Chemistry

An Overview about the Chemical Element Gadolinium



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Gadolinium

Symbol: Gd

Atomic Number: 64

Atomic Mass: 157.25 amu (atomic mass units)

Melting Point: 1311.0°C (1584.15 K, 2391.8°F)

Boiling Point: 3233.0°C (3506.15 K, 5851.4°F)

Number of Protons: 64

Number of Electrons: 64

Number of Neutrons: 93

Classification: Rare Earth Metal

Crystal Structure: Hexagonal

Density @ 293 K: 7.895 grams per cubic centimeter

Color: Silver

In 1880, while examining the spectrographs produced by the minerals gadolinite and dydymia the Swiss chemist, Jean Charles Galissard de Marignac, noted the lines caused by a new element. This element was the lanthanide or lanthanoid gadolinium. The element's name comes from the mineral gadolinite, named after the Finnish mineralogist and discoverer of the element yttrium, Johann Gadolin.

Paul-Emile Loq de Biosbaudran separated Gadolinia or gadolinium oxide from the ores in 1886. Pure gadolinium was not obtainable until the recent developments of solvent extraction and ion exchange chromatography methods. These methods enable the separation of metals from lanthanide salts. Sulfuric acid, hydrochloric acid and sodium hydroxide extract lanthanide salts from mineral ores. Reduction of the salt gadolinium tri-fluoride, using calcium metal, produces pure gadolinium metal.

Gadolinium is a silvery white colored lustrous metal. It is ferromagnetic (can be attracted by a magnet). While fairly stable in dry air, in moist air a film of gadolinium oxide forms on its surface. This oxide film will "spall off" to reveal fresh metal for further oxidation. Of all the known elements, gadolinium has the highest ability to capture neutrons by thermal capture.

There are seven naturally occurring isotopes of gadolinium. Five of these isotopes are stable while the other two have extremely long half-lives. The most common, naturally occurring isotope is gadolinium-158, which makes up 24.84 % of the total. In order of abundance the rest are gadolinium-160 (21.86 %, unstable), gadolinium-156 (15.65 %), gadolinium-157 (15.65 %), gadolinium-155 (14.80 %), gadolinium-154 (2.18 %) and gadolinium-152 (0.02 %, unstable). There are about thirty other manufactured isotopes of gadolinium with half-lives ranging from about 200 nanoseconds to 48.27 days.

The most common mineral ores used to supply gadolinium are monazite sand and bastnasite. In addition to a number of rare earth elements, monazite sand also contains the highly radioactive element thorium. Therefore, care is essential when extracting rare earth elements from this mineral.

Gadolinium has a number of industrial uses.

* The neutron capture ability of the element is of use in the making of control rods for nuclear reactors. The isotopes best suited for this are gadolinium-155 and gadolinium-157. These isotopes have an abundance of 14.80% and 15.65% respectively. The relatively low amounts of suitable isotopes in the gadolinium rods means that the rods lose their effectiveness fairly quickly and need regular replacement.

* Garnets, made of a mixture gadolinium and yttrium, are used in microwave technology.

* When alloyed to chromium, iron and other metals it improves their workability. Such alloys also have an increased resistance to oxidation and high temperatures.

* Compounds of gadolinium are used as phosphors in color televisions.

* It is used in the production of CD discs.

* Injecting solutions containing gadolinium compounds into patients undergoing Magnetic Resonance Imaging (MRI) improves the definition of the images obtained.

Reference Sources:

Los Alamos National Laboratory's Chemistry Division

Jefferson Lab Science Education

Web Elements

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