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] 4f7 5d1 6s2
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
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
Main article: Isotopes of gadolinium iso NA half-life DM DE ( MeV) DP 152Gd 0.20% 1.08×1014 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% >1.3×1021 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

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 (Gd₂O₂S: 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 - Gd₂SiO_5: Ce).

Gallium Gadolinium Garnet (Gd₃Ga₅O₁₂) 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
  • GdF₃
• Chlorides
  • GdCl₃
• Bromides
  • GdBr₃
• Iodides
  • GdI₃
• Oxides
  • Gd₂O₃
• Sulfides
  • Gd₂S₃
• 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 1.3×10²¹ years (the decay is not observed, only the lower limit on the half-life is known), alpha-decaying ¹⁵²Gd with a half-life of 1.08×10¹⁴ years, and ¹⁵⁰Gd with a half-life of 1.79×10⁶ 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.