Page 377 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

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Encyclopedia of Physical Science and Technology EN014A-653 July 28, 2001 20:55

Rare Earth Elements

and Materials

Zhiping Zheng John E. Greedan

University of Arizona McMaster University

I. The Rare Earth Elements
II. Chemical Physics of the Rare Earths
III. Rare Earth Materials
IV. Technological Applications
V. Catalysis and Other Chemical Applications

GLOSSARY Luminescence The phenomenon of the emission of light
from materials under excitation is called luminescence.
Bastnasite Common rare earth ore of composition Luminescence may be divided into phosphorescence
REFCO 3 (fluorocarbonate) rich in La, Ce, Pr, and Nd. and fluorescence.
Cathode ray tube An electron tube, or evacuated glass Mischmetal Alloy or mixture of La, Ce, Pr, and Nd met-
container, having at one end a cathode, or negative elec- als that is cheapter to produce than separated metals.
trode, and a device called an electron gun that projects Monazite and xenotime Rare earth ores of composition
a beam of electrons against a luminescent screen at the REPO 4 (phosphate). Xenotime is nearly pure YPO 4 .
opposite end of the tube. Permanent magnets Materials that retain their magnetic
Contrast agents Contrast agents are a class of pharma- properties after having been exposed to a magnetic
ceuticals that when administered to a patient, enter and field.
pass through anatomic regions of interest to provide Phosphors Solid-state materials exhibiting lumines-
transient contrast enhancement. cence.
Lanthanide contraction Systematic decrease in atomic
and ionic size that occurs from lanthanum (La) to
lutetium (Lu). The difference in size between adjacent THE RARE EARTH elements are those from atomic
elements is only about 1% but the cumulative effect is numbers 57 (lanthanum) to 71 (lutetium) inclusive and
about a 20% reduction. elements 21 (scandium) and 39 (yttrium). They represent
Liquid–liquid extraction Technique for the large-scale the largest group of chemically similar elements, but their
separation of the rare earth elements involving the physical properties differ markedly due to subtle features
countercurrent flow of two immiscible solvents. of electronic structure. Because of the similarity between

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