Gadolinium, Gd, Atomic number 64

General

Gadolinium is a chemical element with the element symbol Gd and atomic number 64. In the periodic table it is in the group of lanthanides and is thus also one of the rare earth metals.

The first element of the yttrium earths in the periodic table was 1880 found spectroscopically by Jean Charles de Marignac in Galissard didymium and gadolinite. 1886 he put it forth as a white oxide of Y samarskite and called out samarskite. In the same year, Paul Emile Lecoq de Boisbaudran ago gadolinia and also called the new element to the discoverer of the mineral gadolinite, the Finnish chemist Johan Gadolin, Gadolinium.

Only 1935 Georges Urbain succeeded in the representation of the metal.

Of course, comes only in gadolinium compounds. Technically significant monazite and bastnaesite are. The Gadolinitvorkommen in the pit Ytterby, north of Stockholm, are now exhausted.

Extraction

After extensive separation of the other Gadoliniumbegleiter, the oxide with hydrogen fluoride to Gadoliniuimfluorid reacted. Subsequently, this reduced with calcium to form calcium fluoride to the metallic gadolinium. The removal of residual calcium residues and contaminants carried in an additional remelting in vacuum.

Special features

The silvery white to gray-white lustrous rare earth metal is ductile and malleable. At temperatures above 1508 K transforms the densest packing of spheres in a body-centered cubic crystal structure at. In dry air is relatively stable gadolinium, in moist air it forms a non-protective, and loosely adhering oxide layer from flaking. With water it reacts slowly. In dilute acids, it dissolves.

Gadolinium has 49.000 neighbors because of its isotope contained Gd-157 (with 254.000 barn) the highest thermal neutron capture cross section for all known stable elements (only the unstable Xe-135 exceeds Gd-157 by about a factor 10). The high burn-up rate (burn-out-rate) limited use as a control rod in nuclear reactors, a strong.

Together with dysprosium, Holmium, Erbium and terbium, are assigned the same group of the lanthanides, It belongs to the single elements - except iron, Cobalt and nickel - have a ferromagnetism. However, it has to first under its ferromagnetic Curie temperature of 292,5 K (19,3 ° C) be accommodated.[6]

Contrary to many references gadolinium is not superconductive. This is based on the experience, impurities that ferromagnetic materials like iron and gadolinium, the superconductivity destruction of other elements. There are, however, ceramic high-temperature superconductors of the type known Ba2GdCu3O7-x with a transition temperature between 80-85 K.

Dusts of metallic gadolinium are fire- and potentially dangerous.

Use

Gadolinium is used for the preparation of gadolinium-yttrium garnet for microwave applications. Oxysulfides used for the production of green phosphor for luminescent screens (Radar).

Intravenously injected gadolinium(III)-Connections, such as gadopentetate dimeglumine, serve as a contrast agent in magnetic resonance imaging studies. These are due to the high toxicity of free gadolinium ions complexing with a high complex-, such as DTPA chelates (Diethylenetriaminepentaacetic) and DOTA (1,4,7,10-Tetraazacyclododecan-1 ,4,7,10-tetraessigsäure, Gd = gadoteric acid), used. The seven unpaired electrons in the f shell is strongly paramagnetic gadolinium. The contrast agent allowing the surrounding protons - mainly water - relax more quickly. This contrasts the differences between various tissues increased significantly in an MRI scan.
Even for studies on the brain, these contrast agents are used, because the gadolinium complexes can not cross the blood-brain barrier in healthy patients and therefore a blood-brain barrier disruption - a reference to an abnormal event (e.g.. Hypoperfusion, Tumor, Inflammation) - To make visible.

Gadolinium gallium garnet was used for the preparation of magnetic bubble storage. Also in the production of rewritable compact discs, it is applicable.

Additions of 1 % Gadolinium increase the workability and high temperature- and oxidation resistance of iron- and chromium alloys. Corresponding Gadoliniumeisenkobalt alloys can be used for opto-magnetic data storage.

Gadolinium may, since it has a Curie point near the room temperature, in refrigerators, the function on the principle of the adiabatic magnetization, Find use. Such cooling devices would no ozone-depleting chlorofluorocarbons, hydrochlorofluorocarbons (CFC) and manage possessed no mechanical parts subject to wear.

Gadolinium is used in the form of gadolinium oxide in modern fuel as burnable absorber material, the fuel assemblies according to one change at the beginning of the cycle of operation by an excess of nuclear fuel resulting limited to high reactivity of the reactor. With increasing fuel burnup of gadolinium is also reduced.[7]

With terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) is a frequently used technique in the X-ray scintillator. Gd2O2S:Tb emits light having a wavelength of 545nm.

There is no known biological function of the gadolinium.

Free gadolinium ions behave similarly to calcium ions, that is, They are built mainly in the liver and the skeletal system and can remain there for years. Free gadolinium also affected as a calcium antagonist - the ionic radii of calcium and gadolinium are almost identical - the contractility of the myocardium and inhibits the clotting system.[9]

Intravenously administered solutions of free gadolinium ions are acutely toxic. Affected by the toxicity include the smooth and striated muscle, mitochondrial function and blood clotting.[10]

The toxicity of free gadolinium is highly classified as. In complexed form, as the gadolinium contrast agent approved in the present, however, it is good considering the contraindications are generally compatible. Since 2006 There are increasing reports, that patients with kidney failure after administration of gadolinium chelates of various, especially Gd-DTPA, can lead to symptoms of nephrogenic systemic fibrosis.

General
Name, Symbol

Atomic number

Gadolinium, Gd, 64
Series Lanthanides
group, Period, Block The, 6, f
Appearance silvery white
CAS-Nummer 7440-54-2
Mass fraction of element 5,9 ppm
Atomic
Atomic mass 157,25 you
Atomradius 188 pm
Kovalenter Radius 196 pm
Elektronenkonf. [Car] 4f(7) 5d(1) 6s2
1. Ionization 593,4 KJ / mol
2. Ionization 1170 KJ / mol
3. Ionization 1990 KJ / mol
Physically
Physical State fixed
Crystal structure hexagonal
Density 7,886 g/cm3 (25 ° C)
Magnetism paramagnetisch (χm = 0,12)
Melting point 1585 K (1312 C)
Boiling point 3523 K (3250 C)
Molar Volume 19,90 * 10(-6)m(3)/mol
Heat of vaporization 305 KJ / mol
Schmelzwärme 10,0 KJ / mol
Electrical conductivity 0,763*10(6) A/(V * m)
Thermal conductivity 11 W /(m*K)
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