Gadolinium (Gd)

• Element Symbol: Gd
• Atomic Number: 64
• Atomic Mass: 157.25
• Group # in Periodic Table: n/a
• Group Name: Lanthanides
• Period in Periodic Table: 6
• Block of Periodic Table: f-block
• Discovered by: Jean Charles Galissard de Marignac (1880)

Gadolinium is a moderately hard, silvery-gray metal. It is part of the lanthanide series of elements, which includes elements with atomic numbers from 57 to 71 in the periodic table. Like the other elements in this series, gadolinium is a rare earth element. It is a component of a variety of minerals in Earth’s crust, including bastnaesite, gadolinite, monazite, and samarskite. Gadolinium is not found in its pure form in nature.

Gadolinium was discovered in 1880 by Swiss chemist Jean-Charles Galissard de Marignac when he extracted an oxide containing a new rare earth element from a sample of the mineral samarskite. In 1886 French chemist Paul-Émile Lecoq de Boisbaudran was able to produce a pure sample of the element. It was named after the mineral gadolinite, which in turn was named for Finnish chemist Johan Gadolin, who was one of the first to discover and isolate rare earth elements from minerals in Ytterby, Sweden. Gadolinium was only the second element to be named after a person. It is the only element to have a Hebrew root. Gadolin means "great" in Hebrew.

Physical Properties

Gadolinium is a silvery-gray element with a metallic luster that is a solid in its standard state—that is, its state at 298 kelvins (K). It is moderately hard, malleable, and ductile. Gadolinium has a density of 7.901 grams per cubic centimeter (g/cm³) at standard state. Its melting point is 1313 degrees Celsius (ºC). Its boiling point is 3250 ºC. The specific heat of gadolinium is 240 joules per kilogram-kelvin (J/kg·K). Gadolinium is a good conductor of both heat and electricity. Its thermal conductivity is 11 watts per meter-kelvin (W/m·K). Its electrical conductivity is 7.7 × 10⁵ siemens per meter (S/m). Its resistivity is 1.3 × 10⁻⁶ meter-ohms (m·Ω).

Gadolinium is ferromagnetic at temperatures around 293 K and below. A ferromagnetic element is able to strongly attract other materials even though it is electrically uncharged. Gadolinium is paramagnetic above 293 K. This means it has only a small response to the magnetic field. Gadolinium rises in temperature when it is subjected to a magnetic field.

Chemical Properties

Gadolinium has a simple, closely packed, hexagonal crystal structure at temperatures below 1538 K. At temperatures higher than this, it has a body-centered cubic crystal structure. A variety of gadolinium compounds produce green or red phosphors. Gadolinium is stable in dry air, but it tarnishes in humid air. It reacts quickly in hot water to form gadolinium hydroxide and hydrogen gas. This element reacts with all halogens at high temperatures and dissolves in many diluted acids to form colorless solutions. However, gadolinium does not dissolve in hydrofluoric acid. It instead forms a protective gadolinium trifluoride layer on the acid’s surface. Gadolinium combines with a wide variety of elements to form inorganic compounds.

The electron affinity of gadolinium is 50 kilojoules per mole (kJ/mol). Gadolinium has three valence electrons. Its ionization energies are 593.4, 1170, 1990, and 4250 kJ/mol. Its electronegativity is 1.2.

Gadolinium has six naturally occurring stable isotopes. The most common of these is gadolinium-158, which represents around 25 percent of the gadolinium on Earth. The other natural stable isotopes, in order of abundance in Earth’s crust, are gadolinium-160, gadolinium-156, gadolinium-157, gadolinium-155, and gadolinium-154. Gadolinium-152 is the one naturally occurring radioactive isotope of this element. It has a half-life of 1.08 × 10¹⁴ years. Thirty-one other radioactive isotopes of gadolinium have been produced. This element has an electron configuration of [Xe]4f⁷5d¹6s².

Applications

Gadolinium is most commonly found in the minerals bastnaesite and monazite. At 6.2 parts per million, this element is one of the most abundant lanthanides in Earth’s crust. It is similar to nickel and arsenic in its abundance.

Australia, Brazil, China, India, Sri Lanka, and the United States are all producers of gadolinium. Around 399 tons of this metal are produced each year. The amount of gadolinium available for mining is estimated at slightly less than one million tons.

Gadolinium is obtained by first subjecting crushed minerals to solvent-solvent extraction. At the end of the extraction process, ion exchange is used to isolate gadolinium salts. These salts are then heated with calcium at high temperatures in an argon atmosphere to produce pure gadolinium metal.

The radioactive isotope gadolinium-153 can be produced inside a nuclear reactor. This isotope emits gamma radiation and can be used to check the accuracy of medical imaging systems.

Small amounts of gadolinium are often added to metal alloys. Gadolinium helps reduce oxidation and improve the malleability and ductility of alloys. It can also preserve the strength of alloys when they are subjected to high temperatures.

Some solid oxide fuel cells use gadolinium as an electrolyte. Gadolinium compounds have also been tested as refrigerant materials that could be used in magnetic refrigeration systems. These systems use a magnetic field to reduce the temperature of the refrigerant material. This effect causes cooling without the use of chemical refrigerants, which have been linked to ozone depletion and climate change.

Gadolinium is an excellent neutron absorber. This characteristic makes it highly useful inside the core of a nuclear fission reactor. Control rods and shields inside the reactor often contain gadolinium. The ability of gadolinium to absorb neutrons also makes it useful for neutron imaging. This is a form of medical imaging that uses neutrons instead of x-rays. Neutron imaging allows physicians to examine interior portions of the body that do not show up well on x-rays.

Another type of medical imaging that involves gadolinium is magnetic resonance imaging, or MRI. Gadolinium chelates are used in the contrast agents that are injected into patients during an MRI. The gadolinium responds to the magnetic fields generated throughout the procedure. This response makes internal tissues more visible on the images created by the MRI. Some gadolinium-based contrast agents are designed to accumulate in particular tissues during an MRI procedure. This tendency helps physicians identify tumors and other abnormal growths.

The gadolinium chelates used during MRI procedures were initially thought to be entirely safe. However, studies have shown some links between gadolinium chelate use and kidney damage in patients who already have some form of kidney disease. Alternative contrast agents may be considered for these patients.

Bibliography

Aldersey-Williams, Hugh. Periodic Tales: A Cultural History of the Elements, from Arsenic to Zinc. New York: Viking, 2011. Print.

"Gadolinium." Periodic Table. Royal Soc. of Chemistry, 2015. Web. 10 Sept. 2015.

"Gadolinium (Gd)." Encyclopædia Britannica. Encyclopædia Britannica, 16 Feb. 2014. Web. 10 Sept. 2015.

Gray, Theodore. The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog, 2009. Print.

Parsons, Paul, and Gail Dixon. The Periodic Table: A Visual Guide to the Elements. New York: Quercus, 2014. Print.

Penfield, Jeffrey G., and Robert F. Reilly Jr. "What Nephrologists Need to Know about Gadolinium." Nature Clinical Practice Nephrology 3.12 (2007): 654–68. Web. 10 Sept. 2015.

"Technical Data for Gadolinium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 10 Sept. 2015.