64
  Gd  
157.250000
Gadolinium

Name: Gadolinium
Symbol: Gd
Atomic Number: 64
Atomic Weight: 157.250000
Family: Rare Earth Elements
CAS RN: 7440-54-2
Description: A silvery white metal, it is malleable, ductile and ferromagnetic.
State (25C): Solid
Oxidation states: +3

Molar Volume: 19.9 cm3/mole
Valence Electrons: 4f75d16s2

Boiling Point:  3539K, 3266C, 5911F
Melting Point:
1585K, 1312C, 2394F
Electrons Energy Level: 2, 8, 18, 25, 9, 2
Isotopes: 30 + 6 Stable + 4 meta states
Heat of Vaporization: 359.4 kJ/mol
Heat of Fusion: 10.05 kJ/mol
Density: 7.895g/cm3  @  300K
Specific Heat: 0.23 J/gK
Atomic Radius: 2.54
Ionic Radius: 0.938
Electronegativity: 1.2 (Pauling); 1.11 (Allrod Rochow)
Vapor Pressure: 24400 Pa @ 1312C
57
La
138.9
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0

1s2 2s2p6 3s2p6d10 4s2p6d10f7 5s2p6d1 6s2

History

In 1880, Swiss chemist Jean Charles Galissard de Marignac observed spectroscopic lines on the mixture then known as didymia and gadolinite, (Ce, La, Nd, Y)2FeBe2Si2O10; French chemist Paul Emile Lecoq de Boisbaudran separated gadolinia, the oxide of Gadolinium from Monsander's "yttria" in 1886.  Today, gadolinium is primarily obtained from the minerals monazite, (Ce, La, Th, Nd, Y)PO4 and bastnasite, (Ce,La,Y)CO3F.

Gadolinium (from 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 elements. Two common combining elements are oxygen and sulfur. For example, gadolinia contains gadolinium oxide (Gd2O3).

Characteristics

Gadolinium is a soft, 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 1508oK, it transforms into its beta form, which has a body-centered cubic structure.  The metal can be prepared by the reduction of the anhydrous fluoride with metallic calcium.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f7
5s2 5p6 5d1
6s2

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 1.083oK.   It is strongly magnetic at room temperature, and exhibits ferromagnetic properties below room temperature.

Gadolinium demonstates a magnetocaloric effect whereby its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. The effect is considerably stronger for the gadolinium alloy Gd5(Si2Ge2).

The metal has a very large capacity for absorbing thermal neutrons, making it an excellent material for control rods in fission power plants

Occurrence

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

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 gadolinium compounds are used as intravenous radiocontrast agents to enhance images in medical magnetic resanance imaging.  Magnevist is the most widespread example.

Besides 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 - Gd2SiO5: Ce).

Gadolinium gallium 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.

The metal has unusual superconductive properties.  As little as 1% gadolinium has been found to improve the workability and resistance of iron, chromium, and related alloys to high temperatures and oxidation.  Gadolinium ethyl sulfate has extremely low noise characteristics and may find use in duplicating the performance of amplifiers, such as the maser.  The metal is ferromagnetic. Gadolinium is unique for its high magnetic moment and for its special Curie temperature (above which ferromagnetism vanishes) lying just at room temperature.  This suggests uses as a magnetic component that senses hot and cold.

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

Value

In 1994, the cost of gadolinium was abou US $ 0.12 per gram, and it has only increased in value by about US$ 0.01 per gram since then.

1994.....$55 per pound (or $0.115 per gram)
1995.....$55 per pound (or $0.115 per gram)
1996.....$115 per kilogram (or $0.115 per gram)
1997.....$115 per kilogram (or $0.115 per gram)
1998.....$115 per kilogram (or $0.115 per gram)
1999.....$115 per kilogram (or $0.115 per gram)
2000.....$130 per kilogram (or $0.13 per gram)
2001.....$130 per kilogram (or $0.13 per gram)
2002.....$130 per kilogram (or $0.13 per gram)
2003.....$130 per kilogram (or $0.13 per gram)
2004.....$130 per kilogram (or $0.13 per gram)
2005.....$130 per kilogram (or $0.13 per gram)

Compounds

Fluorides Chlorides Bromides
GdF3 GdCl3 GdBr3
Iodides Oxides Sulfides
GdI3 Gd2O3 Gd2S3
  Nitrides  
  GdN  

Isotopes

Gadolinium has the greatest ability to capture thermal neutrons of all known elements and can be used as control rods for nuclear reactors.  Unfortunately, the two isotopes best suited for neutron capture, 155Gd and 157Gd, are present in gadolinium in small amounts.  As a result, gadolinium control rods quickly lose their effectiveness.

Naturally occurring gadolinium is composed of 6 stable isotopes154Gd, 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 1.31021 years (the decay is not observed, only the lower limit on the half-life is known), alpha-decaying 152Gd with a half-life of 1.081014 years, and 150Gd with a half-life of 1.79106 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 110 seconds), 145mGd (t 85 seconds) and 141mGd (t 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.

atom.gif (700 bytes)

Isotope  
Atomic Mass
 
Half-Life
134Gd 133.95537 ~0.4 seconds
135Gd 134.95257 1.1 seconds
136Gd 135.94734 ~1 seconds
137Gd 136.94502 2.2 seconds
138Gd 137.94012 4.7 seconds
139Gd 138.93824 5.7 seconds
139mGd   4.8 seconds
140Gd 139.93367 15.8 seconds
141Gd 140.932126 14 seconds
141mGd   24.5 seconds
142Gd 141.92812 70.2 seconds
143Gd 142.92675 39 seconds
143mGd   110.0 seconds
144Gd 143.92296 4.47 minutes
145Gd 144.921709 23.0 minutes
145mGd   85 seconds
146Gd 145.918311 48.27 days
147Gd 146.919094 38.06 hours
148Gd 147.918115 74.6 years
149Gd 148.919341 9.28 days
150Gd 149.918659 1.79 x 106 years
151Gd 150.920348 124 days
152Gd 151.9197910 1.08 x 1014 years
153Gd 152.9217495 240.4 days
154Gd 153.9208656 Stable
155Gd 154.9226220 Stable
156Gd 155.9221227 Stable
157Gd 156.9239601 Stable
158Gd 157.9241039 Stable
159Gd 158.9263887 18.479 hours
160Gd 159.9270541 Stable
161Gd 160.9296692 3.646 minutes
162Gd 161.930985 8.4 minutes
163Gd 162.93399 68 seconds
164Gd 163.93586 45 seconds
165Gd 164.93938 10.3 seconds
166Gd 165.94160 4.8 seconds
167Gd 166.94557 ~3 seconds
168Gd 167.94836 ~300 ms
169Gd 168.95287 ~1 seconds

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.

Precautions

In the free ionic state gadolinium is highly toxic but is generally regarded as safe when administered as a chelated compound. The compounds can be classified by whether they are macro-cyclic or linear geometry and whether they are ionic or not. Cyclical ionic Gd compounds being considered the least likely to release the Gd ion and hence the most safe.  The US Food and Drug Administration approved Gd chelated contrast agents include: Omniscan, Multihance, Magnevist, ProHance, Vasovist and OptMARK.

Gadolinium MRI contrast agents have proved safer than the iodinated contrast agents used in X-ray radiography or computed tomography.  Anaphylactoid reactions are rare, occurring in approx. 0.03-0.1%.

Although gadolinium agents have proved useful for patients with renal impairment, in patients with severe renal failure requiring dialysis there is a risk of a rare but serious illnesses, such as Nephrogenic Systemic Fibrosis and Nephrogenic Fibrosing Demopathy, that may be linked to the use of certain gadolinium-containing agents.  Although a causal link has not been definitively established, current guidelines in the United States are that dialysis patients should only receive gadolinium agents where essential, and that dialysis should be performed as soon as possible after the scan is complete, in order to remove the agent from the body promptly.

atom.gif (700 bytes)

Gadolinium Data

 

Atomic Structure

Atomic Radius (): 2.54
Atomic Volume cm3/mol : 19.9
Covalent Radius: 1.61
Crystal Structure: Hexagonal (HEX)
Ionic Radius: 0.938

Chemical Properties

Electrochemical Equivalents: 1.9557g/amp-hr
Electron Work Function: 3.1 eV
Electronegativity: 1.2 (Pauling); 1.11 (Allrod Rochow)
Heat of Fusion: 10.05 kJ/mol
First Ionization Potential: 6.15
Second Ionization Potential: 12.095
Third Ionization Potential: 20.635
Valence Electron Potential: 46.1 -eV
Ionization Energy (eV): unknown

Physical Properties

Atomic Mass Average: 157.25
Boiling Point: 3546K (3273C or 5923F)
Melting Point: 1586K (1313C or 2395F)
Heat of Vaporization: 359.4 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 8.6E-6
Electrical Conductivity: 0.00736 106/cm
Thermal Conductivity: 0.106 W/cmK
Density: 7.895g/cm3  @  300K
Enthalpy of Atomization: 352 kJ/mole @ 25C
Enthalpy of Fusion: 10.05 kJ/mole
Enthalpy of Vaporization: 359.4 kJ/mole
Molar Volume: 19.9 cm3/mole
Specific Heat: 0.23 J/gK or 0.230 J/g mol
Vapor Pressure: 24400 Pa @ 1312C
Estimated Crustal Abundance: 6.2 milligrams per kilogram
Estimated Oceanic Abundance: 710-7 milligrams per liter

Miscellaneous

Evaporation Heat (kJ/mol): 398
First Ionizing Energy (kJ/mol): 594.2
Lattice Constant (): 3.640
Lattice C/A Ratio: 1.588