Scandium

21 calcium ← scandium → titanium - ↑ Sc ↓ Y periodic table
General
Name, Symbol, Number	scandium, Sc, 21
Chemical series	transition metals
Group, Period, Block	3, 4, d
Appearance	silvery white
Atomic mass	44.955912(6) g/mol
Electron configuration	[Ar] 3d1 4s2
Electrons per shell	2, 8, 9, 2
Physical properties
Phase	solid
Density (near r.t.)	2.985 g/cm³
Liquid density at m.p.	2.80 g/cm³
Melting point	1814 K (1541 °C, 2806 °F)
Boiling point	3109 K (2836 °C, 5136 °F)
Heat of fusion	14.1 kJ/mol
Heat of vaporization	332.7 kJ/mol
Heat capacity	(25 °C) 25.52 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1645 1804 (2006) (2266) (2613) (3101)
Atomic properties
Crystal structure	hexagonal
Oxidation states	3 (weakly basic oxide)
Electronegativity	1.36 (Pauling scale)
Ionization energies (more)	1st: 633.1 kJ/mol
	2nd: 1235.0 kJ/mol
	3rd: 2388.6 kJ/mol
Atomic radius	160 pm
Atomic radius (calc.)	184 pm
Covalent radius	144 pm
Miscellaneous
Magnetic ordering	???
Electrical resistivity	(r.t.) (α, poly) calc. 562 nΩ·m
Thermal conductivity	(300 K) 15.8 W/(m·K)
Thermal expansion	(r.t.) (α, poly) 10.2 µm/(m·K)
Speed of sound (thin rod)	(r.t.) 74.4 m/s
Shear modulus	29.1 GPa
Bulk modulus	56.6 GPa
Poisson ratio	0.279
Brinell hardness	750 MPa
CAS registry number	7440-20-2
Notable isotopes
Main article: Isotopes of scandium iso NA half-life DM DE (MeV) DP 44mSc syn 58.61 h IT 0.2709 44Sc γ 1.0, 1.1, 1.1 - ε - 44Ca 45Sc 100% Sc is stable with 24 neutrons 46Sc syn 83.79 d β- 0.3569 46Ti γ 0.889, 1.120 - 47Sc syn 3.3492 d β- 0.44, 0.60 47Ti γ 0.159 - 48Sc syn 43.67 h β- 0.661 48Ti γ 0.9, 1.3, 1.0 -

Scandium (chemical symbol Sc, atomic number 21) is a soft, silvery, white metal. Scandium ore occurs in rare minerals from Scandinavia and elsewhere. It is sometimes considered along with yttrium and the lanthanides and actinides, to be a rare earth.

Occurrence and isolation

Scandium is distributed sparsely on Earth, occurring only as trace quantities in various minerals. It is never found as a free metal. Rare minerals from Scandinavia and Madagascar—such as thortveitite, euxenite, and gadolinite—are the only known concentrated sources of this element. It is also found in residues that remain after tungsten is extracted from wolframite, and in the byproducts of uranium-mill tailings.

Scandium is more common in the Sun and certain stars than on Earth. It is only the fiftieth most common element on Earth (thirty-fifth most abundant in the Earth's crust), but it is the twenty-third most common element in the Sun.

The blue color of the aquamarine variety of beryl is thought to be produced by the presence of scandium impurities in it.

The present main source of scandium metal is from military stockpiles in parts of the former Soviet Union (mainly in Ukraine), which were themselves obtained from uranium tailings. There is no primary production in the Americas, Europe, or Australia.

History

In 1869, Dmitri Mendeleev used his periodic law to predict the existence and some properties of three unknown elements, including one that he called ekaboron.

Apparently unaware of that prediction, Lars Fredrick Nilson and his team were looking for rare earth metals in the spring of 1879. Using spectral analysis, they found a new element in the minerals euxenite and gadolinite. They named it scandium, from the Latin word Scandia meaning "Scandinavia." In attempting to isolate scandium, they processed 10 kilograms of euxenite and produced about 2.0 grams of a very pure scandium oxide (Sc₂O₃).

Per Teodor Cleve of Sweden concluded that scandium corresponded well to the hoped-for ekaboron, and he notified Mendeleev of this in August.

Fischer, Brunger, and Grienelaus prepared metallic scandium for the first time in 1937. They performed electrolysis of a molten combination of potassium, lithium, and scandium chlorides, at a temperature of 700 to 800°C. Tungsten wires in a pool of liquid zinc were the electrodes in a graphite crucible. The first pound of 99% pure scandium metal was not produced until 1960.

Notable characteristics

Scandium is situated between calcium and titanium in period 4 of the periodic table. It is the first transition metal in period 4. In addition, it lies at the top of group 3 (former group 3B), just above yttrium. Chemically, it resembles yttrium (and the rare earth metals) more than it resembles titanium.

Silvery when pure, scandium develops a slightly yellowish or pinkish cast when exposed to air. It is a soft, light metal. It is resistant to corrosion by acids. For example, it is not attacked by a 1:1 mixture of nitric acid(HNO₃) and hydrofluoric acid (HF).

In most of its compounds, the oxidation state of scandium is +3. Thus scandium is sometimes seen as the oxide, Sc₂0₃, or the chloride, ScCl₃.

Isotopes

Naturally occurring scandium is composed of one stable isotope, ⁴⁵Sc. In addition, many radioactive isotopes have been produced artificially, with atomic mass numbers ranging from 36 to 60. The three most stable radioisotopes are: ⁴⁶Sc, with a half-life of 83.8 days; ⁴⁷Sc, with a half-life of 3.35 days; and ⁴⁸Sc, with a half-life of 43.7 hours. The remaining radioactive isotopes have half-lives that are less than 4 hours, and the majority of these have half-lives that are less than 2 minutes.

Compounds

• See also Scandium compounds.

Applications

Since it is a very rare metal, scandium doesn't have many applications. If it were more common, it might be useful in the making of aircraft and spacecraft structures, probably alloyed with other metals.

It is also used in various lacrosse sticks. The light yet strong metal is need for precise accuracy and speed.

Approximately 20 kg (as Sc₂O₃) of scandium is used annually in the United States to make high-intensity lights. Scandium iodide added to mercury-vapor lamps produces an efficient artificial light source that resembles sunlight, and which allows good color-reproduction with TV cameras. About 80 kg of scandium is used in light bulbs globally per year. The radioactive isotope Sc-46 is used in oil refineries as a tracing agent.

The main application of scandium by weight is in aluminium-scandium alloys for minor aerospace industry components, and for unusual designs sports equipment (bikes, baseball bats, firearms, etc.) which rely on high performance materials. However, titanium, being much more common, and similar in lightness and strength, is much more widely used, with tons found in some aircraft, especially military ones.

When added to aluminium, scandium substantially lowers the rate of recrystallization and associated grain-growth in weld heat-affected zones. Aluminium, being a face-centred-cubic metal, is not particularly subject to the strengthening effects of the decrease in grain diameter. However, the presence of fine dispersions of Al₃Sc does increase strength by a small measure, much as any other precipitate system in aluminium alloys. It is added to aluminum alloys primarily to control that otherwise excessive grain growth in the heat-affected zone of weldable structural aluminium alloys, which gives two knock-on effects; greater strengthening via finer precipitation of other alloying elements and by reducing the precipitate-free zones that normally exist at the grain boundaries of age-hardening aluminium alloys.

The original use of scandium-aluminium alloys was in the nose cones of some USSR submarine-launched ballistic missiles (SLBMs). The strength of the resulting nose cone was enough to enable it to pierce the ice-cap without damage, and so, enabling a missile launch while still submerged under the Arctic ice cap.

See also

• Scandium compounds
• Scandium minerals

References

ISBN links support NWE through referral fees

• Greenwood, N.N.; and Earnshaw, A. (1998). Chemistry of the Elements (2nd Edition). New York: Elsevier. Online version available at [1], accessed on November 29, 2006.
• Cotton, F. Albert; and Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley. ISBN 0-471-02775-8.
• Scandium Los Alamos National Laboratory. Accessed on November 29, 2006.
• Scandium SPECTRUM Chemical Fact Sheet. Accessed on November 29, 2006.

External links

• WebElements.com – Scandium

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