving
. This produces reactor-grade zirconium that is about 10 times more expensive than the hafnium-contaminated commercial grade.
Hafnium must be removed from zirconium for nuclear applications because hafnium has a neutron absorption cross-section 600 times greater than zirconium.
The separated hafnium can be used for reactor control rods
Like other transition metal
s, zirconium forms a wide range of inorganic compounds
and coordination complex
es. In general, these compounds are colourless diamagnetic solids wherein zirconium has the oxidation state
+4. Far fewer Zr(III) compounds are known, and Zr(II) is very rare.
Oxides, nitrides, and carbides
The most common oxide is zirconium dioxide
, also known as ''zirconia''. This clear to white-coloured solid has exceptional fracture toughness
(for a ceramic) and chemical resistance, especially in its cubic
These properties make zirconia useful as a thermal barrier coating, although it is also a common diamond
Zirconium monoxide, ZrO, is also known and S-type star
s are recognised by detection of its emission lines.
has the unusual property of shrinking in all dimensions when heated, whereas most other substances expand when heated.
is a rare water-soluble zirconium complex with the relatively complicated formula r4(OH)12(H2O)16
and zirconium nitride
are refractory solids. The carbide is used for drilling tools and cutting edges. Zirconium hydride phases are also known.
Lead zirconate titanate
(PZT) is the most commonly used piezoelectric material, with applications such as ultrasonic transducers, hydrophones, common rail injectors, piezoelectric transformers and micro-actuators.
Halides and pseudohalides
All four common halides are known, ZrF4
, and ZrI4
. All have polymeric structures and are far less volatile than the corresponding monomeric titanium tetrahalides. All tend to hydrolyse
to give the so-called oxyhalides and dioxides.
The corresponding tetraalkoxide
s are also known. Unlike the halides, the alkoxides dissolve in nonpolar solvents. Dihydrogen hexafluorozirconate is used in the metal finishing industry as an etching agent to promote paint adhesion.
is key to Ziegler–Natta catalyst
s, used to produce polypropylene
. This application exploits the ability of zirconium to reversibly form bonds to carbon. Zirconocene dibromide ((C5
), reported in 1952 by Birmingham and Wilkinson
, was the first organozirconium compound. Schwartz's reagent
, prepared in 1970 by P. C. Wailes and H. Weigold, is a metallocene
used in organic synthesis
for transformations of alkenes
Most complexes of Zr(II) are derivatives of zirconocene, one example being (C5
The zirconium-containing mineral zircon and related minerals (jargoon
, hyacinth, jacinth
, ligure) were mentioned in biblical writings.
The mineral was not known to contain a new element until 1789,
analyzed a jargoon from the island of Ceylon (now Sri Lanka). He named the new element Zirkonerde (zirconia).
attempted to isolate this new element in 1808 through electrolysis, but failed.
Zirconium metal was first obtained in an impure form in 1824 by Berzelius
by heating a mixture of potassium and potassium zirconium fluoride in an iron tube.
The ''crystal bar process
'' (also known as the ''Iodide Process''), discovered by Anton Eduard van Arkel
and Jan Hendrik de Boer
in 1925, was the first industrial process for the commercial production of metallic zirconium. It involves the formation and subsequent thermal decomposition of zirconium tetraiodide
, and was superseded in 1945 by the much cheaper Kroll process
developed by William Justin Kroll
, in which zirconium tetrachloride is reduced by magnesium:
+ 2 Mg → Zr + 2 MgCl2
Approximately 900,000 tonnes of zirconium ores were mined in 1995, mostly as zircon.
Most zircon is used directly in high-temperature applications. Because it is refractory, hard, and resistant to chemical attack, zircon finds many applications. Its main use is as an opacifier, conferring a white, opaque appearance to ceramic materials. Because of its chemical resistance, zircon is also used in aggressive environments, such as moulds for molten metals.
) is used in laboratory crucibles, in metallurgical furnaces, and as a refractory material.
Because it is mechanically strong and flexible, it can be sintered
into ceramic knives
and other blades.
) and the cubic zirconia
) are cut into gemstones for use in jewelry.
Zirconium dioxide is a component in some abrasive
s, such as grinding wheels and sandpaper
A small fraction of the zircon is converted to the metal, which finds various niche applications. Because of zirconium's excellent resistance to corrosion, it is often used as an alloying agent in materials that are exposed to aggressive environments, such as surgical appliances, light filaments, and watch cases. The high reactivity of zirconium with oxygen at high temperatures is exploited in some specialised applications such as explosive primers and as getter
s in vacuum tube
s. The same property is (probably) the purpose of including Zr nanoparticles as pyrophoric
material in explosive weapons such as the BLU-97/B Combined Effects Bomb
. Burning zirconium was used as a light source in some photographic flashbulbs
. Zirconium powder with a mesh size from 10 to 80 is occasionally used in pyrotechnic compositions to generate sparks
. The high reactivity of zirconium leads to bright white sparks.
Cladding for nuclear reactor fuels consumes about 1% of the zirconium supply,
mainly in the form of zircaloy
s. The desired properties of these alloys are a low neutron-capture cross-section
and resistance to corrosion under normal service conditions.
Efficient methods for removing the hafnium impurities were developed to serve this purpose.
One disadvantage of zirconium alloys is the reactivity with water, producing hydrogen
, leading to degradation of the fuel rod cladding
: Zr + 2 H2
O → ZrO2
+ 2 H2
Hydrolysis is very slow below 100 °C, but rapid at temperature above 900 °C. Most metals undergo similar reactions. The redox reaction is relevant to the instability of fuel assemblies
at high temperatures. This reaction occurred in the reactors 1, 2 and 3 of the Fukushima I Nuclear Power Plant
(Japan) after the reactor cooling was interrupted by the earthquake and tsunami
disaster of March 11, 2011, leading to the Fukushima I nuclear accidents
. After venting the hydrogen in the maintenance hall of those three reactors, the mixture of hydrogen with atmospheric oxygen
exploded, severely damaging the installations and at least one of the containment buildings.
Zirconium is a constituent of the uranium zirconium hydride
(UZrH) nuclear fuel used in TRIGA
Space and aeronautic industries
Materials fabricated from zirconium metal and ZrO2
are used in space vehicles where resistance to heat is needed.
High temperature parts such as combustors, blades, and vanes in jet engine
s and stationary gas turbine
s are increasingly being protected by thin ceramic
layers, usually composed of a mixture of zirconia and yttria
Zirconium-bearing compounds are used in many biomedical applications, including dental implants and crowns
, knee and hip replacements, middle-ear ossicular
chain reconstruction, and other restorative and prosthetic
Zirconium binds urea
, a property that has been utilized extensively to the benefit of patients with chronic kidney disease
For example, zirconium is a primary component of the sorbent
column dependent dialysate regeneration and recirculation system known as the REDY system, which was first introduced in 1973. More than 2,000,000 dialysis
treatments have been performed using the sorbent column in the REDY system. Although the REDY system was superseded in the 1990s by less expensive alternatives, new sorbent-based dialysis systems are being evaluated and approved by the U.S. Food and Drug Administration
(FDA). Renal Solutions developed the DIALISORB technology, a portable, low water dialysis system. Also, developmental versions of a Wearable Artificial Kidney have incorporated sorbent-based technologies.
Sodium zirconium cyclosilicate
is used by mouth in the treatment of hyperkalemia
. It is a selective sorbent designed to trap potassium
ions in preference to other ions
throughout the gastrointestinal tract.
A mixture of monomeric and polymeric Zr4+
complexes with hydroxide
, called Aluminium zirconium tetrachlorohydrex gly
or AZG, is used in a preparation as an antiperspirant in many deodorant products. It is selected for its ability to obstruct pores in the skin and prevent sweat from leaving the body.
Zirconium carbonate (3ZrO2
O) was used in lotions to treat poison ivy
but was discontinued because it occasionally caused skin reactions.
Although zirconium has no known biological role, the human body contains, on average, 250 milligrams of zirconium, and daily intake is approximately 4.15 milligrams (3.5 milligrams from food and 0.65 milligrams from water), depending on dietary habits.
Zirconium is widely distributed in nature and is found in all biological systems, for example: 2.86 μg/g in whole wheat, 3.09 μg/g in brown rice, 0.55 μg/g in spinach
, 1.23 μg/g in eggs, and 0.86 μg/g in ground beef. Further, zirconium is commonly used in commercial products (e.g. deodorant
sticks, aerosol antiperspirants
) and also in water purification (e.g. control of phosphorus
pollution, bacteria- and pyrogen-contaminated water).
[Lee DBN, Roberts M, Bluchel CG, Odell RA. (2010) Zirconium: Biomedical and nephrological applications. ASAIO J 56(6):550-556.]
Short-term exposure to zirconium powder can cause irritation, but only contact with the eyes requires medical attention. Persistent exposure to zirconium tetrachloride
results in increased mortality in rats and guinea pigs and a decrease of blood hemoglobin
and red blood cell
s in dogs. However, in a study of 20 rats given a standard diet containing ~4% zirconium oxide, there were no adverse effects on growth rate, blood and urine parameters, or mortality. The U.S. Occupational Safety and Health Administration
(OSHA) legal limit (permissible exposure limit
) for zirconium exposure is 5 mg/m3
over an 8-hour workday. The National Institute for Occupational Safety and Health
(NIOSH) recommended exposure limit
(REL) is 5 mg/m3
over an 8-hour workday and a short term limit of 10 mg/m3
. At levels of 25 mg/m3
, zirconium is immediately dangerous to life and health
. However, zirconium is not considered an industrial health hazard.
Furthermore, reports of zirconium-related adverse reactions are rare and, in general, rigorous cause-and-effect relationships have not been established.
No evidence has been validated that zirconium is carcinogenic or genotoxic.
Among the numerous radioactive isotopes of zirconium, 93
Zr is among the most common. It is released as a product of nuclear fission
U and 239
Pu, mainly in nuclear power plants and during nuclear weapons tests in the 1950s and 1960s. It has a very long half-life (1.53 million years), its decay emits only low energy radiations, and it is not considered as highly hazardous.
Chemistry in its element podcast
(MP3) from the Royal Society of Chemistry
's Chemistry WorldZirconium
at ''The Periodic Table of Videos
'' (University of Nottingham)