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{{Infobox scandium}}
'''Scandium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Sc''' and [[atomic number]] 21. It is a silvery-white metallic [[d-block|d-block element]]. Historically, it has been classified as a [[rare-earth element]],<ref>{{cite web| url = http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf| title = IUPAC Recommendations, Nomenclature of Inorganic Chemistry| archive-url = https://web.archive.org/web/20080527204340/http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf| archive-date = 2008-05-27}}</ref> together with [[yttrium]] and the [[lanthanide]]s. It was discovered in 1879 by spectral analysis of the [[mineral]]s [[euxenite]] and [[gadolinite]] from [[Scandinavia]].<ref>{{Citation |last1=Samson |first1=Iain M. |title=Scandium |date=2016 |encyclopedia=Encyclopedia of Geochemistry: A Comprehensive Reference Source on the Chemistry of the Earth |pages=1–5 |editor-last=White |editor-first=William M. |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-39193-9_281-1 |isbn=978-3-319-39193-9 |last2=Chassé |first2=Mathieu |url=https://hal.archives-ouvertes.fr/hal-01420736 }}</ref>

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 alloy]]s were discovered. Its use in such alloys remains its only major application. The global trade of scandium oxide is 15–20 [[tonne]]s per year.<ref name="USGS">{{cite web |title=Mineral Commodity Summaries 2020 |url=https://pubs.usgs.gov/periodicals/mcs2020/mcs2020-scandium.pdf |website=US Geological Survey Mineral Commodities Summary 2020 |publisher=US Geological Survey |access-date=10 February 2020 |ref=USGS}}</ref>

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.

==Properties==

===Chemical characteristics===
Scandium is a soft metal with a silvery appearance. It develops a slightly yellowish or pinkish cast when [[redox|oxidized]] by air. It is susceptible to weathering and dissolves slowly in most dilute [[acids]]. It does not react with a 1:1 mixture of [[nitric acid]] ({{chem2|HNO3}}) and 48.0% [[hydrofluoric acid]] ({{chem2|HF}}), possibly due to the formation of an impermeable [[passivation (chemistry)|passive layer]]. Scandium turnings ignite in the air with a brilliant yellow flame to form [[scandium oxide]].<ref>"[http://periodic.lanl.gov/21.shtml Scandium]." Los Alamos National Laboratory. Retrieved 2013-07-17.</ref>

===Isotopes===
{{Main|Isotopes of scandium}}
In nature, scandium is found exclusively as the [[isotope]] <sup>45</sup>Sc, which has a [[nuclear spin]] of {{frac|7|2}}; this is its only stable isotope.<ref name=Meierfrankenfeld2011>{{Cite journal |last1=Meierfrankenfeld |first1=D. |last2=Bury |first2=A. |last3=Thoennessen |first3=M. |date=2011 |title=Discovery of scandium, titanium, mercury, and einsteinium isotopes |url=https://linkinghub.elsevier.com/retrieve/pii/S0092640X10000914 |journal=Atomic Data and Nuclear Data Tables |language=en |volume=97 |issue=2 |pages=134–151 |doi=10.1016/j.adt.2010.11.001|arxiv=1003.5128 |bibcode=2011ADNDT..97..134M }}</ref>

The known isotopes of scandium range from <sup>37</sup>Sc to <sup>63</sup>Sc,{{NUBASE2020|name}} and the most stable radioisotopes are <sup>46</sup>Sc with a [[half-life]] of 83.76 days, <sup>47</sup>Sc with a half-life of 3.3492 days, <sup>48</sup>Sc at 43.67 hours, [[Scandium-44|<sup>44</sup>Sc]] at 4.042 hours, and <sup>43</sup>Sc at 3.891 hours. All others have half-lives shorter than an hour, and the majority of these shorter than 15 seconds. The most stable [[meta state]] is <sup>44m3</sup>Sc with half-life 58.6&nbsp;hours; this is the lightest isotope with a long-lived isomer.

The low mass isotopes are very difficult to create.<ref name=Meierfrankenfeld2011/> The initial detection of <sup>37</sup>Sc and <sup>38</sup>Sc only resulted in the characterization of their mass excess.<ref name="37,38Sc">{{cite journal | last1=Dronchi | first1=N. | last2=Charity | first2=R. J. | last3=Sobotka | first3=L. G. | last4=Brown | first4=B. A. | last5=Weisshaar | first5=D. | last6=Gade | first6=A. | last7=Brown | first7=K. W. | last8=Reviol | first8=W. | last9=Bazin | first9=D. | last10=Farris | first10=P. J. | last11=Hill | first11=A. M. | last12=Li | first12=J. | last13=Longfellow | first13=B. | last14=Rhodes | first14=D. | last15=Paneru | first15=S. N. | last16=Gillespie | first16=S. A. | last17=Anthony | first17=A. K. | last18=Rubino | first18=E. | last19=Biswas | first19=S. | title=Evolution of shell gaps in the neutron-poor calcium region from invariant-mass spectroscopy of <sup>37,38</sup>Sc, <sup>35</sup>Ca, and <sup>34</sup>K | journal=Physical Review C | volume=110 | issue=3 | date=2024-09-12 | issn=2469-9985 | doi=10.1103/PhysRevC.110.L031302| osti=2440923 }}</ref><ref>[https://frib.msu.edu/public/nuclides/newly-discovered Latest discovered isotopes], Discovery of Nuclides Project</ref>

The primary [[decay mode]] of ground-state scandium isotopes at masses lower than the only stable isotope, <sup>45</sup>Sc, is [[electron capture]] (or [[positron emission]]), but the lightest isotopes (<sup>37</sup>Sc to <sup>39</sup>Sc) undergo [[proton emission]] instead, all three of these producing [[calcium]] isotopes. The primary decay mode for heavier isotopes is [[beta emission]], producing [[titanium]] isotopes.{{NUBASE2020|name}}

===Occurrence===
In [[abundance of elements in Earth's crust|Earth's crust]], scandium is not rare. Estimates vary from 18 to 25&nbsp;ppm, which is comparable to the abundance of [[cobalt]] (20–30&nbsp;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 the [[Sun]]<ref name="rubber">{{cite book|title= CRC Handbook of Chemistry and Physics|first= David R.|last= Lide|date= 2004|isbn= 978-0-8493-0485-9|pages= [https://archive.org/details/crchandbookofche81lide/page/4 4–28]|publisher= CRC Press|location= Boca Raton|url-access= registration|url= https://archive.org/details/crchandbookofche81lide/page/4}}</ref> and the 26th most abundant element in the stars.<ref>{{Cite web |title=Chemistry for Kids: Elements - Scandium |url=https://www.ducksters.com/science/chemistry/scandium.php |access-date=2024-06-12 |website=www.ducksters.com}}</ref> However, scandium is distributed sparsely and occurs in trace amounts in many [[mineral]]s.<ref>{{cite book |first= F.|last= Bernhard|chapter= Scandium mineralization associated with hydrothermal lazurite-quartz veins in the Lower Austroalpie Grobgneis complex, East Alps, Austria|title= Mineral Deposits in the Beginning of the 21st Century|date= 2001|isbn= 978-90-265-1846-1 |publisher= Balkema |location= Lisse}}</ref> Rare minerals from Scandinavia<ref name="Thort">{{cite journal|title= Scandium – Mineraler I Norge|first= Roy|last= Kristiansen|journal= Stein|date= 2003|pages= 14–23|language= no|url= http://www.nags.net/Stein/2003/Sc-mineraler.pdf}}</ref> and [[Madagascar]]<ref name="Mada">{{cite journal|journal=Geological Journal|volume= 22|page= 253|date= 1987|title= Mineralized pegmatites in Africa|first= O.|last= von Knorring|author2=Condliffe, E. |issue= S2|doi= 10.1002/gj.3350220619|bibcode= 1987GeolJ..22S.253V}}</ref> such as [[thortveitite]], [[euxenite]], and [[gadolinite]] are the only known concentrated sources of this element, all of which are sources of other rare earths. Thortveitite can contain up to 45% [[scandium oxide]].<ref name="Thort" />

The stable form of scandium is created in [[supernova]]e via the [[r-process]].<ref>{{cite journal|author= Cameron, A.G.W.|title=Stellar Evolution, Nuclear Astrophysics, and Nucleogenesis |journal=CRL-41|date=June 1957|url=http://www.fas.org/sgp/eprint/CRL-41.pdf}}</ref> Also, scandium is created by [[cosmic ray spallation]] of the more abundant [[iron peak|iron-peak]] nuclei. Example reactions are:

*<sup>28</sup>Si + 17n → <sup>45</sup>Sc (r-process)
*<sup>56</sup>Fe + p → <sup>45</sup>Sc + <sup>11</sup>C + n (cosmic ray spallation)

==Production==
The world production of scandium is in the order of 15–20 tonnes per year, in the form of [[scandium oxide]]. The demand is slightly higher,<ref>{{Cite journal |last1=Phoung |first1=Sinoun |last2=Williams |first2=Eric |last3=Gaustad |first3=Gabrielle |last4=Gupta |first4=Ajay |date=2023-05-15 |title=Exploring global supply and demand of scandium oxide in 2030 |journal=Journal of Cleaner Production |language=en |volume=401 |article-number=136673 |doi=10.1016/j.jclepro.2023.136673 |s2cid=257338829 |issn=0959-6526|doi-access=free |bibcode=2023JCPro.40136673P }}</ref> and both the production and demand keep increasing. In 2003, only three mines produced scandium: the uranium and [[iron]] mines in [[Zhovti Vody]] in Ukraine, the rare-earth mines in [[Bayan Obo]], China, and the apatite mines in the [[Kola Peninsula]], Russia.{{citation needed|date=May 2023}} Since then, many other countries have built scandium-producing facilities, including 5 tonnes/year (7.5 tonnes/year {{chem2|Sc2O3}}) by [[Nickel Asia Corporation]] and [[Sumitomo Metal Mining]] in the Philippines.<ref name="SMMPressRelease">{{cite web|url=http://www.smm.co.jp/E/news/release/uploaded_files/20160428en.pdf|title=Establishment of Scandium Recovery Operations|access-date=2018-10-26}}</ref><ref name="SMMAbstract">{{cite web|url=http://www.programmaster.org/PM/PM.nsf/ApprovedAbstracts/3D8E40595EA68C5C852581330004CB19?OpenDocument|publisher=TMS|first=Fumio|last=Iwamoto|title=Commercial Scandium Oxide Production by Sumitomo Metal Mining Co. Ltd.|access-date=2018-10-26|archive-date=2021-02-27|archive-url=https://web.archive.org/web/20210227054756/http://www.programmaster.org/PM/PM.nsf/ApprovedAbstracts/3D8E40595EA68C5C852581330004CB19?OpenDocument}}</ref> 
In the United States, NioCorp Development hopes{{when|date=February 2020}} to raise $1 billion<ref>{{cite press release |url=https://www.niocorp.com/niocorp-announces-final-closing-of-non-brokered-private-placement-for-aggregate-gross-proceeds-of-c1-77-million/ | title=NioCorp Announces Final Closing of Non-Brokered Private Placement for Aggregate Gross Proceeds of C$1.77 Million | access-date=2019-05-18}}</ref> toward opening a niobium mine at its Elk Creek site in southeast [[Nebraska]],<ref>{{cite news |url=http://www.omaha.com/money/long-discussed-niobium-mine-in-southeast-nebraska-is-ready-to/article_33913f7a-93fa-11e7-9144-8f1cad9c36eb.html|title=Long-discussed niobium mine in southeast Nebraska is ready to move forward, if it gathers $1 billion in financing |access-date=2019-05-18|last1=Hammel|first1=Paul|date=8 September 2017|website=Omaha World-Herald}}</ref> which may be able to produce as much as 95 tonnes of scandium oxide annually.<ref>{{citation |url=http://niocorp.com/wp-content/uploads/NIoCorp_Corporate_Presentation.pdf |title=NioCorp Superalloy Materials The Elk Creek Superalloy Materials Project |access-date=2019-05-18 |archive-date=2021-08-19 |archive-url=https://web.archive.org/web/20210819204036/http://niocorp.com/wp-content/uploads/NIoCorp_Corporate_Presentation.pdf }}</ref> In each case, scandium is a byproduct of the extraction of other elements and is sold as scandium oxide.<ref name="Deschamps">{{cite web|first= Y.|last= Deschamps|access-date= 2008-10-21|url= http://www.mineralinfo.org/Substance/Scandium/Sc.pdf|publisher= mineralinfo.com|title= Scandium|archive-url= https://web.archive.org/web/20120324033608/http://www.mineralinfo.org/Substance/Scandium/Sc.pdf|archive-date= 2012-03-24}}</ref><ref name="USGS2015">{{cite web|url= https://minerals.usgs.gov/minerals/pubs/commodity/scandium/mcs-2015-scand.pdf|publisher= United States Geological Survey |title= Mineral Commodity Summaries 2015: Scandium}}</ref><ref name="usgs">[https://minerals.usgs.gov/minerals/pubs/commodity/scandium/ Scandium]. USGS.</ref>

To produce metallic scandium, the oxide is converted to [[scandium fluoride]] and then [[redox|reduced]] with metallic [[calcium]].<ref>{{Cite journal |last1=Fujii |first1=Satoshi |last2=Tsubaki |first2=Shuntaro |last3=Inazu |first3=Naomi |last4=Suzuki |first4=Eiichi |last5=Wada |first5=Yuji |date=2017-09-27 |title=Smelting of Scandium by Microwave Irradiation |journal=Materials |language=en |volume=10 |issue=10 |page=1138 |doi=10.3390/ma10101138 |issn=1996-1944 |pmc=5666944 |pmid=28953241|bibcode=2017Mate...10.1138F |doi-access=free }}</ref>

* {{Chem2|Sc2O3 + 6HF -> 2ScF3 + 3H2O}}
* {{Chem2|2ScF3 + 3Ca -> 3CaF2 + 2Sc}}

[[Madagascar]] and the [[Iveland]]-[[Evje]] region in Norway have the only deposits of minerals with high scandium content, [[thortveitite]] {{chem2|(Sc,Y)2(Si2O7}}), but these are not being exploited.<ref name="USGS2015" /> The mineral [[kolbeckite]] {{chem2|ScPO4*2H2O}} has a very high scandium content but is not available in any larger deposits.<ref name="USGS2015" />

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.<ref>{{Cite journal |last=Zakharov |first=V. V. |date=2014-09-01 |title=Combined Alloying of Aluminum Alloys with Scandium and Zirconium |journal=Metal Science and Heat Treatment |language=en |volume=56 |issue=5 |pages=281–286 |doi=10.1007/s11041-014-9746-5 |bibcode=2014MSHT...56..281Z |s2cid=135839152 |issn=1573-8973}}</ref> Scandium-stabilized zirconia enjoys a growing market demand for use as a high-efficiency [[electrolyte]] in [[solid oxide fuel cell]]s.{{cn|date=December 2024}}

The [[USGS]] 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.<ref>{{Cite web |url=https://www.usgs.gov/centers/nmic/mineral-commodity-summaries |title=Mineral Commodity Summaries |publisher=USGS |access-date=2020-09-13 }}</ref>

==Compounds==
{{Category see also|Scandium compounds|Scandium minerals}}
Scandium chemistry is almost completely dominated by the trivalent ion, Sc<sup>3+</sup>. The radii of M<sup>3+</sup> 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.<ref>{{Cite book |last=Horovitz |first=Chaim T. |url=https://books.google.com/books?id=xaPaBwAAQBAJ |title=Biochemistry of Scandium and Yttrium, Part 1: Physical and Chemical Fundamentals |date=2012-12-06 |publisher=Springer Science & Business Media |isbn=978-1-4615-4313-8 |language=en}}</ref>
:{|class="wikitable"
|+ Ionic radius (pm)
|-
|[[aluminium|Al]]||Sc||[[yttrium|Y]]||[[lanthanum|La]]||[[lutetium|Lu]]
|-
|53.5||74.5||90.0||103.2||86.1
|}

===Oxides and hydroxides===
The oxide [[scandium oxide|{{chem|Sc|2|O|3}}]] and the hydroxide {{chem|Sc(OH)|3}} are [[amphoteric]]:<ref>{{cite book|author=Cotton, Simon |title=Lanthanide and actinide chemistry|url=https://books.google.com/books?id=lvQpiVHrb78C&pg=PA108|access-date=2011-06-23|date=2006|publisher=John Wiley and Sons|isbn=978-0-470-01006-8|pages=108–}}</ref>
:{{chem|Sc(OH)|3}} + 3 {{chem|OH|-}} → {{chem|[Sc(OH)|6|]|3−}} (scandate ion)
:{{chem|Sc(OH)|3}} + 3 {{chem|H|+}} + 3 {{chem|H|2|O}} → {{chem|[Sc(H|2|O)|6|]|3+}}

α- and γ-ScOOH are isostructural with their [[aluminium hydroxide oxide]] counterparts.<ref>{{cite journal|last=Christensen|first=A. Nørlund|author2=Stig Jorgo Jensen|date=1967|title=Hydrothermal Preparation of α-ScOOH and of γ-ScOOH. Crystal Structure of α-ScOOH|journal= Acta Chemica Scandinavica|volume=21|pages=1121–126|doi= 10.3891/acta.chem.scand.21-0121|doi-access=free}}</ref> Solutions of {{chem|Sc|3+}} in water are acidic due to [[hydrolysis]].

===Halides and pseudohalides===
The [[halide]]s {{chem2|ScX3}}, where X= [[scandium chloride|Cl]], [[scandium bromide|Br]], or [[scandium triiodide|I]], are very soluble in water, but [[scandium fluoride|{{chem2|ScF3}}]] is insoluble. In all four halides, the scandium is 6-coordinated. The halides are [[Lewis acids]]; for example, [[scandium fluoride|{{chem2|ScF3}}]] dissolves in a solution containing excess fluoride ion to form {{chem2|[ScF6](3−)}}. The coordination number 6 is typical for Sc(III). In the larger Y<sup>3+</sup> and La<sup>3+</sup> ions, [[coordination number]]s of 8 and 9 are common. [[Scandium triflate]] is sometimes used as a [[Lewis acid]] catalyst in [[organic chemistry]].<ref>{{cite journal |doi =10.1055/s-1999-5997 |title= SYNLETT Spotlight 12: Scandium Triflate |author= Deborah Longbottom |journal= [[Synlett]] |year= 1999 |issue= 12 |page= 2023 |volume =1999|doi-access= free }}</ref>

===Organic derivatives===
{{Main|Organoscandium chemistry}}
Scandium forms a series of organometallic compounds with [[cyclopentadienyl complex|cyclopentadienyl]] ligands (Cp), similar to the behavior of the lanthanides. One example is the chlorine-bridged dimer, {{chem2|[ScCp2Cl]2}} and related derivatives of [[pentamethylcyclopentadienyl]] ligands.<ref>{{cite journal|title=Model Ziegler-Natta ''α''-Olefin Polymerization Catalysts Derived from [{(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>)SiMe<sub>2</sub>(η<sup>1</sup>-NCMe<sub>3</sub>)}(PMe<sub>3</sub>)Sc(μ<sub>2</sub>-H)]<sub>2</sub> and [{(η<sup>5</sup>C<sub>5</sub>Me<sub>4</sub>)SiMe<sub>2</sub>(η<sup>1</sup>NCMe<sub>3</sub>)}Sc(μ<sup>1</sup>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>)]<sub>2</sub>. Synthesis, Structures and Kinetic and Equilibrium Investigations of the Catalytically active Species in Solution|last=Shapiro|first=Pamela J.|display-authors=etal|journal=Journal of the American Chemical Society|volume=116|issue=11|page=4623 |date=1994|doi=10.1021/ja00090a011}}</ref>

=== Uncommon oxidation states ===

Compounds that feature scandium in oxidation states other than +3 are rare but well characterized. The blue-black compound {{chem2|CsScCl3}} is one of the simplest. This material adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers.<ref>{{cite journal|last=Corbett|first=J. D.|date=1981|title=Extended metal-metal bonding in halides of the early transition metals |journal=Accounts of Chemical Research|volume=14|pages=239–246|doi= 10.1021/ar00068a003|issue=8}}</ref> [[Scandium hydride]] is not well understood, although it appears not to be a [[hydride|saline hydride]] of Sc(II).<ref name="McGuire" /> As is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase.<ref name="Smith" /> Scandium borides and carbides are [[non-stoichiometric compound|non-stoichiometric]], as is typical for neighboring elements.<ref name="Holleman">Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.</ref>

Lower oxidation states (+2, +1, 0) have also been observed in organoscandium compounds.<ref>{{cite journal|author=Polly L. Arnold|author2=F. Geoffrey|author3=N. Cloke|author4=Peter B. Hitchcock|author5=John F. Nixon|name-list-style=amp|date=1996|title=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=Journal of the American Chemical Society|volume=118|issue=32|pages=7630–7631|doi= 10.1021/ja961253o|bibcode=1996JAChS.118.7630A }}</ref><ref name="Cloke1991"/><ref>{{cite journal|display-authors=5|author=Ana Mirela Neculai|author2=Dante Neculai|author3=Herbert W. Roesky|author4=Jörg Magull|author5=Marc Baldus|author6=Ovidiu Andronesi|author7=Martin Jansen|date=2002|title=Stabilization of a Diamagnetic Sc<sup>I</sup>Br Molecule in a Sandwich-Like Structure |journal=Organometallics|volume=21|pages=2590–2592|doi= 10.1021/om020090b|issue=13}}</ref><ref>{{cite journal|author=Polly L. Arnold|author2=F. Geoffrey|author3=N. Cloke|author4=John F. Nixon|name-list-style=amp |date=1998|title=The first stable scandocene: synthesis and characterisation of bis(η-2,4,5-tri-tert-butyl-1,3-diphosphacyclopentadienyl)scandium(II) |journal= Chemical Communications|issue=7|pages=797–798|doi= 10.1039/A800089A}}</ref>

==History==
[[Dmitri Mendeleev]], who is referred to as the father of the [[periodic table]], predicted the existence of an element ''[[Mendeleev's predicted elements#Ekaboron and scandium|ekaboron]]'', with an [[atomic mass]] between 40 and 48 in 1869. [[Lars Fredrik Nilson]] and his team [[discovery of the chemical elements|detected this element]] in the minerals [[euxenite]] and [[gadolinite]] in 1879. Nilson prepared 2&nbsp;grams of [[scandium oxide]] of high purity.<ref name="Nilsonfr">{{cite journal|title= Sur l'ytterbine, terre nouvelle de M. Marignac|url= http://gallica.bnf.fr/ark:/12148/bpt6k30457/f639.table |journal= [[Comptes Rendus]]|author= Nilson, Lars Fredrik|volume= 88 |date= 1879|pages= 642–647|language=fr}}</ref><ref name="Nilsonde">{{cite journal|title= Ueber Scandium, ein neues Erdmetall|journal= [[Berichte der deutschen chemischen Gesellschaft]]|volume= 12|issue= 1|date= 1879|pages= 554–557|author= Nilson, Lars Fredrik|doi= 10.1002/cber.187901201157|language=de|url= https://zenodo.org/record/1425172}}</ref> He named the element scandium, from the [[Latin]] ''Scandia'' meaning "Scandinavia". Nilson was apparently unaware of Mendeleev's prediction, but [[Per Teodor Cleve]] recognized the correspondence and notified Mendeleev.<ref>{{cite journal|title= Sur le scandium |url= http://gallica.bnf.fr/ark:/12148/bpt6k3046j/f432.table|journal= Comptes Rendus|last= Cleve|first=Per Teodor |volume= 89 |date= 1879|pages=419–422|language=fr}}</ref><ref name="Weeks">{{cite book |last1=Weeks |first1=Mary Elvira |title=The discovery of the elements |date=1956 |publisher=Journal of Chemical Education |location=Easton, PA |url=https://archive.org/details/discoveryoftheel002045mbp |edition=6th }}</ref>

Metallic scandium was produced for the first time in 1937 by [[electrolysis]] of a [[eutectic]] mixture of [[potassium]], [[lithium]], and [[scandium chloride]]s, at 700–800&nbsp;°[[Celsius|C]].<ref>{{cite journal|title= Über das metallische Scandium |journal= [[Zeitschrift für anorganische und allgemeine Chemie]]|volume= 231 |issue= 1–2 |date= 1937 |pages= 54–62 |first= Werner|last= Fischer |author2= Brünger, Karl |author3= Grieneisen, Hans|doi= 10.1002/zaac.19372310107|bibcode= 1937ZAACh.231...54F|language=de}}</ref> The first pound of 99% pure scandium metal was produced in 1960. Production of aluminium alloys began in 1971, following a US patent.<ref>Burrell, A. Willey Lower "Aluminum scandium alloy" {{US patent|3,619,181}} issued on November 9, 1971.</ref> Aluminium-scandium alloys were also developed in the [[USSR]].<ref name="Zark">{{cite journal|title= Effect of Scandium on the Structure and Properties of Aluminum Alloys|journal= Metal Science and Heat Treatment|volume= 45|date= 2003|page= 246|doi= 10.1023/A:1027368032062|first= V. V.|last= Zakharov|issue= 7/8|bibcode= 2003MSHT...45..246Z|s2cid= 135389572}}</ref>

Laser crystals of gadolinium-scandium-gallium garnet (GSGG) were used in strategic defense applications developed for the [[Strategic Defense Initiative]] (SDI) in the 1980s and 1990s.<ref>{{cite web|last=Hedrick|first=James B.|title=Scandium|url=http://www.reehandbook.com/scandium.html|work=REEhandbook|publisher=Pro-Edge.com|access-date=2012-05-09|archive-url=https://web.archive.org/web/20120602220148/http://reehandbook.com/scandium.html|archive-date=2012-06-02}}</ref><ref>{{cite journal |url= https://books.google.com/books?id=7cie1S3hpC0C&pg=PA26 |title= Star-wars intrigue greets scandium find |journal= New Scientist |date= 1987 |page= 26 |first= Tony |last= Samstag }}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

==Applications==

===Aluminium alloys===
{{Main|Aluminium–scandium alloys}}
[[File:Mig-29 on landing.jpg|thumb|right |Parts of the [[Mikoyan-Gurevich MiG-29|MiG-29]] are made from Al-Sc alloy.<ref name="Ahmad2003">{{cite journal|doi=10.1007/s11837-003-0224-6|title=The properties and application of scandium-reinforced aluminum|date=2003|first= Zaki|last= Ahmad|journal=JOM|volume=55|page=35|issue=2|bibcode= 2003JOM....55b..35A|s2cid=8956425}}</ref>]]
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 the [[Mikoyan-Gurevich MiG-21]] and [[Mikoyan MiG-29|MiG-29]].<ref name="Ahmad2003" />

The addition of scandium to aluminium limits the grain growth in the heat zone of welded aluminium components. This has two beneficial effects: the precipitated {{chem2|Al3Sc}} forms smaller crystals than in other [[aluminium alloy]]s,<ref name="Ahmad2003" /> and the volume of precipitate-free zones at the grain boundaries of age-hardening aluminium alloys is reduced.<ref name="Ahmad2003" /> The {{chem2|Al3Sc}} precipitate is a coherent precipitate that strengthens the aluminum matrix by applying elastic strain fields that inhibit dislocation movement (i.e., plastic deformation). {{chem2|Al3Sc}} has an equilibrium L1<sub>2</sub> superlattice structure exclusive to this system.<ref>{{Cite journal|last1=Knipling|first1=Keith E.|last2=Dunand|first2=David C.|last3=Seidman|first3=David N.|date=2006-03-01|title=Criteria for developing castable, creep-resistant aluminum-based alloys – A review|url=https://www.hanser-elibrary.com/doi/abs/10.3139/146.101249|journal=Zeitschrift für Metallkunde|volume=97|issue=3|pages=246–265|doi=10.3139/146.101249|s2cid=4681149|issn=0044-3093|url-access=subscription}}</ref> 

A fine dispersion of nano scale precipitate can be achieved via heat treatment that can also strengthen the alloys through order hardening.<ref>{{Cite journal|last1=Knipling|first1=Keith E.|last2=Karnesky|first2=Richard A.|last3=Lee|first3=Constance P.|last4=Dunand|first4=David C.|last5=Seidman|first5=David N.|date=2010-09-01|title=Precipitation evolution in Al–0.1Sc, Al–0.1Zr and Al–0.1Sc–0.1Zr (at.%) alloys during isochronal aging|url=http://www.sciencedirect.com/science/article/pii/S1359645410003393|journal=Acta Materialia|language=en|volume=58|issue=15|pages=5184–5195|doi=10.1016/j.actamat.2010.05.054|bibcode=2010AcMat..58.5184K|issn=1359-6454|url-access=subscription}}</ref> Recent developments include the additions of transition metals such as [[zirconium]] (Zr) and rare earth metals like [[erbium]] (Er) produce shells surrounding the spherical {{chem2|Al3Sc}} precipitate that reduce coarsening.<ref>{{Cite journal|last1=Booth-Morrison|first1=Christopher|last2=Dunand|first2=David C.|last3=Seidman|first3=David N.|date=2011-10-01|title=Coarsening resistance at 400°C of precipitation-strengthened Al–Zr–Sc–Er alloys|url=http://www.sciencedirect.com/science/article/pii/S135964541100543X|journal=Acta Materialia|language=en|volume=59|issue=18|pages=7029–7042|doi=10.1016/j.actamat.2011.07.057|bibcode=2011AcMat..59.7029B|issn=1359-6454|url-access=subscription}}</ref> 

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.<ref>{{Cite journal|last1=De Luca|first1=Anthony|last2=Dunand|first2=David C.|last3=Seidman|first3=David N.|date=2016-10-15|title=Mechanical properties and optimization of the aging of a dilute Al-Sc-Er-Zr-Si alloy with a high Zr/Sc ratio|journal=Acta Materialia|language=en|volume=119|pages=35–42|doi=10.1016/j.actamat.2016.08.018|bibcode=2016AcMat.119...35D|issn=1359-6454|doi-access=free}}</ref> These have made {{chem2|Al3Sc}} somewhat competitive with titanium alloys along with a wide array of applications. However, [[titanium alloy]]s, which are similar in lightness and strength, are cheaper and much more widely used.<ref name="Schwarz2004">{{cite book|url=https://books.google.com/books?id=aveTxwZm40UC&pg=PA2274|page=2274|author=Schwarz, James A.|author2=Contescu, Cristian I.|author3=Putyera, Karol |publisher=CRC Press|date= 2004|isbn=978-0-8247-5049-7|title=Dekker encyclopédia of nanoscience and nanotechnology|volume=3}}</ref>

The alloy {{chem2|Al20Li20Mg10Sc20Ti30}} is as strong as titanium, light as aluminium, and hard as some ceramics.<ref>{{Cite journal |doi = 10.1080/21663831.2014.985855|title = A Novel Low-Density, High-Hardness, High-entropy Alloy with Close-packed Single-phase Nanocrystalline Structures|journal = Materials Research Letters|volume = 3|issue = 2|pages = 95–99|year = 2015|last1 = Youssef|first1 = Khaled M.|last2 = Zaddach|first2 = Alexander J.|last3 = Niu|first3 = Changning|last4 = Irving|first4 = Douglas L.|last5 = Koch|first5 = Carl C.|doi-access = free}}</ref>

Some items of sports equipment, which rely on lightweight high-performance materials, have been made with scandium-aluminium alloys, including [[baseball bat]]s,<ref name="bat">{{cite journal|title= A batty business: Anodized metal bats have revolutionized baseball. But are finishers losing the sweet spot?|journal= Metal Finishing|volume= 104 |page= 61|doi= 10.1016/S0026-0576(06)80099-1|date= 2006|first= Steve|last= Bjerklie|issue= 4}}</ref> tent poles and [[bicycle frame]]s and [[list of bicycle parts|components]].<ref>{{cite web|url= http://www.eastonbike.com/downloadable_files_unprotected/r&d_files/R&D-03%20Scandium.pdf|title= Easton Technology Report: Materials / Scandium|publisher= EastonBike.com|access-date= 2009-04-03}}</ref> [[Lacrosse sticks]] are also made with scandium. The American firearm manufacturing company [[Smith & Wesson]] produces semi-automatic pistols and revolvers with frames of scandium alloy and cylinders of titanium or carbon steel.<ref name="James2004">{{cite book|author=James, Frank|title=Effective handgun defense|url=https://books.google.com/books?id=XT5TRli0OdcC&pg=PA207|access-date=2011-06-08|date=15 December 2004|publisher=Krause Publications|isbn=978-0-87349-899-9|pages=207–}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="Sweeney2004">{{cite book|author=Sweeney, Patrick|title=The Gun Digest Book of Smith & Wesson|url=https://books.google.com/books?id=eBxEBgJBG0MC&pg=PA34|access-date=2011-06-08|date=13 December 2004|publisher=Gun Digest Books|isbn=978-0-87349-792-3|pages=34–}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

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 trademark [[Scalmalloy]] which claims very high strength & ductility.<ref>{{cite web|url = https://www.tctmagazine.com/additive-manufacturing-3d-printing-news/apworks-metal-additive-manufacturing-material-formula-1/ |title = APWORKS' Scalmalloy metal additive manufacturing material approved for use in Formula 1 |date = 2 July 2020 |publisher = TCT |access-date=2023-10-11}}</ref>

===Light sources===
The first scandium-based metal-halide lamps were patented by [[General Electric]] and made in North America, although they are now produced in all major industrialized countries. Approximately 20&nbsp;kg of scandium (as {{chem2|Sc2[[O]]3}}) is used annually in the [[United States]] for high-intensity discharge lamps.<ref name="CRC">Hammond, C. R. in ''CRC Handbook of Chemistry and Physics'' 85th ed., Section 4; The Elements.</ref> One type of [[metal-halide lamp]], similar to the [[mercury-vapor lamp]], is made from [[scandium triiodide]] and [[sodium iodide]]. This lamp is a white-light source with high [[color rendering index]] that sufficiently resembles sunlight to allow good color-reproduction with [[television|TV]] cameras.<ref>{{cite book|title= Lighting Control: Technology and Applications|first= Robert S.|last= Simpson|publisher= Focal Press|date= 2003|isbn= 978-0-240-51566-3|url= https://books.google.com/books?id=GEIhCl2T-2EC&pg=PT147|page= 108}}</ref> About 80&nbsp;kg of scandium is used in metal-halide lamps/light bulbs globally per year.<ref>{{Cite journal |title=Scandium International Mining |url=https://scandiummining.com/site/assets/files/3650/file1.pdf |journal=Hallgarten & Company}}</ref>

Dentists use erbium-chromium-doped yttrium-scandium-gallium garnet ({{chem2|Er,Cr:YSGG}}) lasers for cavity preparation and in endodontics.<ref>{{cite book|chapter-url= https://books.google.com/books?id=vkVY3JwqvrgC&pg=PA464 |pages= 464–465 |chapter= History of Laser Dentistry|title= Lasers in Dermatology and Medicine|isbn= 978-0-85729-280-3|last1= Nouri|first1= Keyvan|date= 2011-11-09|publisher= Springer }}</ref>

===Other===
The [[radioactive isotope]] <sup>46</sup>Sc is used in [[oil refinery|oil refineries]] as a tracing agent.<ref name="CRC" /> [[Scandium triflate]] is a catalytic [[Lewis acid]] used in [[organic chemistry]].<ref>{{cite journal|journal= [[Pure and Applied Chemistry]]|volume= 72|issue= 7|pages= 1373–1380|date= 2000|title= Green Lewis acid catalysis in organic synthesis|first= Shu|last= Kobayashi|author2=Manabe, Kei |url= http://www.iupac.org/publications/pac/2000/7207/7207pdf/7207kobayashi_1373.pdf|doi= 10.1351/pac200072071373|s2cid= 16770637}}</ref>

The 12.4 keV nuclear transition of <sup>45</sup>Sc has been studied as a reference for timekeeping applications, with a theoretical precision as much as three orders of magnitude better than the current [[caesium]] reference clocks.<ref name="Shvyd'ko 2023">{{cite journal |last1=Shvyd'ko |first1=Yuri| last2=Röhlsberger| first2=Ralf |last3=Kocharovskaya |first3=Olga |display-authors=etal |title=Resonant X-ray excitation of the nuclear clock isomer <sup>45</sup>Sc |journal=Nature |volume=622 |date=2023 |issue=7983 |issn=0028-0836  |pmid=37758953 |pmc=10584683 |doi=10.1038/s41586-023-06491-w |pages=471–475|bibcode=2023Natur.622..471S }}</ref>

Scandium has been proposed for use in [[Solid oxide fuel cell|solid oxide fuel cells (SOFCs)]] as a dopant in the electrolyte material, typically [[zirconia| zirconia (ZrO₂)]].<ref>{{cite journal |last1=Mathur |first1=Lakshya |last2=Jeon |first2=Sang-Yun |year=2024 |title=Ternary co-doped ytterbium-scandium stabilized zirconia electrolyte for solid oxide fuel cells |journal=Solid State Ionics |volume=408 |article-number=116507 |doi=10.1016/j.ssi.2024.116507}}</ref> [[Scandium oxide |Scandium oxide (Sc₂O₃)]] is one of several possible additives to enhance the ionic conductivity of the [[zirconia]], improving the overall thermal stability, performance and efficiency of the fuel cell.<ref>{{Cite journal |last=Dokiya |first=Masayuki |date=2002-12-01 |title=SOFC system and technology |url=https://linkinghub.elsevier.com/retrieve/pii/S0167273802003454 |journal=Solid State Ionics |series=PROCEEDINGS OF INTERNATIONAL CONFERENCE ON SOLID STATE IONICS, (MATERIALS AND PROCESSES FOR ENERGY AND ENVIRONMENT), CAIRNS, AUSTRALIA, 8-13 JULY, 2001 |volume=152-153 |pages=383–392 |doi=10.1016/S0167-2738(02)00345-4 |issn=0167-2738|url-access=subscription }}</ref> This application would be particularly valuable in clean energy technologies, as SOFCs can utilize a variety of fuels and have high energy conversion efficiencies.<ref>{{cite journal |first1=Zhishan |last1=Li |first2=Meiting |last2=Guo |year=2024 |title=Utilization of Thermocatalysts in Solid Oxide Fuel Cells (SOFCs) Fed with Hydrogen-Rich Fuels: A Mini-Review |journal=Energy Fuels |volume=38 |issue=12 |pages=10673–10690 |doi=10.1021/acs.energyfuels.4c01609 |bibcode=2024EnFue..3810673L }}</ref>

==Health and safety==
Elemental scandium is considered non-toxic, though extensive animal testing of scandium compounds has not been done.<ref>{{cite book|title= Biochemistry of Scandium and Yttrium|first= Chaim T.|last= Horovitz|author2=Birmingham, Scott D. |publisher= Springer|date= 1999|isbn= 978-0-306-45657-2|url= https://books.google.com/books?id=1ZTQlCWKjmgC}}</ref> The [[median lethal dose]] (LD<sub>50</sub>) levels for [[scandium chloride]] for rats have been determined as 755&nbsp;mg/kg for [[intraperitoneal injection|intraperitoneal]] and 4&nbsp;g/kg for oral administration.<ref>{{cite journal|title= Pharmacology and toxicology of scandium chloride|volume= 51|journal= Journal of Pharmaceutical Sciences|first= Thomas J.|last= Haley|author2= Komesu, L.|author3= Mavis, N.|author4= Cawthorne, J.|author5= Upham, H. C.|doi= 10.1002/jps.2600511107|date= 1962|pmid=13952089|issue= 11|pages= 1043–5|bibcode= 1962JPhmS..51.1043H}}</ref> 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 to [[gallium]], with similar hazards involving its poorly soluble [[scandium(III) hydroxide|hydroxide]].<ref>{{Cite journal |last=Ganrot |first=P. O. |date=1986 |title=Metabolism and Possible Health Effects of Aluminum |journal=Environmental Health Perspectives |volume=65 |pages=363–441 |doi=10.2307/3430204 |jstor=3430204 |pmid=2940082 |pmc=1474689 |issn=0091-6765}}</ref>

==Notes==
{{Notelist}}

==References==
{{Reflist|30em}}

==Further reading==
{{Library resources box|onlinebooks=yes}}
*{{cite book |first=Eric R. |last=Scerri |title=The Periodic System: Its Story and Its Significance |publisher=Oxford University Press |location=Oxford, UK |date=2007 |oclc=62766695 |isbn=978-0-19-530573-9 |url=https://books.google.com/books?id=yPtSszJMOO0C}}

==External links==
{{Wiktionary}}
{{Commons}}
*[http://www.periodicvideos.com/videos/021.htm Scandium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
*[http://www.webelements.com/webelements/elements/text/Sc/index.html WebElements.com – Scandium]
*{{cite EB1911|wstitle=Scandium |short=x}}

{{Scandium compounds}}
{{Periodic table (navbox)}}
{{Authority control}}
{{Good article}}

[[Category:Scandium| ]]
[[Category:Chemical elements]]
[[Category:Transition metals]]
[[Category:Chemical elements with hexagonal close-packed structure]]
[[Category:Chemical elements predicted by Dmitri Mendeleev]]