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, or copper, and is widely distributed
in the Earth's crust. Most of the world's
commercial 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 the interaction
of the sharp light absorption bands of neodymium
with ambient light enriched with the sharp
visible emission bands of mercury, trivalent
europium or terbium. 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 aluminium
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 important use of neodymium is 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, high performance hobby
DC electric motors, 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 (for example in hybrid cars)
and generators (for example aircraft and wind
turbine electric 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, exposing
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 Nd2O3Neodymium 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 (s) + 6 H2O (l) → 2 Nd(OH)3 (aq) +
3 H2 (g)Neodymium metal reacts vigorously
with all the halogens:
2 Nd (s) + 3 F2 (g) → 2 NdF3 (s) [a violet
substance]
2 Nd (s) + 3 Cl2 (g) → 2 NdCl3 (s) [a mauve
substance]
2 Nd (s) + 3 Br2 (g) → 2 NdBr3 (s) [a violet
substance]
2 Nd (s) + 3 I2 (g) → 2 NdI3 (s) [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 (s) + 3 H2SO4 (aq) → 2 Nd3+ (aq) +
3 SO2−4 (aq) + 3 H2 (g)
=== Compounds ===
Neodymium compounds include
halides: neodymium(III) fluoride (NdF3); neodymium(III)
chloride (NdCl3); neodymium(III) bromide (NdBr3);
neodymium(III) iodide (NdI3)
oxides: neodymium(III) oxide (Nd2O3)
sulfides: neodymium(II) sulfide (NdS), neodymium(III)
sulfide (Nd2S3)
nitrides: neodymium(III) nitride (NdN)
hydroxide: neodymium(III) hydroxide (Nd(OH)3)
phosphide: neodymium phosphide (NdP)
carbide: neodymium carbide (NdC2)
nitrate: neodymium(III) nitrate (Nd(NO3)3)
sulfate: neodymium(III) sulfate (Nd2(SO4)3)Some
neodymium compounds have colors that 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 (27.2% of the natural abundance),
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 (alpha decay with a half-life
(t1/2) of 2.29×1015 years) and 150Nd (double
beta decay, t1/2 = 7×1018 years, approximately).
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 (t1/2 = 5.5 hours),
135mNd (t1/2 = 5.5 minutes) and 133m1Nd (t1/2
~70 seconds).
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 (praseodymium)
isotopes and the primary products after are
element Pm (promethium) 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 (νέος), new, and didymos
(διδύμος), 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 (above 99%) 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,
(Ce,La,Nd,Pr)CO3F, and purified by solvent
extraction. Ion-exchange purification is reserved
for preparing the highest purities (typically
>99.99%). 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 rarely found in nature as a free
element, but rather it occurs in ores such
as monazite and bastnäsite (these are mineral
group names rather than single mineral names)
that contain small amounts of all rare-earth
metals. In these minerals neodymium is rarely
dominant (as in the case of lanthanum), with
cerium being the most abundant lanthanide;
some exceptions include monazite-(Nd) and
kozoite-(Nd). 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's 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.
As of January 2010 the Chinese government
has imposed strategic material 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 to US$350 per
kilogram, down from the mid-2011 peak of US$500/kg.
The price of neodymium oxide fell from $200/kg
in 2011 to $40 in 2015, largely due to illegal
production in China which circumvented government
restrictions. The uncertainty of pricing and
availability have caused companies (particularly
Japanese ones) to create permanent magnets
and associated electric motors with fewer
rare-earth metals; however, so far they have
been unable to eliminate the need for neodymium.Neodymium
is typically 10–18% of the rare-earth content
of commercial deposits of the light rare-earth-element
minerals bastnäsite and monazite. With neodymium
compounds being the most strongly colored
for the trivalent lanthanides, it 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, United States. 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 bastnäsite-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.
=== Magnets ===
Neodymium magnets (actually an alloy, Nd2Fe14B)
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 lower 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 (only wind turbines with "permanent
magnet" generators use neodymium). For example,
drive electric motors of each Toyota Prius
require one kilogram (2.2 pounds) 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
(1054–1064 nm), e.g. Nd:YAG (yttrium aluminium
garnet), Nd:YLF (yttrium lithium fluoride),
Nd:YVO4 (yttrium orthovanadate), and Nd:glass.
Neodymium-doped crystals (typically Nd:YVO4)
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 (AWE), the HELEN (High Energy
Laser Embodying Neodymium) 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 (terawatt
scale), high energy (megajoules) 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 (Nd:glass) is produced by
the inclusion of neodymium oxide (Nd2O3) 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 ("wisteria"), Cambridge ("heatherbloom"),
and Steuben ("wisteria"), and elsewhere (e.g.
Lalique, in France, or Murano). 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.
Another application is the creation of selective
astronomical filters to reduce the effect
of light pollution from sodium and fluorescent
lighting while passing other colours, especially
dark red hydrogen-alpha emission from nebulae.
Neodymium is also used to remove the green
color caused by iron contaminants from glass.
Neodymium is a component of "didymium" (referring
to mixture of salts of neodymium and praseodymium)
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. The similar absorption of the yellow
mercury emission line at 578 nm is the principal
cause of the blue color observed for neodymium
glass under traditional white-fluorescent
lighting.
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.The
use of neodymium in automobile rear-view mirrors,
to reduce the glare at night, has been patented.Similar
to its use in glasses, neodymium salts are
used as a colorant for enamels.
== Precautions ==
Neodymium metal dust is combustible and therefore
an 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.
== Further reading ==
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
