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 ''
zargun'' (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 and
opacifier, 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
isotopes occur naturally, three of which are stable. Zirconium compounds have no known biological role.
Characteristics

Zirconium 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, 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 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).
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,
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. Zirconium exists in the β-phase until the melting point.
Isotopes
Naturally occurring zirconium is composed of five isotopes.
90Zr,
91Zr,
92Zr and
94Zr are stable, although
94Zr is predicted to undergo
double beta decay (not observed experimentally) with a
half-life of more than 1.10×10
17 years.
96Zr has a half-life of 2.4×10
19 years, and is the longest-lived radioisotope of zirconium. Of these natural isotopes,
90Zr is the most common, making up 51.45% of all zirconium.
96Zr 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 1.53×10
6 years.
110Zr, 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
88Zr, which decays by
electron capture.
Five isotopes of zirconium also exist as
metastable isomers:
83mZr,
85mZr,
89mZr,
90m1Zr,
90m2Zr and
91mZr. Of these,
90m2Zr has the shortest half-life at 131 nanoseconds.
89mZr is the longest lived with a half-life of 4.161 minutes.
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
zircon (ZrSiO
4), 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
tonnes worldwide
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 and
kosnarite.
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.
Production

Zirconium is a by-product of the mining and processing of the
titanium minerals
ilmenite and
rutile, 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 and
rutile are removed.
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 with
magnesium 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 (K
2ZrF
6), which is less soluble in water than the analogous hafnium derivative.
Fractional distillation 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.
Compounds
Like other
transition metals, zirconium forms a wide range of
inorganic compounds and
coordination complexes. 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, ZrO
2, also known as ''zirconia''. This clear to white-coloured solid has exceptional
fracture toughness (for a ceramic) and chemical resistance, especially in its
cubic form.
These properties make zirconia useful as a thermal barrier coating, although it is also a common
diamond substitute.
Zirconium monoxide, ZrO, is also known and
S-type stars are recognised by detection of its emission lines.
Zirconium tungstate has the unusual property of shrinking in all dimensions when heated, whereas most other substances expand when heated.
Zirconyl chloride is a rare water-soluble zirconium complex with the relatively complicated formula
r4(OH)12(H2O)16l
8.
Zirconium carbide 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,
ZrCl4,
ZrBr4, 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 tetra
alkoxides 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.
Organic derivatives
Organozirconium chemistry is key to
Ziegler–Natta catalysts, used to produce
polypropylene. This application exploits the ability of zirconium to reversibly form bonds to carbon. Zirconocene dibromide ((C
5H
5)
2ZrBr
2), 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 and
alkynes.
Most complexes of Zr(II) are derivatives of zirconocene, one example being (C
5Me
5)
2Zr(CO)
2.
History
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,
when
Klaproth analyzed a jargoon from the island of Ceylon (now Sri Lanka). He named the new element Zirkonerde (zirconia).
Humphry Davy 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:
:ZrCl
4 + 2 Mg → Zr + 2 MgCl
2
Applications
Approximately 900,000 tonnes of zirconium ores were mined in 1995, mostly as zircon.
Compounds
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.
Zirconium dioxide (ZrO
2) 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.
Zircon (ZrSiO
4) and the
cubic zirconia (ZrO
2) are cut into gemstones for use in jewelry.
Zirconium dioxide is a component in some
abrasives, such as grinding wheels and
sandpaper.
Metal
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
getters in
vacuum tubes. 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.
Nuclear applications
Cladding for nuclear reactor fuels consumes about 1% of the zirconium supply,
mainly in the form of
zircaloys. 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 H
2O → ZrO
2 + 2 H
2
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 reactors.
Space and aeronautic industries
Materials fabricated from zirconium metal and ZrO
2 are used in space vehicles where resistance to heat is needed.
High temperature parts such as combustors, blades, and vanes in
jet engines and stationary
gas turbines are increasingly being protected by thin
ceramic layers, usually composed of a mixture of zirconia and
yttria.
Medical uses
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 devices.
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 Zr
4+ and Al
3+ complexes with
hydroxide,
chloride and
glycine, 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.
Defunct applications
Zirconium carbonate (3ZrO
2·CO
2·H
2O) was used in lotions to treat
poison ivy but was discontinued because it occasionally caused skin reactions.
Safety
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 cells 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/m
3 over an 8-hour workday. The
National Institute for Occupational Safety and Health (NIOSH)
recommended exposure limit (REL) is 5 mg/m
3 over an 8-hour workday and a short term limit of 10 mg/m
3. At levels of 25 mg/m
3, 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,
93Zr is among the most common. It is released as a
product of nuclear fission of
235U and
239Pu, 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.
See also
*
Zirconium alloys
*
Zirconia light
References
External links
Chemistry in its element podcast(MP3) from the
Royal Society of Chemistry's
Chemistry WorldZirconiumat ''
The Periodic Table of Videos'' (University of Nottingham)
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Category:Chemical elements
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