Scandium is present in most of the deposits of rare-earth anduranium 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 onaluminium alloys were discovered. Its use in such alloys remains its only major application. The global trade of scandium oxide is 15–20tonnes per year.[11]
The properties of scandium compounds are intermediate between those ofaluminium andyttrium. Adiagonal relationship exists between the behavior ofmagnesium and scandium, just as there is betweenberyllium and aluminium. In the chemical compounds of the elements in group 3, the predominantoxidation state is +3.
Scandium is a soft metal with a silvery appearance. It develops a slightly yellowish or pinkish cast whenoxidized by air. It is susceptible to weathering and dissolves slowly in most diluteacids. It does not react with a 1:1 mixture ofnitric acid (HNO3) and 48.0%hydrofluoric acid (HF), possibly due to the formation of an impermeablepassive layer. Scandium turnings ignite in the air with a brilliant yellow flame to formscandium oxide.[12]
In nature, scandium is found exclusively as theisotope45Sc, which has anuclear spin of7⁄2; this is its only stable isotope.[13]
The known isotopes of scandium range from37Sc to62Sc.[8] The most stable radioisotope is46Sc, which has ahalf-life of 83.8 days. Others are47Sc, 3.35 days; thepositron emitter44Sc, 4 hours; and48Sc, 43.7 hours. All of the remainingradioactive isotopes have half-lives less than 4 hours, and the majority of them have half-lives less than 2 minutes. The low mass isotopes are very difficult to create.[13] The initial detection of37Sc and38Sc only resulted in the characterization of their mass excess.[14][15]Scandium also has fivenuclear isomers: the most stable of these is44m2Sc (t1/2 = 58.6 h).[16]
The primarydecay mode of ground-state scandium isotopes at masses lower than the only stable isotope,45Sc, iselectron capture (orpositron emission), but the lightest isotopes (37Sc to39Sc) undergoproton emission instead, all three of these producingcalcium isotopes. The primary decay mode at masses above45Sc isbeta emission, producingtitanium isotopes.[8]
InEarth's crust, scandium is not rare. Estimates vary from 18 to 25 ppm, which is comparable to the abundance ofcobalt (20–30 ppm). Scandium is only the 50th most common element on Earth (35th most abundant element in the crust), but it is the 23rd most common element in theSun[17] and the 26th most abundant element in the stars.[18] However, scandium is distributed sparsely and occurs in trace amounts in manyminerals.[19] Rare minerals from Scandinavia[20] andMadagascar[21] such asthortveitite,euxenite, andgadolinite are the only known concentrated sources of this element. Thortveitite can contain up to 45% of scandium in the form ofscandium oxide.[20]
The world production of scandium is in the order of 15–20 tonnes per year, in the form ofscandium oxide. The demand is slightly higher,[23] and both the production and demand keep increasing. In 2003, only three mines produced scandium: the uranium andiron mines inZhovti Vody in Ukraine, the rare-earth mines inBayan Obo, China, and the apatite mines in theKola Peninsula, Russia.[citation needed] Since then, many other countries have built scandium-producing facilities, including 5 tonnes/year (7.5 tonnes/yearSc2O3) byNickel Asia Corporation andSumitomo Metal Mining in the Philippines.[24][25] In the United States, NioCorp Development hopes[when?] to raise $1 billion[26] toward opening a niobium mine at its Elk Creek site in southeastNebraska,[27] which may be able to produce as much as 95 tonnes of scandium oxide annually.[28] In each case, scandium is a byproduct of the extraction of other elements and is sold as scandium oxide.[29][30][31]
Madagascar and theIveland-Evje region in Norway have the only deposits of minerals with high scandium content,thortveitite(Sc,Y)2(Si2O7), but these are not being exploited.[30] The mineralkolbeckiteScPO4·2H2O has a very high scandium content but is not available in any larger deposits.[30]
The absence of reliable, secure, stable, long-term production has limited the commercial applications of scandium. Despite this low level of use, scandium offers significant benefits. Particularly promising is the strengthening of aluminium alloys with as little as 0.5% scandium.[33] Scandium-stabilized zirconia enjoys a growing market demand for use as a high-efficiencyelectrolyte insolid oxide fuel cells.[citation needed]
TheUSGS reports that, from 2015 to 2019 in the US, the price of small quantities of scandium ingot has been $107 to $134 per gram, and that of scandium oxide $4 to $5 per gram.[34]
Scandium chemistry is almost completely dominated by the trivalent ion, Sc3+. The radii of M3+ ions in the table below indicate that the chemical properties of scandium ions have more in common with yttrium ions than with aluminium ions. In part because of this similarity, scandium is often classified as a lanthanide-like element.[35]
ThehalidesScX3, where X=Cl,Br, orI, are very soluble in water, butScF3 is insoluble. In all four halides, the scandium is 6-coordinated. The halides areLewis acids; for example,ScF3 dissolves in a solution containing excess fluoride ion to form[ScF6]3−. The coordination number 6 is typical for Sc(III). In the larger Y3+ and La3+ ions,coordination numbers of 8 and 9 are common.Scandium triflate is sometimes used as aLewis acid catalyst inorganic chemistry.[38]
Scandium forms a series of organometallic compounds withcyclopentadienyl ligands (Cp), similar to the behavior of the lanthanides. One example is the chlorine-bridged dimer,[ScCp2Cl]2 and related derivatives ofpentamethylcyclopentadienyl ligands.[39]
Compounds that feature scandium in oxidation states other than +3 are rare but well characterized. The blue-black compoundCsScCl3 is one of the simplest. This material adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers.[40]Scandium hydride is not well understood, although it appears not to be asaline hydride of Sc(II).[6] As is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase.[5] Scandium borides and carbides arenon-stoichiometric, as is typical for neighboring elements.[41]
Lower oxidation states (+2, +1, 0) have also been observed in organoscandium compounds.[42][4][43][44]
Metallic scandium was produced for the first time in 1937 byelectrolysis of aeutectic mixture ofpotassium,lithium, andscandium chlorides, at 700–800 °C.[49] The first pound of 99% pure scandium metal was produced in 1960. Production of aluminium alloys began in 1971, following a US patent.[50] Aluminium-scandium alloys were also developed in theUSSR.[51]
Laser crystals of gadolinium-scandium-gallium garnet (GSGG) were used in strategic defense applications developed for theStrategic Defense Initiative (SDI) in the 1980s and 1990s.[52][53]
The main application of scandium by weight is in aluminium-scandium alloys for minor aerospace industry components. These alloys contain between 0.1% and 0.5% of scandium. They were used in Russian military aircraft, specifically theMikoyan-Gurevich MiG-21 andMiG-29.[54]
The addition of scandium to aluminium limits the grain growth in the heat zone of welded aluminium components. This has two beneficial effects: the precipitatedAl3Sc forms smaller crystals than in otheraluminium alloys,[54] and the volume of precipitate-free zones at the grain boundaries of age-hardening aluminium alloys is reduced.[54] TheAl3Sc precipitate is a coherent precipitate that strengthens the aluminum matrix by applying elastic strain fields that inhibit dislocation movement (i.e., plastic deformation).Al3Sc has an equilibrium L12 superlattice structure exclusive to this system.[55] A fine dispersion of nano scale precipitate can be achieved via heat treatment that can also strengthen the alloys through order hardening.[56] Recent developments include the additions of transition metals such aszirconium (Zr) and rare earth metals likeerbium (Er) produce shells surrounding the sphericalAl3Sc precipitate that reduce coarsening.[57] These shells are dictated by the diffusivity of the alloying element and lower the cost of the alloy due to less Sc being substituted in part by Zr while maintaining stability and less Sc being needed to form the precipitate.[58] These have madeAl3Sc somewhat competitive with titanium alloys along with a wide array of applications. However,titanium alloys, which are similar in lightness and strength, are cheaper and much more widely used.[59]
The alloyAl20Li20Mg10Sc20Ti30 is as strong as titanium, light as aluminium, and hard as some ceramics.[60]
Some items of sports equipment, which rely on lightweight high-performance materials, have been made with scandium-aluminium alloys, includingbaseball bats,[61] tent poles andbicycle frames andcomponents.[62]Lacrosse sticks are also made with scandium. The American firearm manufacturing companySmith & Wesson produces semi-automatic pistols and revolvers with frames of scandium alloy and cylinders of titanium or carbon steel.[63][64]
Since 2013, Apworks GmbH, a spin-off of Airbus, have marketed a high strength Scandium containing aluminium alloy processed using metal 3D-Printing (Laser Powder Bed Fusion) under the trademarkScalmalloy which claims very high strength & ductility.[65]
The first scandium-based metal-halide lamps were patented byGeneral Electric and made in North America, although they are now produced in all major industrialized countries. Approximately 20 kg of scandium (asSc2O3) is used annually in theUnited States for high-intensity discharge lamps.[66] One type ofmetal-halide lamp, similar to themercury-vapor lamp, is made fromscandium triiodide andsodium iodide. This lamp is a white-light source with highcolor rendering index that sufficiently resembles sunlight to allow good color-reproduction withTV cameras.[67] About 80 kg of scandium is used in metal-halide lamps/light bulbs globally per year.[68]
Dentists use erbium-chromium-doped yttrium-scandium-gallium garnet (Er,Cr:YSGG) lasers for cavity preparation and in endodontics.[69]
The 12.4 keV nuclear transition of45Sc has been studied as a reference for timekeeping applications, with a theoretical precision as much as three orders of magnitude better than the currentcaesium reference clocks.[71]
Scandium has been proposed for use insolid oxide fuel cells (SOFCs) as a dopant in the electrolyte material, typically zirconia (ZrO₂).[72]Scandium oxide (Sc₂O₃) is one of several possible additives to enhance the ionic conductivity of thezirconia, improving the overall thermal stability, performance and efficiency of the fuel cell.[73] This application would be particularly valuable in clean energy technologies, as SOFCs can utilize a variety of fuels and have high energy conversion efficiencies.[74]
Elemental scandium is considered non-toxic, though extensive animal testing of scandium compounds has not been done.[75] Themedian lethal dose (LD50) levels forscandium chloride for rats have been determined as 755 mg/kg forintraperitoneal and 4 g/kg for oral administration.[76] In the light of these results, compounds of scandium should be handled as compounds of moderate toxicity. Scandium appears to be handled by the body in a manner similar togallium, with similar hazards involving its poorly solublehydroxide.[77]
^abArblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^abCloke, F. Geoffrey N.; Khan, Karl & Perutz, Robin N. (1991). "η-Arene complexes of scandium(0) and scandium(II)".J. Chem. Soc., Chem. Commun. (19):1372–1373.doi:10.1039/C39910001372.
^abSmith, R. E. (1973). "Diatomic Hydride and Deuteride Spectra of the Second Row Transition Metals".Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences.332 (1588):113–127.Bibcode:1973RSPSA.332..113S.doi:10.1098/rspa.1973.0015.S2CID96908213.
^abMcGuire, Joseph C.; Kempter, Charles P. (1960). "Preparation and Properties of Scandium Dihydride".Journal of Chemical Physics.33 (5):1584–1585.Bibcode:1960JChPh..33.1584M.doi:10.1063/1.1731452.
^Weast, Robert (1984).CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110.ISBN0-8493-0464-4.
^Samson, Iain M.; Chassé, Mathieu (2016), "Scandium", in White, William M. (ed.),Encyclopedia of Geochemistry: A Comprehensive Reference Source on the Chemistry of the Earth, Cham: Springer International Publishing, pp. 1–5,doi:10.1007/978-3-319-39193-9_281-1,ISBN978-3-319-39193-9
^"Mineral Commodity Summaries 2020"(PDF).US Geological Survey Mineral Commodities Summary 2020. US Geological Survey. Retrieved10 February 2020.
^"Scandium." Los Alamos National Laboratory. Retrieved 2013-07-17.
^Dronchi, N.; Charity, R. J.; Sobotka, L. G.; Brown, B. A.; Weisshaar, D.; Gade, A.; Brown, K. W.; Reviol, W.; Bazin, D.; Farris, P. J.; Hill, A. M.; Li, J.; Longfellow, B.; Rhodes, D.; Paneru, S. N.; Gillespie, S. A.; Anthony, A. K.; Rubino, E.; Biswas, S. (2024-09-12). "Evolution of shell gaps in the neutron-poor calcium region from invariant-mass spectroscopy of37,38Sc,35Ca, and34K".Physical Review C.110 (3).doi:10.1103/PhysRevC.110.L031302.ISSN2469-9985.
^Bernhard, F. (2001). "Scandium mineralization associated with hydrothermal lazurite-quartz veins in the Lower Austroalpie Grobgneis complex, East Alps, Austria".Mineral Deposits in the Beginning of the 21st Century. Lisse: Balkema.ISBN978-90-265-1846-1.
^Shapiro, Pamela J.; et al. (1994). "Model Ziegler-Nattaα-Olefin Polymerization Catalysts Derived from [{(η5-C5Me4)SiMe2(η1-NCMe3)}(PMe3)Sc(μ2-H)]2 and [{(η5C5Me4)SiMe2(η1NCMe3)}Sc(μ1CH2CH2CH3)]2. Synthesis, Structures and Kinetic and Equilibrium Investigations of the Catalytically active Species in Solution".Journal of the American Chemical Society.116 (11): 4623.doi:10.1021/ja00090a011.
^Corbett, J. D. (1981). "Extended metal-metal bonding in halides of the early transition metals".Accounts of Chemical Research.14 (8):239–246.doi:10.1021/ar00068a003.
^Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001.ISBN0-12-352651-5.
^Polly L. Arnold; F. Geoffrey; N. Cloke; Peter B. Hitchcock & John F. Nixon (1996). "The First Example of a Formal Scandium(I) Complex: Synthesis and Molecular Structure of a 22-Electron Scandium Triple Decker Incorporating the Novel 1,3,5-Triphosphabenzene Ring".Journal of the American Chemical Society.118 (32):7630–7631.Bibcode:1996JAChS.118.7630A.doi:10.1021/ja961253o.
^Ana Mirela Neculai; Dante Neculai; Herbert W. Roesky; Jörg Magull; Marc Baldus; et al. (2002). "Stabilization of a Diamagnetic ScIBr Molecule in a Sandwich-Like Structure".Organometallics.21 (13):2590–2592.doi:10.1021/om020090b.
^Polly L. Arnold; F. Geoffrey; N. Cloke & John F. Nixon (1998). "The first stable scandocene: synthesis and characterisation of bis(η-2,4,5-tri-tert-butyl-1,3-diphosphacyclopentadienyl)scandium(II)".Chemical Communications (7):797–798.doi:10.1039/A800089A.
^Bjerklie, Steve (2006). "A batty business: Anodized metal bats have revolutionized baseball. But are finishers losing the sweet spot?".Metal Finishing.104 (4): 61.doi:10.1016/S0026-0576(06)80099-1.
^Mathur, Lakshya; Jeon, Sang-Yun (2024). "Ternary co-doped ytterbium-scandium stabilized zirconia electrolyte for solid oxide fuel cells".Solid State Ionics.408: 116507.doi:10.1016/j.ssi.2024.116507.
^Dokiya, Masayuki (2002-12-01)."SOFC system and technology".Solid State Ionics. PROCEEDINGS OF INTERNATIONAL CONFERENCE ON SOLID STATE IONICS, (MATERIALS AND PROCESSES FOR ENERGY AND ENVIRONMENT), CAIRNS, AUSTRALIA, 8-13 JULY, 2001.152–153:383–392.doi:10.1016/S0167-2738(02)00345-4.ISSN0167-2738.
^Li, Zhishan; Guo, Meiting (2024). "Utilization of Thermocatalysts in Solid Oxide Fuel Cells (SOFCs) Fed with Hydrogen-Rich Fuels: A Mini-Review".Energy Fuels.38 (12):10673–10690.doi:10.1021/acs.energyfuels.4c01609.
^Haley, Thomas J.; Komesu, L.; Mavis, N.; Cawthorne, J.; Upham, H. C. (1962). "Pharmacology and toxicology of scandium chloride".Journal of Pharmaceutical Sciences.51 (11):1043–5.doi:10.1002/jps.2600511107.PMID13952089.
_NIST_ASD_emission_spectrum.png)
