Zirconium | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Pronunciation | /zɜːrˈkoʊniəm/ | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Appearance | silvery white | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Standard atomic weight Ar°(Zr) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Zirconium in the periodic table | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Atomic number (Z) | 40 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Group | group 4 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Period | period 5 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Block | d-block | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electron configuration | [ Kr ] 4d2 5s2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrons per shell | 2, 8, 18, 10, 2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Physical properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Phase at STP | solid | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Melting point | 2125 K (1852 °C,3365 °F) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Boiling point | 4650 K(4377 °C,7911 °F) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Density (near r.t.) | 6.52 g/cm3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
when liquid (at m.p.) | 5.8 g/cm3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of fusion | 14 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of vaporization | 591 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Molar heat capacity | 25.36 J/(mol·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Vapor pressure
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Atomic properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Oxidation states | −2, 0, +1, [3] +2, +3, +4 (an amphoteric oxide) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electronegativity | Pauling scale: 1.33 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Ionization energies |
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Atomic radius | empirical:160 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Covalent radius | 175±7 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Spectral lines of zirconium | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Other properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Natural occurrence | primordial | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Crystal structure | hexagonal close-packed (hcp) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Speed of sound thin rod | 3800 m/s(at 20 °C) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thermal expansion | 5.7 µm/(m⋅K)(at 25 °C) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thermal conductivity | 22.6 W/(m⋅K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrical resistivity | 421 nΩ⋅m(at 20 °C) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Magnetic ordering | paramagnetic [4] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Young's modulus | 88 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Shear modulus | 33 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Bulk modulus | 91.1 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Poisson ratio | 0.34 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mohs hardness | 5.0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Vickers hardness | 820–1800 MPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Brinell hardness | 638–1880 MPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CAS Number | 7440-67-7 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
History | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Naming | after zircon, zargun زرگون meaning "gold-colored". | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Discovery | Martin Heinrich Klaproth (1789) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
First isolation | Jöns Jakob Berzelius (1824) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Isotopes of zirconium | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Zirconium is a chemical element; it has symbol Zr and atomic number 40. The name zirconium is derived from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian zargun (zircon; zar-gun, "gold-like" or "as gold"). [7] It is a lustrous, grey-white, strong transition metal that closely resembles hafnium and, to a lesser extent, titanium.
Zirconium forms a variety of inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. Five isotopes occur naturally, four of which are stable.
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 compounds have no known biological role.
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. [8] 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. [9] However, it will dissolve in hydrochloric and sulfuric acid, especially when fluorine is present. [10] Alloys with zinc are magnetic at less than 35 K. [9]
The melting point of zirconium is 1855 °C (3371 °F), and the boiling point is 4409 °C (7968 °F). [9] 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. [11]
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. [12]
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 1.10×1017 years. 96Zr has a half-life of 2.4×1019 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. [13]
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 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. [13]
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. [13]
Zirconium has a concentration of about 130 mg/kg within the Earth's crust and about 0.026 μg/L in sea water. [14] 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 (ZrSiO4), a silicate mineral, [8] which is found primarily in Australia, Brazil, India, Russia, South Africa and the United States, as well as in smaller deposits around the world. [15] As of 2013, two-thirds of zircon mining occurs in Australia and South Africa. [16] Zircon resources exceed 60 million tonnes worldwide [17] and annual worldwide zirconium production is approximately 900,000 tonnes. [14] Zirconium also occurs in more than 140 other minerals, including the commercially useful ores baddeleyite and eudialyte. [18]
Zirconium is relatively abundant in S-type stars, and 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. [9]
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. [19]
Zirconium is a by-product formed after mining and processing of the titanium minerals ilmenite and rutile, as well as tin mining. [20] 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. [17]
Collected from coastal waters, zircon-bearing sand is purified by spiral concentrators to separate 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. [9] The resulting metal is sintered until sufficiently ductile for metalworking. [15]
Commercial zirconium metal typically contains 1–3% of hafnium, [21] 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. [22] Several separation schemes are in use. [21] 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. In India, TBP-Nitrate solvent extraction process is used for the separation
Zr and Hf can also be separated by fractional crystallization of potassium hexafluorozirconate (K2ZrF6), 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. [23] The separated hafnium can be used for reactor control rods. [24]
Like other transition metals, zirconium forms a wide range of inorganic compounds and coordination complexes. [25] 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.
The most common oxide is zirconium dioxide, ZrO2, 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. [26] These properties make zirconia useful as a thermal barrier coating, [27] although it is also a common diamond substitute. [26] Zirconium monoxide, ZrO, is also known and S-type stars are recognised by detection of its emission lines. [28]
Zirconium tungstate has the unusual property of shrinking in all dimensions when heated, whereas most other substances expand when heated. [9] Zirconyl chloride is a rare water-soluble zirconium complex with the relatively complicated formula [Zr4(OH)12(H2O)16]Cl8.
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.
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 tetraalkoxides 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. [29]
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 ((C5H5)2ZrBr2), reported in 1952 by Birmingham and Wilkinson, was the first organozirconium compound. [30] Schwartz's reagent, prepared in 1970 by P. C. Wailes and H. Weigold, [31] is a metallocene used in organic synthesis for transformations of alkenes and alkynes. [32]
Most complexes of Zr(II) are derivatives of zirconocene, one example being (C5Me5)2Zr(CO)2.
The zirconium-containing mineral zircon and related minerals (jargoon, jacinth, or hyacinth, ligure) were mentioned in biblical writings. [9] [22] The mineral was not known to contain a new element until 1789, [33] when Klaproth analyzed a jargoon from the island of Ceylon (now Sri Lanka). He named the new element Zirkonerde (zirconia). [9] Humphry Davy attempted to isolate this new element in 1808 through electrolysis, but failed. [8] 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. [9]
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 (ZrI4), and was superseded in 1945 by the much cheaper Kroll process developed by William Justin Kroll, in which zirconium tetrachloride (ZrCl4) is reduced by magnesium: [15] [34]
Approximately 900,000 tonnes of zirconium ores were mined in 1995, mostly as zircon. [21]
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 (ZrO2) is used in laboratory crucibles, in metallurgical furnaces, and as a refractory material [9] Because it is mechanically strong and flexible, it can be sintered into ceramic knives and other blades. [35] Zircon (ZrSiO4) and cubic zirconia (ZrO2) are cut into gemstones for use in jewelry. Zircon is also used in dating of rocks.
Zirconium dioxide is a component in some abrasives, such as grinding wheels and sandpaper. [33]
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. [36]
Cladding for nuclear reactor fuels consumes about 1% of the zirconium supply, [21] 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. [15] [9] 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:
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. [37] 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.
Materials fabricated from zirconium metal and ZrO2 are used in space vehicles where resistance to heat is needed. [22]
High temperature parts such as combustors, blades, and vanes in jet engines and stationary gas turbines are increasingly being protected by thin ceramic layers and/or paintable coatings, usually composed of a mixture of zirconia and yttria. [38] [39]
Zirconium is also used as a material of first choice for hydrogen peroxide (H2O2) tanks, propellant lines, valves, and thrusters, in propulsion space systems such as these equipping the Sierra Space's Dream Chaser spaceplane [40] where the thrust is provided by the combustion of kerosene and hydrogen peroxide, a powerful, but unstable, oxidizer. The reason is that zirconium has an excellent corrosion resistance to H2O2 and, above all, do not catalyse its spontaneous self-decomposition as the ions of many transition metals do. [40] [41]
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. [42]
Zirconium binds urea, a property that has been utilized extensively to the benefit of patients with chronic kidney disease. [42] 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. [43] 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.[ citation needed ]
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. [44]
A mixture of monomeric and polymeric Zr4+ and Al3+ 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.
Zirconium carbonate (3ZrO2·CO2·H2O) was used in lotions to treat poison ivy but was discontinued because it occasionally caused skin reactions. [8]
Hazards | |
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NFPA 704 (fire diamond) |
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. [45] 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. [45] 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). [42]
Short-term exposure to zirconium powder can cause irritation, but only contact with the eyes requires medical attention. [46] 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. [47] 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. [48] However, zirconium is not considered an industrial health hazard. [42] Furthermore, reports of zirconium-related adverse reactions are rare and, in general, rigorous cause-and-effect relationships have not been established. [42] No evidence has been validated that zirconium is carcinogenic or genotoxic. [49]
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. [50]
The actinide or actinoid series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.
Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1922, by Dirk Coster and George de Hevesy. making it one of the last two stable elements to be discovered. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.
Scandium is a chemical element; it has symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.
Thorium is a chemical element. It has the symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive gray when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.
Zircon is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is ZrSiO4. An empirical formula showing some of the range of substitution in zircon is (Zr1–y, REEy)(SiO4)1–x(OH)4x–y. Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.
Zirconium dioxide, sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant.
A period 5 element is one of the chemical elements in the fifth row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.
Group 4 is the second group of transition metals in the periodic table. It contains the four elements titanium (Ti), zirconium (Zr), hafnium (Hf), and rutherfordium (Rf). The group is also called the titanium group or titanium family after its lightest member.
In materials science, a refractory is a material that is resistant to decomposition by heat or chemical attack that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium. Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, which are repelled electrostatically.
Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.
Zirconium hydride describes an alloy made by combining zirconium and hydrogen. Hydrogen acts as a hardening agent, preventing dislocations in the zirconium atom crystal lattice from sliding past one another. Varying the amount of hydrogen and the form of its presence in the zirconium hydride controls qualities such as the hardness, ductility, and tensile strength of the resulting zirconium hydride. Zirconium hydride with increased hydrogen content can be made harder and stronger than zirconium, but such zirconium hydride is also less ductile than zirconium.
Zirconium carbide (ZrC) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering.
Zirconium(IV) chloride, also known as zirconium tetrachloride, is an inorganic compound frequently used as a precursor to other compounds of zirconium. This white high-melting solid hydrolyzes rapidly in humid air.
Zirconium(II) hydride is a molecular chemical compound with the chemical formula ZrH2. It is a grey crystalline solid or dark gray to black powder. It has been prepared by laser ablation and isolated at low temperature.
Zirconium silicate, also zirconium orthosilicate, ZrSiO4, is a chemical compound, a silicate of zirconium. It occurs in nature as zircon, a silicate mineral. Powdered zirconium silicate is also known as zircon flour.
This page describes how uranium dioxide nuclear fuel behaves during both normal nuclear reactor operation and under reactor accident conditions, such as overheating. Work in this area is often very expensive to conduct, and so has often been performed on a collaborative basis between groups of countries, usually under the aegis of the Organisation for Economic Co-operation and Development's Committee on the Safety of Nuclear Installations (CSNI).
Corium, also called fuel-containing material (FCM) or lava-like fuel-containing material (LFCM), is a material that is created in a nuclear reactor core during a nuclear meltdown accident. Resembling lava in consistency, it consists of a mixture of nuclear fuel, fission products, control rods, structural materials from the affected parts of the reactor, products of their chemical reaction with air, water, steam, and in the event that the reactor vessel is breached, molten concrete from the floor of the reactor room.
Zirconium nitrate is a volatile anhydrous transition metal nitrate salt of zirconium with formula Zr(NO3)4. It has alternate names of zirconium tetranitrate, or zirconium(IV) nitrate.
Hafnium compounds are compounds containing the element hafnium (Hf). Due to the lanthanide contraction, the ionic radius of hafnium(IV) (0.78 ångström) is almost the same as that of zirconium(IV) (0.79 angstroms). Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties. Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides. At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Some compounds of hafnium in lower oxidation states are known.