Scandium is a chemical element with symbol Sc and atomic number 21. A
silvery-white metallic d-block element, it has historically been
classified as a rare earth element, together with yttrium and the
lanthanides. It was discovered in 1879 by spectral analysis of the
minerals euxenite and gadolinite from Scandinavia.
Scandium is present in most of the deposits of rare-earth and uranium
compounds, but it is extracted from these ores in only a few mines
worldwide. Because of the low availability and the difficulties in the
preparation of metallic scandium, which was first done in 1937,
applications for scandium were not developed until the 1970s. The
positive effects of scandium on aluminium alloys were discovered in
the 1970s, and its use in such alloys remains its only major
application. The global trade of scandium oxide is about 10 tonnes per
The properties of scandium compounds are intermediate between those of
aluminium and yttrium. A diagonal relationship exists between the
behavior of magnesium and scandium, just as there is between beryllium
and aluminium. In the chemical compounds of the elements in group 3,
the predominant oxidation state is +3.
1.1 Chemical characteristics
4.1 Oxides and hydroxides
4.2 Halides and pseudohalides
4.3 Organic derivatives
4.4 Uncommon oxidation states
7 Health and safety
8 See also
10 Further reading
11 External links
Scandium is a soft metal with a silvery appearance. It develops a
slightly yellowish or pinkish cast when oxidized by air. It is
susceptible to weathering and dissolves slowly in most dilute acids.
It does not react with a 1:1 mixture of nitric acid (HNO3) and 48%
hydrofluoric acid (HF), possibly due to the formation of an
impermeable passive layer.
Scandium turnings ignite in air with a
brilliant yellow flame to form scandium(III) oxide.
Main article: Isotopes of scandium
In nature, scandium is found exclusively as the isotope 45Sc, which
has a nuclear spin of 7/2; this is its only stable isotope. Thirteen
radioisotopes have been characterized with the most stable being 46Sc,
which has a half-life of 83.8 days; 47Sc, 3.35 days; the
positron emitter 44Sc, 4 h; and 48Sc, 43.7 hours. All of the
remaining radioactive isotopes have half-lives less than 4 hours,
and the majority of these have half-lives less than 2 minutes.
This element also has five meta states, with the most stable being
44mSc (t1/2 = 58.6 h).
The isotopes of scandium range from 36Sc to 60Sc. The primary decay
mode at masses lower than the only stable isotope, 45Sc, is electron
capture, and the primary mode at masses above it is beta emission. The
primary decay products at atomic weights below 45Sc are calcium
isotopes and the primary products from higher atomic weights are
In Earth's crust, scandium is not rare. Estimates vary from 18 to
25 ppm, which is comparable to the abundance of cobalt
Scandium is only the 50th most common element on
Earth (35th most abundant in the crust), but it is the 23rd most
common element in the Sun. However, scandium is distributed
sparsely and occurs in trace amounts in many minerals. Rare
minerals from Scandinavia and Madagascar such as thortveitite,
euxenite, and gadolinite are the only known concentrated sources of
Thortveitite can contain up to 45% of scandium in the
form of scandium(III) oxide.
The stable form of scandium is created in supernovas via the
The world production of scandium is in the order of 10 tonnes per
year, in the form of scandium oxide. The demand is about 50% higher,
and both the production and demand keep increasing. In 2003, only
three mines produced scandium: the uranium and iron mines in Zhovti
Vody in Ukraine, the rare-earth mines in Bayan Obo, China, and the
apatite mines in the Kola peninsula, Russia; since then many other
countries have built scandium-producing facilities. In each case
scandium is a byproduct from the extraction of other elements and is
sold as scandium oxide.
To produce metallic scandium, the oxide is converted to scandium
fluoride and reduced with metallic calcium.
Madagascar and Iveland-
Evje region in
Norway have the only deposits of
minerals with high scandium content, thortveitite (Sc,Y)2(Si2O7) and
kolbeckite ScPO4·2H2O, but these are not being exploited.
The absence of reliable, secure, stable, and long-term production has
limited commercial applications of scandium. Despite this low level of
use, scandium offers significant benefits. Particularly promising is
the strengthening of aluminium alloys with as little as 0.5% scandium.
Scandium-stabilized zirconia enjoys a growing market demand for use as
a high-efficiency electrolyte in solid oxide fuel cells.
Because of its rarity, it is among the most expensive elements. Price
for pure scandium fluctuates between 4 000 and 20 000 US dollars per
kilogram. Meanwhile, the limited market generates a variety of prices
at any given time. In 2010, at the peak of the rare-earths shortage,
the price of scandium rose to over 15,000 US dollars per kilogram, and
the widely commercially used scandium oxide (Sc2O3) was selling above
7 000 US dollars per kilogram. Since then the limited demand coupled
with steady production keeps the price at its 20-year average.
See also: the categories
Scandium compounds and
Scandium chemistry is almost completely dominated by the trivalent
ion, Sc3+. The radii of M3+ ions in the table below indicate that the
chemical properties of scandium ions have more in common with yttrium
ions than with aluminium ions. In part because of this similarity,
scandium is often classified as a lanthanide-like element.
Ionic radii (pm)
Oxides and hydroxides
The oxide Sc
3 and the hydroxide Sc(OH)
3 are amphoteric:
3 + 3 OH− → [Sc(OH)
3 + 3 H+ + 3 H
2O → [Sc(H
α- and γ-ScOOH are isostructural with their aluminium oxide
hydroxide counterparts. Solutions of Sc3+ in water are acidic due
Halides and pseudohalides
The halides ScX3, where X = Cl, Br, or I, are very soluble in water,
but ScF3 is insoluble. In all four halides, the scandium is
6-coordinated. The halides are Lewis acids; for example, ScF3
dissolves in a solution containing excess fluoride ion to form
[ScF6]3−. The coordination number 6 is typical for Sc(III). In the
larger Y3+ and La3+ ions, coordination numbers of 8 and 9 are common.
Scandium(III) triflate is sometimes used as a
Lewis acid catalyst in
Main article: Organoscandium chemistry
Scandium forms a series of organometallic compounds with
cyclopentadienyl ligands (Cp), similar to the behavior of the
lanthanides. One example is the chlorine-bridged dimer, [ScCp2Cl]2 and
related derivatives of pentamethylcyclopentadienyl ligands.
Uncommon oxidation states
Compounds that feature scandium in the oxidation state other than +3
are rare but well characterized. The blue-black compound CsScCl3 is
one of the simplest. This material adopts a sheet-like structure that
exhibits extensive bonding between the scandium(II) centers.
Scandium hydride is not well understood, although it appears not to be
a saline hydride of Sc(II). As is observed for most elements, a
diatomic scandium hydride has been observed spectroscopically at high
temperatures in the gas phase.
Scandium borides and carbides are
non-stoichiometric, as is typical for neighboring elements.
Lower oxidation states (+2, +1, 0) have also been observed in
Dmitri Mendeleev, who is referred to as the father of the periodic
table, predicted the existence of an element ekaboron, with an atomic
mass between 40 and 48 in 1869.
Lars Fredrik Nilson
Lars Fredrik Nilson and his team
detected this element in the minerals euxenite and gadolinite in 1879.
Nilson prepared 2 grams of scandium oxide of high purity.
He named the element scandium, from the
Latin Scandia meaning
"Scandinavia". Nilson was apparently unaware of Mendeleev's
Per Teodor Cleve
Per Teodor Cleve recognized the correspondence and
Metallic scandium was produced for the first time in 1937 by
electrolysis of a eutectic mixture of potassium, lithium, and scandium
chlorides, at 700–800 °C. The first pound of 99% pure
scandium metal was produced in 1960. Production of aluminium alloys
began in 1971, following a US patent. Aluminium-scandium alloys
were also developed in the USSR.
Laser crystals of gadolinium-scandium-gallium garnet (GSGG) were used
in strategic defense applications developed for the Strategic Defense
Initiative (SDI) in the 1980s and 1990s.
Parts of the MiG-29 are made from Al-Sc alloy.
The addition of scandium to aluminium limits the grain growth in the
heat zone of welded aluminium components. This has two beneficial
effects: the precipitated Al3Sc forms smaller crystals than in other
aluminium alloys, and the volume of precipitate-free zones at the
grain boundaries of age-hardening aluminium alloys is reduced.
Both of these effects increase the usefulness of the alloy.[why?]
However, titanium alloys, which are similar in lightness and strength,
are cheaper and much more widely used.
The alloy Al20Li20Mg10Sc20Ti30 is as strong as titanium, light as
aluminium, and hard as ceramic.
The main application of scandium by weight is in aluminium-scandium
alloys for minor aerospace industry components. These alloys contain
between 0.1% and 0.5% of scandium. They were used in the Russian
military aircraft, specifically the MiG-21 and MiG-29.
Some items of sports equipment, which rely on high-performance
materials, have been made with scandium-aluminium alloys, including
baseball bats and bicycle frames and components. Lacrosse
sticks are also made with scandium. The American firearm manufacturing
company Smith & Wesson produces semi-automatic pistols and
revolvers with frames of scandium alloy and cylinders of titanium or
Dentists use erbium-chromium-doped yttrium-scandium-gallium garnet
(Er,Cr:YSGG) lasers for cavity preparation and in endodontics.
The first scandium-based metal-halide lamps were patented by General
Electric and initially made in North America, although they are now
produced in all major industrialized countries. Approximately
20 kg of scandium (as Sc2O3) is used annually in the United
States for high-intensity discharge lamps. One type of
metal-halide lamp, similar to the mercury-vapor lamp, is made from
scandium iodide and sodium iodide. This lamp is a white-light source
with high color rendering index that sufficiently resembles sunlight
to allow good color-reproduction with TV cameras. About 80 kg
of scandium is used in metal-halide lamps/light bulbs globally per
The radioactive isotope 46Sc is used in oil refineries as a tracing
Scandium triflate is a catalytic
Lewis acid used in organic
Health and safety
Elemental scandium is considered non-toxic, though extensive animal
testing of scandium compounds has not been done. The median lethal
dose (LD50) levels for scandium(III) chloride for rats have been
determined as 4 mg/kg for intraperitoneal and 755 mg/kg for
oral administration. In the light of these results, compounds of
scandium should be handled as compounds of moderate toxicity.
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