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= Erbium =
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Introduction
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Erbium is a chemical element; it has symbol Er and atomic number 68. A
silvery-white solid metal when artificially isolated, natural erbium
is always found in chemical combination with other elements. It is a
lanthanide, a rare-earth element, originally found in the gadolinite
mine in Ytterby, Sweden, which is the source of the element's name.
Erbium's principal uses involve its pink-colored Er3+ ions, which have
optical fluorescent properties particularly useful in certain laser
applications. Erbium-doped glasses or crystals can be used as optical
amplification media, where Er3+ ions are optically pumped at around
980 or and then radiate light at in stimulated emission. This
process results in an unusually mechanically simple laser optical
amplifier for signals transmitted by fiber optics. The wavelength is
especially important for optical communications because standard
single mode optical fibers have minimal loss at this particular
wavelength.
In addition to optical fiber amplifier-lasers, a large variety of
medical applications (e.g. dermatology, dentistry) rely on the erbium
ion's emission (see Er:YAG laser) when lit at another wavelength,
which is highly absorbed in water in tissues, making its effect very
superficial. Such shallow tissue deposition of laser energy is helpful
in laser surgery, and for the efficient production of steam which
produces enamel ablation by common types of dental laser.
Physical properties
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Erbium(III) chloride in sunlight, showing some pink fluorescence of
Er+3 from natural ultraviolet.
A trivalent element, pure erbium metal is malleable (or easily
shaped), soft yet stable in air, and does not oxidize as quickly as
some other rare-earth metals. Its salts are rose-colored, and the
element has characteristic sharp absorption spectra bands in visible
light, ultraviolet, and near infrared. Otherwise it looks much like
the other rare earths. Its sesquioxide is called erbia. Erbium's
properties are to a degree dictated by the kind and amount of
impurities present. Erbium does not play any known biological role,
but is thought to be able to stimulate metabolism.
Erbium is ferromagnetic below 19 K, antiferromagnetic between 19 and
80 K and paramagnetic above 80 K.
Erbium can form propeller-shaped atomic clusters Er3N, where the
distance between the erbium atoms is 0.35 nm. Those clusters can be
isolated by encapsulating them into fullerene molecules, as confirmed
by transmission electron microscopy.
Like most rare-earth elements, erbium is usually found in the +3
oxidation state. However, it is possible for erbium to also be found
in the 0, +1 and +2 oxidation states.
Chemical properties
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Erbium metal retains its luster in dry air, however will tarnish
slowly in moist air and burns readily to form erbium(III) oxide:
:4 Er + 3 O2 → 2 Er2O3
Erbium is quite electropositive and reacts slowly with cold water and
quite quickly with hot water to form erbium hydroxide:
:2 Er (s) + 6 H2O (l) → 2 Er(OH)3 (aq) + 3 H2 (g)
Erbium metal reacts with all the halogens:
:2 Er (s) + 3 F2 (g) → 2 ErF3 (s) [pink]
:2 Er (s) + 3 Cl2 (g) → 2 ErCl3 (s) [violet]
:2 Er (s) + 3 Br2 (g) → 2 ErBr3 (s) [violet]
:2 Er (s) + 3 I2 (g) → 2 ErI3 (s) [violet]
Erbium dissolves readily in dilute sulfuric acid to form solutions
containing hydrated Er(III) ions, which exist as rose red [Er(OH2)9]3+
hydration complexes:
:2 Er (s) + 3 H2SO4 (aq) → 2 Er3+ (aq) + 3 (aq) + 3 H2 (g)
Isotopes
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Naturally occurring erbium is composed of 6 stable isotopes, Er, Er,
Er, Er, Er, and Er, with Er being the most abundant (33.503% natural
abundance). 32 radioisotopes have been characterized, with the most
stable being Er with a half-life of , Er with a half-life of , Er with
a half-life of , Er with a half-life of , and Er with a half-life of .
All of the remaining radioactive isotopes have half-lives that are
less than , and the majority of these have half-lives that are less
than 4 minutes. This element also has 26 meta states, with the most
stable being Er with a half-life of .
The isotopes of erbium range in Er to Er. The primary decay mode
before the most abundant stable isotope, Er, is electron capture, and
the primary mode after is beta decay. The primary decay products
before Er are element 67 (holmium) isotopes, and the primary products
after are element 69 (thulium) isotopes.
Er has been identified as useful for use in Auger therapy, as it
decays via electron capture and emits no gamma radiation. It can also
be used as a radioactive tracer to label antibodies and peptides,
though it cannot be detected by any kind of imaging for the study of
its biological distribution. The isotope can be produced via the
bombardment of Er with Tm or Er with Ho, the latter of which is more
convenient due to Ho being a stable primordial isotope, though it
requires an initial supply of Er.
Oxides
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Erbium(III) oxide (also known as erbia) is the only known oxide of
erbium, first isolated by Carl Gustaf Mosander in 1843, and first
obtained in pure form in 1905 by Georges Urbain and Charles James. It
has a cubic structure resembling the bixbyite motif. The Er3+ centers
are octahedral. The formation of erbium oxide is accomplished by
burning erbium metal, erbium oxalate or other oxyacid salts of erbium.
Erbium oxide is insoluble in water and slightly soluble in heated
mineral acids. The pink-colored compound is used as a phosphor
activator and to produce infrared-absorbing glass.
Halides
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Erbium(III) fluoride is a pinkish powder that can be produced by
reacting erbium(III) nitrate and ammonium fluoride. It can be used to
make infrared light-transmitting materials and up-converting
luminescent materials, and is an intermediate in the production of
erbium metal prior to its reduction with calcium. Erbium(III) chloride
is a violet compounds that can be formed by first heating erbium(III)
oxide and ammonium chloride to produce the ammonium salt of the
pentachloride ([NH4]2ErCl5) then heating it in a vacuum at 350-400 °C.
It forms crystals of the aluminium chloride type, with monoclinic
crystals and the point group 'C'2/m. Erbium(III) chloride hexahydrate
also forms monoclinic crystals with the point group of 'P'2/'n'
('P'2/'c') - 'C'42h. In this compound, erbium is octa-coordinated to
form ions with the isolated completing the structure.
Erbium(III) bromide is a violet solid. It is used, like other metal
bromide compounds, in water treatment, chemical analysis and for
certain crystal growth applications. Erbium(III) iodide is a slightly
pink compound that is insoluble in water. It can be prepared by
directly reacting erbium with iodine.
Organoerbium compounds
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Organoerbium compounds are very similar to those of the other
lanthanides, as they all share an inability to undergo π backbonding.
They are thus mostly restricted to the mostly ionic cyclopentadienides
(isostructural with those of lanthanum) and the σ-bonded simple alkyls
and aryls, some of which may be polymeric.
History
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Erbium (for Ytterby, a village in Sweden) was discovered by Carl
Gustaf Mosander in 1843. Mosander was working with a sample of what
was thought to be the single metal oxide yttria, derived from the
mineral gadolinite. He discovered that the sample contained at least
two metal oxides in addition to pure yttria, which he named "erbia"
and "terbia" after the village of Ytterby where the gadolinite had
been found. Mosander was not certain of the purity of the oxides and
later tests confirmed his uncertainty. Not only did the "yttria"
contain yttrium, erbium, and terbium; in the ensuing years, chemists,
geologists and spectroscopists discovered five additional elements:
ytterbium, scandium, thulium, holmium, and gadolinium.
Erbia and terbia, however, were confused at this time. Marc
Delafontaine, a Swiss spectroscopist, mistakenly switched the names of
the two elements in his work separating the oxides erbia and terbia.
After 1860, terbia was renamed erbia and after 1877 what had been
known as erbia was renamed terbia. Fairly pure Er2O3 was independently
isolated in 1905 by Georges Urbain and Charles James. Reasonably pure
erbium metal was not produced until 1934 when Wilhelm Klemm and
Heinrich Bommer reduced the anhydrous chloride with potassium vapor.
Occurrence
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The concentration of erbium in the Earth crust is about 2.8 mg/kg and
in seawater 0.9 ng/L. (Concentration of less abundant elements may
vary with location by several orders of magnitude making the relative
abundance unreliable). Like other rare earths, this element is never
found as a free element in nature but is found in monazite and
bastnäsite ores. It has historically been very difficult and expensive
to separate rare earths from each other in their ores but ion-exchange
chromatography methods developed in the late 20th century have greatly
reduced the cost of production of all rare-earth metals and their
chemical compounds.
The principal commercial sources of erbium are from the minerals
xenotime and euxenite, and most recently, the ion adsorption clays of
southern China. Consequently, China has now become the principal
global supplier of this element. In the high-yttrium versions of these
ore concentrates, yttrium is about two-thirds of the total by weight,
and erbia is about 4-5%. When the concentrate is dissolved in acid,
the erbia liberates enough erbium ion to impart a distinct and
characteristic pink color to the solution. This color behavior is
similar to what Mosander and the other early workers in the
lanthanides saw in their extracts from the gadolinite minerals of
Ytterby.
Production
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Crushed minerals are attacked by hydrochloric or sulfuric acid that
transforms insoluble rare-earth oxides into soluble chlorides or
sulfates. The acidic filtrates are partially neutralized with caustic
soda (sodium hydroxide) to pH 3-4. Thorium precipitates out of
solution as hydroxide and is removed. After that the solution is
treated with ammonium oxalate to convert rare earths into their
insoluble oxalates. The oxalates are converted to oxides by annealing.
The oxides are dissolved in nitric acid that excludes one of the main
components, cerium, whose oxide is insoluble in HNO3. The solution is
treated with magnesium nitrate to produce a crystallized mixture of
double salts of rare-earth metals. The salts are separated by ion
exchange. In this process, rare-earth ions are sorbed onto suitable
ion-exchange resin by exchange with hydrogen, ammonium or cupric ions
present in the resin. The rare earth ions are then selectively washed
out by suitable complexing agent. Erbium metal is obtained from its
oxide or salts by heating with calcium at under argon atmosphere.
Lasers and optics
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A large variety of medical applications (i.e., dermatology, dentistry)
utilize erbium ion's emission (see Er:YAG laser), which is highly
absorbed in water (absorption coefficient about ). Such shallow tissue
deposition of laser energy is necessary for laser surgery, and the
efficient production of steam for laser enamel ablation in dentistry.
Common applications of erbium lasers in dentistry include ceramic
cosmetic dentistry and removal of brackets in orthodontic braces; such
laser applications have been noted as more time-efficient than
performing the same procedures with rotary dental instruments.
Erbium-doped optical silica-glass fibers are the active element in
erbium-doped fiber amplifiers (EDFAs), which are widely used in
optical communications. The same fibers can be used to create fiber
lasers. In order to work efficiently, erbium-doped fiber is usually
co-doped with glass modifiers/homogenizers, often aluminium or
phosphorus. These dopants help prevent clustering of Er ions and
transfer the energy more efficiently between excitation light (also
known as optical pump) and the signal. Co-doping of optical fiber with
Er and Yb is used in high-power Er/Yb fiber lasers. Erbium can also be
used in erbium-doped waveguide amplifiers.
Other applications
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When added to vanadium as an alloy, erbium lowers hardness and
improves workability. An erbium-nickel alloy Er3Ni has an unusually
high specific heat capacity at liquid-helium temperatures and is used
in cryocoolers; a mixture of 65% Er3Co and 35% Er0.9Yb0.1Ni by volume
improves the specific heat capacity even more.
Erbium oxide has a pink color, and is sometimes used as a colorant for
glass, cubic zirconia and porcelain. The glass is then often used in
sunglasses and jewellery, or where infrared absorption is needed.
Erbium is used in nuclear technology in neutron-absorbing control
rods. or as a burnable poison in nuclear fuel design.
Biological role and precautions
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Erbium does not have a biological role, but erbium salts can stimulate
metabolism. Humans consume 1 milligram of erbium a year on average.
The highest concentration of erbium in humans is in the bones, but
there is also erbium in the human kidneys and liver.
Erbium is slightly toxic if ingested, but erbium compounds are
generally not toxic. Ionic erbium behaves similar to ionic calcium,
and can potentially bind to proteins such as calmodulin. When
introduced into the body, nitrates of erbium, similar to other rare
earth nitrates, increase triglyceride levels in the liver and cause
leakage of hepatic (liver-related) enzymes to the blood, though they
uniquely (along with gadolinium and dysprosium nitrates) increase RNA
polymerase II activity. Ingestion and inhalation are the main routes
of exposure to erbium and other rare earths, as they do not diffuse
through unbroken skin.
Metallic erbium in dust form presents a fire and explosion hazard.
Further reading
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* 'Guide to the Elements - Revised Edition', Albert Stwertka (Oxford
University Press; 1998), .
External links
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* [
http://education.jlab.org/itselemental/ele068.html It's Elemental -
Erbium]
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Original Article:
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