|Name, symbol, number||zirconium, Zr, 40|
|Element category||transition metal|
|Group, period, block||4, 5, d|
|Standard atomic weight||91.224 g·mol−1|
|Electron configuration||[Kr] 5s2 4d2|
|Electrons per shell||2, 8, 18, 10, 2 (Image)|
|Density (near r.t.)||6.52 g·cm−3|
|Liquid density at m.p.||5.8 g·cm−3|
|Melting point||2128 K, 1855 °C, 3371 °F|
|Boiling point||4682 K, 4409 °C, 7968 °F|
|Heat of fusion||14 kJ·mol−1|
|Heat of vaporization||573 kJ·mol−1|
|Specific heat capacity||(25 °C) 25.36 J·mol−1·K−1|
|Oxidation states||4, 3, 2, 1,
|Electronegativity||1.33 (Pauling scale)|
|Ionization energies||1st: 640.1 kJ·mol−1|
|2nd: 1270 kJ·mol−1|
|3rd: 2218 kJ·mol−1|
|Atomic radius||160 pm|
|Covalent radius||175±7 pm|
|Crystal structure||hexagonal close-packed|
|Electrical resistivity||(20 °C) 421 nΩ·m|
|Thermal conductivity||(300 K) 22.6 W·m−1·K−1|
|Thermal expansion||(25 °C) 5.7 µm·m−1·K−1|
|Speed of sound (thin rod)||(20 °C) 3800 m/s|
|Young's modulus||88 GPa|
|Shear modulus||33 GPa|
|Bulk modulus||91.1 GPa|
|Vickers hardness||903 MPa|
|Brinell hardness||650 MPa|
|CAS registry number||7440-67-7|
|Most stable isotopes|
|Main article: Isotopes of zirconium|
Zirconium (pronounced /zərˈkoʊniəm/ zər-KOH-ni-əm) is a chemical element with the symbol Zr and atomic number 40. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium. Zirconium is used as an alloying agent for its strong resistance to corrosion. It is never found as a native metal; it is obtained mainly from the mineral zircon, which can be purified with chlorine. Zirconium was first isolated in an impure form in 1824 by Jöns Jakob Berzelius.
Zirconium has no known biological role. Zirconium forms both inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. There are five naturally-occurring isotopes, three of which are stable. Short-term exposure to zirconium powder causes minor irritation, and inhalation of zirconium compounds can cause skin and lung granulomas.
Zirconium is a lustrous, grayish-white, soft, ductile, and malleable metal which is solid at room temperature, though it becomes hard and brittle at lower purities. In powder form, zirconium is highly flammable, but the solid form is far 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 become magnetic below 35 K.
Zirconium's melting point is at 1855°C, and its boiling point 4409°C. Zirconium has an electronegativity of 1.33 on the Pauling scale. Of the elements within d-block, zirconium has the fourth lowest electronegativity after yttrium, lutetium, and hafnium.
Because of zirconium's excellent resistance to corrosion, it is often used as an alloying agent in materials that are exposed to corrosive agents, such as surgical appliances, explosive primers, vacuum tube getters and filaments. Zirconium dioxide (ZrO2) is used in laboratory crucibles, metallurgical furnaces, as a refractory material, and it can be sintered into a ceramic knife. Zircon (ZrSiO4) is cut into gemstones for use in jewelry. Zirconium carbonate (3ZrO2·CO2·H2O) was used in lotions to treat poison ivy, but this was discontinued because it occasionally caused bad skin reactions.
Ninety percent of all zirconium produced is used in nuclear reactors (in the form of zircaloys) because of its low neutron-capture cross-section and resistance to corrosion. Zirconium alloys are used in space vehicle parts for their resistance to heat, an important quality given the extreme heat associated with atmospheric reentry. Zirconium is also a component in some abrasives, such as grinding wheels and sandpaper. Zirconium is used in weapons such as the BLU-97/B Combined Effects Bomb for incendiary effect.
High temperature parts such as combustors, blades and vanes in modern jet engines and stationary gas turbines are to an ever increasing extent being protected by thin ceramic layers which reduce the metal temperatures below and keep them from undergoing (too) extensive deformation which could possibly result in early failure. They are absolutely necessary for the most modern gas turbines which are driven to ever higher firing temperatures to produce more electricity at less CO2. These ceramic layers are usually composed by a mixture of zirconium and yttrium oxide.
Upon being collected from coastal waters, the solid mineral zircon is purified by spiral concentrators to remove excess sand and gravel and by magnetic separators to remove ilmenite and rutile. The byproducts can then be dumped back into the water safely, as they are all natural components of beach sand. The refined zircon is then purified into pure zirconium by chlorine or other agents, then sintered until sufficiently ductile for metalworking. Zirconium and hafnium are both contained in zircon and they are quite difficult to separate due to their similar chemical properties.
The zirconium-containing mineral zircon, or its variations (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 Sri Lanka in the Indian Ocean. He named the new element Zirkonerde (zirconia). Humphry Davy attempted to isolate this new element in 1808 through electrolysis, but failed. Zirconium (from Syriac ܙܐܪܓܥܢܥ zargono, Arabic zarkûn ئشقنعى from Persian zargûn زرگون meaning "gold like") was first isolated in an impure form in 1824 by Berzelius by heating a mixture of potassium and potassium-zirconium fluoride in a small decomposition process conducted in an iron tube.
The crystal bar process (or 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 pure metallic zirconium. The process involved thermally decomposing zirconium tetraiodide. It was superseded in 1945 by the much cheaper Kroll process developed by William Justin Kroll, in which zirconium tetrachloride is broken down by magnesium.
Zirconium has a concentration of about 130 mg/kg within the earth's crust and about 0.026 μg/L in sea water, though it is never found in nature as a native metal. The principal commercial source of zirconium is the zirconium 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.
Zircon 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, zircon prices have steadily increased from $360 to $840 per metric ton. Zirconium also occurs in more than 140 other recognized mineral species including baddeleyite and kosnarite. This metal is commercially produced mostly by the reduction of the zirconium(IV) chloride with magnesium metal in the Kroll process. Commercial-quality zirconium for most uses still has a content of 1% to 3% hafnium.
This element 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.
Zirconium has no known biological role, though zirconium salts are of low toxicity. The human body contains, on average, only 1 milligram of zirconium, and daily intake is approximately 50 μg per day. Zirconium content in human blood is as low as 10 parts per billion. Aquatic plants readily take up soluble zirconium, but it is rare in land plants. 70% of plants have no zirconium content at all, and those that do have as little as 5 parts per billion.
As a transition metal, zirconium forms various inorganic compounds, such as zirconium dioxide (ZrO2). This compound, also referred to as zirconia, has exceptional fracture toughness and chemical resistance, especially in its cubic form. These properties make zirconia useful as a thermal barrier coating, though it is also a common diamond substitute. Zirconium tungstate is an unusual substance in that it shrinks in all directions when heated, whereas most other substances expand when heated. ZrZn2 is one of only two substances to exhibit superconductivity and ferromagnetism simultaneously, with the other being UGe2. Other inorganic zirconium compounds include zirconium(II) hydride, zirconium nitride, and zirconium tetrachloride (ZrCl4), which is used in the Friedel-Crafts reaction.
Organozirconium chemistry is the study of compounds containing a carbon-zirconium bond. These organozirconium compounds are often employed as polymerization catalysts. The first such compound was zirconocene dibromide, prepared in 1952 by John M. Birmingham at Harvard University. 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.
Naturally-occurring zirconium is composed of five isotopes. 90Zr, 91Zr, and 92Zr are stable. 94Zr has a half-life of 1.10×1017 years. 96Zr has a half-life of 2.4×1019 years, making it 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.
28 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 years. 110Zr, the heaviest isotope of zirconium, is also the shortest-lived, with an estimated half-life of only 30 milliseconds. Radioactive isotopes at or above mass number 93 decay by β−, whereas those at or below 89 decay by β+. The only exception is 88Zr, which decays by ε.
Zirconium also has six 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.
Short-term exposure to zirconium powder can cause irritation, but only contact with the eyes requires medical attention. Inhalation of zirconium compounds can cause skin and lung granulomas. Zirconium aerosols can cause pulmonary granulomas. Persistent exposure to zirconium tetrachloride resulted in increased mortality in rats and guinea pigs and a decrease of blood hemoglobin and red blood cells in dogs. OSHA recommends a 5 mg/m3 time weighted average limit and a 10 mg/m3 short-term exposure limit.
ZIRCONIUM [[[symbol]] Zr, atomic weight 90 6 (0= 16)], a metallic chemical element. Klaproth in 1789 analysed the mineral zircon or hyacinth and found it to contain a new earth, which he called "zirconia." The metal was obtained by Berzelius as an iron-grey powder by heating potassium zirconofluoride with metallic potassium. The amorphous metal also results when the chloride is heated with sodium; the oxide reduced with magnesium; or when fused potassium zircono fluoride is electrolysed (Wedekind, Zeit. Elektrochem., 1904, 10, p. 331). Troost produced crystallized zirconium by fusing the double fluoride with aluminium in a graphite crucible at the temperature of melting iron, and extracting the aluminium from the melt with hydrochloric acid. It is more conveniently prepared by heating the oxide with carbon in the electric furnace. The crystals look like antimony, and are brittle, and so hard as to scratch glass and rubies; their specific gravity is 4.25. The powdery metal burns readily in air; the crystalline metal requires to be heated in an oxyhydrogen flame before it catches fire. Mineral acids generally attack the crystallized metal very little even in the heat; aqua regia, however, dissolves it readily, and so does hydrofluoric acid. In its chemical affinities zirconium resembles titanium, cerium and thorium; it occurs in company with these elements, and is tetravalent in its more important salts.
Zirconium oxide or zirconia, Zr02, has become important since its application to the manufacture of mantles for incandescent gas-lighting. For its extraction from zircon the mineral is heated and quenched in water to render it brittle, and then reduced to a fine powder, which is fused with three to four parts of acid potassium fluoride in a platinum crucible. When the mass is quietly fusing, the crucible is heated for two hours in a wind-furnace. The porcelain-like melt is powdered, boiled with water, and acidified with hydrofluoric acid, and the residual potassium fluosilicate is filtered off. The filtrate on cooling deposits crystals of potassium zirconofluoride, K 2 ZrF 6, which are purified by crystallization from hot water. The double fluoride is decomposed with hot concentrated sulphuric acid; the mixed sulphate is dissolved in water; and the zirconia is precipitated with ammonia in the cold. The precipitate, being difficult to wash, is (after a preliminary washing) re-dissolved in hydrochloric acid and re-precipitated with ammonia. Zirconium hydroxide, Zr(OH) 4, as thus obtained, is quite appreciably soluble in water and easily in mineral acids, with formation of zirconium salts, e.g. ZrC1 4. But, if the hydroxide is precipitated in the heat, it demands concentrated acids for its solution. The hydroxide readily loses its water at a dull red heat and passes into anhydride with vivid incandescence. Zirconia can be obtained crystalline, in a form isomorphous with cassiterite and rutile, by fusing the amorphous modification with borax, and dissolving out with sulphuric acid. The anhydrous oxide is with difficulty soluble even in hydrofluoric acid; but a mixture of two parts of concentrated sulphuric acid and one of water dissolves it on continued heating as the sulphate, Zr(S04)2. Zirconia, when heated to whiteness, remains unfused, and radiates a fine white light, which suggested its utilization for making incandescent gas mantles; and, in the form of disks, as a substitute for the lime-cylinders ordinarily employed in "limelight." Zirconia, like stannic and titanic oxides, unites not only with acids but also with basic oxides. For instance, if it be fused with sodium carbonate, sodium zirconate, Na2Zr03, is formed. If the carbonate be in excess, the salt Na4Zr04 results, which when treated with water gives Na2Zr8017 12H20, which crystallizes in hexagonal plates. When heated in a loosely covered crucible with magnesium the nitride Zr 2 N 3 is formed (Wedekind, Zeit. anorg. Chem., 1905, 45, p. 385).
Zirconium hydride, ZrH2, is supposed to be formed when zirconia is heated with magnesium in an atmosphere of hydrogen. Zirconium fluoride, ZrF4, is obtained as glittering monoclinic tables (with 3H 2 0) by heating zirconia with acid ammonium fluoride. It forms double salts, named zircono-fluorides, which are isomorphous with the stanniand titani-fluorides. Zirconium chloride, ZrC1 4, is prepared as a white sublimate by igniting a mixture of zirconia and charcoal in a current of chlorine. It has the exact vapour-density corresponding to the formula. It dissolves in water with evolution of heat; on evaporation a basic salt, ZrOC1 2.8H 2 0, separates out in star-shaped acicular aggregates. Zirconium bromide, ZrBr 4, is formed similarly to the chloride. Water gives the oxybromide ZrOBr 2. Zirconium iodide, Zr14, was obtained as a yellow, microcrystalline solid by acting with hydriodic acid on heated zirconium (Wedekind, Ber., 1904, 37, p. 1135). It fumes in air; with water it gives ZrOI 2.8H 2 0; and with alcohol ethyl iodide and zirconium hydroxide are formed. The iodide combines with liquid ammonia to form ZrI 4.8NH 3 i and with ether to give Zr14.4(C2H5)20. Zirconium combines with sulphur to form a sulphide, and with carbon to form several carbides. The sulphate, Zr(S04)2, is a white mass obtained by dissolving the oxide or hydroxide in sulphuric acid, evaporating and heating the mass to nearly a red heat. Since it forms a series of double sulphates, Ruer (Zeit. anorg. Chem., 1904, 42, p. 87) regards it as a dibasic acid, ZrOS04 S04H2, and that the crystalline sulphate is ZrOS04 S04H2.3H20 (not Zr(S04)2.4H20). Zirconium also forms double sulphates of the type Zr203(S04M)2 nH20, where M =K, Rb, Cs, and n=8 for K, 15 for Rb, 11 for Cs (Rosenheim and Frank, Ber., 1905, 38, p. 812). The atomic weight was determined by Marignac to be 90.03; Bailey (Proc. Roy. Soc., 1890, 46, p. 74) deduced the value 89.95.
[[File: |thumb|left|Zirconium, crystal bar]]