Gadolinium

{ syn. }

{ syn. }

0.20%

{ syn. }

2.18%

14.80%

20.47%

15.65%

24.84 %

{ syn. }

21.86 %

Attention

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

• 7.1 toxicity

History

The element was first discovered in 1880 by Swiss chemist Jean Charles de Galissard Marignac. , He studied the components of Samarskite and their different solubility in potassium sulfate solutions. Were formed depending on the solubility of several fractions. In one of the groups he found in the absorption spectrum of the spectral lines of an unknown element. This he called, as he could not obtain sufficient material for an exact determination, Yα. In addition, he was in another group that he also unknown Yβ, but this soon turned out that it was the found already by Marc Delafontaine and Paul Émile Lecoq de Boisbaudran samarium. After the existence of Yα by William Crookes and Paul Émile Lecoq de Boisbaudran could be confirmed Lecoq de Boisbaudran called on 19 April 1886, the new element in consultation with Marignac gadolinium, in honor of the Finnish chemist Johan Gadolin, with the symbol Gd

Metallic Gadolinium was first won in 1935 by Félix Trombe. He used for the electrolytic reduction of a melt of gadolinium ( III) chloride, potassium chloride and lithium chloride at 625-675 ° C to cadmium electrodes. A short time later he discovered along with Georges Urbain and Pierre -Ernest Weiss ferromagnetism of the element.

Occurrence

Gadolinium is a rare element on Earth, its share of the Earth's continental crust is 6.2 ppm.

The element is used in many of the rare earth minerals present in different amounts. Is particularly high gadolinium content in minerals such as xenotime the ytterbium earths, in Xenotimvorkommen from Malaysia, the gadolinium is about 4 %. Also contains monazite depending on the deposit of 1.5 to 2 % of the element in proportion with the bastnaesite 0.15 to 0.7 %, however, is lower. There is only a single known mineral, in which gadolinium is the rare earth metal with the highest percentage. It is the very rare uranyl Lepersonnit - (Gd ) with the chemical composition of Ca (Gd, Dy ) 2 ( UO2) 24 ( SiO 4 ) 4 ( CO3 ) 8 ( OH) 24 · 48H2O.

Production and representation

On the basis of the similarity, and because gadolinium is contained only in small quantities in the ore, the separation of the other lanthanides is difficult. After digestion of the raw materials such as monazite or Bastnäsit with sulfuric acid or sodium hydroxide to separate different ways are possible. A next ion exchange -based liquid-liquid extraction process is particularly important. Here, the cerium is in bastnasite as a starting material is initially separated in the form of cerium ( IV) oxide, and the remaining rare earth elements dissolved in hydrochloric acid. Then be separated from the light by means of a mixture of DEHPA ( di (2- ethylhexyl) phosphoric acid) and kerosene in liquid -liquid extraction, europium, gadolinium, samarium and the heavier rare earth metals. The former can be separated chemically by reduction to divalent europium and precipitation as sparingly soluble europium ( II ) sulfate. For separation of gadolinium, samarium, and the rest of the turn, the liquid-liquid extraction is used. The mixture is dissolved in dilute hydrochloric acid, treated with a mixture of trimethylbenzenes and DEHPA ( Shellsol A ), and separated in a mixer-settler apparatus.

Recovering elemental gadolinium is possible with the calcium on the reduction of gadolinium (III ) fluoride.

Gadolinium is produced only to a lesser extent and needs, the most important producer is like all the rare earth metals People's Republic of China.

Properties

Physical Properties

The silvery white to off-white shiny metal of the rare earths is ductile and malleable. It crystallizes in a hexagonal closest- crystal structure with lattice parameters a = 363 pm and c = 578 pm. Above 1262 ° C is the structure into a body-centered cubic structure.

In addition to this high-temperature phase, several high-pressure phases are known. The sequence of the phases corresponds to that of the other lanthanides (except europium and ytterbium ). The hexagonal structure follows ( all at room temperature) at pressures above 1.5 GPa, a structure of the samarium type, above 6.5 GPa is a double hexagonal crystal structure stable. A face-centered cubic packing is most stable at pressures from 26 to 33 GPa. At still higher pressures still are known a double - face-centered cubic structure and the monoclinic Gd -VIII.

Gadolinium is next dysprosium, holmium, erbium, terbium and thulium one of the lanthanides, which has ferromagnetism. Having a Curie temperature of 292.5 C ( 19.3 ° C), it has the highest Curie temperature, all lanthanides, but iron, cobalt and nickel have higher. Above this temperature, it is paramagnetic with a magnetic susceptibility χm of 0.12.

Because of these magnetic properties of gadolinium also has a very strong temperature-dependent heat capacity. At low temperatures ( below 4 C ) initially dominates, as metals common to the electronic heat capacity Cel (where Cel = γ · T with γ = 6.38 mJ · mol -1 · K-2 and T is the temperature). For higher temperatures, the Debye heat capacity is decisive ( with the Debye temperature? D = 163.4 K). Below the Curie temperature, the heat capacity will be too strong, which is due to the spin system. It reaches 56 J · mol -1 · K-1 at 290 K to an almost immediate break at higher temperatures below 31 J · mol -1 · K -1.

Gadolinium is a component of ceramic high-temperature superconductor of the type Ba2GdCu3O7 -x having a critical temperature of 94.5 K. The pure element is not superconductive.

Gadolinium has 49,000 barn because of its contained isotope Gd -157 ( with barn 254,000 ) have the highest thermal neutron cross all known stable elements (only the unstable Xe -135 reaches about ten times by Gd -157 ). The high rate of burn (burn -out rate) limited use as a control rod in a nuclear reactor strong.

Chemical Properties

In dry air, gadolinium is relatively stable in moist air, it forms a non- protective, loosely adhering and peeling of the oxide layer. With water it reacts slowly. In dilute acids it dissolves. Dusts of metallic gadolinium are fire and explosion hazard.

Use

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

Intravenously injected gadolinium ( III) compounds, such as gadopentetate dimeglumine, serve as contrast agents in magnetic resonance imaging in testing. To be due to the high toxicity of free gadolinium ions complexing with high complexation, such as the chelates of DTPA ( diethylenetriaminepentaacetic acid ) and DOTA ( 1,4,7,10 -tetraazacyclododecane -1 ,4,7,10 -tetraacetic acid, with Gd = gadoteric acid ) was used. Through the seven unpaired electrons in the f shell gadolinium is strongly paramagnetic. The contrast agent allows so the surrounding protons - mainly water - to relax faster. This increases the contrast differences between different tissues significantly in an MRI scan.

For studies of the brain, these contrast agents can not be used because the gadolinium complexes do not cross the intact blood -brain barrier.

Gadolinium- gallium garnet has been used for the production of magnetic bubble memories. In the manufacture of re-writable compact discs, it is used.

Addition of 1% gadolinium increase the workability and the high temperature and oxidation resistance of iron and chromium alloys. Corresponding gadolinium -iron-cobalt alloys can be used for the optical magnetic data storage.

Gadolinium could be because it has a Curie point near room temperature, found in refrigerators that work on the principle of adiabatic magnetization use. Such cooling devices would do without ozone -depleting chlorofluorocarbons (CFCs ) and possessed no -wearing mechanical parts.

Gadolinium is used in the form of gadolinium oxide in modern fuel burnable absorber material as that limits after a fuel change at the beginning of the operating cycle of the product created by an excess of nuclear fuel to high reactivity of the reactor. With increasing burnup of the fuel elements and the gadolinium is degraded.

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

Compounds

• Gadolinium ( III) oxide Gd2O3
• Gadolinium (III ) fluoride GdF3
• Gadolinium ( III) chloride GdCl3
• Gadolinium (III ) bromide GdBr3
• Gadolinium (III ) iodide GdI3
• Gadolinium ( II) iodide GdI2; black substance which is ferromagnetic.

• Gallium gadolinium garnet Ga3Gd5O12
• Gadoteric acid
• Gadopentetate dimeglumine

Physiology

There is no known biological function of gadolinium.

Toxicity

Free gadolinium ions behave similarly to calcium ions, that is, they are built mainly in the liver and in the skeletal system and can remain there for years. Free gadolinium affects also as a calcium antagonist - the ionic radii of calcium and gadolinium are nearly equal to - the contractility of the myocardium and to inhibit the coagulation system.

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.

The toxicity of free gadolinium is classified as high. In complexed form, as the gadolinium present in the approved contrast agents, however, it is taking into account the contraindications generally well tolerated. Since 2006, there are increasing reports that may occur in renal failure patients after administration of various chelates of gadolinium, especially Gd -DTPA, the clinical picture of nephrogenic systemic fibrosis. A new study provides evidence that gadolinium after repeated MRIs to deposits and possibly structural damage could result in the brain in contrast agents. Whether it really comes down to injury, but could not yet be determined.