Scandium
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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.
Contents
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 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 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 .
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 (t½ 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.
Precautions
NFPA 704
See also
References
External links
For a full list of external links and suppliers see [Chemical sources]
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