Erbium is a chemical element in the lanthanide series, with 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
on Earth. As such, it is a rare earth element which is associated with several
other rare elements in the mineral gadolinite from Ytterby in Sweden, where
yttrium, ytterbium, and terbium were discovered.
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 erbium ions are optically pumped at around 980 or
6994148000000000000♠1480 nm and then radiate light at
6994153000000000000♠1530 nm in stimulated emission. This process
results in an unusually mechanically simple laser optical amplifier for
signals transmitted by fiber optics. The 6994155000000000000♠1550 nm 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 rely on the erbium ion's 6994294000000000000♠2940 nm
emission, 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.
Characteristics = Physical properties =
A trivalent element, pure erbium metal is malleable, 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. = Chemical properties =
Erbium metal tarnishes slowly in 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 + 6 H2O → 2 Er(OH)3 + 3 H2
Erbium metal reacts with all the halogens:
2 Er + 3 F2 → 2 ErF3 [pink] 2 Er + 3 Cl2 → 2 ErCl3 [violet]
2 Er + 3 Br2 → 2 ErBr3 [violet] 2 Er + 3 I2 → 2 ErI3 [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 + 3 H2SO4 → 2 Er3+ + 3 SO2−
4 + 3 H2 = Isotopes =
Naturally occurring erbium is composed of 6 stable isotopes, 162Er, 164Er,
166Er, 167Er, 168Er, and 170Er with 166Er being the most abundant. 29
radioisotopes have been characterized, with the most stable being 169Er with a
half-life of 7005812160000000000♠9.4 d, 172Er with a half-life of
7005177480000000000♠49.3 h, 160Er with a half-life of 7005102888000000000♠28.58
h, 165Er with a half-life of 7004372960000000000♠10.36 h, and 171Er
with a half-life of 7004270576000000000♠7.516 h. All of the
remaining radioactive isotopes have half-lives that are less than
7004126000000000000♠3.5 h, and the majority of these have half-lives that
are less than 4 minutes. This element also has 13 meta states, with the most
stable being 167mEr with a half-life of 7000226900000000000♠2.269 s.
The isotopes of erbium range in atomic weight from 7002142966300000000♠142.9663
u to 7002176954100000000♠176.9541 u. The primary decay mode before the most
abundant stable isotope, 166Er, is electron capture, and the primary mode
after is beta decay. The primary decay products before 166Er are element 67
isotopes, and the primary products after are element 69 isotopes.
History Erbium was discovered by Carl Gustaf
Mosander in 1843. Mosander separated "yttria" from the mineral gadolinite
into three fractions which he called yttria, erbia, and terbia. He named the
new element after the village of Ytterby where large concentrations of yttria and
erbium are located. Erbia and terbia, however, were confused at this time.
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 metal wasn't produced
until 1934 when Klemm and Bommer reduced the anhydrous chloride with potassium
vapor. It was only in the 1990s that the price for Chinese-derived erbium oxide
became low enough for erbium to be considered for use as a colorant in art
glass. Occurrence
The concentration of erbium in the Earth crust is about 2.8 mg/kg and in the sea
water 0.9 ng/L. This concentration is enough to make erbium about 45th in
elemental abundance in the Earth's crust.
Like other rare earths, this element is never found as a free element in nature
but is found bound in monazite sand 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 brought down 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; in consequence, 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 would have seen in their
extracts from the gadolinite minerals of Ytterby.
Production 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 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 7003172315000000000♠1450 °C under argon
atmosphere. Applications
Erbium's everyday uses are varied. It is commonly used as a photographic filter,
and because of its resilience it is useful as a metallurgical additive.
Other uses: Used in nuclear technology in
neutron-absorbing control rods. When added to vanadium as an alloy,
erbium lowers hardness and improves workability.
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
cheap jewelry. Erbium-doped optical silica-glass fibers
are the active element in erbium-doped fiber amplifiers, 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 aluminum or phosphorus. These dopants
help prevent clustering or Er-ions and transfer the energy more efficiently
between the Er ions 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. 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. A large variety of medical applications
utilize erbium ion's 6994294000000000000♠2940 nm emission,
which is highly absorbed in water. Such shallow tissue deposition of laser
energy is necessary for laser surgery, and the efficient production of steam
for laser enamel ablation in dentistry. Biological role
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. = Toxicity =
Erbium is slightly toxic if ingested, but erbium compounds are not toxic.
Metallic erbium in dust form presents a fire and explosion hazard.
See also Erbium compounds
Terbium Ytterbium
Yttrium References
Further reading Guide to the Elements – Revised Edition,
Albert Stwertka, ISBN 0-19-508083-1. External links
WebElements.com – Erbium It's Elemental – Erbium