|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|
|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)|
(weakly basic oxide)
|Electronegativity||1.36 (Pauling scale)|
|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|
|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)|
|Speed of sound (thin rod)||(r.t.) 74.4 m/s|
|Shear modulus||29.1 GPa|
|Bulk modulus||56.6 GPa|
|Brinell hardness||750 MPa|
|CAS registry number||7440-20-2|
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 a rare element that chemically resembles yttrium and is sometimes considered a rare earth, along with yttrium, the lanthanides, and actinides.
This element is mainly used in alloys with aluminum for minor components needed by the aerospace industry and for high-performance sports equipment, including bicycles, baseball bats, and firearms. Scandium oxide is used to make high-intensity lights, and scandium iodide is used in mercury-vapor lamps. A radioactive isotope of scandium [Sc-46] is used as a tracing agent in oil refineries.
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 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.
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 ten kilograms of euxenite and produced about two 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 percent pure scandium metal was not produced until 1960.
Scandium is situated between calcium and titanium in period four of the periodic table. It is the first transition metal in period four. In addition, it lies at the top of group three (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).
When added to weldable structural aluminum alloys, scandium strengthens the alloys by lowering the rate of recrystallization and associated grain growth in the heat-affected zones.
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.
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 four hours, and the majority of these have half-lives that are less than two minutes.
- Scandium(III) chloride, scandium chloride, or scandium trichloride (ScCl3): The pure compound is a white crystalline solid that is hygroscopic (absorbs moisture from the air). It is an ionic compound with a high melting point (960 °C). It is primarily of interest in the research laboratory. At high temperatures, it reacts with scandium metal to produce a broad family of scandium chlorides, including Sc5Cl8 and Sc7Cl12. Scandium(III) chloride is used in halide lamps, optical fibers, electronic ceramics, and lasers.
- Scandium(III) oxide, scandium oxide, or scandia (Sc2O3): This amorphous, white powder is an ionic compound. Given its resistance to heat and thermal shock, it is used in high-temperature systems. In addition, it is used in electronic ceramics and glass composition (as a helper material). The oxide will dissolve in alkali to form scandate salts. In this respect, it is more similar to aluminum oxide than to yttrium oxide or lanthanum oxide.
As a very rare metal, scandium has a limited number of applications, some of which are noted below.
- The main application of scandium by weight is in aluminum-scandium alloys for minor aerospace industry components and for sports equipment—such as specially designed bikes, baseball bats, lacrosse sticks, and firearms—requiring strong, lightweight, high-performance materials. Yet titanium, being much more readily available and similar in lightness and strength, is more widely used, with tons of it used in some military aircraft.
- Approximately 20 kilograms (kg) of scandium (as Sc2O3) 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 allows good color-reproduction with television 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.
- Earlier, scandium-aluminum alloys were used in the nose cones of some Soviet submarine-launched ballistic missiles (SLBMs). The resulting nose cone was sufficiently strong to enable it to pierce the ice cap without damage, thus enabling a missile launch from a submarine under the Arctic ice cap.
- C.R. Hammond. CRC Handbook of Chemistry and Physics, 85th ed., Section 4; The Elements.
- Cotton, F. Albert and Wilkinson, Geoffrey. 1980. Advanced Inorganic Chemistry, 4th ed. New York: Wiley. ISBN 0-471-02775-8
- Greenwood, N.N. and Earnshaw, A. 1998. Chemistry of the Elements, 2nd Edition. New York: Elsevier. ISBN 0750633654
- Scandium Los Alamos National Laboratory. Retrieved December 9, 2007.
- Scandium SPECTRUM Chemical Fact Sheet. Retrieved December 9, 2007.
- Stwertka, Albert. 2002. A Guide to the Elements, 2nd ed. Oxford: Oxford University Press. ISBN 0195150279
All links retrieved November 2, 2019.
- Scandium WebElements.com.
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