Neodymium is a chemical element with symbol
Nd and atomic number 60. It is a soft silvery
metal that tarnishes in air. Neodymium was
discovered in 1885 by the Austrian chemist
Carl Auer von Welsbach. It is present in significant
quantities in the ore minerals monazite and
bastnäsite. Neodymium is not found naturally
in metallic form or unmixed with other lanthanides,
and it is usually refined for general use.
Although neodymium is classed as a "rare earth",
it is a fairly common element, no rarer than
cobalt, nickel, and copper, and is widely
distributed in the Earth's crust. Most of
the world's neodymium is mined in China.
Neodymium compounds were first commercially
used as glass dyes in 1927, and they remain
a popular additive in glasses. The color of
neodymium compounds—due to the Nd3+ ion—is
often a reddish-purple but it changes with
the type of lighting, due to fluorescent effects.
Some neodymium-doped glasses are also used
in lasers that emit infrared with wavelengths
between 1047 and 1062 nanometers. These have
been used in extremely high power applications,
such as experiments in inertial confinement
fusion.
Neodymium is also used with various other
substrate crystals, such as yttrium aluminum
garnet in the Nd:YAG laser. This laser usually
emits infrared at a wavelength of about 1064
nanometers. The Nd:YAG laser is one of the
most commonly used solid-state lasers.
Another chief use of neodymium is as the free
pure element. It is used as a component in
the alloys used to make high-strength neodymium
magnets—powerful permanent magnets. These
magnets are widely used in such products as
microphones, professional loudspeakers, in-ear
headphones, and computer hard disks, where
low magnet mass or volume, or strong magnetic
fields are required. Larger neodymium magnets
are used in high power versus weight electric
motors and generators.
Characteristics
Physical properties
Neodymium, a rare earth metal, was present
in the classical mischmetal at a concentration
of about 18%. Metallic neodymium has a bright,
silvery metallic luster, but as one of the
more reactive lanthanide rare-earth metals,
it quickly oxidizes in ordinary air. The oxide
layer that forms then peels off, and this
exposes the metal to further oxidation. Thus
a centimeter-sized sample of neodymium completely
oxidizes within a year.
Neodymium commonly exists in two allotropic
forms, with a transformation from a double
hexagonal to a body-centered cubic structure
taking place at about 863 °C.
Chemical properties
Neodymium metal tarnishes slowly in air and
it burns readily at about 150 °C to form
neodymium(III) oxide:
4 Nd + 3 O2 → 2 Nd2O3
Neodymium is a quite electropositive element,
and it reacts slowly with cold water, but
quite quickly with hot water to form neodymium(III)
hydroxide:
2 Nd + 6 H2O → 2 Nd(OH)3 + 3 H2
Neodymium metal reacts vigorously with all
the halogens:
2 Nd + 3 F2 → 2 NdF3 [a violet substance]
2 Nd + 3 Cl2 → 2 NdCl3 [a mauve substance]
2 Nd + 3 Br2 → 2 NdBr3 [a violet substance]
2 Nd + 3 I2 → 2 NdI3 [a green substance]
Neodymium dissolves readily in dilute sulfuric
acid to form solutions that contain the lilac
Nd(III) ion. These exist as a [Nd(OH2)9]3+
complexes:
2 Nd + 3 H2SO4 → 2 Nd3+ + 3 SO2−
4 + 3 H2
Compounds
Neodymium compounds include
halides: neodymium(III) fluoride; neodymium(III)
chloride; neodymium(III) bromide; neodymium(III)
iodide
oxides: neodymium(III) oxide
sulfides: neodymium(II) sulfide, neodymium(III)
sulfide
nitrides: neodymium(III) nitride
hydroxide: neodymium(III) hydroxide3)
phosphide: neodymium phosphide
carbide: neodymium carbide
nitrate: neodymium(III) nitrate3)
sulfate: neodymium(III) sulfate3)
Some neodymium compounds have colors which
vary based upon the type of lighting.
Isotopes
Naturally occurring neodymium is a mixture
of five stable isotopes, 142Nd, 143Nd, 145Nd,
146Nd and 148Nd, with 142Nd being the most
abundant, and two radioisotopes, 144Nd and
150Nd. In all, 31 radioisotopes of neodymium
have been detected as of 2010, with the most
stable radioisotopes being the naturally occurring
ones: 144Nd of 2.29×1015 years) and 150Nd.
All of the remaining radioactive isotopes
have half-lives that are shorter than eleven
days, and the majority of these have half-lives
that are shorter than 70 seconds. Neodymium
also has 13 known meta states, with the most
stable one being 139mNd, 135mNd and 133m1Nd.
The primary decay modes before the most abundant
stable isotope, 142Nd, are electron capture
and positron decay, and the primary mode after
is beta minus decay. The primary decay products
before 142Nd are element Pr isotopes and the
primary products after are element Pm isotopes.
History
Neodymium was discovered by Baron Carl Auer
von Welsbach, an Austrian chemist, in Vienna
in 1885. He separated neodymium, as well as
the element praseodymium, from a material
known as didymium by means of fractional crystallization
of the double ammonium nitrate tetrahydrates
from nitric acid, while following the separation
by spectroscopic analysis; however, it was
not isolated in relatively pure form until
1925. The name neodymium is derived from the
Greek words neos, new, and didymos, twin.
Double nitrate crystallization was the means
of commercial neodymium purification until
the 1950s. Lindsay Chemical Division was the
first to commercialize large-scale ion-exchange
purification of neodymium. Starting in the
1950s, high purity neodymium was primarily
obtained through an ion exchange process from
monazite, a mineral rich in rare earth elements.
The metal itself is obtained through electrolysis
of its halide salts. Currently, most neodymium
is extracted from bastnäsite,CO3F, and purified
by solvent extraction. Ion-exchange purification
is reserved for preparing the highest purities.
The evolving technology, and improved purity
of commercially available neodymium oxide,
was reflected in the appearance of neodymium
glass that resides in collections today. Early
neodymium glasses made in the 1930s have a
more reddish or orange tinge than modern versions
which are more cleanly purple, due to the
difficulties in removing the last traces of
praseodymium in the era when manufacturing
relied upon fractional crystallization technology.
Occurrence and production
Neodymium is never found in nature as the
free element, but rather it occurs in ores
such as monazite and bastnäsite that contain
small amounts of all the rare earth metals.
The main mining areas are in China, the United
States, Brazil, India, Sri Lanka, and Australia.
The reserves of neodymium are estimated at
about eight million tonnes. Although it belongs
to the rare earth metals, neodymium is not
rare at all. Its abundance in the Earth crust
is about 38 mg/kg, which is the second highest
among rare-earth elements, following cerium.
The world's production of neodymium was about
7,000 tonnes in 2004. The bulk of current
production is from China, whose government
has recently imposed strategic materials controls
on the element, raising some concerns in consuming
countries and causing skyrocketing prices
of neodymium and other rare-earth metals.
As of late 2011, 99% pure neodymium was traded
in world markets for US$300–350 per kilogram,
down from the mid-2011 peak of $500/kg.
Neodymium is typically 10–18% of the rare
earth content of commercial deposits of the
light rare earth element minerals bastnasite
and monazite. With neodymium compounds being
the most strongly colored for the trivalent
lanthanides, that percentage of neodymium
can occasionally dominate the coloration of
rare earth minerals—when competing chromophores
are absent. It usually gives a pink coloration.
Outstanding examples of this include monazite
crystals from the tin deposits in Llallagua,
Bolivia; ancylite from Mont Saint-Hilaire,
Quebec, Canada; or lanthanite from the Saucon
Valley, Pennsylvania, US. As with neodymium
glasses, such minerals change their colors
under the differing lighting conditions. The
absorption bands of neodymium interact with
the visible emission spectrum of mercury vapor,
with the unfiltered shortwave UV light causing
neodymium-containing minerals to reflect a
distinctive green color. This can be observed
with monazite-containing sands or bastnasite-containing
ore.
Applications
Neodymium has an unusually large specific
heat capacity at liquid-helium temperatures,
so is useful in cryocoolers.
Probably because of similarities to Ca2+,
Nd3+ has been reported to promote plant growth.
Rare earth element compounds are frequently
used in China as fertilizer.
Samarium-neodymium dating is useful for determining
the age relationships of rocks and meteorites.
Size and strength of volcanic eruption can
be predicted by scanning for neodymium isotopes.
Small and large volcanic eruptions produce
lava with different neodymium isotope composition.
From the composition of isotopes, scientists
predict how big the coming eruption will be,
and use this information to warn residents
of the intensity of the eruption.
Magnets
Neodymium magnets are the strongest permanent
magnets known. A neodymium magnet of a few
grams can lift a thousand times its own weight.
These magnets are cheaper, lighter, and stronger
than samarium-cobalt magnets. However, they
are not superior in every aspect, as neodymium-based
magnets lose their magnetism at high temperatures
and tend to rust, while samarium-cobalt magnets
do not.
Neodymium magnets appear in products such
as microphones, professional loudspeakers,
in-ear headphones, guitar and bass guitar
pick-ups, and computer hard disks where low
mass, small volume, or strong magnetic fields
are required. Neodymium magnet electric motors
have also been responsible for the development
of purely electrical model aircraft within
the first decade of the 21st century, to the
point that these are displacing internal combustion–powered
models internationally. Likewise, due to this
high magnetic capacity per weight, neodymium
is used in the electric motors of hybrid and
electric automobiles, and in the electricity
generators of some designs of commercial wind
turbines. For example, drive electric motors
of each Toyota Prius require one kilogram
of neodymium per vehicle.
Neodymium doped lasers
Certain transparent materials with a small
concentration of neodymium ions can be used
in lasers as gain media for infrared wavelengths,
e.g. Nd:YAG, Nd:YLF, Nd:YVO4, and Nd:glass.
Neodymium-doped crystals generate high-powered
infrared laser beams which are converted to
green laser light in commercial DPSS hand-held
lasers and laser pointers.
The current laser at the UK Atomic Weapons
Establishment, the HELEN 1-terawatt neodymium-glass
laser, can access the midpoints of pressure
and temperature regions and is used to acquire
data for modeling on how density, temperature,
and pressure interact inside warheads. HELEN
can create plasmas of around 106 K, from which
opacity and transmission of radiation are
measured.
Neodymium glass solid-state lasers are used
in extremely high power, high energy multiple
beam systems for inertial confinement fusion.
Nd:glass lasers are usually frequency tripled
to the third harmonic at 351 nm in laser
fusion devices.
Neodymium glass for other applications
Neodymium glass is produced by the inclusion
of neodymium oxide in the glass melt. Usually
in daylight or incandescent light neodymium
glass appears lavender, but it appears pale
blue under fluorescent lighting. Neodymium
may be used to color glass in delicate shades
ranging from pure violet through wine-red
and warm gray.
The first commercial use of purified neodymium
was in glass coloration, starting with experiments
by Leo Moser in November 1927. The resulting
"Alexandrite" glass remains a signature color
of the Moser glassworks to this day. Neodymium
glass was widely emulated in the early 1930s
by American glasshouses, most notably Heisey,
Fostoria, Cambridge, and Steuben, and elsewhere.
Tiffin's "twilight" remained in production
from about 1950 to 1980. Current sources include
glassmakers in the Czech Republic, the United
States, and China.
The sharp absorption bands of neodymium cause
the glass color to change under different
lighting conditions, being reddish-purple
under daylight or yellow incandescent light,
but blue under white fluorescent lighting,
or greenish under trichromatic lighting. This
color-change phenomenon is highly prized by
collectors. In combination with gold or selenium,
beautiful red colors result. Since neodymium
coloration depends upon "forbidden" f-f transitions
deep within the atom, there is relatively
little influence on the color from the chemical
environment, so the color is impervious to
the thermal history of the glass. However,
for the best color, iron-containing impurities
need to be minimized in the silica used to
make the glass. The same forbidden nature
of the f-f transitions makes rare-earth colorants
less intense than those provided by most d-transition
elements, so more has to be used in a glass
to achieve the desired color intensity. The
original Moser recipe used about 5% of neodymium
oxide in the glass melt, a sufficient quantity
such that Moser referred to these as being
"rare earth doped" glasses. Being a strong
base, that level of neodymium would have affected
the melting properties of the glass, and the
lime content of the glass might have had to
be adjusted accordingly.
Light transmitted through neodymium glasses
shows unusually sharp absorption bands; the
glass is used in astronomical work to produce
sharp bands by which spectral lines may be
calibrated. Neodymium is also used to remove
the green color caused by iron contaminants
from glass. Neodymium is a component of "didymium"
used for coloring glass to make welder's and
glass-blower's goggles; the sharp absorption
bands obliterate the strong sodium emission
at 589 nm.
Neodymium and didymium glass are used in color-enhancing
filters in indoor photography, particularly
in filtering out the yellow hues from incandescent
lighting.
Similarly, neodymium glass is becoming widely
used more directly in incandescent light bulbs.
These lamps contain neodymium in the glass
to filter out yellow light, resulting in a
whiter light which is more like sunlight.
Neodymium has been patented for use in automobile
rear-view mirrors, to reduce the glare at
night.
Similar to its use in glasses, neodymium salts
are used as a colorant for enamels.
Precautions
Neodymium metal dust is a combustion and explosion
hazard. Neodymium compounds, as with all rare
earth metals, are of low to moderate toxicity;
however its toxicity has not been thoroughly
investigated. Neodymium dust and salts are
very irritating to the eyes and mucous membranes,
and moderately irritating to skin. Breathing
the dust can cause lung embolisms, and accumulated
exposure damages the liver. Neodymium also
acts as an anticoagulant, especially when
given intravenously.
Neodymium magnets have been tested for medical
uses such as magnetic braces and bone repair,
but biocompatibility issues have prevented
widespread application. Commercially available
magnets made from neodymium are exceptionally
strong, and can attract each other from large
distances. If not handled carefully, they
come together very quickly and forcefully,
causing injuries. For example, there is at
least one documented case of a person losing
a fingertip when two magnets he was using
snapped together from 50 cm away.
Another risk of these powerful magnets is
that if more than one magnet is ingested,
they can pinch soft tissues in the gastrointestinal
tract. This has led to at least 1,700 emergency
room visits and necessitated the recall of
the Buckyballs line of toys, which were construction
sets of small neodymium magnets.
References
Books
The Industrial Chemistry of the Lanthanons,
Yttrium, Thorium and Uranium, by R. J. Callow,
Pergamon Press, 1967.
Lindsay Chemical Division, American Potash
and Chemical Corporation, Price List, 1960.
Chemistry of the Lanthanons, by R. C. Vickery,
Butterworths, 1953.
External links
USGS Rare Earth Commodity Summary 2006
It's Elemental—Neodymium
