Zirconium

Zirconium or zirconium. Chemical element whose symbol is Zr, with atomic number 40 and atomic mass 91,224. It is located in group 4 of the periodic table and belongs to the transition elements . Solid gray – white, glossy, hard and resistant to corrosion , similar in appearance to steel, is one of the most abundant elements and is widely distributed in the earth ‘s crust.

Summary

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  • 1 History
  • 2 Natural state and abundance
  • 3 Structure
  • 4 Isotopes
  • 5 Physical properties
  • 6 Chemical properties
  • 7 Obtaining
    • 1 Zirconium and its alloys
  • 8 Production
    • 1 Separation of zirconium and hafnium
  • 9 Applications
  • 10 Health Effects
  • 11 Sources
  • 12 Bibliography

History

The etymological origin of zirconium or zirconium, as it is also known, comes from the Persian word zargun, – زرگون ​​which means “golden color”. The main mineral stone from which this element is extracted is called zircon, although it is also known as jergón or hyacinth. There is knowledge of zirconium from very ancient times; zirconium and some of its variations are mentioned in mythical accounts in the Bible .

It was discovered in 1789 by Martin Heinrich Klaproth from zircon (Zr [SiO 4 ]) and badeleyite (ZrO 2 ), a gemstone known since ancient times, which analyzed a jargon from Ceylon, in the Indian Ocean , naming the new element like zirconia.

In 1824 Jons Jakov Berzelius isolated it in an impure state by reducing potassium and zirconium fluoride , K 2 ZrF 6 with potassium, for which he heated a mixture of potassium and zirconium and potassium fluoride through a decomposition process developed by him. After treatment with water , drying and prolonged heating in dilute hydrochloric acid, he obtained a powder similar to carbon black and determined its atomic mass .

Until this time it was unknown that natural zirconium always contains small amounts of hafnium . Without this information, the atomic mass measurements were always high. It is very similar to hafnium, these minerals are mixtures of the two; geological processes have not been able to separate them.

Natural state and abundance

It is found in nature as part of numerous minerals, not as a native metal, which reflects its intrinsic instability with respect to water . Its concentration in the earth’s crust is approximately 130 mg / kg and around 0.026 mg / L in seawater. It ranks 18th in abundance, but despite being very common, it is usually only found in very small amounts and very small crystals (typically 0.1 mm), so it was once considered a rare element.

Zirconium is mainly found in intrusive siliceous rocks, such as granite. The raw materials are generally secondary deposits, called pleasure deposits. These are formed when the surrounding rock degrades and the remains of zirconium remain as they are more resistant to the elements. Furthermore, such deposits can be caused by running water, which flushes the zircon crystals and deposits them elsewhere. In contrast, primary deposits are often low in zirconium content and are not profitable for mining.

The main commercial source of zirconium is the mineral zircon (zirconium silicate, ZrSiO 4 ), which is found primarily in deposits in Australia , Brazil , India , Russia, and the United States , as well as in smaller deposits around the world.

80% of zircon mining occurs in Australia and South Africa . Zircon reserves exceed 60 million tons worldwide and global annual zirconia production is approximately 900,000 tons.

It is found in 140 other minerals, including baddeleyite (ZrO 2 ), kosnarite, and eudialite (Na 4 (CaCeFeMn) 2 ZrSi 6 O 17 (OHCl) 2 ). Zirconium and hafnium are found in zircon in a 50 to 1 ratio and it is very difficult to separate them. It is also found in other minerals, such as badeleyite .

It is also abundant in S-type stars and has been detected in the Sun and in meteorites . In addition, a high amount of zirconium oxide (compared to that present in the earth’s crust) has been found in lunar samples brought by the Apoyo program.

Structure

At room temperature, zirconium has a compact hexagonal crystalline structure, α-Zr, of the same type as magnesium. At 863 ° C it changes to a centered cubic crystal structure, β-Zr, similar to that of tungsten. Zirconium preserves the β-phase up to melting point 8.

Isotopes

Zirconium of natural origin is made up of four stable isotopes: 90 Zr, 91 Zr, 92 Zr, 94 Zr and a radioisotope with a very long half-life 96 Zr. The 94 Zr may suffer a double beta decay (not observed experimentally) with an average life of more than 1.10 × 1017 years. The 96 has a half life of 2.4 × 1019 years, making it the longest radioisotope of zirconium. Of these naturally occurring isotopes , 90 Zr is the most common, accounting for 51.45% of all zirconium, while 96Zr is the least common, comprising only 2.80% zirconium.

Twenty-eight artificial isotopes of zirconium have been synthesized, ranging in the atomic mass of 78 to 110. 93 Zr is the longest-lived artificial isotope, with a half-life of 1.53 × 106 years. The 110Zr is the heaviest isotope of zirconium, and also the shortest in duration, and the half-life is estimated to be only 30 milliseconds. Most have half-lives of less than one day, except for 95 Zr (64.02 days), 88 Zr (63.4 days), and 89 Zr (78.41 hours). Radioisotopes at or above mass number 93 disintegrate by beta β – decay, while those at or below 89 by β + decay .

The only exception is 88 Zr, which decays by electron capture ε. There are also five isotopes of zirconium in the form of metastable isomers: 83 mZr, 85 mZr, 89 mZr, 90 M1Zr, 90 m2Zr, and 91 mZr. Of these, 90 m2Zr has the shortest half-life 131 nanoseconds, while 89 mZr is the longest with a half-life of 4.161 minutes.

Physical properties

  • State of aggregation: solid at room temperature.
  • Appearance: greyish white, lustrous.
  • Density : 6.501 g / cm 3at 25 ° C), lighter than steel with a hardness similar to copper.
  • Melting point : 1855 ° C (3371 ° F).
  • Boiling point : 4371 ° C (7900 ° F).
  • Electronegativity : 1.33 on the Pauling scale.

Of the d-block elements, zirconium has the fourth lowest electronegativity after yttrium, lutetium, and hafnium.

Zinc alloys become magnetic below 35K. ZrZn 2 is one of the two substances that present superconductivity and ferromagnetism simultaneously, the other is UGe 2 . Below 0.55K, zirconium is superconducting.

Pure is ductile and malleable, it is easy to roll and forge. But small impurities of hydrogen , carbon or nitrogen make it brittle and difficult to process. Despite its poor electrical conductivity, it is a relatively good thermal conductor. If we compare it with titanium , slightly higher.

The properties of zirconium and the heavier homologue, hafnium, are similar due to lanthanide contraction. This makes the atomic radii similar, these two metals, however, differ considerably in their density. A property of great importance for the use of zirconium in nuclear reactors is its low neutron capture cross section.

Chemical properties

It is very chemically reactive and is only found in combination. In most reactions it binds with oxygen in preference to other elements, being found in the earth’s crust only as the oxide ZrO 2 , baddeleyite, or as part of the oxide complexes, such as zircon, elpidite and eudialite. From a commercial point of view, zircon is its most important mineral. Zirconium and hafnium are practically indistinguishable in their chemical properties, and they are only found together.

Zirconium forms a thin and compact oxide layer, passivated and therefore inert. It has a high resistance to corrosion by alkalis, acids, salt water and other agents. Aqueous bases react with zirconium. But it can be dissolved by hydrofluoric acid (HF), surely forming complexes with fluorides. Also, it will dissolve in a mixture of hydrochloric and sulfuric acid especially when fluorine is present .

Its most common oxidation states are 2 + , 3 + and 4 + .

The 4 + oxidation state prevails in almost all its compounds. Halides have been prepared in which the oxidation state is 2+ and 3+ ; While zirconium is often part of anionic or cationic complexes, there is no definitive evidence for the monovalent zirconium ion in some of its compounds.

It is highly resistant to corrosion to many common acids and alkalis.

When finely divided, it is highly flammable, it can spontaneously burn in contact with air (it reacts earlier with nitrogen than with oxygen), especially at high temperatures. In compact form it is much less prone to ignition, at moderate pressures it reacts only red-hot with oxygen and nitrogen . But at high pressure zirconium reacts with oxygen at room temperature, since the zirconium oxide formed is soluble in the molten metal.

The free energies of formation of its compounds indicate that zirconium would react only with any of the nonmetals, except inert gases, at common temperatures. In practice, the metal has been found to be unreactive at room temperature, because an invisible oxide layer forms on the surface. The coating makes the metal passive, and it remains shiny in the air indefinitely. At elevated temperatures it is highly reactive with non-metallic elements and many of the metallic elements, and forms solid and solution compounds.

Obtaining

Zirconium is obtained as a by-product of the mining and processing of heavy metal ores of titanium, ilmenite (FeTiO 3 ) and rutile (TiO 2 ), and also from tin mining.

Zirconium and its alloys

Refractory metals and alloys are of great interest in the construction of rockets, spaceships and atomic reactors, some parts and assemblies of which work at temperatures of 1500-2500º C. Molybdenum, tungsten, chromium, tantalum, niobium and zirconium.

Production

Zircon is a by-product of the mining and processing of the titanium ores ilmenite and rutile , as well as tin mining . Between 2003 and 2007 , zircon prices have risen steadily from $ 360 to $ 840 per ton.

Upon being collected from coastal waters, the zirconia sand they contain is purified by spiral concentrators to remove the lighter materials, which are then safely placed back into the water, as they are all natural components of sand from the beach. Magnetic separation removes the minerals from the titanium ilmenite and rutile. Most zircon is used directly in commercial applications, but a small percentage is converted to metal .

The first step consists of obtaining the zirconium dioxide by melting the zircon with sodium hydroxide , chemical digestion. The direct reduction of zirconium oxide with carbon (as in the blast furnace process) is not possible, as carbides that are very difficult to separate are formed. The majority of metallic zirconium is produced by the reduction of zirconium (IV) chloride with metallic magnesium in the Kroll process.

The resulting metal is sintered until it is ductile enough for metallurgy. In semi-industrial processes, the electrolysis of molten salts can be carried out, obtaining powdered zirconium that can later be used in powder metallurgy. To obtain the metal with greater purity, the van Arkel-de Boer process is followed based on the dissociation of zirconium iodide, obtaining a metal zirconium sponge called crystal-bar. For which, zirconium with iodine is heated to about 200ºC under vacuum to obtain zirconium iodide (IV). This decomposes on a hot wire, 1200 ° C, again into iodine , which remains gaseous, and zirconium which is deposited on the wire.

Both in this case, as in the previous one, the obtained sponge is melted to obtain the ingot. Commercial grade zirconia, even following the van Arkel-de Boer process, still has a 1% to 3% hafnium content.20 This contaminant is not important for most uses except for nuclear applications.

Zirconium and hafnium separation

Commercial zircon generally contains 1 to 2.5% hafnium. For usual applications this is not problematic because the chemical properties of hafnium and zirconium are quite similar. But the neutron absorption properties differ strongly, which is why the separation of hafnium from zirconium is required for applications involving nuclear reactors. Various separation methods are in use. The liquid-liquid extraction of the thiocyanate and the oxide derivatives exploits the slightly higher solubility of the hafnium derivative in methyl isobutyl ketone compared to water . This method is used primarily in the United States .

Zirconium and hafnium can also be separated by fractional crystallization from potassium hexafluorozirconate (K 2 ZrF 6 ), which is less soluble in water than the analogous hafnium derivative. Fractional distillation of tetrachlorides, also called extractive distillation , is used mainly in Europe . A quadruple VAM (Vacuum Arc Melting) process, combined with hot extrusion and different rolling applications is cured using autoclaving high pressure high temperature gas, resulting in reactor grade zirconium approximately 10 times more expensive than the contaminated commercial grade of hafnium.

Hafnium separation is especially important for nuclear applications since Hf has very high neutron absorption cross-section, about 600 times that of zirconia, and therefore has to be removed due to reactor applications.

Applications

The first practical application of zirconia is used as a flash in photography . Mainly (around 90% of the consumed) it is used linked to the production of energy, generally alloyed, zircaloy, in nuclear reactors , due to its resistance to corrosion and very low neutron capture section. The hafnium capture section is high, so it is necessary to separate them for this application (for others, it is not necessary), generally through an extraction process with two non-miscible solvents, or by using ion exchange resins.

It is used as an additive in steels, obtaining very resistant materials. Nickel alloys are also used in the chemical industry for their resistance to corrosive substances, especially for valves, pumps , pipes and heat exchangers.

Impure zirconium oxides are used to make laboratory crucibles (which withstand sudden changes in temperature), furnace lining, and as a refractory material in the ceramic and glass industries . Stabilized with yttrium, it is widely used in dentistry for the fabrication of fixed prostheses, removable prostheses , and implant abutments. It is also used for joint replacement as it is a bio-inert material like titanium .

It is also used in heat exchangers, vacuum tubes and bulb filaments and in the manufacture of antiperspirants.

For military purposes it is used as an incendiary agent, such as the dragon’s breath cartridge. Alloyed with niobium, it exhibits superconductivity at low temperatures, so it can be used to make superconducting magnets. On the other hand, zinc alloy is magnetic below 35 K.

Zirconium oxide is used in jewelry; It is an artificial gem called zirconia that imitates diamond .

We can add an industry in its early days: the manufacture of cutting blades, which can be extremely strong and durable, outperforming the best steel alloys. Today we can find commercial and professional knives and other kitchen accessories. It is used as an additive to make synthetic sands.

It is used in nuclear reactors (due to its low neutron capture section). It is also used as a refractory and opacifier, and in small amounts as an alloying agent for its strong resistance to corrosion.

Zirconium compounds are used in the ceramic industry: refractory, glazed, varnished, cast molds and abrasive sands, electrical ceramic components. Incorporating zirconium oxide into glass significantly increases its resistance to alkalis. Zirconium metal is used almost exclusively for cladding uranium fuel elements in nuclear plants. Another significant application is that of photographic flash.

It is used as a precious stone, due to its high refractive index and visual appeal, and its use in jewelry is abundant .

Thanks to the peculiarity of absorbing gases, zirconium is used as a getter in vacuum technology and as a degasser in metallurgy.

Health effects

Zirconium and its salts generally have low systemic toxicity.

Zirconium 95 is one of the radionuclides implicated in atmospheric tests for nuclear weapons. It is among the radionuclides that have produced and will continue to produce increased cancer risks for decades and centuries to come.

Compounds containing zirconium are not very common, and their inherent toxicity is low. Metal dust can burn in contact with air, so it must be considered as an agent of risk of fire or explosion. No biological role for this element is known.

 

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