Mineral Facts and Problems: 1985 Edition Page: 655
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RARE-EARTH ELEMENTS AND YTTRIUM
ray, and photoemission spectroscopy; technology and applications;
actinides and lanthanides; inorganic materials; magnetism; in-
termediate valence, hydrides, and catalysis; and organometallic,
solution, and bio-inorganic chemistry (40).
The intensive research in the areas of production,
characteristics, and the use of magnetic rare-earth intermetallic
compounds and permanent magnets was summarized at the 7th
International Workshop on Rare-Earth Permanent Magnets held
in Beijing, China, in 1983 (46).
The Rare-Earth Information Center (RIC), Energy and
Mineral Resources Research Institute, at Iowa State University,
Ames, IA, serves the scientific community by collecting, storing,
and evaluating, and disseminating rare-earth information on
research, uses, and events. The University is also a leading site
of ongoing rare-earth research.
Many of the uses of rare-earths and yttrium are listed in table
5. Only a few of the uses, however, are volume consumers of rare
earths; most consume only small amounts.
The largest use of rare earths is in petroleum cracking catalysts.
The petroleum fluid cracking catalysts (FCC) are comprised of
three principal ingredients, an amorphous silica-alumina refrac-
tory binder, a generally inert filler, and a rare-earth containing
zeolite such as synthetic faujasite. The rare earths provide the
zeolite with structural and thermal stability, high catalytic activity,
and processing selectivity in the production of petroleum end
products (45). The rare-earth-containing FCC's crack the lighter
gas-oil fraction in a high-temperature vapor phase into small
hydrocarbon molecules to produce gasoline, diesel fuel, kerosene,
and an uncracked residual heavy fuel oil. Mixtures of lanthanum,
neodymium, and praseodymium chlorides are the principal rare-
earth compounds used in the production of these catalysts.
Catalysts containing rare earths are used in many other ap-
plications. Cerium nitrate and mischmetal nitrate are effective
catalysts in ammonia synthesis. Water storage compounds for
agricultural use, based on starch-polyacrylonitrile copolymers,
are formed by cerium IV ion catalysis. Cerium is also used as
a catalyst component in hydrocarbon oxygenation reactions, such
as in self-cleaning ovens. Rare-earth phosphate, composed of
either lanthanum or cerium, is used to produce creosol and xylene.
Rare-earth chloride catalysts are used in a process to recover
chlorine from byproduct hydrochloric acid.
Of increasing importance is the use of certain rare-earth
elements as ingredients in glass. Neodymium oxide is used to color
decorative glass from light pink to blue-violet and is added to
welding glasses to protect eyesight from the yellow flare emitted
by sodium vapor. Praseodymium oxide imparts a green color and
is used in special filter glasses and in combination with neodymium
in welding glasses. Erbium oxide colors glass a pale pink and is
used in photochromic glasses and some crystalware. Cerium ox-
ide in combination with titanium dioxide produces an attractive
yellow color used in tableware. By itself, cerium oxide in large
concentrations colors glass a weak yellow color. In ophthalmic
glass cerium-titania is combined with manganese to produce pink-
tinted glasses that absorb ultraviolet light (41).
Cerium additions chemically decolorize glass by oxidizing iron
impurities and shifting light transmission toward yellow by ab-
sorbing more in the blue range. Neodymium oxide is used to
physically decolorize glass by creating complimentary colors that
simulate the color of ferric iron in the glass. This produces light
transmittance across a broad spectrum, giving the glass a neutral
To prevent discoloration, cerium is added to window glass as
a stabilizer against ultraviolet rays from sun light. Cerium is also
added to glass used as radiation-shieldin windows and cathode
ray tube faceplates to protect against browning from higher energy
Lanthanum oxide is added to optical glass to increase the in-
dex of refraction and decrease dispersion of light. Its use is
primarily in camera lenses and other applications requiring a high
degree of light transmission. Lanthanum oxide is sometimes a
component in the glass used in fiber optics.
Yttrium-aluminum-garnets (YAG's) are used as simulated
diamonds and as host crystals for lasers. Neodymium-doped
YAG's produce short-wavelength laser beams that are useful in
cutting and scribing semiconductors and for drilling and welding.
Neodymium as a dopant in laser glass makes use of the element's
fluorescent properties and is preferred because it can operate at
room temperature with relatively high efficiencies. Erbium- and
holmium-doped crystal lasers are used in eye operations.
Neodymium-doped lasers are also being evaluated as energy
sources in laser-fusion research. Gadolinium-gallium-garnets
(GGG's) in thin-film magnetic bubble memory systems and as
substrates are used in communication and computer systems.
Another important application of rare-earth elements is the use
of europium oxide in phosphors for color television picture tubes
and other cathode ray tube displays. In combination with yttrium
oxide, yttrium oxysulfide, or yttrium orthovanadate, a superior
red color is provided. A new type of fluorescent lamp containing
europium, in combination with yttrium oxide and strontium
chlorapatite, emit a white light made up of three narrow spectral
bands which result in a greater perceived brightness than that
of fluorescent lamps currently in use. Terbium-activated
gadolinium or lanthanum oxysulfide phosphors are used to in-
tensify X-ray images.
Rare-earth fluoride prepared from monazite is added to car-
bon arc lighting cores to increase the arc intensity by a factor of
10 and to change the yellowish color of the arc to a light quality
nearly identical to that of sunlight (15). Carbon arc lamps are
used as searchlights and in lighting for color motion picture
photography and projection.
In gas and oil lamp mantles, the emissivity of the thorium com-
pound is such an intense white that small amounts of cerium ox-
ide are added to shift the visible light towards the less intense
orange-green part of the spectrum.
Cerium oxide's major use is in polishing compounds, where
its fine abrasive properties and stability at high speeds and
pressures make it well suited for polishing lenses, mirrors, cut
crystal, television and cathode-ray tube faceplates, gem stones,
and occasionally, plate glass (20).
A ceramic material containing 90% yttrium oxide and 10%
thorium oxide is used for windows for high-temperature furnaces,
microscope lenses for the study of molten materials, and high-
intensity incandescent and discharge lamps. Crucibles composed
of yttrium oxide are used for vacuum melting of reactive metals,
such as titanium, under an inert gas. Yttrium oxide stabilizes zir-
conia and forms one of the best high-temperature, high-strength,
and thermal-shock-resistant refractory compositions, stable under
conditions of oxidation and reduction at elevated temperatures.
Yttrium-iron garnets (YIG's) and gadolinium-iron garnets
(GIG's) are widely used as ferrite materials in microwave applica-
tions. These garnets can be operated in low magnetic fields in
the lower microwave frequencies. Lanthanum and neodymium
are used individually in capacitors; the oxides of the two elements
alter the temperature-compensating, dielectric, and permeabil-
ity properties of the various barium titanate ceramic composi-
tions used in capacitors.
Mischemetal (98% REM) and rare-earth silicide (33% REM)
are the two most common rare-earth alloys used in steel for
desulfurization, deoxidation, and sulfide shape control. Additions
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United States. Bureau of Mines. Mineral Facts and Problems: 1985 Edition, report, Date Unknown; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc12817/m1/663/?q=%22carbon%20arc%22: accessed January 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.