Scandium

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Scandium

Scandium is a chemical element in the periodic table that has the symbol Sc and atomic number 21. A soft, silvery, white transition metal, scandium occurs in rare minerals from Scandinavia and it is sometimes classified along with yttrium and the lanthanides as a rare earth.

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(H N O₃) and 48% HF.

Applications

Approximately 20 kg (as Sc₂O₃) of scandium are used annually in the United States to make high-intensity lights. Scandium iodide added to mercury-vapor lamps produces a highly efficient artificial light source that resembles sunlight and allows good color reproduction with TV cameras. About 80 kg of scandium are used in lightbulbs globally per year. The radioactive isotope Sc-46 is used in oil refinery crackers as a tracing agent. The main application by volume is in aluminium-scandium alloys for the aerospace industry and for sports equipment (bikes, baseball bats, firearms, etc.) which rely on high performance materials. When added to aluminium, scandium substantially lowers the rate of recrystallisation and associated grain-growth in the weld heat-affected zone. Contrary to popular belief and deliberate brochure misinformation by sports equipments companies, the addition of scandium per se does not substantially increase the strength of the alloy. Aluminium, being a face centred cubic metal, is not particularly subject to the strengthening effects of the a decrease in grain diameter. However, the presence of fine dispersions of Al₃Sc do increase strength by a small measure, much as do any other precipitate system in aluminium alloys. It is added to Al 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 surround exist at the grain boundaries of age-hardening aluminium alloys.

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

History

Dmitri Mendeleev used his periodic law, in 1869, to predict the existence 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; using spectrum analysis he found a new element within the minerals euxenite and gadolinite. He named it Scandium, from the Latin Scandia meaning "Scandinavia", and by way of isolating the element he processed 10 kilograms of euxenite with other rare-earth residues, obtaining about 2 grams of very pure scandium oxide (Sc₂O₃). Per Teodor Cleve concluded that scandium corresponded well to the hoped-for ekaboron, and 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 700 to 800°C Tungsten wire in a pool of liquid zinc were the electrodes in a graphite crucible. The first pound of 99% pure scandium metal wasn't produced until 1960.

Occurrence

Scandium is distributed widely on earth, occurring in trace quantities in over 800 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 found in residues that remain after tungsten is extracted from wolframite. The blue color of the aquamarine variety of beryl is thought to be caused by scandium.

Isolation

Thortveitite is the primary source of scandium with uranium mill tailings by-products also being an important source. Pure scandium is commercially produced by reducing scandium fluoride with calcium metal. The main source of scandium is from military stockpiles from the former Soviet Union, which were themselves extracted from uranium tailings. There is no primary production in the Americas or Europe.

Compounds

The most common oxidation state of scandium in Scandium compounds is +3. This element resembles yttrium and rare earth metals more than it resembles aluminium or titanium (which are closer on the periodic table).

See also Scandium compounds.

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 83.79 days, ⁴⁷Sc with a half-life of 3.3492 days, and ⁴⁸Sc with a half-life of 43.67 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 39.978 amu (⁴⁰Sc) to 53.963 amu (⁵⁴Sc). The primary decay mode before the only stable isotope, ⁴⁵Sc, is electron capture and the primary mode after is beta emission. The primary decay products before ⁴⁵Sc are element 20 (calcium) isotopes and the primary products after are element 22 (titanium) isotopes.

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Notable characteristics

Applications

History

Occurrence

Isolation

Compounds

Isotopes

Precautions

See also

References

External links