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 {{{isotopesof}}}]] 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

Scandium is distributed sparsely on earth, occurring only as trace quantities in many minerals. Rare minerals from Scandinavia and Madagascar, such as thortveitite, euxenite, and gadolinite are the only known concentrated sources of this element (which is never found as a free metal). It is also found in residues that remain after tungsten is extracted from wolframite, and from ores after uranium and thorium have been extracted.

Scandium is more common in the sun and certain stars than on Earth. Scandium is only the 50th most common element on earth (35th most abundant in the Earth's crust), but it is the 23rd most common element in the sun.

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

Isolation

Thortveitite is the primary source of scandium. Uranium-mill tailings by-products also are an important source. Pure scandium is commercially produced by reducing scandium fluoride with metallic calcium.

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

History

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

Lars Fredrick Nilson and his team, apparently unaware of that prediction in the spring of 1879, were looking for rare earth metals. By using spectral analysis, they found a new element within the minerals euxenite and gadolinite. They named it scandium, from the Latin Scandia meaning "Scandinavia", and in the process of isolating the scandium, they processed 10 kilograms of euxenite, producing 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, by electrolysis of a eutectic melt 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 a rare, soft, silvery, very light metallic element that develops a slightly yellowish or pinkish cast when exposed to air. This metal is not attacked by a 1:1 mixture of nitric acid(HNO₃) and hydrofluoric acid, HF. The rarity of scandium is not an arbitrary fact. In this area of atomic numbers, the thermonuclear reactions that produced the elements, very much more commonly produces elements with an even atomic number. This is because these elements were usually produced by the fusion of lighter elements with helium-4 nuclei, starting with carbon-12 (element six). Thus, the common elements in the range of scandium are number 18 argon, number 20 calcium, number 22 titanium, number 24 chromium; with the odd-numbered elements 19 potassium, 21 scandium, and 23 vanadium being rarely produced, and much less common. The production of the odd-numbered elements in this range results from much-less common thermonuclear reactions, as is explained elsewhere.

Isotopes

Naturally occurring scandium is composed of 1 stable isotope ⁴⁵Sc. 13 radioisotopes have been characterized with the most stable being 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. All of the remaining radioactive isotopes have half-lifes that are less than 4 hours, and the majority of these have half-lifes that are less than 2 minutes. This element also has 5 meta states with the most stable being ^44mSc (t_½ 58.6 h).

The isotopes of scandium range in atomic weight from 40 amu (⁴⁰Sc) to 54 amu (⁵⁴Sc). 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 titanium isotopes.

Compounds

The most common oxidation state of scandium in compounds is +3. Scandium chemically resembles yttrium and the rare earth metals more than it resembles aluminium or titanium. Thus scandium is sometimes seen as the scandium oxide, (Sc2)(03), and as scandium chloride, Sc(Cl)3.

• 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

• 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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