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Gadolinium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                64             europium ← gadolinium → terbium
                 -
                ↑
                Gd
                ↓
                Cm

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                   Name, Symbol, Number gadolinium, Gd, 64
                                               Chemical series lanthanides
                                            Group, Period, Block n/a, 6, f
                                                  Appearance silvery white
                                              Atomic mass 157.25 (3) g/mol
                                Electron configuration [Xe] 4f^7 5d^1 6s^2
                                    Electrons per shell 2, 8, 18, 25, 9, 2
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 7.90 g·cm^−3
                                     Liquid density at m.p. 7.4 g·cm^−3
                                                     Melting point 1585  K
                                                    (1312 ° C, 2394 ° F)
                                                      Boiling point 3546 K
                                                    (3273 ° C, 5923 ° F)
                                         Heat of fusion 10.05 kJ·mol^−1
                                   Heat of vaporization 301.3 kJ·mol^−1
                          Heat capacity (25 °C) 37.03 J·mol^−1·K^−1

   CAPTION: Vapor pressure (calculated)

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1836 2028 2267 2573 2976 3535

                                                         Atomic properties
                                               Crystal structure hexagonal
                                                        Oxidation states 3
                                                      (mildly basic oxide)
                                    Electronegativity 1.20 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 593.4 kJ·mol^−1
                                                    2nd: 1170 kJ·mol^−1
                                                    3rd: 1990 kJ·mol^−1
                                                      Atomic radius 180 pm
                                              Atomic radius (calc.) 233 pm
                                                             Miscellaneous
                                           Magnetic ordering ferromagnetic
                                 Electrical resistivity ( r.t.) (α, poly)
                                                             1.310 µΩ·m
                       Thermal conductivity (300 K) 10.6 W·m^−1·K^−1
                                    Thermal expansion (100 °C) (α, poly)
                                                            9.4 µm/(m·K)
                               Speed of sound (thin rod) (20 °C) 2680 m/s
                                        Young's modulus (α form) 54.8 GPa
                                          Shear modulus (α form) 21.8 GPa
                                           Bulk modulus (α form) 37.9 GPa
                                             Poisson ratio (α form) 0.259
                                                  Vickers hardness 570 MPa
                                             CAS registry number 7440-54-2
                                                         Selected isotopes

                CAPTION: Main article: Isotopes of gadolinium

                         iso     NA    half-life     DM   DE ( MeV)   DP
                        ^152Gd 0.20%  1.08×10^14 y α      2.205     ^148Sm
                        ^154Gd 2.18%  Gd is stable with 90 neutrons
                        ^155Gd 14.80% Gd is stable with 91 neutrons
                        ^156Gd 20.47% Gd is stable with 92 neutrons
                        ^157Gd 15.65% Gd is stable with 93 neutrons
                        ^158Gd 24.84% Gd is stable with 94 neutrons
                        ^160Gd 21.86% >1.3×10^21 y β^-β^- 1.7       ^160Dy

                                                                References

   Gadolinium ( IPA: /ˌgadəˈlɪniəm/) is a chemical element in the periodic
   table that has the symbol Gd and atomic number 64.

   Gadolinium >99.9% purity
   Enlarge
   Gadolinium >99.9% purity

Notable characteristics

   Gadolinium is a silvery white, malleable and ductile rare earth metal
   with a metallic luster. It crystallizes in hexagonal, close-packed
   alpha form at room temperature; when heated to 1508 K, it transforms
   into its beta form, which has a body-centered cubic structure.

   Unlike other rare earth elements, gadolinium is relatively stable in
   dry air; however, it tarnishes quickly in moist air and forms a loosely
   adhering oxide that spalls off and exposes more surface to oxidation.
   Gadolinium reacts slowly with water and is soluble in dilute acid.

   Gadolinium has the highest thermal neutron capture cross-section of any
   (known) element, 49,000 barns, but it also has a fast burn-out rate,
   limiting its usefulness as a nuclear control rod material.

   Gadolinium becomes superconductive below a critical temperature of
   1.083 K. It is strongly magnetic at room temperature, and exhibits
   ferromagnetic properties below room temperature.

Applications

   Gadolinium is used for making gadolinium yttrium garnets, which have
   microwave applications, and gadolinium compounds are used for making
   phosphors for colour TV tubes. Gadolinium is also used for
   manufacturing compact discs and computer memory.

   Gadolinium is used in nuclear marine propulsion systems as a burnable
   poison. The gadolinium slows the initial reaction rate, but as it
   decays other neutron poisons accumulate, allowing for long-running
   cores. Gadolinium is also used as a secondary, emergency shut-down
   measure in some nuclear reactors, particularly of the CANDU type.

   Gadolinium also possesses unusual metallurgic properties, with as
   little as 1% of gadolinium improving the workability and resistance of
   iron, chromium and related alloys to high temperatures and oxidation.

   Because of their paramagnetic properties, solutions of organic
   gadolinium complexes and gadolinium compounds are used as intravenous
   radiocontrast agents to enhance images in medical magnetic resonance
   imaging.

   Beside MRI, Gadolinium (Gd) is also used in other imaging. In X-ray,
   gadolinium is containing in the phosphor layer suspending in a polymer
   matrix at the detector. Terbium-doped gadolinium oxysulfide
   (Gd[2]O[2]S: Tb) at the phosphor layer is to convert the X-rays
   releasing from the source into light. Gd can emit spectrum at 540nm
   (Green light spectrum = 520 – 570nm), which is very useful for
   enhancing the imaging quality of the X-ray that are exposed to the
   photographic film. Beside Gd’s spectrum range, the compound also has a
   K-edge at 50 kiloelectron volt (keV), which means its absorption of
   X-ray through photoelectric interactions is great. The energy
   conversion of Gd is up to 20%, which means, one-fifth of the X-ray
   striking on the phosphor layer can be converted into light photons.
   Gadolinium oxyorthosilicate (GSO) is a single crystal that is used as a
   scintillator in medical imaging equipment like as Positron Emission
   Tomography ( PET). Another new scintillator for detecting neutron is
   gadolinium orthosilicate (GSO - Gd[2]SiO[5:] Ce).

   Gallium Gadolinium Garnet (Gd[3]Ga[5]O[12]) is a material with good
   optical properties, and is used in fabrication of various optical
   components and as substrate material for magneto–optical films.

   In the future, gadolinium ethyl sulfate, which has extremely low noise
   characteristics, may be used in masers. Furthermore, gadolinium's high
   magnetic movement and low Curie temperature (which lies just at room
   temperature) suggest applications as a magnetic component for sensing
   hot and cold.

   Due the extremely high neutron cross-section of Gadolinium, this
   element is very effective for use with neutron radiography.

History

   In 1880, Swiss chemist Jean Charles Galissard de Marignac observed
   spectroscopic lines due to gadolinium in samples of didymium and
   gadolinite; French chemist Paul Émile Lecoq de Boisbaudran separated
   gadolinia, the oxide of Gadolinium, from Mosander's yttria in 1886. The
   element itself was isolated only recently.

   Gadolinium, like the mineral gadolinite, is named after Finnish chemist
   and geologist Johan Gadolin.

   In older literature the natural form of the element is often called an
   "earth", meaning that element came from the Earth. Accordingly -
   Gadolinium is the element that comes from the earth, gadolinia. Earths
   are compounds of the element and one or more other element. Two common
   combining elements are oxygen and sulfur. For example, gadolinia
   contains gadolinium oxide (Gd2O3).

Biological role

   Gadolinium has no known biological role. It is used as a component of
   MRI contrast agents as in the 3+ oxidation state the metal has 7
   unpaired f electrons. This causes water around the contrast agent to
   relax quickly enhancing the quality of the MRI scan.

Occurrence

   Gadolinium is never found in nature as the free element, but is
   contained in many rare minerals such as monazite and bastnäsite. It
   occurs only in trace amounts in the mineral gadolinite which was also
   named for Johan Gadolin. Today, it is prepared by ion exchange and
   solvent extraction technique, or by the reduction of its anhydrous
   fluoride with metallic calcium.

Compounds

   Compounds of gadolinium include:
     * Fluorides
          + GdF[3]
     * Chlorides
          + GdCl[3]
     * Bromides
          + GdBr[3]
     * Iodides
          + GdI[3]
     * Oxides
          + Gd[2]O[3]
     * Sulfides
          + Gd[2]S[3]
     * Nitrides
          + GdN

Isotopes

   Naturally occurring gadolinium is composed of 5 stable isotopes,
   ^154Gd, ^155Gd, ^156Gd, ^157Gd and ^158Gd, and 2 radioisotopes, ^152Gd
   and ^160Gd, with ^158Gd being the most abundant (24.84% natural
   abundance). 30 radioisotopes have been characterized with the most
   stable being ^160Gd with a half-life of more than 1.3×10^21 years (the
   decay is not observed, only the lower limit on the half-life is known),
   alpha-decaying ^152Gd with a half-life of 1.08×10^14 years, and ^150Gd
   with a half-life of 1.79×10^6 years. All of the remaining radioactive
   isotopes have half-lifes that are less than 74.7 years, and the
   majority of these have half lifes that are less than 24.6 seconds. This
   element also has 4 meta states with the most stable being ^143mGd (t[½]
   110 seconds), ^145mGd (t[½] 85 seconds) and ^141mGd (t[½] 24.5
   seconds).

   The primary decay mode before the most abundant stable isotope, ^158Gd,
   is electron capture and the primary mode after is beta minus decay. The
   primary decay products before ^158Gd are element Eu (Europium) isotopes
   and the primary products after are element Tb (Terbium) isotopes.

Precautions

   As with the other lanthanides, gadolinium compounds are of low to
   moderate toxicity, although their toxicity has not been investigated in
   detail. Also, in patients on dialysis, there are data suggesting that
   it may cause Nephrogenic Systemic Fibrosis, formerly known as
   Nephrogenic Dermopathy. See: Grobner T. Related Articles, Gadolinium--a
   specific trigger for the development of nephrogenic fibrosing
   dermopathy and nephrogenic systemic fibrosis? Nephrol Dial Transplant.
   2006 Apr;21(4):1104-8. Epub 2006 Jan 23.
   Retrieved from " http://en.wikipedia.org/wiki/Gadolinium"
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   with only minor checks and changes (see www.wikipedia.org for details
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