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Jai Ganesh

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Registered: 2005-06-28

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Scandium

Scandium

Gist

It is a silvery-white metallic d-block element. Historically, it has 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 mainly used for research purposes. It has, however, great potential because it has almost as low a density as aluminium and a much higher melting point. An aluminium-scandium alloy has been used in Russian MIG fighter planes, high-end bicycle frames and baseball bats.

Summary

Scandium is a chemical element; it has symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has 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 difficulties in the preparation of metallic scandium, which was first done in 1937, applications for scandium were not developed until the 1970s, when the positive effects of scandium on aluminium alloys were discovered. Its use in such alloys remains its only major application. The global trade of scandium oxide is 15–20 tonnes per year.

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.

Details

Scandium (Sc), chemical element, a rare-earth metal of Group 3 of the periodic table.

Scandium is a silvery white, moderately soft metal. It is fairly stable in air but will slowly change its colour from silvery white to a yellowish appearance because of formation of Sc2O3 oxide on the surface. The metal slowly dissolves in diluted acids—except hydrofluoric acid (HF), in which a protective trifluoride layer prevents further reaction. Scandium is paramagnetic from 0 K (−273 °C, or −460 °F) to its melting point (1,541 °C, or 2,806 °F). It becomes superconducting at −273.1 °C (−459.6 °F) at pressures exceeding 186 kilobars.

After Russian chemist Dmitry Ivanovich Mendeleyev in 1871 predicted this element’s existence, tentatively calling it ekaboron, Swedish chemist Lars Fredrik Nilson in 1879 discovered its oxide, scandia, in the rare-earth minerals gadolinite and euxenite, and Swedish chemist Per Teodor Cleve later in 1879 identified scandium as the hypothetical ekaboron. Scandium is found in small proportions, generally less than 0.2 percent, in many of the heavy lanthanide ores and in many tin, uranium, and tungsten ores. Thortveitite (a scandium silicate) is the only mineral containing large amounts of scandium, about 34 percent, but unfortunately this mineral is quite rare and is not an important source of scandium. The cosmic abundance of scandium is relatively high. Although it is only about the 50th most abundant element on Earth (its abundance is similar to that of beryllium), it is about the 23rd most abundant element in the Sun.

In nature, scandium exists in the form of one stable isotope, scandium-45. Among 25 (excluding nuclear isomers) radioactive isotopes with masses ranging from 36 to 61, the most stable is scandium-46 (half-life of 83.79 days), and the least stable is scandium-39 (half-life of less than 300 nanoseconds).

Scandium is separated from the other rare earths by precipitation of the insoluble potassium scandium sulfate or by extraction of scandium thiocyanate by diethyl ether. The metal itself was first prepared in 1938 by the electrolysis of potassium, lithium, and scandium chlorides in a eutectic mixture (i.e., a mixture having the lowest melting point possible with those components). Scandium is now produced mostly as a by-product of uranium extraction from the mineral davidite, which contains about 0.02 percent scandium oxide. Scandium exists in two allotropic (structural) forms. The α-phase is close-packed hexagonal with a = 3.3088 Å and c = 5.2680 Å at room temperature. The β-phase is body-centred cubic with an estimated a = 3.73 Å at 1,337 °C (2,439 °F).

Only a few uses of this unusual transition metal have been developed, mostly due to scandium’s limited availability and high cost. Its low density and high melting point suggest applications as an alloying agent for lightweight metals for military and high-performance applications. The major uses of scandium are as an alloy additive to aluminum-based alloys for sporting goods and in high-intensity metal halide lamps. When alloyed with aluminum and aluminum-based alloys, scandium limits high-temperature grain growth.

The chemistry of scandium bears a closer resemblance to that of the other rare-earth elements of oxidation state +3 than to that of aluminum or titanium. Some of its behaviour, however, is atypical of the rare earths because of its significantly smaller ionic radius (1.66 Å for coordination number 12) as compared with the rare-earth average (1.82 Å for coordination number 12). For this reason, the Sc3+ ion is a relatively strong acid and has a much greater tendency to form complex ions.

Element Properties

atomic number  :  21
atomic weight  :  44.95591
melting point  :  1,541 °C (2,806 °F)
boiling point  :  2,836 °C (5,137 °F)
specific gravity  :  2.989 (24 °C, or 75 °F)
oxidation state  :  +3.

Additional Information:

Appearance

A silvery metal that tarnishes in air, burns easily and reacts with water.

Uses

Scandium is mainly used for research purposes. It has, however, great potential because it has almost as low a density as aluminium and a much higher melting point. An aluminium-scandium alloy has been used in Russian MIG fighter planes, high-end bicycle frames and baseball bats.

Scandium iodide is added to mercury vapour lamps to produce a highly efficient light source resembling sunlight. These lamps help television cameras to reproduce colour well when filming indoors or at night-time.

The radioactive isotope scandium-46 is used as a tracer in oil refining to monitor the movement of various fractions. It can also be used in underground pipes to detect leaks.

Biological role

Scandium has no known biological role. It is a suspected carcinogen.

Natural abundance

Scandium is very widely distributed, and occurs in minute quantities in over 800 mineral species. It is the main component of the very rare and collectable mineral thortveitite, found in Scandinavia.

Scandium can be recovered from thortveitite or extracted as a by-product from uranium mill tailings (sandy waste material). Metallic scandium can be prepared by reducing the fluoride with calcium metal. It can also be prepared by electrolysing molten potassium, lithium and scandium chlorides, using electrodes of tungsten wire and molten zinc.

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