Rare earth information
Cerium is the most abundant of the rare earths. It is characterized chemically
by having two valence states, the +3 cerous and +4 ceric states. The ceric state
is the only non-trivalent rare earth ion stable in aqueous solutions. It is, therefore,
strongly acidic. It is also a strong oxidizer. The cerous state closely resembles
the other trivalent rare earths. Cerium salts that have been characterized include
carbonates, nitrates, chlorides, fluorides, carbonates and sulfides.
The numerous commercial applications for cerium include metallurgy,
glass and glass polishing, ceramics, catalysts, and in phosphors.
In steel manufacturing it is used to remove free oxygen and
sulfur by forming stable oxysulfides and by tying up undesirable
trace elements, such as lead and antimony.
It is considered to be the most efficient glass polishing
agent for precision optical polishing. It is also used to
decolor glass by keeping iron in its ferrous state. The ability
of cerium-doped glass to block out ultra violet light is utilized
in the manufacturing of medical glassware and aerospace windows.
It is also used to prevent polymers from darkening in sunlight
and to suppress discoloration of television glass. It is applied
to optical components to improve performance.
Cerium is also used in a variety of ceramics, including dental
compositions and as a phase stabilizer in zirconia-based products.
Ceria plays several catalytic roles. In catalytic converters it acts as a stabilizer
for the high surface area alumina, as a promoter of the water-gas shift reaction,
as an oxygen storage component and as an enhancer of the NOX reduction capability
of Rhodium. Cerium is added to the dominant catalyst for the production of styrene
from ethylbenezene to improve styrene formation. It is used in FCC catalysts containing
zeolites to provide both catalytic reactivity in the reactor and thermal stability
in the regenerator.
The role of cerium in phosphors is not as the emitting atom,
but as a "sensitizer."
Lanthanum is the first element in the rare earth or lanthanide
series. It is the model for all the other trivalent rare earths.
After cerium, it is the second most abundant of the rare earths.
Lanthanum-rich lanthanide compositions have been used extensively
for cracking reactions in FCC catalysts, especially to manufacture
low-octane fuel for heavy crude oil.
It is utilized in green phosphors based on the aluminate
Lanthanide zirconates are used for their catalytic and conductivity
properties and lanthanum stabilized zirconia has useful electical
and mechanical properties.
It is utilized in laser crystals based on the yttrium-lanthanum-fluoride
Dysprosium is most commonly used as in neodymium-iron-boron
high strength permanent magnets. While it has one of the highest
magnetic moments of any of the rare earths (10.6µB),
this has not resulted in an ability to perform on its own
as a practical alternative to neodymium compositions. It is
however now an essential additive in NdFeB production.
It is also used in special ceramic compositions based on
Recent research has examined the use of dysprosium in dysprosium-iron-garnet
(DyIG) and silicon implanted with dysprosium and holmium to form donor centers.
Erbium has application in glass coloring, as an amplifier
in fiber optics, and in lasers for medical and dental use.
The ion has a very narrow absorption band coloring erbium
salts pink. It is therefore used in eyeware and decorative
glassware. It can neutralize discoloring impurities such as
ferric ions and produce a neutral gray shade. It is used in
a variety of glass products for this purpose.
It is particularly useful as an amplifier for fiber optic
data transfer. Erbium lases at the wavelength required to
provide an efficient optical method of amplification, 1.55
microns. As shown below under recent research, many interesting
developments are occurring in this area.
Lasers based on Er:YAG are ideally suited for surgical applications
because of its ability to deliver energy without thermal build-up
in tissue .
Europium is utilized primarily for its unique luminescent
behavior. Excitation of the Europium atom by absorption of
ultra violet radiation can result in specific energy level
transitions within the atom creating an emission of visible
In energy efficient fluorescent lighting, Europium provides
not only the necessary red, but also the blue. Several commercial
blue phosphors are based on Europium. See additional discussion
Its luminesence is also valuable in medical, surgical and
Gadolinium is utilized for both its high magnetic moment
(7.94µB) and in phosphors and scintillator material.
When complexed with EDTA ligands, it is used as an injectable
contrast agent for patients undergoing magnetic resonance
imaging. With its high magnetic moment, gadolinium can reduce
relaxation times and thereby enhance signal intensity.
The extra stable half-full 4f electron shell with no low
lying energy levels creates applications as an inert phosphor
host. Gadolinium can therefore act as hosts for x-ray cassettes
and in scintillator materials for computer tomography.
Holmium has the highest magnetic moment (10.6µB) of
any naturally occurring element. Because of this it has been
used to create the highest known magnetic fields by placing
it within high strength magnets as a pole piece or magnetic
This magnetic property also has value in yttrium-iron-garnet
(YIG) lasers for microwave equipment.
Holmium lases at a human eye safe 2.08 microns allowing its
use in a variety of medical and dental applications in both
yttrium-aluminum-garnet (YAG) and yttrium-lanthanum-fluoride
(YLF) solid state lasers. The wavelength allows for use in
silica fibers designed for shorter wavelengths while still
providing the cutting strength of longer wave length equipment.
Lutetium is the last member of the rare earth series. Unlike
most rare earths it lacks a magnetic moment. It also has the
smallest metallic radius of any rare earth. It is perhaps
the least naturally abundant of the lanthanides.
It is the ideal host for x-ray phosphors because it produces
the densest known white material, lutetium tantalate (LuTaO4).
It is utilized as a dopant in matching lattice parameters
of certain substrate garnet crystals, such as indium-gallium-garnet
(IGG) crystals due its lack of a magnetic moment.
After cerium and lanthanum, neodymium is the most abundant
of the rare earths. It shows similiar charteristics to the
other trivalent lanthanides.
Primary applications include lasers, glass coloring and tinting,
dielectrics and, most importantly, as the fundemental basis
for neodymium-iron-boron (Nd2Fe14B) permanent magnets.
The neodymium-based magnet was first introduced in 1982 simultaneously
by Sumitomo Specialty Metals (Japan) and General Motors (USA)
and commercialized in 1986. It is used extensively in the
automotive industry with many applications including starter
motors, brake systems, seat adjusters and car stereo speakers.
Its largest application is in the voice coil motors used in
computer disk drives. Other uses include medical magnetic
imaging equipment. For more on neodymium magnets, see Magnetic
Neodymium has a strong absorption band centered at 580 nm,
which is very close to the human eye's maximum level of sensitivity
making it useful in protective lenses for welding goggles.
It is also used in CRT displays to enhance contrast between
reds and greens. It is highly valued in glass manufacturing
for its attractive purple coloring to glass.
Neodymium is included in many formulations of barium titanate,
used as dielectric coatings and in multi-layer capacitors
essential to electronic equipment.
Ytrrium-aluminum-garnet (YAG) solid state lasers utilize
neodymium because it has optimal absorption and emitting wavelengths.
Nd-based YAG lasers are used in various medical applications,
drilling, welding and material processing.
Praseodymium resembles the typical trivalent
rare earths, however, it will exhibit a +4 state when stabilized
in a zirconia host. The element is found in most all light
rare earth derivatives.
It is highly valued for ceramics as a bright yellow pigment
in praseodymium doped zirconia because of its optimum reflectance
at 560 nm.
Much research is being done on its optical properties for
use in amplification of telecommunication systems, including
as a doping agent in fluoride fibers.
It is also used in the scintillator for medical CAT scans.
Samarium is primarily utilized in the production of samarium-cobalt
(Sm2Co17) permanent magnets. It is also used in laser applications
and for its dielectric properties.
Samarium-cobalt magnets replaced the more expensive platinum-cobalt
magnets in the early 1970s. While now overshadowed by the
less expensive neodymium-iron-boron magnet, they are still
valued for their ability to function at high temeratures.
They are utilized in lightweight electronic equipment where
size or space is a limiting factor and where functionality
at high temperature is a concern. Applications include electronic
watches, aeospace equipment, microwave technology and servomotors.
For more information on either samarium-cobalt or neodymium-iron-boron
magnets, see Magnetic Products.
Because of its weak spectral absorption band samarium is
used in the filter glass on Nd:YAG solid state lasers to surround
the laser rod to improve efficiency by absorbing stray emissions.
Samarium forms stable titanate compounds with useful dielectric
properties suitable for coatings and in capacitors at microwave
Terbium is primarily used in phosphors, particularly in fluorescent
lamps and as the high intensity green emitter used in projection
televisions, such as the yttrium-aluminum-garnet (Tb:YAG)
Terbium responds efficiently to x-ray excitation and is,
therefore, used as an x-ray phosphor.
Terbium alloys are also used in magneto-optic recording films,
such as Tb-Fe-Co.
Ytterbium is being applied to numerous fiber amplifier and
fiber optic technologies and in various lasing applications.
It has a single dominant absorption band at 985 in the infra-red
making it useful in silicon photocells to directly convert
radiant energy to electricity.
Ytterbium metal increases its electrical resistance when
subjected to very high stresses. This property is used in
stress gauges for monitoring ground deformations from earthquakes
and nuclear explosions.
It is also used as in thermal barrier system bond coatings
on nickel, iron and other transitional metal alloy substrates.
Yttrium has the highest thermo-dynamic affinity for oxygen
of any element. This characteristic is the basis for many
of its applications. While not part of the rare earth series,
it resembles the heavy rare earths which are sometimes referred
to as the yttrics for this reason.
Another unique characteristic derives from its ability to
form crystals with useful properties.
Some of the many applications of yttrium include in ceramics
for crucibles for molten reactive metals, in florescent lighting
phosphors, computer displays and automotive fuel consumption
Yttria stabilized zirconium oxide are used in high temperature
applications, such as in thermal plasma sprays to protect
aerospace high temperature surfaces.
Crystals of the yttrium-iron-garnet (YIG) variety are essential
to microwave communication equipment.
The phosphor Eu:Y2O2S creates the red color in televisions.
Crystals of the yttrium-aluminum-garnet (YAG) variety are
utilized with neodymium in a number of laser applications.
Yttria can also increase the strength of metallic alloys.
Zirconium is primarily used in it's oxide or zirconia form. Zirconium dioxide has a high melting point (2,700ø C) and a low thermal conductivity. Its polymorphism, however, restricts its widespread use in ceramic industry. During a heating process, zirconia will undergo a phase transformation process. The change in volume associated with this transformation makes the usage of pure zirconia in many applications impossible. Addition of some oxides, such as CaO, MgO, and Y2O3, into the zirconia structure in a certain degree results in a solid solution, which is a cubic form and has no phase transformation during heating and cooling. This solid solution material is termed as stabilized zirconia, a valuable refractory. Stabilized zirconia is used as a grinding media and engineering ceramics due to its increased hardness and high thermal shock resistivity. Stabilized zirconia is also used in applications such as oxygen sensors and solid oxide fuel cells due to its high oxygen ion conductivity.
Calcium metal is widely used in metallurgical, chemical
and other industries. It is mainly used as a reducing agent
in the melting of metals, a deoxidant for alloys, a dehydrating
agent for oil, as well as a desulphurizer or a decarburizer
for iron and ferroalloys. It is also used in the production
of calcium battery and maintenance-free lead-calcium-tin