Yttrium is a chemical element with symbol
Y and atomic number 39.
It is a silvery-metallic transition metal
chemically similar to the lanthanides and
has often been classified as a "rare-earth
element".
Yttrium is almost always found in combination
with lanthanide elements in rare-earth minerals,
and is never found in nature as a free element.
89Y is the only stable isotope, and the only
isotope found in the Earth's crust.
In 1787, Carl Axel Arrhenius found a new mineral
near Ytterby in Sweden and named it ytterbite,
after the village.
Johan Gadolin discovered yttrium's oxide in
Arrhenius' sample in 1789, and Anders Gustaf
Ekeberg named the new oxide yttria.
Elemental yttrium was first isolated in 1828
by Friedrich Wöhler.The most important uses
of yttrium are LEDs and phosphors, particularly
the red phosphors in television set cathode
ray tube (CRT) displays.
Yttrium is also used in the production of
electrodes, electrolytes, electronic filters,
lasers, superconductors, various medical applications,
and tracing various materials to enhance their
properties.
Yttrium has no known biological role.
Exposure to yttrium compounds can cause lung
disease in humans.
== Characteristics ==
=== 
Properties ===
Yttrium is a soft, silver-metallic, lustrous
and highly crystalline transition metal in
group 3.
As expected by periodic trends, it is less
electronegative than its predecessor in the
group, scandium, and less electronegative
than the next member of period 5, zirconium;
additionally, it is more electronegative to
its successor in its group, lanthanum, being
closer in electronegativity to the later lanthanides
due to the lanthanide contraction.
Yttrium is the first d-block element in the
fifth period.
The pure element is relatively stable in air
in bulk form, due to passivation of a protective
oxide (Y2O3) film that forms on the surface.
This film can reach a thickness of 10 µm
when yttrium is heated to 750 °C in water
vapor.
When finely divided, however, yttrium is very
unstable in air; shavings or turnings of the
metal can ignite in air at temperatures exceeding
400 °C. Yttrium nitride (YN) is formed when
the metal is heated to 1000 °C in nitrogen.
=== Similarity to the lanthanides ===
The similarities of yttrium to the lanthanides
are so strong that the element has historically
been grouped with them as a rare-earth element,
and is always found in nature together with
them in rare-earth minerals.
Chemically, yttrium resembles those elements
more closely than its neighbor in the periodic
table, scandium, and if physical properties
were plotted against atomic number, it would
have an apparent number of 64.5 to 67.5, placing
it between the lanthanides gadolinium and
erbium.It often also falls in the same range
for reaction order, resembling terbium and
dysprosium in its chemical reactivity.
Yttrium is so close in size to the so-called
'yttrium group' of heavy lanthanide ions that
in solution, it behaves as if it were one
of them.
Even though the lanthanides are one row farther
down the periodic table than yttrium, the
similarity in atomic radius may be attributed
to the lanthanide contraction.One of the few
notable differences between the chemistry
of yttrium and that of the lanthanides is
that yttrium is almost exclusively trivalent,
whereas about half the lanthanides can have
valences other than three; nevertheless, only
for four of the fifteen lanthanides are these
other valences important in aqueous solution
(CeIV, SmII, EuII, and YbII).
=== Compounds and reactions ===
As a trivalent transition metal, yttrium forms
various inorganic compounds, generally in
the oxidation state of +3, by giving up all
three of its valence electrons.
A good example is yttrium(III) oxide (Y2O3),
also known as yttria, a six-coordinate white
solid.Yttrium forms a water-insoluble fluoride,
hydroxide, and oxalate, but its bromide, chloride,
iodide, nitrate and sulfate are all soluble
in water.
The Y3+ ion is colorless in solution because
of the absence of electrons in the d and f
electron shells.Water readily reacts with
yttrium and its compounds to form Y2O3.
Concentrated nitric and hydrofluoric acids
do not rapidly attack yttrium, but other strong
acids do.With halogens, yttrium forms trihalides
such as yttrium(III) fluoride (YF3), yttrium(III)
chloride (YCl3), and yttrium(III) bromide
(YBr3) at temperatures above roughly 200 °C.
Similarly, carbon, phosphorus, selenium, silicon
and sulfur all form binary compounds with
yttrium at elevated temperatures.Organoyttrium
chemistry is the study of compounds containing
carbon–yttrium bonds.
A few of these are known to have yttrium in
the oxidation state 0.
(The +2 state has been observed in chloride
melts, and +1 in oxide clusters in the gas
phase.)
Some trimerization reactions were generated
with organoyttrium compounds as catalysts.
These syntheses use YCl3 as a starting material,
obtained from Y2O3 and concentrated hydrochloric
acid and ammonium chloride.Hapticity is a
term to describe the coordination of a group
of contiguous atoms of a ligand bound to the
central atom; it is indicated by the Greek
character eta, η. Yttrium complexes were
the first examples of complexes where carboranyl
ligands were bound to a d0-metal center through
a η7-hapticity.
Vaporization of the graphite intercalation
compounds graphite–Y or graphite–Y2O3
leads to the formation of endohedral fullerenes
such as Y@C82.
Electron spin resonance studies indicated
the formation of Y3+ and (C82)3− ion pairs.
The carbides Y3C, Y2C, and YC2 can be hydrolyzed
to form hydrocarbons.
=== Isotopes and nucleosynthesis ===
Yttrium in the Solar System was created through
stellar nucleosynthesis, mostly by the s-process
(≈72%), but also by the r-process (≈28%).
The r-process consists of rapid neutron capture
of lighter elements during supernova explosions.
The s-process is a slow neutron capture of
lighter elements inside pulsating red giant
stars.
Yttrium isotopes are among the most common
products of the nuclear fission of uranium
in nuclear explosions and nuclear reactors.
In the context of nuclear waste management,
the most important isotopes of yttrium are
91Y and 90Y, with half-lives of 58.51 days
and 64 hours, respectively.
Though 90Y has a short half-life, it exists
in secular equilibrium with its long-lived
parent isotope, strontium-90 (90Sr) with a
half-life of 29 years.All group 3 elements
have an odd atomic number, and therefore few
stable isotopes.
Scandium has one stable isotope, and yttrium
itself has only one stable isotope, 89Y, which
is also the only isotope that occurs naturally.
However, the lanthanide rare earths contain
elements of even atomic number and many stable
isotopes.
Yttrium-89 is thought to be more abundant
than it otherwise would be, due in part to
the s-process, which allows enough time for
isotopes created by other processes to decay
by electron emission (neutron → proton).
Such a slow process tends to favor isotopes
with atomic mass numbers (A = protons + neutrons)
around 90, 138 and 208, which have unusually
stable atomic nuclei with 50, 82, and 126
neutrons, respectively.
89Y has a mass number close to 90 and has
50 neutrons in its nucleus.
At least 32 synthetic isotopes of yttrium
have been observed, and these range in atomic
mass number from 76 to 108.
The least stable of these is 106Y with a half-life
of >150 ns (76Y has a half-life of >200 ns)
and the most stable is 88Y with a half-life
of 106.626 days.
Apart from the isotopes 91Y, 87Y, and 90Y,
with half-lives of 58.51 days, 79.8 hours,
and 64 hours, respectively, all the other
isotopes have half-lives of less than a day
and most of less than an hour.Yttrium isotopes
with mass numbers at or below 88 decay primarily
by positron emission (proton → neutron)
to form strontium (Z = 38) isotopes.
Yttrium isotopes with mass numbers at or above
90 decay primarily by electron emission (neutron
→ proton) to form zirconium (Z = 40) isotopes.
Isotopes with mass numbers at or above 97
are also known to have minor decay paths of
β− delayed neutron emission.Yttrium has
at least 20 metastable ("excited") isomers
ranging in mass number from 78 to 102.
Multiple excitation states have been observed
for 80Y and 97Y.
While most of yttrium's isomers are expected
to be less stable than their ground state,
78mY, 84mY, 85mY, 96mY, 98m1Y, 100mY, and
102mY have longer half-lives than their ground
states, as these isomers decay by beta decay
rather than isomeric transition.
== History ==
In 1787, army lieutenant and part-time chemist
Carl Axel Arrhenius found a heavy black rock
in an old quarry near the Swedish village
of Ytterby (now part of the Stockholm Archipelago).
Thinking that it was an unknown mineral containing
the newly discovered element tungsten, he
named it ytterbite and sent samples to various
chemists for analysis.
Johan Gadolin at the University of Åbo identified
a new oxide (or "earth") in Arrhenius' sample
in 1789, and published his completed analysis
in 1794.
Anders Gustaf Ekeberg confirmed the identification
in 1797 and named the new oxide yttria.
In the decades after Antoine Lavoisier developed
the first modern definition of chemical elements,
it was believed that earths could be reduced
to their elements, meaning that the discovery
of a new earth was equivalent to the discovery
of the element within, which in this case
would have been yttrium.In 1843, Carl Gustaf
Mosander found that samples of yttria contained
three oxides: white yttrium oxide (yttria),
yellow terbium oxide (confusingly, this was
called 'erbia' at the time) and rose-colored
erbium oxide (called 'terbia' at the time).
A fourth oxide, ytterbium oxide, was isolated
in 1878 by Jean Charles Galissard de Marignac.
New elements were later isolated from each
of those oxides, and each element was named,
in some fashion, after Ytterby, the village
near the quarry where they were found (see
ytterbium, terbium, and erbium).
In the following decades, seven other new
metals were discovered in "Gadolin's yttria".
Since yttria was found to be a mineral and
not an oxide, Martin Heinrich Klaproth renamed
it gadolinite in honor of Gadolin.Friedrich
Wöhler mistakenly thought he had isolated
the metal in 1828 from a volatile chloride
he supposed to be yttrium chloride, but Heinrich
Rose proved otherwise in 1843 and correctly
isolated the element himself that year.
Until the early 1920s, the chemical symbol
Yt was used for the element, after which Y
came into common use.In 1987, yttrium barium
copper oxide was found to achieve high-temperature
superconductivity.
It was only the second material known to exhibit
this property, and it was the first known
material to achieve superconductivity above
the (economically important) boiling point
of nitrogen.
== Occurrence ==
=== 
Abundance ===
Yttrium is found in most rare-earth minerals,
it is found in some uranium ores, but is never
found in the Earth's crust as a free element.
About 31 ppm of the Earth's crust is yttrium,
making it the 28th most abundant element,
400 times more common than silver.
Yttrium is found in soil in concentrations
between 10 and 150 ppm (dry weight average
of 23 ppm) and in sea water at 9 ppt.
Lunar rock samples collected during the American
Apollo Project have a relatively high content
of yttrium.Yttrium has no known biological
role, though it is found in most, if not all,
organisms and tends to concentrate in the
liver, kidney, spleen, lungs, and bones of
humans.
Normally, as little as 0.5 milligrams is found
in the entire human body; human breast milk
contains 4 ppm.
Yttrium can be found in edible plants in concentrations
between 20 ppm and 100 ppm (fresh weight),
with cabbage having the largest amount.
With as much as 700 ppm, the seeds of woody
plants have the highest known concentrations.As
of April 2018 there are reports of the discovery
of very large reserves of rare-earth elements
on a tiny Japanese island.
Minami-Torishima Island, also known as Marcus
Island, is described as having "tremendous
potential" for rare-earth elements and yttrium
(REY), according to a study published in Scientific
Reports.
"This REY-rich mud has great potential as
a rare-earth metal resource because of the
enormous amount available and its advantageous
mineralogical features," the study reads.
The study shows that more than 16 million
tons of rare-earth elements could be "exploited
in the near future."
Including ytrrium (Y), which is used in products
like camera lenses and mobile phone screens,
the rare-earth elements found are: Europium
(EU), Terbium (Tb) and Dysprosium (Dy).
=== Production ===
Since yttrium is chemically so similar to
the lanthanides, it occurs in the same ores
(rare-earth minerals) and is extracted by
the same refinement processes.
A slight distinction is recognized between
the light (LREE) and the heavy rare-earth
elements (HREE), but the distinction is not
perfect.
Yttrium is concentrated in the HREE group
because of its ion size, though it has a lower
atomic mass.
Rare-earth elements (REEs) come mainly from
four sources:
Carbonate and fluoride containing ores such
as the LREE bastnäsite ([(Ce, La, etc.)(CO3)F])
contain an average of 0.1% of yttrium compared
to the 99.9% for the 16 other REEs.
The main source for bastnäsite from the 1960s
to the 1990s was the Mountain Pass rare earth
mine in California, making the United States
the largest producer of REEs during that period.
The name "bastnäsite" is actually a group
name, and the Levinson suffix is used in the
correct mineral names, e.g., bästnasite-(Y)
has Y as a prevailing element.
Monazite ([(Ce, La, etc.)PO4]), which is mostly
phosphate, is a placer deposit of sand created
by the transportation and gravitational separation
of eroded granite.
Monazite as a LREE ore contains 2% (or 3%)
yttrium.
The largest deposits were found in India and
Brazil in the early 20th century, making those
two countries the largest producers of yttrium
in the first half of that century.
Of the monazite group, the Ce-dominant member,
monazite-(Ce), is the most common one.
Xenotime, a REE phosphate, is the main HREE
ore containing as much as 60% yttrium as yttrium
phosphate (YPO4).
This applies to xenotime-(Y).
The largest mine is the Bayan Obo deposit
in China, making China the largest exporter
for HREE since the closure of the Mountain
Pass mine in the 1990s.
Ion absorption clays or Lognan clays are the
weathering products of granite and contain
only 1% of REEs.
The final ore concentrate can contain as much
as 8% yttrium.
Ion absorption clays are mostly in southern
China.
Yttrium is also found in samarskite and fergusonite
(which also stand for group names).One method
for obtaining pure yttrium from the mixed
oxide ores is to dissolve the oxide in sulfuric
acid and fractionate it by ion exchange chromatography.
With the addition of oxalic acid, the yttrium
oxalate precipitates.
The oxalate is converted into the oxide by
heating under oxygen.
By reacting the resulting yttrium oxide with
hydrogen fluoride, yttrium fluoride is obtained.
When quaternary ammonium salts are used as
extractants, most yttrium will remain in the
aqueous phase.
When the counter-ion is nitrate, the light
lanthanides are removed, and when the counter-ion
is thiocyanate, the heavy lanthanides are
removed.
In this way, yttrium salts of 99.999% purity
are obtained.
In the usual situation, where yttrium is in
a mixture that is two-thirds heavy-lanthanide,
yttrium should be removed as soon as possible
to facilitate the separation of the remaining
elements.
Annual world production of yttrium oxide had
reached 600 tonnes by 2001; by 2014 it had
increased to 7,000 tons.
Global reserves of yttrium oxide were estimated
in 2014 to be more than 500,000 tons.
The leading countries for these reserves included
Australia, Brazil, China, India, and the United
States.
Only a few tonnes of yttrium metal are produced
each year by reducing yttrium fluoride to
a metal sponge with calcium magnesium alloy.
The temperature of an arc furnace of greater
than 1,600 °C is sufficient to melt the yttrium.
== Applications ==
=== 
Consumer ===
The red component of color television cathode
ray tubes is typically emitted from an yttria
(Y2O3) or yttrium oxide sulfide (Y2O2S) host
lattice doped with europium (III) cation (Eu3+)
phosphors.
The red color itself is emitted from the europium
while the yttrium collects energy from the
electron gun and passes it to the phosphor.
Yttrium compounds can serve as host lattices
for doping with different lanthanide cations.
Tb3+ can be used as a doping agent to produce
green luminescence.
As such yttrium compounds such as yttrium
aluminium garnet (YAG) are useful for phosphors
and are an important component of white LEDs.
Yttria is used as a sintering additive in
the production of porous silicon nitride.
It is used as a common starting material for
material science and for producing other compounds
of yttrium.
Yttrium compounds are used as a catalyst for
ethylene polymerization.
As a metal, yttrium is used on the electrodes
of some high-performance spark plugs.
Yttrium is used in gas mantles for propane
lanterns as a replacement for thorium, which
is radioactive.Currently under development
is yttrium-stabilized zirconia as a solid
electrolyte and as an oxygen sensor in automobile
exhaust systems.
=== Garnets ===
Yttrium is used in the production of a large
variety of synthetic garnets, and yttria is
used to make yttrium iron garnets (Y3Fe5O12,
also "YIG"), which are very effective microwave
filters.
Yttrium, iron, aluminium, and gadolinium garnets
(e.g. Y3(Fe,Al)5O12 and Y3(Fe,Ga)5O12) have
important magnetic properties.
YIG is also very efficient as an acoustic
energy transmitter and transducer.
Yttrium aluminium garnet (Y3Al5O12 or YAG)
has a hardness of 8.5 and is also used as
a gemstone in jewelry (simulated diamond).
Cerium-doped yttrium aluminium garnet (YAG:Ce)
crystals are used as phosphors to make white
LEDs.YAG, yttria, yttrium lithium fluoride
(LiYF4), and yttrium orthovanadate (YVO4)
are used in combination with dopants such
as neodymium, erbium, ytterbium in near-infrared
lasers.
YAG lasers can operate at high power and are
used for drilling and cutting metal.
The single crystals of doped YAG are normally
produced by the Czochralski process.
=== Material enhancer ===
Small amounts of yttrium (0.1 to 0.2%) have
been used to reduce the grain sizes of chromium,
molybdenum, titanium, and zirconium.
Yttrium is used to increase the strength of
aluminium and magnesium alloys.
The addition of yttrium to alloys generally
improves workability, adds resistance to high-temperature
recrystallization, and significantly enhances
resistance to high-temperature oxidation (see
graphite nodule discussion below).Yttrium
can be used to deoxidize vanadium and other
non-ferrous metals.
Yttria stabilizes the cubic form of zirconia
in jewelry.Yttrium has been studied as a nodulizer
in ductile cast iron, forming the graphite
into compact nodules instead of flakes to
increase ductility and fatigue resistance.
Having a high melting point, yttrium oxide
is used in some ceramic and glass to impart
shock resistance and low thermal expansion
properties.
Those same properties make such glass useful
in camera lenses.
=== Medical ===
The radioactive isotope yttrium-90 is used
in drugs such as Yttrium Y 90-DOTA-tyr3-octreotide
and Yttrium Y 90 ibritumomab tiuxetan for
the treatment of various cancers, including
lymphoma, leukemia, liver, ovarian, colorectal,
pancreatic and bone cancers.
It works by adhering to monoclonal antibodies,
which in turn bind to cancer cells and kill
them via intense β-radiation from the yttrium-90
(see Monoclonal antibody therapy).A technique
called radioembolization is used to treat
hepatocellular carcinoma and liver metastasis.
Radioembolization is a low toxicity, targeted
liver cancer therapy that uses millions of
tiny beads made of glass or resin containing
radioactive yttrium-90.
The radioactive microspheres are delivered
directly to the blood vessels feeding specific
liver tumors/segments or lobes.
It is minimally invasive and patients can
usually be discharged after a few hours.
This procedure may not eliminate all tumors
throughout the entire liver, but works on
one segment or one lobe at a time and may
require multiple procedures.Also see Radioembolization
in the case of combined cirrhosis and Hepatocellular
carcinoma.
Needles made of yttrium-90, which can cut
more precisely than scalpels, have been used
to sever pain-transmitting nerves in the spinal
cord, and yttrium-90 is also used to carry
out radionuclide synovectomy in the treatment
of inflamed joints, especially knees, in sufferers
of conditions such as rheumatoid arthritis.A
neodymium-doped yttrium-aluminium-garnet laser
has been used in an experimental, robot-assisted
radical prostatectomy in canines in an attempt
to reduce collateral nerve and tissue damage,
and erbium-doped lasers are coming into use
for cosmetic skin resurfacing.
=== Superconductors ===
Yttrium is a key ingredient in the yttrium
barium copper oxide (YBa2Cu3O7, aka 'YBCO'
or '1-2-3') superconductor developed at the
University of Alabama and the University of
Houston in 1987.
This superconductor is notable because the
operating superconductivity temperature is
above liquid nitrogen's boiling point (77.1
K).
Since liquid nitrogen is less expensive than
the liquid helium required for metallic superconductors,
the operating costs for applications would
be less.
The actual superconducting material is often
written as YBa2Cu3O7–d, where d must be
less than 0.7 for superconductivity.
The reason for this is still not clear, but
it is known that the vacancies occur only
in certain places in the crystal, the copper
oxide planes, and chains, giving rise to a
peculiar oxidation state of the copper atoms,
which somehow leads to the superconducting
behavior.
The theory of low temperature superconductivity
has been well understood since the BCS theory
of 1957.
It is based on a peculiarity of the interaction
between two electrons in a crystal lattice.
However, the BCS theory does not explain high
temperature superconductivity, and its precise
mechanism is still a mystery.
What is known is that the composition of the
copper-oxide materials must be precisely controlled
for superconductivity to occur.This superconductor
is a black and green, multi-crystal, multi-phase
mineral.
Researchers are studying a class of materials
known as perovskites that are alternative
combinations of these elements, hoping to
develop a practical high-temperature superconductor.
== Precautions ==
Yttrium currently has no biological role,
and it can be highly toxic to humans and other
animals.Water-soluble compounds of yttrium
are considered mildly toxic, while its insoluble
compounds are non-toxic.
In experiments on animals, yttrium and its
compounds caused lung and liver damage, though
toxicity varies with different yttrium compounds.
In rats, inhalation of yttrium citrate caused
pulmonary edema and dyspnea, while inhalation
of yttrium chloride caused liver edema, pleural
effusions, and pulmonary hyperemia.Exposure
to yttrium compounds in humans may cause lung
disease.
Workers exposed to airborne yttrium europium
vanadate dust experienced mild eye, skin,
and upper respiratory tract irritation—though
this may be caused by the vanadium content
rather than the yttrium.
Acute exposure to yttrium compounds can cause
shortness of breath, coughing, chest pain,
and cyanosis.
The Occupational Safety and Health Administration
(OSHA) limits exposure to yttrium in the workplace
to 1 mg/m3 over an 8-hour workday.
The National Institute for Occupational Safety
and Health (NIOSH) recommended exposure limit
(REL) is 1 mg/m3 over an 8-hour workday.
At levels of 500 mg/m3, yttrium is immediately
dangerous to life and health.
Yttrium dust is flammable.
== See also ==
== Notes
