Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
27 décembre 2011 2 27 /12 /décembre /2011 09:44

Thulium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the second least abundant of the lanthanides (promethium is only found in trace quantities on Earth). It is an easily workable metalwith a bright silvery-gray luster.Sony VAIO VGN-Z590UAB Battery

Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers.

Physical properties

Pure thulium metal has a bright, silvery luster. It is reasonably stable in air, but should be protected from moisture. The metal is soft, malleable, and ductile.Thulium is ferromagnetic below 32 K, antiferromagnetic between 32 and 56 K andparamagnetic above 56 K.Sony VAIO VGN-Z591U/B Battery

Chemical properties

Thulium metal tarnishes slowly in air and burns readily at 150 °C to form thulium(III) oxide:

4 Tm + 3 O2 ? 2 Tm2O3

Thulium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form thulium hydroxide:Sony VAIO VGN-Z59G Battery

2 Tm (s) + 6 H2O (l) ? 2 Tm(OH)3 (aq) + 3 H2 (g)

Thulium reacts with all the halogens. Reactions are slow at room temperature, but are vigorous above 200 °C:

2 Tm (s) + 3 F2 (g) ? 2 TmF3 (s) [white]

2 Tm (s) + 3 Cl2 (g) ? 2 TmCl3 (s) [yellow]

2 Tm (s) + 3 Br2 (g) ? 2 TmBr3 (s) [white]

2 Tm (s) + 3 I2 (g) ? 2 TmI3 (s) [yellow]

Thulium dissolves readily in dilute sulfuric acid to form solutions containing the pale green Tm(III) ions, which exist as a [Tm(OH2)9]3+ complexes:Sony VAIO VGN-Z620D Battery

2 Tm (s) + 3 H2SO4 (aq) ? 2 Tm3+ (aq) + 3 SO2?

4 (aq) + 3 H2 (g)

Thulium reacts with various metallic and non-metallic elements forming a range of binary compounds, including TmN, TmS, TmC2, Tm2C3, TmH2, TmH3, TmSi2, TmGe3, TmB4, TmB6 and TmB12. In those compounds, thulium exhibits valence states +2, +3 and +4, however, the +3 state is most common and only this state has been observed in Tm solutions.Sony VAIO VGN-Z620N/B Battery

Naturally occurring thulium is composed of one stable isotope, Tm-169 (100% natural abundance). Thirty one radioisotopes have been characterized, with the most stable being Tm-171 with a half-life of 1.92 years, Tm-170 with a half-life of 128.6 days, Tm-168 with a half-life of 93.1 days, and Tm-167 with a half-life of 9.25 days.Sony VAIO VGN-Z650N/B Battery

All of the remaining radioactive isotopes have half-lives that are less than 64 hours, and the majority of these have half-lives that are less than 2 minutes. This element also has 14 meta states, with the most stable being Tm-164m (t½ 5.1 minutes), Tm-160m (t½ 74.5 seconds) and Tm-155m (t½ 45 seconds).Sony VAIO VGN-Z670N/B Battery

The isotopes of thulium range in atomic weight from 145.966 u (Tm-146) to 176.949 u (Tm-177). The primary decay mode before the most abundant stable isotope, Tm-169, is electron capture, and the primary mode after is beta emission. The primary decay products before Tm-169 are element 68 (erbium) isotopes, and the primary products after are element 70 (ytterbium) isotopes.Sony VAIO VGN-Z690CTO Battery

Thulium was discovered by Swedish chemist Per Teodor Cleve in 1879 by looking for impurities in the oxides of other rare earth elements (this was the same method Carl Gustaf Mosander earlier used to discover some other rare earth elements). Cleve started by removing all of the known contaminants of erbia (Er2O3).Sony VAIO VGN-Z690NAX Battery

Upon additional processing, he obtained two new substances; one brown and one green. The brown substance was the oxide of the element holmium and was named holmia by Cleve, and the green substance was the oxide of an unknown element. Cleve named the oxide thulia and its element thulium afterThule, Scandinavia.Sony VAIO VGN-Z690PAB Battery

Thulium was so rare that none of the early workers had enough of it to purify sufficiently to actually see the green color; they had to be content with spectroscopically observing the strengthening of the two characteristic absorption bands, as erbium was progressively removed.Sony VAIO VGN-Z690PCB Battery

The first researcher to obtain nearly pure thulium was Charles James, a British expatriate working on a large scale at New Hampshire College in Durham. In 1911 he reported his results, having used his discovered method of bromate fractional crystallization to do the purification. He famously needed 15,000 "operations" to establish that the material was homogeneous.Sony VAIO VGN-Z690PDB Battery

High-purity thulium oxide was first offered commercially in the late 1950s, as a result of the adoption of ion-exchangeseparation technology. Lindsay Chemical Division of American Potash & Chemical Corporation offered it in grades of 99% and 99.9% purity.Sony VAIO VGN-Z690PEB Battery

The price per kilogram has oscillated between US$4,600 and $13,300 in the period from 1959 to 1998 for 99.9% purity, and it was second highest for lanthanides behind lutetium.

Occurrence and production

The element is never found in nature in pure form, but it is found in small quantities in minerals with other rare earths. Its abundance in the Earth crust is 0.5 mg/kg.Sony VAIO VGN-Z690PFB Battery

Thulium is principally extracted from monazite (~0.007% thulium) ores found in river sands, through ion-exchange. Newer ion-exchange and solvent-extraction techniques have led to easier separation of the rare earths, which has yielded much lower costs for thulium production.Sony VAIO VGN-Z690YAD Battery

The principal sources today are the ion adsorption clays of southern China. In these, where about two-thirds of the total rare-earth content is yttrium, thulium is about 0.5% (or about tied with lutetium for rarity). The metal can be isolated through reduction of its oxide with lanthanummetal or by calcium reduction in a closed container.Sony VAIO VGN-Z691Y/B Battery

None of thulium's natural compounds are commercially important.

Applications

Rare and expensive, thulium has few applications:

Laser

Holmium-chromium-thulium triple-doped YAG (Ho:Cr:Tm:YAG, or Ho,Cr,Tm:YAG) is an active laser medium material with high efficiency.Sony VAIO VGN-Z691Y/X Battery

It lases at 2097 nm and is widely used in military, medicine, and meteorology. Single-element thulium-doped YAG (Tm:YAG) lasers operate between 1930 and 2040 nm. The wavelength of thulium-based lasers is very efficient for superficial ablation of tissue, with minimal coagulation depth in air or in water. This makes thulium lasers attractive for laser-based surgery.Sony VAIO VGN-Z698Y/X Battery

X-ray source

Despite its high cost, portable X-ray devices use thulium that has been bombarded in a nuclear reactor as a radiation source. These sources are available for about one year, as tools in medical and dental diagnosis, as well as to detect defects in inaccessible mechanical and electronic components.Sony VAIO VGN-Z699JAB Battery

Such sources do not need extensive radiation protection – only a small cup of lead.

Thulium-170 is gaining popularity as an X-ray source for cancer treatment via brachytherapy.[13] This isotope has a half-life of 128.6 days and five major emission lines of comparable intensity (7.4, 51.354, 52.389, 59.4 and 84.253 keV).Sony VAIO VGN-Z70B Battery

Others

Thulium has been used in high temperature superconductors similarly to yttrium. Thulium potentially has use in ferrites, ceramic magnetic materials that are used inmicrowave equipment.Thulium is also similar to scandium in that it is used in arc lighting for its unusual spectrum, in this case, its green emission lines, which are not covered by other elements.Sony VAIO VGN-Z71JB Battery

Biological role and precautions

Thulium has no known biological role, although it has been noted that it stimulates metabolism. Soluble thulium salts are regarded as slightly toxic if taken in large amounts, but the insoluble salts are non-toxic.Sony VAIO VGN-Z73FB Battery

Thulium is not taken up by plant roots to any extent and thus does not get into the human food chain. Vegetables typically contain only one milligram of thulium per tonne (dry weight).

Ytterbium is a chemical element with the symbol Yb and atomic number 70.Sony VAIO VGN-Z790DKX Battery

A soft silvery metallic element, ytterbium is a rare earth element of the lanthanide series and is found in the minerals gadolinite, monazite, andxenotime. The element is sometimes associated with yttrium or other related elements and is used in certain steels.Sony VAIO VGN-Z790DMR Battery

Natural ytterbium is a mix of seven stable isotopes. Ytterbium-169, an artificially produced isotope, is used as a gamma ray source.

Physical properties

Ytterbium is a soft, malleable and ductile chemical element that displays a bright silvery luster when in its pure form.Sony VAIO VGN-Z790DND Battery

It is a rare earth element, and it is readily attacked and dissolved by the strong mineral acids. It reacts slowly with coldwater and it oxidizes slowly in air.

Ytterbium has three allotropes labeled by the Greek letters alpha, beta and gamma; their transformation temperatures are ?13 °C and 795 °C.Sony VAIO VGN-Z820DB Battery

The beta allotrope exists at room temperature, and it has a face-centered cubic crystal structure. The high-temperature gamma allotrope has a body-centered cubic crystalline structure.

Normally, the beta allotrope has a metallic electrical conductivity, but it becomes a semiconductor when exposed to a pressure of about 16,000 atmospheres (1.6 GPa).Sony VAIO VGN-Z820G/B Battery

Its electrical resistivity increases ten times upon compression to 39,000 atmospheres (3.9 GPa), but then drops to about 10% of its room-temperature resistivity at about 40,000 atm (4.0 GPa).

In contrast with the other rare-earth metals, which usually have antiferromagnetic and/or ferromagnetic properties at lowtemperatures, ytterbium is paramagnetic at any temperatures above 1.0 kelvin.Sony VAIO VGN-Z890GLX Battery

With a melting point of 824 °C and a boiling point of 1196 °C ytterbium has a smaller range of liquid temperatures than any other metal.

Chemical properties

Ytterbium metal tarnishes slowly in air and burns readily at 200 °C to form ytterbium(III) oxide (Yb2O3) or less stable ytterbium monoxide (YbO)Sony VAIO VGN-Z890GMR Battery

Ytterbium is quite electropositive, and it reacts slowly with cold water and quite quickly with hot water to form ytterbium hydroxide:

2 Yb (s) + 6 H2O (l) ? 2 Yb(OH)3 (aq) + 3 H2 (g)

Ytterbium reacts with all the halogens:

2 Yb (s) + 3 F2 (g) ? 2 YbF3 (s) [white]

2 Yb (s) + 3 Cl2 (g) ? 2 YbCl3 (s) [white]

2 Yb (s) + 3 Br2 (g) ? 2 YbBr3 (s) [white]

2 Yb (s) + 3 I2 (g) ? 2 YbI3 (s) [white]Sony VAIO VGN-Z898H/X Battery

The ytterbium(III) ion absorbs light in the near infrared range of wavelengths, but not in visible light, so that the mineralytterbia, Yb2O3, is white in color, and the salts of ytterbium of colorless anions are also colorless. Ytterbium dissolves readily in dilute sulfuric acid to form solutions that contain the colorless Yb(III) ions, which exist as a [Yb(OH2)9]3+complexes:Sony VAIO VGN-Z90FS Battery

2 Yb (s) + 3 H2SO4 (aq) ? 2 Yb3+ (aq) + 3 SO2?

4 (aq) + 3 H2 (g)

Chemical compounds

The chemical behavior of ytterbium is similar to that of the rest of the lanthanides. Most ytterbium compounds are found in the oxidation state +3, and its salts in this oxidation state are nearly colorless.Sony VAIO VGN-Z90NS Battery

Like europium, samarium, and thulium, the trihalogens of ytterbium can be reduced by hydrogen or by the addition of the metal reduced to the dihalogens, in this case the for example YbCl2. The oxidation state +2 reacts in some ways similarly to the alkaline earth metal compounds, for example the Ytterbium(II) oxide (YbO) shows the same structure as calcium oxide (CaO).Sony VAIO VGN-Z90PS Battery

  • Halides: YbCl2, YbBr3, YbCl3, YbF3
  • Oxides: Yb2O3
  • hydroxide: ytterbium hydroxide, Yb(OH)3

Natural ytterbium is composed of seven stable isotopes: 168Yb, 170Yb, 171Yb, 172Yb, 173Yb, 174Yb, and 176Yb, with 174Yb being the most abundant isotope, at 31.8% of the natural abundance).Sony VAIO VGN-Z90S Battery

27 radioisotopes have been observed, with the most stable ones being Yb-169 with a half-life of 32.0 days, 175Yb with a half-life of 4.18 days, and 166Yb with a half-life of 56.7 hours. All of its remaining radioactive isotopes have half-lives that are less than two hours, and the majority of these have half-lives that are less than 20 minutes.Sony VAIO VGN-Z90US Battery

Ytterbium also has 12 meta states, with the most stable being Yb-169m (t½ 46 seconds).

The isotopes of ytterbium range in atomic weight from 147.9674 atomic mass unit (u) for 148Yb to 180.9562 u for 181Yb. Its primary decay mode at weights lower than the most abundant stable isotope, 174Yb, is electron capture, and the primary decay mode above the atomic mass number of 174 is beta decay.Sony VAIO VGN-Z91DS Battery

The primary decay products at atomic masses lower than 174 arethulium isotopes, and the primary products from above 174 u are element (lutetium isotopes. Interestingly in modern quantum optics, the different isotopes of ytterbium follow either Bose-Einstein statistics or Fermi-Dirac statistics, leading to significant behavior in optical lattices.Sony VAIO VGN-Z91JS Battery

Ytterbium was discovered by the Swiss chemist Jean Charles Galissard de Marignac in the year 1878. Marignac found a new component in the earth then known as erbia, and he named it ytterbia, for Ytterby, the Swedish village near where he found the new component of erbium.Sony VAIO VGN-Z91PS Battery

Marignac suspected that ytterbia was a compound of a new element that he called "ytterbium".

In 1907, the French chemist Georges Urbain separated Marignac's ytterbia into two components: neoytterbia and lutecia. Neoytterbia would later become known as the element ytterbium, and lutecia would later be known as the element lutetium.Sony VAIO VGN-Z91YS Battery

Carl Auer von Welsbach independently isolated these elements from ytterbia at about the same time, but he called them aldebaranium and cassiopeium.

The chemical and physical properties of ytterbium could not be determined with any precision until 1953, when the first nearly pure ytterbium metal was produced by using ion-exchange processes.Sony VAIO VGN-Z92DS Battery

The price of ytterbium was relatively stable between 1953 and 1998 at about US$ 1,000/kg.

Occurrence

Ytterbium is found with other rare earth elements in several rare minerals. It is most often recovered commercially frommonazite sand (0.03% ytterbium). Sony VAIO VGN-Z92JS Battery

The element is also found in euxenite and xenotime. The main mining areas are China, United States, Brazil, India, Sri Lanka, and Australia; and reserves of ytterbium are estimated as one million tonnes. Ytterbium is normally difficult to separate from other rare earths,Sony VAIO VGN-Z92PS Battery

but ion-exchange and solvent extraction techniques developed in the mid to late 20th century have simplified separation. Known compounds of ytterbium are rare and have not yet been well characterized. The abundance of ytterbium in the Earth crust is about 3 mg/kg.Sony VAIO VGN-Z92YS Battery

The most important current (2008) sources of ytterbium are the ionic adsorption clays of southern China. The "High Yttrium" concentrate derived from some versions of these comprise about two thirds yttria by weight, and 3–4% ytterbia.Sony VAIO VGN-Z93FS Battery

As an even-numbered lanthanide, in accordance with the Oddo-Harkins rule, ytterbium is significantly more abundant than its immediate neighbors, thulium and lutetium, which occur in the same concentrate at levels of about 0.5% each. The world production of ytterbium is only about 50 tonnes per year, reflecting the fact that ytterbium has few commercial applications.Sony VAIO VGN-Z93GS Battery

Microscopic traces of ytterbium are used as a dopant in the ytterbium YAG laser, or Yb:YAG laser, a solid-state laser in which ytterbium is the element that undergoes stimulated emission of electromagnetic radiation.Sony VAIO VGN-Z93HS Battery

Production

Recovery of ytterbium from ores involves several processes which are common to most rare-earth elements: 1) processing, 2) separation of Yb from other rare earths, 3) preparation of the metal. If the starting ore is gadolinite, it is digested with hydrochloric or nitric acid which dissolves the rare-earth metals. Sony VAIO VGN-Z93VS Battery

The solution is treated with sodium oxalate or oxalic acid to precipitate rare earths as oxalates. For euxenite, ore is processed either by fusion with potassium bisulfate or withhydrofluoric acid. Monazite or xenotime are heated either with sulfuric acid or with caustic soda.Sony A1258274A Battery

Ytterbium is separated from other rare earths either by ion exchange or by reduction with sodium amalgam. In the latter method, a buffered acidic solution of trivalent rare earths is treated with molten sodium mercury alloy, which reduces and dissolves Yb3+. The alloy is treated with hydrochloric acid.Sony VGP-BPL10 Battery

The metal is extracted from the solution as oxalate and converted to oxide by heating. The oxide is reduced to metal by heating with lanthanum, aluminium, cerium or zirconium in high vacuum. The metal is purified by sublimation and collected over a condensed plate.Sony VGP-BPS10 Battery

Source of gamma rays

The 169Yb isotope has been used as a radiation source substitute for a portable X-ray machine when electricity was not available. Like X-rays, gamma rays pass through soft tissues of the body, but are blocked by bones and other dense materials. Thus, small 169Yb samples (which emit gamma rays) act like tiny X-ray machines useful for radiography of small objects.Sony VGP-BPS10/S Battery

Experiment shows that radiographs taken with 169Yb source are roughly equivalent to those taken with X-rays having energies between 250 and 350 keV.[9]

Doping of stainless steel

Ytterbium can also be used as a dopant to help improve the grain refinement, strength, and other mechanical properties of stainless steel. Some ytterbium alloys have rarely been used in dentistry.Sony VGP-BPS10A/B Battery

Yb as dopant of active media

Yb is used as dopant in optical materials, usually in the form of ions in active laser media. Several powerful double-clad fiber lasers and disk lasers use Yb3+ ions as dopant at concentration of several atomic percent. Glasses (optical fibers), crystals and ceramics with Yb3+ are used.Sony VGP-BPS10B Battery

Ytterbium is often used as a doping material (as Yb3+) for high power and wavelength-tunable solid state lasers. Yb lasers commonly radiate in the 1.06–1.12 µm band being optically pumped at wavelength 900 nm–1 µm, dependently on the host and application. Small quantum defect makes Yb prospective dopant for efficient lasers andpower scaling.Sony VGP-BPS10A Battery

The kinetic of excitations in Yb-doped materials is simple and can be described within concept of effective cross-sections; for the most of Yb-doped laser materials (as for many other optically pumped gain media), the McCumber relation holds,although the application to the Yb-doped composite materials was under discussion.Sony VGP-BPS11 Battery

Usually, low concentrations of Yb are used. At high concentration of excitations, the Yb-doped materials show photodarkening (glass fibers) or ever switch to the broadband emission  (crystals and ceramics) instead of the efficient laser action.Sony VGP-BPL11 Battery

This effect may be related with not only overheating, but also conditions of the charge compensation at high concentration of Yb ions.

Others

Ytterbium metal increases its electrical resistivity when subjected to high stresses. This property is used in stress gauges to monitor ground deformations from earthquakes and explosions.Sony VGP-BPL12 Battery

Precautions

Although ytterbium is fairly stable chemically, it should be stored in air-tight containers and in an inert atmosphere to protect the metal from air and moisture. All compounds of ytterbium should be treated as highly toxic although initial studies appear to indicate that the danger is minimal.Sony VGP-BPS12 Battery

Ytterbium compounds are, however, known to cause irritation to the skin and eye, and some might be teratogenic.[20] Metallic ytterbium dust poses a fire and explosion hazard.

Lutetium is a chemical element with the symbol Lu and atomic number 71.Sony VGP-BPL13 Battery

It is the last element in the lanthanide series, which, along with lanthanide contraction, explains several important properties of lutetium, such as it having the highest hardness or density among lanthanides. Unlike other lanthanides, the element lies in the d-block of the periodic table;Sony VGP-BPS13 Battery

however, lanthanum is sometimes placed on the d-block lanthanide position. Chemically, lutetium is a typical lanthanide: its only common oxidation state is +3, seen in its oxide, halides and other compounds. In an aqueous solution, like compounds of other late lanthanides, soluble lutetium compounds form a complex with nine water molecules.Sony VGP-BPS13/B Battery

Lutetium was independently discovered in 1907 by French scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach, and American chemist Charles James. All of these men found lutetium as an impurity in the mineral ytterbia, which was previously thought to consist entirely of ytterbium.Sony VGP-BPS13/S Battery

The dispute on the priority of the discovery occurred shortly after, with Urbain and von Welsbach accusing each other of publishing results influenced by the published research of the other; the naming honor went to Urbain as he published his results earlier. He chose the name lutecium for the new element but in 1949 the spelling of element 71 was changed to lutetium.Sony VGP-BPS13/S Battery

In 1909, the priority was finally granted to Urbain and his names were adopted as official ones; however, the name cassiopeium (or later cassiopium) for element 71 proposed by von Welsbach was used by many German scientists until the 1950s. Like other lanthanides, lutetium is one of the elements that traditionally were included in the classification "rare earths."Sony VGP-BPS13A/B Battery

Lutetium is rare and expensive; consequently, it has few specific uses. For example, a radioactive isotope lutetium-176 is used in nuclear technology to determine the age of meteorites. Lutetium usually occurs in association with the elementyttrium and is sometimes used in metal alloys and as a catalyst in various chemical reactions.Sony VGP-BPS13A/S Battery

Physical properties

A lutetium atom has 71 electrons, arranged in order [Xe]4f145d16s2.[2] When entering a chemical reaction, the atom loses its two outermost electrons and the only 5d-electron, which does not belong to an open subshell. Lutetium atoms are smaller than atoms of other lanthanides, due to the lanthanide contraction.Sony VGP-BPS13AS Battery

Lutetium is a silvery white corrosion-resistant trivalent metal. Many properties of lutetium metal relies on its last position of lanthanides and the lanthanide contraction — or, to be more accurate, the subsequent fact atomic radius of lutetium is the smallest among the lanthanides and is ? smaller than that of the biggest lanthanide, lanthanum.Sony VGP-BPS13B/B Battery

For example, lutetium (compared to other lanthanides) has the highest density, melting point, and hardness.

Chemical properties and compounds

Lutetium is a basic metal that always assumes +3 oxidation state in compounds.Sony VGP-BPS13B/Q Battery

However, it is common to name compounds both using and not using Stock nomenclature (for example, lutetium(III) chloride and lutetium chloride); once again, this is in accordance with other lanthanides.

Aqueous solutions of most lutetium salts are colorless and form white crystalline solids upon drying, with the common exception of the iodide.Sony VGP-BPS13B/S Battery

The soluble salts, such as nitrate, sulfate and acetate form hydrates upon crystallization. Theoxide, hydroxide, fluoride, carbonate, phosphate and oxalate are insoluble in water.

Lutetium metal is slightly instable in air at standard conditions, but it burns readily at 150 °C to form lutetium oxide.Sony VGP-BPS13Q Battery

The resulting compound is known to adsorb water and carbon dioxide, and may be used to remove vapors of these compounds from closed atmospheres. Similar observations are made during reaction between lutetium and water (slow when cold and fast when hot); lutetium hydroxide is formed in the reaction.Sony VGP-BPS13S Battery

Lutetium metal is known to react with four lightest halogens to form trihalides; all of them (except the fluoride) are soluble in water.

Lutetium dissolves readily in weak acids[6] and dilute sulfuric acid to form solutions containing the colorless lutetium ions, which exist as a [Lu(H2O)9]3+ complex:Sony VGP-BPL7 Battery

2 Lu + 3 H2SO4 + 18 H2O ? 2 [Lu(H2O)9]3+ + 3 SO2–4 + 3 H2?

Lutetium occurs on the Earth in form of two isotopes: lutetium-175 and lutetium-176. Out of these two, only the former is stable, making the element monoisotopic.Sony VGP-BPS7 Battery

The latter one, lutetium-176, decays via beta decay with a half-life of 3.78×1010years; it makes about one fortieth of the natural lutetium.[8] To date, 32 synthetic radioisotopes of the element have been characterized, ranging in mass from 149.973 (lutetium-150) to 183.961 (lutetium-184);Sony VGP-BPL8 Battery

the most stable such isotopes are lutetium-174 with a half-life of 3.31 years, and lutetium-173 with a half-life of 1.37 years.[8] All of the remainingradioactive isotopes have half-lives that are less than 9 days, and the majority of these have half-lives that are less than half an hour.Sony VGP-BPL8A Battery

Isotopes lighter than the stable lutetium-175 decay via electron capture (to produce isotopes of ytterbium), with some alpha and positron emission); the heavier isotopes decay primarily via beta decay, producing hafnium isotopes.[8]

The element also has 42 nuclear isomers, with masses of 150, 151, 153—162, 166—180 (not every mass number corresponds to only one isomer).Sony VGP-BPL8B Battery

The most stable of them are lutetium-177m, with half-life of 160.4 days and lutetium-174m, with half-life of 142 days; this is longer than half-lives of the ground states of all radioactive lutetium isotopes, except only for lutetium-173, 174, and 176.[8]

Lutetium (Latin: Lutetia meaning Paris) was independently discovered in 1907 by French scientist Georges Urbain,Sony VGP-BPS8 Battery

Austrian mineralogist Baron Carl Auer von Welsbach, and American chemist Charles James.[9] All of these men found lutetium as an impurity in the mineral ytterbia, which was thought by Swiss chemist Jean Charles Galissard de Marignac (and most others) to consist entirely of the element ytterbium.Sony VGP-BPS8A Battery

After the impurity was found out to consist of two different elements, the scientists proposed different names for the elements. Urbain chose the names neoytterbium and lutecium. Welsbach proposed the names cassiopeium for element 71 (after the constellation Cassiopeia)Sony VGP-BPS8B Battery

and aldebaranium for the new name of ytterbium but these naming proposals were rejected (although many German scientists in the 1950s called the element 71 cassiopium).[12] The dispute on the priority of the discovery is documented in two articles in which Urbain and von Welsbach accuse each other of publishing results influenced by the published research of the other.Sony VGP-BPL9 Battery

The Commission on Atomic Mass, which was responsible for the attribution of the names for the new elements, settled the dispute in 1909 by granting priority to Urbain and adopting his names as official ones. It is important that the separation of lutetium from Marignac's ytterbium was first described by Urbain rather than von Welsbach.Sony VGP-BPS9 Battery

An obvious problem with this decision was that Urbain was one of the four members of the commission.[13] After Urbain's names were recognized, the name neoytterbium was eventually reverted to ytterbium. Lutecium was the recognized name almost worldwide but in 1949 the spelling of element 71 was changed to lutetium.Sony VGP-BPS9/B Battery

Ironically, Charles James, who had modestly stayed out of the argument as to priority, worked on a much larger scale than the others, and undoubtedly possessed the largest supply of lutetium at the time.[14]

Only 46 years after its discovery, the lutetium metal was produced in 1953.Sony VGP-BPS9/S Battery

Occurrence and production

Found with almost all other rare-earth metals but never by itself, lutetium is very difficult to separate from other elements. The principal commercially viable ore of lutetium is the rare earth phosphate mineral monazite: (Ce,La,etc.)PO4 which contains 0.0001% of the element.Sony VGP-BPS9A Battery

The abundance of lutetium in the Earth crust is only about 0.5 mg/kg. The main mining areas are China,United States, Brazil, India, Sri Lanka and Australia. The world production of lutetium (in the form of oxide) is about 10 tonnes per year. Pure lutetium metal is very difficult to prepare.Sony VGP-BPS9A/B Battery

It is one of the rarest and most expensive of the rare earth metals with the price about US$10,000 per kilogram, or about one-fourth that of gold.

Crushed minerals are treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths.Sony VGP-BPS9A/S Battery

Thoriumprecipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths into their insoluble oxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in HNO3.Sony VGP-BPS9B Battery

Several rare earth metals, including lutetium, are separated as a double salt with ammonium nitrate by crystallization. Lutetium is separated by ion exchange. In this process, rare-earth ions are sorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. Sony VGP-BPX11 Battery

Lutetium salts are then selectively washed out by suitable complexing agent. Lutetium metal is then obtained byreduction of anhydrous LuCl3 or LuF3 by either an alkali metal or alkaline earth metal.

2 LuCl3 + 3 Ca ? 2 Lu + 3 CaCl2Sony VGP-BPL18 Battery

Applications

Because of the rarity and high price, lutetium has very few commercial uses. However, stable lutetium can be used as catalysts in petroleum cracking in refineriesand can also be used in alkylation, hydrogenation, and polymerization applications.Sony VGP-BPS18 Battery

Lutetium aluminium garnet (Al5Lu3O12) has been proposed for use as a lens material in high refractive index immersion lithography.  Additionally, a tiny amount of lutetium is added as a dopant to gadolinium gallium garnet (GGG), which is used in magnetic bubble memory devices.Sony VGP-BPL20 Battery

Cerium-doped lutetium oxyorthosilicate (LSO) is currently the preferred compound for detectors in positron emission tomography (PET).[19][20] Lutetium is used as a phosphor in LED light bulbs.[21]

Aside from stable lutetium, its radioactive isotopes have several specific uses.Sony VGP-BPS20/B Battery

The suitable half-life and decay mode made lutetium-176 used as a pure beta emitter, using lutetium which has been exposed to neutron activation, and in lutetium–hafnium dating to date meteorites.  The synthetic isotope lutetium-177 bound to octreotate (a somatostatin analogue), is used experimentally in targeted radionuclide therapy for neuroendocrine tumors.Sony VGP-BPS20/S Battery

Lutetium tantalate (LuTaO4) is the densest known stable white material (density 9.81 g/cm3) and therefore is an ideal host for X-ray phosphors.  The only denser white material is thorium dioxide, with density of 10 g/cm3, but the thorium it contains is radioactive.Sony VGP-BPL21 Battery

Precautions

Like other rare-earth metals, lutetium is regarded as having a low degree of toxicity, but its compounds should be handled with care nonetheless: for example, lutetium fluoride inhalation is dangerous and the compound irritates skin.Sony VGP-BPS21 Battery

Lutetium nitrate may be dangerous as it may explode and burn once heated. Lutetium oxide powder is toxic as well if inhaled or ingested.[6]

Similarly to other group 3 elements and lanthanides, lutetium has no biological role, but it is found even in the highest known organism, the humans, concentrating in bones, and to a lesser extent in the liver and kidneys.Sony VGP-BPS21/S Battery

Lutetium salts are known to cause metabolism and they occur together with other lanthanide salts in nature; the element is the least abundant in the human body of all lanthanides. Human diets have not been monitored for lutetium content, so it is not known how much the average human takes in,Sony VGP-BPS21A Battery

but estimations show the amount is only about several micrograms per year, all coming from tiny amounts taken by plants. Soluble lutetium salts are mildly toxic, but insoluble ones are not.

Hafnium is a chemical element with the symbol Hf and atomic number 72.Sony VGP-BPS21A/B Battery

A lustrous, silvery gray,tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence waspredicted by Dmitri Mendeleev in 1869. Hafnium was the penultimate stable isotope element to be discovered (rhenium was identified two years later).Sony VGP-BPS21B Battery

Hafnium is named for Hafnia, the Latin name for "Copenhagen", where it was discovered.

Hafnium is used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuitsat 45 nm and smaller feature lengths. Some superalloys used for special applications contain hafnium in combination withniobium, titanium, or tungsten.Sony VGP-BPL22 Battery

Hafnium's large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.Sony VGP-BPS22 Battery

Physical characteristics

Hafnium is a shiny, silvery, ductile metal that is corrosion-resistant and chemically similar to zirconium (due to its having the same number of valence electrons and being in the same group). The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity.Sony VGP-BPS22/A Battery

A notable physical difference between these metals is their density, with zirconium having about one-half the density of hafnium. The most notable nuclear properties of hafnium are its high thermal neutron-capture cross-section and that the nuclei of several different hafnium isotopes readily absorb two or more neutrons apiece.Sony VGP-BPS22A Battery

In contrast with this, zirconium is practically transparent to thermal neutrons, and it is commonly used for the metal components of nuclear reactors – especially the claddings of their nuclear fuel rods.

Chemical characteristics

Hafnium reacts in air to form a protective film that inhibits further corrosion.Sony VGP-BPL23 Battery

The metal is not readily attacked by acids but can be oxidized with halogens or it can be burnt in air. Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air—similar to that obtained in Dragon's Breath.[3] The metal is resistant to concentrated alkalis.Sony VGP-BPS23 Battery

The chemistry of hafnium and zirconium is so similar that the two cannot be separated on the basis of differing chemical reactions. The melting points and boiling points of the compounds and the solubility in solvents are the major differences in the chemistry of these twin elements.Sony VGP-BPS23/B Battery

At least 34 isotopes of hafnium have been observed, ranging in mass number from 153 to 186. The five stable isotopes are in the range of 176 to 180. The radioactive isotopes' half-lives range from only 400 ms for 153Hf,[6] to 2.0 petayears (1015 years) for the most stable one, 174Hf.Sony VGP-BPS23/D Battery

The nuclear isomer 178m2Hf was at the center of a controversy for several years regarding its potential use as a weapon.

Occurrence

Hafnium is estimated to make up about 5.8 ppm of the Earth's upper crust by weight.Sony VGP-BPS23/G Battery

It does not exist as a free element in nature, but is found combined in solid solution for zirconium in natural zirconium compounds such as zircon, ZrSiO4, which usually has about 1 – 4 % of the Zr replaced by Hf. Rarely, the Hf/Zr ratio increases during crystallization to give the isostructural mineral 'hafnon' (Hf,Zr)SiO4, with atomic Hf > Zr.Sony VGP-BPS23/P Battery

An old (obsolete) name for a variety of zircon containing unusually high Hf content is alvite.

A major source of zircon (and hence hafnium) ores are heavy mineral sands ore deposits,pegmatites particularly in Brazil and Malawi, and carbonatite intrusions particularly the Crown Polymetallic Deposit at Mount Weld, Western Australia. Sony VGP-BPS23/W Battery

A potential source of hafnium is trachyte tuffs containing rare zircon-hafnium silicates eudialyte or armstrongite, atDubbo in New South Wales, Australia.[9]

Hafnium reserves are projected to last under 10 years if the world population increases and demand grows.Sony Limited Edition 007 Battery

Production

The heavy mineral sands ore deposits of the titanium ores ilmenite and rutile yield most of the mined zirconium, and therefore also most the hafnium.[11]

Zirconium is a good nuclear fuel-rod cladding metal, with the desirable properties of a very low neutron capture cross-section and good chemical stability at high temperatures.Sony VAIO VGC-LB15 Battery

However, because of hafnium's neutron-absorbing properties, hafnium impurities in zirconium would cause it to be far less useful for nuclear-reactor applications. Thus, a nearly complete separation of zirconium and hafnium is necessary for their use in nuclear power. The production of hafnium-free zirconium is the main source for hafnium.Sony VGN-AR Series Battery

The chemical properties of hafnium and zirconium are nearly identical, which makes the two difficult to separate.[12] The methods first used — fractional crystallization of ammonium fluoride salts[13] or the fractionated distillation of the chloride[14] — have not proven suitable for an industrial-scale production.Sony VGN-CR Series Battery

After zirconium was chosen as material for nuclear reactor programs in the 1940s, a separation method had to be developed. Liquid-liquid extraction processes with a wide variety of solvents were developed and are still used for the production of hafnium.[15]About half of all hafnium metal manufactured is produced as a by-product of zirconium refinement.Sony VIAO VGN-G Series Battery

The end product of the separation is hafnium(IV) chloride.[16] The purified hafnium(IV) chloride is converted to the metal by reduction with magnesium or sodium, as in the Kroll process.[17]

HfCl4 + 2 Mg (1100 °C) ? 2 MgCl2 + Hf

Further purification is effected by a chemical transport reaction developed by Arkel and de Boer:Sony VIAO VGN-G118 Battery

In a closed vessel, hafnium reacts with iodine at temperatures of 500 °C, forming hafnium(IV) iodide; at a tungsten filament of 1700 °C the reverse reaction happens, and the iodine and hafnium are set free. The hafnium forms a solid coating at the tungsten filament, and the iodine can react with additional hafnium, resulting in a steady turn over.Sony VIAO VGN-G118CN/B Battery

Hf + 2 I2 (500 °C) ? HfI4

HfI4 (1700 °C) ? Hf + 2 I2

Chemical compounds

Hafnium and zirconium form nearly identical series of chemical compounds. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides.Sony VIAO VGN-G118CN/T Battery

At higher temperatures, hafnium reacts withoxygen, nitrogen, carbon, boron, sulfur, and silicon.[19] Due to the lanthanide contraction of the elements in the sixth period, zirconium and hafnium have nearly identical ionic radii. The ionic radius of Zr4+ is 0.79 angstrom and that of Hf4+ is 0.78 angstrom.Sony VIAO VGN-G218 Battery

Hafnium(IV) chloride and hafnium(IV) iodide have some applications in the production and purification of hafnium metal. They are volatile solids with polymeric structures.[4] These tetrachlorides are precursors to various organohafnium compounds such as hafnocene dichloride and tetrabenzylhafnium.Sony VGN-TZ121 Battery

The white hafnium oxide (HfO2), with a melting point of 2812 °C and a boiling point of roughly 5100 °C, is very similar tozirconia, but slightly more basic.[4] Hafnium carbide is the most refractory binary compound known, with a melting point over 3890 °C, and hafnium nitride is the most refractory of all known metal nitrides, with a melting point of 3310 °C.Sony VGN-TZ13 Battery

This has led to proposals that hafnium or its carbides might be useful as construction materials that are subjected to very high temperatures. The mixed carbide tantalum hafnium carbide (Ta4HfC5) possesses the highest melting point of any currently known compound, 4215 °C.m" title="Sony VGN-TZ131 laptop battery">Sony VGN-TZ131 Battery

In his report on The Periodic Law of the Chemical Elements, in 1869, Dmitri Mendeleev had implicitly predicted the existence of a heavier analog of titanium and zirconium. At the time of his formulation in 1871, Mendeleev believed that the elements were ordered by their atomic masses and placed lanthanum (element 57) in the spot below zirconium.Sony VGN-TZ132N Battery

The exact placement of the elements and the location of missing elements was done by determining the specific weight of the elements and comparing the chemical and physical properties.

The X-ray spectroscopy done by Henry Moseley in 1914 showed a direct dependency between spectral line and effective nuclear charge.Sony VGN-TZ132/N Battery

This led to the nuclear charge, or atomic number of an element, being used to ascertain its place within the periodic table. With this method, Moseley determined the number of lanthanides and showed the gaps in the atomic number sequence at numbers 43, 61, 72, and 75.Sony VGN-TZ17N Battery

The discovery of the gaps led to an extensive search for the missing elements. In 1914, several people claimed the discovery after Henry Moseley predicted the gap in the periodic table for the then-undiscovered element 72.  Georges Urbain asserted that he found element 72 in the rare earth elements in 1907 and published his results on celtium in 1911.Sony VGN-TZ16N Battery

Neither the spectra nor the chemical behavior matched with the element found later, and therefore his claim was turned down after a long-standing controversy.  The controversy was partly because the chemists favored the chemical techniques which led to the discovery ofceltium,Sony VGN-TZ18N Battery

while the physicists relied on the use of the new X-ray spectroscopy method that proved that the substances discovered by Urbain did not contain element 72. By early 1923, several physicists and chemists such as Niels Bohr  and Charles R. Bury  suggested that element 72 should resemble zirconium and therefore was not part of the rare earth elements group.Sony VAIO VGN-AR47G/E1 Battery

These suggestions were based on Bohr's theories of the atom, the X-ray spectroscopy of Mosley, and the chemical arguments of Friedrich Paneth.

Encouraged by these suggestions and by the reappearance in 1922 of Urbain's claims that element 72 was a rare earth element discovered in 1911, Dirk Coster and Georg von Hevesy were motivated to search for the new element in zirconium ores.Sony VAIO VGN-AR520E Battery

Hafnium was discovered by the two in 1923 in Copenhagen, Denmark, validating the original 1869 prediction of Mendeleev. It was ultimately found in zircon in Norway through X-ray spectroscopy analysis. The place where the discovery took place led to the element being named for the Latin name for "Copenhagen", Hafnia, the home town of Niels Bohr.Sony VAIO VGN-AR53DB Battery

Today, the Faculty of Science of the University of Copenhagen uses in its seal a stylized image of the hafnium atom.

Hafnium was separated from zirconium through repeated recrystallization of the double ammonium or potassium fluorides by Valdemar Thal Jantzen and von Hevesey.Sony VAIO VGN-AR54DB Battery

Anton Eduard van Arkel and Jan Hendrik de Boer were the first to prepare metallic hafnium by passing hafnium tetra-iodide vapor over a heated tungsten filament in 1924. This process for differential purification of zirconium and hafnium is still in use today.Sony VAIO VGN-AR550E Battery

In 1923, four predicted elements were still missing from the periodic table: 43 (technetium) and 61 (promethium) are radioactive elements and are only present in trace amounts in the environment,  thus making elements 75 (rhenium) and 72 (hafnium) the last two unknown non-radioactive elements.Sony VAIO VGN-AR55DB Battery

Since rhenium was discovered in 1925,[37] hafnium was the next to last element with stable isotopes to be discovered.

Applications

Several details contribute to the fact that there are only a few technical uses for hafnium:Sony VAIO VGN-AR630E Battery

First, the close similarity between hafnium and zirconium makes it possible to use zirconium for most of the applications; second, hafnium was first available as pure metal after the use in the nuclear industry for hafnium-free zirconium in the late 1950s. Furthermore, the low abundance and difficult separation techniques necessary make it a scarce commodity.Sony VAIO VGN-AR64DB Battery

Most of the hafnium produced is used in the production of control rods for nuclear reactors.

Nuclear reactors

The nuclei of several hafnium isotopes can each absorb multiple neutrons. This makes hafnium a good material for use in the control rods for nuclear reactors. Its neutron-capture cross-section is about 600 times that of zirconium.Sony VAIO VGN-AR65DB Battery

(Other elements that are good neutron-absorbers for control rods are cadmium and boron.) Excellent mechanical properties and exceptional corrosion-resistance properties allow its use in the harsh environment of a pressurized water reactors.  The German research reactor FRM II uses hafnium as a neutron absorber.Sony VAIO VGN-AR660U Battery

Alloys

Hafnium is used in iron, titanium, niobium, tantalum, and other metal alloys. An alloy used for liquid rocket thruster nozzles, for example the main engine of the Apollo Lunar Modules is C103, which consists of 89% niobium, 10% hafnium and 1% titanium.Sony VAIO VGN-AR690U Battery

Small additions of hafnium increase the adherence of protective oxide scales on nickel based alloys. It improves thereby thecorrosion resistance especially under cyclic temperature conditions that tend to break oxide scales by inducing thermal stresses between the bulk material and the oxide layer.Sony VAIO VGN-AR71ZU Battery


Partager cet article

Repost 0
Published by batterys - dans Laptop Battery
commenter cet article

commentaires