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Scandium, 21Sc
Two samples of rounded dark gray scandium crystals and a metal cube of the same material
Scandium
Pronunciation/ˈskændiəm/ ⓘ ​(SKAN-dee-əm)
Appearancesilvery white
Standard atomic weight Ar°(Sc)
Scandium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
–
↑
Sc
↓
Y
calcium ← scandium → titanium
Atomic number (Z)21
Groupgroup 3
Periodperiod 4
Block  d-block
Electron configuration[Ar] 3d1 4s2
Electrons per shell2, 8, 9, 2
Physical properties
Phase at STPsolid
Melting point1814 K ​(1541 °C, ​2806 °F)
Boiling point3109 K ​(2836 °C, ​5136 °F)
Density (at 20° C)2.989 g/cm3 [3]
when liquid (at m.p.)2.80 g/cm3
Heat of fusion14.1 kJ/mol
Heat of vaporization332.7 kJ/mol
Molar heat capacity25.52 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1645 1804 (2006) (2266) (2613) (3101)
Atomic properties
Oxidation statescommon: +3
0,[4] +1,[5] +2[6]
ElectronegativityPauling scale: 1.36
Ionization energies
  • 1st: 633.1 kJ/mol
  • 2nd: 1235.0 kJ/mol
  • 3rd: 2388.6 kJ/mol
  • (more)
Atomic radiusempirical: 162 pm
Covalent radius170±7 pm
Van der Waals radius211 pm
Color lines in a spectral range
Spectral lines of scandium
Other properties
Natural occurrenceprimordial
Crystal structure ​hexagonal close-packed (hcp) (hP2)
Lattice constants
Hexagonal close packed crystal structure for scandium
a = 330.89 pm c = 526.80 pm (at 20 °C)[3]
Thermal expansion9.97×10−6/K (at 20 °C)[a]
Thermal conductivity15.8 W/(m⋅K)
Electrical resistivityα, poly: 562 nΩ⋅m (at r.t., calculated)
Magnetic orderingparamagnetic
Molar magnetic susceptibility+315.0×10−6 cm3/mol (292 K)[7]
Young's modulus74.4 GPa
Shear modulus29.1 GPa
Bulk modulus56.6 GPa
Poisson ratio0.279
Brinell hardness736–1200 MPa
CAS Number7440-20-2
History
Namingafter Scandinavia
PredictionDmitri Mendeleev (1871)
DiscoveryLars Fredrik Nilson (1879)
First isolationW. Fischer, K. Brünger, H. Grieneisen (1937)
Isotopes of scandium
Main isotopes[8] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
43Sc synth 3.891 h β+ 43Ca
44Sc synth 4.042 h β+ 44Ca
44m3Sc synth 58.61 h IT 44Sc
β+ 44Ca
45Sc 100% stable
46Sc synth 83.757 d β− 46Ti
47Sc synth 3.3492 d β− 47Ti
48Sc synth 43.67 h β− 48Ti
 Category: Scandium
| references

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,[9] together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.[10]

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.[11]

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

[edit]

Chemical characteristics

[edit]

Scandium is a soft metal with a silvery appearance. It develops a slightly yellowish or pinkish cast when 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 (HNO3) and 48.0% hydrofluoric acid (HF), possibly due to the formation of an impermeable passive layer. Scandium turnings ignite in the air with a brilliant yellow flame to form scandium oxide.[12]

Isotopes

[edit]
Main article: Isotopes of scandium

In nature, scandium is found exclusively as the isotope 45Sc, which has a nuclear spin of 7⁄2; this is its only stable isotope.[13]

The known isotopes of scandium range from 37Sc to 63Sc,[8] and the most stable radioisotopes are 46Sc with a half-life of 83.76 days, 47Sc with a half-life of 3.3492 days, 48Sc at 43.67 hours, 44Sc at 4.042 hours, and 43Sc 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 44m3Sc with half-life 58.6 hours; this is the lightest isotope with a long-lived isomer.

The low mass isotopes are very difficult to create.[13] The initial detection of 37Sc and 38Sc only resulted in the characterization of their mass excess.[14][15]

The primary decay mode of ground-state scandium isotopes at masses lower than the only stable isotope, 45Sc, is electron capture (or positron emission), but the lightest isotopes (37Sc to 39Sc) undergo proton emission instead, all three of these producing calcium isotopes. The primary decay mode for heavier isotopes is beta emission, producing titanium isotopes.[8]

Occurrence

[edit]

In Earth's crust, scandium is not rare. Estimates vary from 18 to 25 ppm, which is comparable to the abundance of cobalt (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 the Sun[16] and the 26th most abundant element in the stars.[17] However, scandium is distributed sparsely and occurs in trace amounts in many minerals.[18] Rare minerals from Scandinavia[19] and Madagascar[20] 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.[19]

The stable form of scandium is created in supernovae via the r-process.[21] Also, scandium is created by cosmic ray spallation of the more abundant iron-peak nuclei. Example reactions are:

  • 28Si + 17n → 45Sc (r-process)
  • 56Fe + p → 45Sc + 11C + n (cosmic ray spallation)

Production

[edit]

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,[22] 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] Since then, many other countries have built scandium-producing facilities, including 5 tonnes/year (7.5 tonnes/year Sc2O3) by Nickel Asia Corporation and Sumitomo Metal Mining in the Philippines.[23][24] In the United States, NioCorp Development hopes[when?] to raise $1 billion[25] toward opening a niobium mine at its Elk Creek site in southeast Nebraska,[26] which may be able to produce as much as 95 tonnes of scandium oxide annually.[27] In each case, scandium is a byproduct of the extraction of other elements and is sold as scandium oxide.[28][29][30]

To produce metallic scandium, the oxide is converted to scandium fluoride and then reduced with metallic calcium.[31]

  • Sc2O3 + 6HF → 2ScF3 + 3H2O
  • 2ScF3 + 3Ca → 3CaF2 + 2Sc

Madagascar and the Iveland-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.[29] The mineral kolbeckite ScPO4·2H2O has a very high scandium content but is not available in any larger deposits.[29]

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.[32] Scandium-stabilized zirconia enjoys a growing market demand for use as a high-efficiency electrolyte in solid oxide fuel cells.[citation needed]

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.[33]

Compounds

[edit]
See also the categories Scandium compounds and Scandium minerals

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.[34]

Ionic radius (pm)
Al Sc Y La Lu
53.5 74.5 90.0 103.2 86.1

Oxides and hydroxides

[edit]

The oxide Sc
2O
3 and the hydroxide Sc(OH)
3 are amphoteric:[35]

Sc(OH)
3 + 3 OH−
 → [Sc(OH)
6]3−
 (scandate ion)
Sc(OH)
3 + 3 H+
 + 3 H
2O → [Sc(H
2O)
6]3+

α- and γ-ScOOH are isostructural with their aluminium hydroxide oxide counterparts.[36] Solutions of Sc3+
 in water are acidic due to hydrolysis.

Halides and pseudohalides

[edit]

The halides ScX3, where X= Cl, Br, or I, are very soluble in water, but ScF3 is insoluble. In all four halides, the scandium is 6-coordinated. The halides are Lewis 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 a Lewis acid catalyst in organic chemistry.[37]

Organic derivatives

[edit]
Main article: Organoscandium chemistry

Scandium forms a series of organometallic compounds with cyclopentadienyl ligands (Cp), similar to the behavior of the lanthanides. One example is the chlorine-bridged dimer, [ScCp2Cl]2 and related derivatives of pentamethylcyclopentadienyl ligands.[38]

Uncommon oxidation states

[edit]

Compounds that feature scandium in oxidation states other than +3 are rare but well characterized. The blue-black compound CsScCl3 is one of the simplest. This material adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers.[39] Scandium hydride is not well understood, although it appears not to be a saline 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 are non-stoichiometric, as is typical for neighboring elements.[40]

Lower oxidation states (+2, +1, 0) have also been observed in organoscandium compounds.[41][4][42][43]

History

[edit]

Dmitri Mendeleev, who is referred to as the father of the periodic table, predicted the existence of an element ekaboron, with an atomic mass between 40 and 48 in 1869. Lars Fredrik Nilson and his team detected this element in the minerals euxenite and gadolinite in 1879. Nilson prepared 2 grams of scandium oxide of high purity.[44][45] 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.[46][47]

Metallic scandium was produced for the first time in 1937 by electrolysis of a eutectic mixture of potassium, lithium, and scandium chlorides, at 700–800 °C.[48] The first pound of 99% pure scandium metal was produced in 1960. Production of aluminium alloys began in 1971, following a US patent.[49] Aluminium-scandium alloys were also developed in the USSR.[50]

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.[51][52]

Applications

[edit]

Aluminium alloys

[edit]
Main article: Aluminium–scandium alloys
Parts of the MiG-29 are made from Al-Sc alloy.[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 the Mikoyan-Gurevich MiG-21 and MiG-29.[53]

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 Al3Sc forms smaller crystals than in other aluminium alloys,[53] and the volume of precipitate-free zones at the grain boundaries of age-hardening aluminium alloys is reduced.[53] The Al3Sc 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.[54]

A fine dispersion of nano scale precipitate can be achieved via heat treatment that can also strengthen the alloys through order hardening.[55] Recent developments include the additions of transition metals such as zirconium (Zr) and rare earth metals like erbium (Er) produce shells surrounding the spherical Al3Sc precipitate that reduce coarsening.[56]

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.[57] These have made Al3Sc 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.[58]

The alloy Al20Li20Mg10Sc20Ti30 is as strong as titanium, light as aluminium, and hard as some ceramics.[59]

Some items of sports equipment, which rely on lightweight high-performance materials, have been made with scandium-aluminium alloys, including baseball bats,[60] tent poles and bicycle frames and components.[61] 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.[62][63]

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.[64]

Light sources

[edit]

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 kg of scandium (as Sc2O3) is used annually in the United States for high-intensity discharge lamps.[65] 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 TV cameras.[66] About 80 kg of scandium is used in metal-halide lamps/light bulbs globally per year.[67]

Dentists use erbium-chromium-doped yttrium-scandium-gallium garnet (Er,Cr:YSGG) lasers for cavity preparation and in endodontics.[68]

Other

[edit]

The radioactive isotope 46Sc is used in oil refineries as a tracing agent.[65] Scandium triflate is a catalytic Lewis acid used in organic chemistry.[69]

The 12.4 keV nuclear transition of 45Sc 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.[70]

Scandium has been proposed for use in solid oxide fuel cells (SOFCs) as a dopant in the electrolyte material, typically zirconia (ZrO₂).[71] 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.[72] This application would be particularly valuable in clean energy technologies, as SOFCs can utilize a variety of fuels and have high energy conversion efficiencies.[73]

Health and safety

[edit]

Elemental scandium is considered non-toxic, though extensive animal testing of scandium compounds has not been done.[74] The median lethal dose (LD50) levels for scandium chloride for rats have been determined as 755 mg/kg for intraperitoneal and 4 g/kg for oral administration.[75] 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 hydroxide.[76]

Notes

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References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Scandium

View on Grokipedia
from Grokipedia
Scandium is a with the symbol Sc and 21. It is a soft, silvery-white that serves as the first element in the third period of the d-block in the periodic table. Discovered in 1879 by Swedish chemist Lars Fredrik Nilson through spectral analysis of the minerals euxenite and , scandium was named after Scandia, the Latin name for , where the discovery minerals originated. Although classified as a alongside and the s due to similar chemical properties, scandium is not part of the lanthanide series and is relatively abundant in the at approximately 22 parts per million (ppm), making it the 31st most common element by crustal abundance. It occurs primarily in trace amounts dispersed in over 800 mineral species, including rare earth-bearing minerals like and , but is rarely concentrated enough for direct ; commercial production is limited, with global output of approximately 30–40 metric tons in 2023 (rising to about 40 tons in 2024), mainly as a by-product of , , or rare earth processing. Scandium's notable properties include a low of 2.99 g/cm³, a high of 1,541 °C, and excellent compatibility with aluminum, enabling the formation of strong, corrosion-resistant alloys that reduce weight in components by up to 20% compared to conventional materials. Key applications include scandium-aluminum alloys for frames and sporting equipment, scandium-stabilized zirconia in oxide fuel cells for efficient energy conversion, and scandium iodide in metal halide lamps for high-intensity lighting in stadiums and . Emerging also explores its role in catalysts for and electronics due to its +3 and low toxicity relative to other rare earths. As of 2025, governments including the U.S. and are investing in domestic scandium production to secure supply chains for and defense.

Properties

Physical properties

Scandium is a soft, silvery-white that develops a yellowish or pinkish cast upon exposure to air due to surface oxidation. It is relatively among metals, with a of 2.99 g/cm³ at 20°C, making it comparable to aluminum in mass but stronger in certain alloys. The element exhibits a high of 1541 °C (1814 K) and a of 2836 °C (3109 K), indicating significant thermal stability suitable for high-temperature applications. In its solid state at , scandium adopts a hexagonal close-packed (hcp) crystal structure with lattice parameters a = 330.9 pm and c = 526.8 pm at 20°C. This structure contributes to its and malleability, though scandium is softer than many transition metals, with a Mohs hardness of approximately 2.5. Mechanically, it has a of 74 GPa, reflecting moderate stiffness, and a of 0.279. Scandium demonstrates good thermal conductivity of 15.8 W/(m·K) at 300 K, which supports its use in heat-resistant materials. Its electrical resistivity is 562 nΩ·m at , indicating moderate conductivity for a metal. The coefficient of is 10.2 × 10⁻⁶ K⁻¹, showing low expansion under heat.
PropertyValueConditions/Source
Atomic radius (empirical)162 pmRSC Periodic Table
Covalent radius170 pmPeriodictable.com
Heat of fusion14.1 kJ/molLenntech
Heat of vaporization352 kJ/molRSC Periodic Table
Molar heat capacity28.33 J/(mol·K)RSC Periodic Table

Chemical properties

Scandium, as the first member of the transition metals, displays chemical behavior influenced by its electron configuration of [Ar] 3d¹ 4s², which allows it to readily lose three electrons to achieve the stable +3 oxidation state in most compounds. This +3 state is the predominant and most stable oxidation state observed in scandium chemistry, particularly in aqueous solutions, although unstable +2 and +0 states have been noted in certain organoscandium complexes. The first ionization energy of scandium is 633.1 kJ/mol, the second is 1235.0 kJ/mol, and the third is 2388.7 kJ/mol, reflecting the energy required to successively remove electrons from the neutral atom, Sc⁺, and Sc²⁺ ions. Scandium's electronegativity is 1.36 on the Pauling scale, indicating moderate electron-attracting power consistent with its position in the periodic table. The metal itself is chemically reactive, tarnishing in moist air to form a thin layer of scandium (Sc₂O₃) with a yellowish or pinkish tint, and it slowly dissolves in dilute acids—such as hydrochloric or —to produce scandium salts and gas, though it resists due to passivation by the . Scandium reacts with , especially when heated, liberating and forming scandium(III) (Sc(OH)₃), and the finely powdered form is pyrophoric, igniting spontaneously in air. These reactions underscore scandium's affinity for oxygen and , leading to the formation of stable ionic compounds where the Sc³⁺ predominates, exhibiting a of typically six in octahedral geometry. Compounds of scandium bridge the properties of aluminum and the lanthanides, with scandium oxide being amphoteric—dissolving in both acids to form scandium salts and in strong bases to yield scandates—while halides like scandium chloride (ScCl₃) and fluoride (ScF₃) are highly ionic and hygroscopic. In , scandium forms complexes such as cyclopentadienyl derivatives (e.g., Cp₃Sc), which are used to study early , though scandium's limited availability restricts widespread application. Overall, scandium's chemistry is less diverse than that of heavier s due to the absence of accessible higher oxidation states beyond +3.

Isotopes

Scandium occurs naturally as a single stable isotope, ^{45}Sc, which makes up 100% of all scandium found in nature and has an atomic mass of 44.955908 u. This monoisotopic composition results in a standard atomic weight of 44.955908(5) for the element. Numerous radioactive isotopes of scandium have been produced artificially, spanning mass numbers from ^{37}Sc to ^{63}Sc, with over 25 known in total. These isotopes decay primarily via beta emission, electron capture, or alpha decay, with half-lives ranging from microseconds to days. The longest-lived among them is ^{46}Sc, which decays by beta emission to stable ^{46}Ti with a half-life of 83.8 days. Other notable isotopes include ^{47}Sc (half-life 3.35 days, beta decay to ^{47}Ti) and ^{44}Sc (half-life 4.04 hours, positron emission and electron capture to ^{44}Ca). Radioactive scandium isotopes find applications in tracing and due to their decay properties. For instance, ^{46}Sc is used as a tracer in oil refining processes to monitor fraction movement and in via gamma emission. Short-lived positron-emitting isotopes like ^{43}Sc ( 3.89 hours) and ^{44}Sc are promising for (PET) imaging, offering higher resolution than longer-lived alternatives while matching scandium's chemistry for targeted . Therapeutic potential exists for ^{47}Sc, which emits medium-energy beta particles suitable for targeted in , with its allowing sufficient time for distribution. The following table summarizes key properties of selected scandium isotopes:
IsotopeHalf-lifePrimary Decay ModeNotable Applications
^{45}ScN/ANatural abundance, alloys
^{46}Sc83.8 daysβ⁻ (to ^{46}Ti)Industrial tracing (oil, pipes)
^{47}Sc3.35 daysβ⁻ (to ^{47}Ti)
^{44}Sc4.04 hoursβ⁺, EC (to ^{44}Ca)PET imaging
^{43}Sc3.89 hoursβ⁺, EC (to ^{43}Ca)PET imaging

Occurrence and production

Natural occurrence

Scandium is the 31st most abundant element in , with an estimated concentration of 18 to 25 parts per million (ppm), making it more abundant than lead but less so than common metals like or . It occurs primarily as a substituting for larger ions such as aluminum, iron, or magnesium in common rock-forming minerals like amphiboles, pyroxenes, and feldspars, rather than forming concentrated deposits. This dispersed distribution results from scandium's geochemical behavior, which favors incorporation into and ultramafic igneous rocks during magmatic processes but limits its concentration in typical ore-forming environments. Although scandium is present in over 800 species in trace amounts, it rarely forms distinct scandium-dominant minerals due to its and compatibility with other elements. The primary scandium is thortveitite, (Sc,Y)₂Si₂O₇, a rare found in granitic pegmatites, where it can contain up to 45% scandium . Other notable scandium-bearing s include bazzite, Be₃(Sc,Al)₂Si₆O₁₈, a beryl-group , and wiikite, a variety of eudialyte enriched in scandium. These minerals occur sporadically in alkaline igneous settings, but their low abundance and small deposit sizes make direct extraction uneconomical. Commercially, scandium is recovered as a by-product from processing of other ores, particularly those containing rare earth elements, , , and , where it substitutes into minerals like and or oxide minerals in carbonatites. Major sources include magmatic deposits in mafic-ultramafic intrusions, which account for approximately 90% of identified global resources, and sedimentary deposits. Significant occurrences are reported in (e.g., Bayan Obo carbonatite), (thortveitite in pegmatites), , , , and the (e.g., aluminum- deposits in and pegmatites in ). Global resources are estimated to exceed 1 million tons, but economic extraction remains limited due to low concentrations, typically below 100 ppm in host rocks.

Commercial production

Scandium is commercially produced almost exclusively as a byproduct of the processing of other metals, with no large-scale primary mining operations currently in place. Global production was approximately 40 metric tons of scandium oxide equivalent in 2024, primarily in China, which accounts for the majority of supply through recovery from iron ore, rare earth, titanium, and zirconium processing streams, including a new facility in Tangshan with 20 tons per year capacity. Other notable sources include nickel-cobalt laterite processing in the Philippines and Russia, uranium extraction in Kazakhstan and Russia, and apatite processing in Russia. In the Philippines, the Taganito HPAL plant recovered about 7 to 8 tons of scandium oxide equivalent in 2024. In Canada, a facility in southwestern Quebec produced 3 tons per year as of 2024, with expansion planned to 12 tons by the end of 2025. This byproduct nature limits production scalability, as scandium recovery depends on the economics of the primary metal operations. The primary commercial recovery method involves hydrometallurgical processes applied to leach solutions or residues from host metal extractions. For instance, in high-pressure acid leaching (HPAL) of laterites, scandium is solubilized alongside and , followed by selective separation using solvent extraction with organophosphorus extractants such as di-(2-ethylhexyl) (D2EHPA) or primary amine extractants. The extracted scandium is then precipitated as or , calcined to scandium (Sc₂O₃), and further reduced to metal using calcium or magnesium in a . A key example is the Taganito HPAL plant in the , operated by Taganito Mining Corp. (a of Sumitomo Metal Mining Co.), which has been commercially recovering scandium since 2017, producing up to 7.5 metric tons of scandium equivalent annually from process streams. In , scandium is recovered from production wastes and rare earth using similar acid leaching and solvent extraction techniques, often achieving recovery rates of 80-95% under optimized conditions with sulfuric or leaching followed by multistage extraction. Russian production, primarily from and processing, employs ion-exchange resins or solvent extraction to isolate scandium from phosphate-rich liquors, contributing an estimated 10-15 tons annually. These methods prioritize efficiency in streams where scandium concentrations are low (typically 10-100 ppm), emphasizing selective separation to avoid contamination with other rare earths or transition metals. Emerging efforts aim to establish primary scandium production to meet growing demand for alloys and fuel cells, but as of 2025, no such facilities are fully commercial at scale. Projects like Australia's Cummins Range deposit and Canada's project focus on direct scandium extraction from scandium-rich minerals such as thortveitite or via flotation, acid leaching, and advanced solvent extraction, potentially scaling to 10-20 tons per year if developed. However, current commercial output remains tied to byproduct recovery, with ongoing research into sustainable methods like or supercritical extraction to improve yields from and byproducts.

History

Discovery

The existence of scandium was first predicted by Russian chemist in 1871, as part of his development of the periodic table. He referred to it as "eka-boron," anticipating an element with an atomic weight around 44, positioned between calcium and , and exhibiting chemical properties akin to , such as forming an oxide of the formula X₂O₃. Scandium was discovered in 1879 by Swedish chemist Lars Fredrik Nilson at . Nilson identified the element while analyzing rare earth extracts from Scandinavian minerals, particularly euxenite and , which had been sourced from localities in and . By processing about 10 kilograms of these minerals, he isolated roughly 2 grams of scandium (Sc₂O₃), confirming its presence as a new through spectroscopic analysis and chemical separation techniques. Shortly after Nilson's announcement, fellow Swedish chemist Per Teodor Cleve independently verified the discovery and noted its close alignment with Mendeleev's eka-boron prediction, including the atomic weight (approximately 44) and oxide formula. This confirmation provided early empirical validation for Mendeleev's periodic system. Nilson named the element scandium in honor of , deriving from the Latin Scandia.

Etymology and early development

The name scandium originates from the Latin word Scandia, referring to , the region where minerals containing the element were first identified. Swedish chemist Lars Fredrik Nilson, who discovered the element in 1879, chose this name to honor his homeland, as the discovery stemmed from spectroscopic analysis of Scandinavian mineral samples such as euxenite and . Following its discovery, early development of scandium focused primarily on isolating and characterizing its compounds rather than the pure metal, due to the element's rarity and the challenges in extraction. Nilson successfully prepared approximately 2 grams of high-purity scandium oxide (Sc₂O₃), which he described in his 1879 paper, confirming its chemical properties through atomic weight determination and spectral lines. Independently, Swedish chemist Per Teodor Cleve verified Nilson's findings the same year by isolating scandium from euxenite and demonstrating that it matched the properties predicted by as "eka-boron" in his periodic table. Progress toward metallic scandium was slow until the . In 1937, German chemists Werner Fischer, Karl Brünger, and Hans Grieneisen achieved the first production of the metal via of a eutectic mixture of , , and scandium chlorides at 700–800 °C, yielding small quantities for initial property studies. This breakthrough enabled further research into scandium's physical characteristics, though large-scale purification remained elusive until 1960, when the first 0.45 kg (1 pound) of 99% pure scandium metal was produced by reduction methods.

Compounds

Oxides and hydroxides

Scandium(III) oxide, Sc₂O₃, also known as scandia, is the primary oxide of scandium and exists as a white, odorless powder with a high of 2485 °C. It is insoluble in and adopts a cubic in the Ia-3 , featuring two inequivalent Sc³⁺ sites coordinated by oxygen atoms in a three-dimensional network similar to other rare earth sesquioxides. This structure contributes to its thermal stability and use in high-temperature applications. Sc₂O₃ is synthesized industrially by calcining scandium or other scandium salts at elevated temperatures, often above 800 °C, to achieve purities exceeding 99.9%. For instance, precipitation of scandium with followed by yields nanoscale Sc₂O₃ particles. Chemically, Sc₂O₃ exhibits basic properties characteristic of group 3 metal oxides, reacting readily with acids to form scandium salts but showing limited reactivity with bases. Its basicity is moderate compared to and oxides, as evidenced by solubility studies in acidic media where it dissolves to form Sc³⁺ ions. The oxide can also be deposited as thin films via (ALD) using precursors like scandium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) and , producing high-purity layers with low carbon and hydrogen content suitable for optical coatings. These films are transparent to wavelengths down to 225 nm and possess high refractive indices, highlighting the material's optical utility. Scandium(III) hydroxide, conventionally represented as Sc(OH)₃, forms as a white gelatinous precipitate upon adding bases like to aqueous scandium(III) solutions at values as low as 4.8–5.0. It is amphoteric, dissolving in both strong acids to yield Sc³⁺ and in concentrated alkalis to form hydroxo complexes such as [Sc(OH)₄]⁻, akin to aluminum . The compound is slightly soluble in , with a saturated solution at approximately 7.85 containing primarily Sc(OH)₃ and minor Sc(OH)₂⁺ species. Structural analyses indicate that the initial precipitate may not be a stoichiometric trihydroxide but rather an oxyhydroxide like ScOOH, which is well-established and stable under ambient conditions. Upon heating, Sc(OH)₃ or ScOOH dehydrates stepwise: first to rhombohedral ScOOH around 300–400 °C, and then to cubic Sc₂O₃ at 430–460 °C, depending on particle size and synthesis conditions. This thermal behavior is exploited in the preparation of pure scandium oxide from hydroxide precursors.

Halides and pseudohalides

Scandium predominantly forms trihalide compounds of the formula ScX₃ (X = F, Cl, Br, I) in its stable +3 , reflecting its group 3 position and lanthanide-like behavior. These halides are ionic solids with scandium cations octahedrally coordinated by six anions, leading to high lattice energies due to the small size and high of Sc³⁺. The structural properties of the , , and salts have been extensively reviewed, revealing a progression from more compact forms to hydrated structures in aqueous environments. For instance, ScCl₃ adopts a layered with ScCl₆ octahedra sharing edges, while hydrated forms like ScCl₃·6H₂O exhibit a more discrete [Sc(H₂O)₆]³⁺ cation surrounded by counterions. Scandium trifluoride (ScF₃) is a , crystalline solid with a rhombohedral structure ( R3̄c) in which each Sc³⁺ is coordinated to six F⁻ ions, forming a distorted octahedral ; this compound is sparingly soluble in (approximately 0.001 g/100 mL at 25°C) but dissolves readily in solutions containing excess to form the hexafluoroscandate(III) complex [ScF₆]³⁻, demonstrating its Lewis acidity. In contrast, the other trihalides—ScCl₃, ScBr₃, and ScI₃—are highly soluble in , forming aquated [Sc(H₂O)₆]³⁺ ions that undergo to produce acidic solutions due to the high of Sc³⁺. These soluble halides can be prepared by direct reaction of scandium metal with the corresponding gas or by from aqueous solutions. The chlorides, bromides, and iodides crystallize in hexagonal or orthorhombic structures, with increasing anion size leading to larger unit cells and weaker Sc–X bonding, as evidenced by decreasing melting points from ScCl₃ (945°C) to ScI₃ (approximately 920°C). All scandium trihalides exhibit Lewis acid behavior, readily forming complexes with additional ligands such as water, ammonia, or excess halide ions; for example, ScCl₃ reacts with to yield [ScCl₄(NH₃)₂]⁻ . Reduced scandium halides, such as Sc₇Cl₁₀ and ScCl, feature metal-metal bonding and cluster structures, but these are less common and typically synthesized under high-temperature or reducing conditions for specialized studies in . Pseudohalides of scandium, which mimic behavior through ligands like dicyanamide [N(CN)₂]⁻, tricyanomethanide [C(CN)₃]⁻, and [SCN]⁻, are less studied but form coordination compounds or double salts. Scandium dicyanamido complexes, such as [Sc(N(CN)₂)₃(H₂O)₃], adopt polymeric structures with bridging pseudohalide ligands and octahedral Sc³⁺ centers, synthesized via metathesis reactions in aqueous media. Similarly, scandium tricyanomethanides like Sc[C(CN)₃]₃(H₂O)₃ crystallize in monoclinic space groups with the pseudohalide acting as a monodentate , exhibiting Raman spectra indicative of weak Sc–C bonding. Thiocyanate appears in double salts, for instance, [Sc₂(μ-C₆H₅NO₂)₃(C₆H₄NO₂)₃][Cr(SCN)₆], where the [Cr(SCN)₆]³⁻ anion provides the pseudohalide framework, highlighting scandium's role in cationic coordination polymers. These compounds underscore scandium's affinity for soft pseudohalide donors, though they remain niche compared to the halides.

Organic derivatives

Scandium forms a variety of organometallic compounds, primarily featuring carbon-scandium bonds with ligands such as cyclopentadienyl (Cp), alkyl, or amidinate groups, which are typically air- and moisture-sensitive due to the metal's high reactivity. These derivatives often exhibit Lewis acidity and have been explored for catalytic applications in , though scandium's early nature limits the stability of low-oxidation-state species compared to later metals. One of the earliest and most studied classes includes cyclopentadienyl-based complexes. For instance, bis(cyclopentadienyl)scandium chloride, (C₅H₅)₂ScCl, is synthesized by reacting scandium trichloride with magnesium cyclopentadienide in , yielding a yellow-green, moisture-sensitive solid that serves as a precursor for further derivatization. Related compounds incorporate substituted cyclopentadienyl ligands, such as pentamethylcyclopentadienyl (Cp*), to enhance steric protection and stability, enabling the formation of alkyl or allyl derivatives for olefin catalysis. Additionally, scandium complexes with η⁸-cyclooctatetraenyl (C₈H₈) ligands demonstrate unique sandwich structures, highlighting scandium's ability to accommodate multidentate π-systems. Alkyl-substituted organoscandium compounds represent another key category, often supported by ancillary s like β-diketiminates or salicylaldiminates to achieve dialkyl configurations. Dialkylscandium complexes with bulky β-diketiminato s are prepared via salt metathesis from scandium chloride precursors and alkyls, revealing distorted tetrahedral geometries with out-of-plane ligand coordination due to scandium's small ; these undergo facile β-hydride elimination, underscoring their reactivity. Similarly, organoscandium alkyl complexes, synthesized from aldimine-supported scandium alkyls, exhibit rapid 1,3-migration of alkyl groups to the carbon at , providing insights into migratory aptitude in early chemistry. Beyond simple alkyls and Cp derivatives, scandium forms complexes with mixed donor ligands, such as amidinates combined with Cp, yielding anionic terminal imido species that display synergistic electronic effects for stabilizing high-oxidation states. These organic derivatives collectively illustrate scandium's coordination preferences, favoring three-coordinate or pseudo-tetrahedral environments, and have contributed to advancements in asymmetric and small-molecule , though challenges in handling their sensitivity persist.

Uncommon oxidation states

While the +3 oxidation state dominates scandium chemistry due to its stable [Ar] configuration after loss of the 4s² and 3d¹ electrons, lower oxidation states (+2, +1, and 0) occur in specialized compounds, often stabilized by metal-metal bonding or bulky ligands in reduced halides and organometallics. These states are unstable in aqueous or oxidative environments and require inert conditions for isolation. The +2 state is represented in inorganic halides like CsScCl₃, a blue-black solid obtained by reducing ScCl₃ with scandium metal in molten CsCl, featuring infinite chains of edge-sharing ScCl₆ octahedra with short Sc-Sc bonds (approximately 3.0 Å) indicative of metal-metal interaction. Similar structures appear in KScCl₃ and Cs₃Sc₂Cl₉, where the latter contains discrete Sc₂Cl₉³⁻ units with a Sc-Sc bond and average Sc of +2.5. In organometallic contexts, +2 scandium is stabilized by β-diketiminate or cyclopentadienyl ligands, as in (BDI)ScR (BDI = β-diketiminate; R = alkyl), enabling reactivity in C-H activation. The +1 state is rarer and confined to organometallic species, such as mononuclear complexes with phosphacyclopentadienyl ligands like [Sc(P₃C₂tBu₂)₂]₂, which may exhibit mixed +1/+2 character but demonstrate formal +1 behavior through electron-rich environments. These compounds are highly air-sensitive and studied for their potential in reductive transformations. Zero-valent scandium appears in arene-bridged complexes, pioneered by Cloke et al., such as [Sc(η⁶-C₆H₃-2,5-(CHMe₂)₂)₂] and related π-bound species with or , where the metal engages in back-bonding to achieve a formally neutral state. These volatile, pyrophoric compounds, often prepared via reduction of Sc(III) precursors, highlight scandium's ability to mimic lanthanide-like low-valent chemistry despite its d-block position.

Applications

Alloys

Scandium is primarily utilized as an alloying element in aluminum-based alloys, where even small additions of 0.1–0.5 wt% significantly enhance mechanical without compromising or adding substantial weight. These aluminum-scandium (Al-Sc) alloys exhibit superior tensile strength, with yield strength increases of up to 150% in 5000-series alloys when 0.25% scandium is added, due to the formation of fine, coherent Al₃Sc precipitates that refine grain structure and inhibit recrystallization. Additionally, scandium improves by strengthening weld zones and eliminating hot cracking tendencies, while boosting resistance and fatigue life, making these alloys outperform traditional high-strength aluminum variants like those reinforced with or . The enhanced properties of Al-Sc alloys stem from scandium's role in promoting equiaxed, fine-grained microstructures during casting and processing, which contribute to better formability and thermal stability up to 300°C. For instance, additions of 0.1% scandium can raise tensile strength by approximately 50 MPa per increment, enabling lightweight components that maintain structural integrity under high stress. These attributes have positioned Al-Sc alloys as a cornerstone in applications, including airframes, bulkheads, and heat shields for like Russia's MiG fighters during the era, where they provided a strength-to-weight ratio superior to conventional aluminum. Beyond aerospace, they find use in automotive extrusions for crash management, marine heat exchangers for , and sporting goods such as frames and bats, leveraging their resistance and durability. While Al-Sc dominates scandium's alloy applications, emerging uses include magnesium-scandium (Mg-Sc) alloys, which incorporate 5–10 wt% scandium to improve high-temperature creep resistance, suitable for structural parts. Scandium also features in titanium-scandium (Ti-Sc) alloys for high-temperature components, enhancing strength and oxidation resistance, and in combining scandium with elements like , magnesium, and to achieve densities comparable to aluminum but with steel-like strength. These niche applications highlight scandium's versatility, though production remains limited by its rarity and cost, confining widespread adoption to high-value sectors.

Light sources and ceramics

Scandium compounds, particularly scandium iodide (ScI₃), play a crucial role in metal halide lamps, a type of high-intensity discharge lighting. These lamps incorporate scandium iodide along with to generate a broad that closely mimics natural daylight, achieving correlated color temperatures around 4000 K and high color rendering indices (CRI > 80). This makes them ideal for applications requiring accurate color reproduction, such as sports stadiums, television studios, and . In the lamp's arc tube, scandium oxide (Sc₂O₃) serves as a to enhance , boost luminous output, and maintain arc stability by increasing ionization potential and reducing color distortion. For instance, sodium-scandium metal lamps from manufacturers like utilize this formulation to achieve superior lumen maintenance and extended lifetimes, particularly when operated at very high frequencies (VHF), where is minimized compared to low-frequency drivers. Globally, scandium consumption for applications is a minor portion of total use, estimated at around 80 kg annually as of 2016. Scandium oxide is also integral to advanced ceramics, valued for its high (approximately 2485°C), , and ability to withstand . As a additive, Sc₂O₃ facilitates the densification of nanostructured ceramics at lower temperatures, enabling the production of transparent materials with optical transparency exceeding 80% in the visible range. These properties make scandium-doped ceramics suitable for high-temperature insulators and structural components in and . In electronic applications, scandium oxide is incorporated into dielectric ceramics, such as those based on alumina (Al₂O₃) or (Ta₂O₅), to form high-capacitance layers with elevated breakdown voltages, supporting compact capacitors in . Additionally, Sc₂O₃ doping enhances the and mechanical strength of yttrium aluminum garnet (YAG)-based ceramics, as seen in scandium-modified Nd:YAG variants that exhibit intensified emission at 1064 nm for solid-state . Its high further enables anti-reflective coatings on optical components, reducing light loss in laser systems and windows.

Emerging and other uses

Scandium plays a pivotal role in solid oxide fuel cells (SOFCs), where scandium-stabilized zirconia serves as an material that enhances ionic conductivity and allows operation at lower temperatures compared to traditional , thereby improving efficiency and reducing material costs. As of 2024, SOFCs and aluminum alloys account for the majority of global scandium consumption, estimated at 30–40 tons annually. Recent advancements include scandium-doped barium stannate and compounds that enable low-temperature hydrogen fuel cells, potentially revolutionizing portable and stationary power systems. In medical applications, scandium radioisotopes such as scandium-43 and scandium-44 are emerging for (PET) imaging, offering longer half-lives than gallium-68 for improved diagnostic accuracy in cancer detection and theranostics. Scandium-47, with its beta-emitting properties, shows promise for targeted radiotherapy, where it can be chelated to biomolecules like analogues to deliver directly to tumor cells while minimizing damage to healthy tissue. Production methods for these isotopes have advanced through linear accelerators and cyclotrons, enabling clinical-scale yields sufficient for multiple patient doses per irradiation. Additive manufacturing represents a growing frontier for scandium, particularly in aluminum-scandium alloys optimized for laser powder-bed fusion, which exhibit superior strength, reduced cracking, and fine grain structures ideal for components. Companies like have developed patented Al-Sc powders, such as modifications to AA535 and AA7075 series, that enable lightweight, high-performance parts for defense and transportation, with ongoing studies targeting economic viability as of 2025. These alloys reduce post-processing needs and support complex geometries unattainable through traditional casting. In , scandium enhances power devices through scandium aluminum (ScAlN) films, which provide wider bandgaps and higher piezoelectric coefficients than conventional materials, enabling more efficient high-frequency transistors and sensors. As a , scandium improves performance in solid-state devices, contributing to advancements in next-generation computing and . Other niche applications include scandium oxide coatings for high-power ultraviolet lasers, where it offers high damage thresholds and refractive indices for durable optical components used in lithography and precision machining. Additionally, scandium-doped glasses demonstrate enhanced neutron shielding properties, finding potential in nuclear imaging devices and therapy equipment due to their density and absorption efficiency. The radioactive isotope scandium-46 serves as a tracer in oil refining and pipeline leak detection, aiding industrial process monitoring.

Health and safety

Biological role

Scandium has no known biological role and is considered non-essential for s or other organisms. Its low natural abundance in the has limited extensive studies on potential functions, but no essential physiological processes involving scandium have been identified. Trace amounts of scandium are present in the environment, with daily intake estimated at less than 0.1 μg, primarily through and , and it does not accumulate significantly in healthy individuals. In patients with chronic renal failure, however, plasma scandium levels can increase and correlate with markers of kidney dysfunction such as and . Although scandium lacks an established role in higher organisms, research has uncovered interactions with microorganisms that suggest modulatory effects rather than essential functions. For instance, low concentrations (10–100 μM) of scandium stimulate antibiotic overproduction by 2- to 25-fold in species, activating biosynthetic gene clusters through mechanisms involving signaling pathways. Similar effects have been observed with other rare earths like , indicating scandium's potential to influence microbial in soil environments. These findings highlight scandium's biogeochemical relevance in microbial ecology but do not imply a vital biological necessity.

Toxicity and environmental impact

Scandium and its compounds exhibit low in animal models. The (LD50) for scandium (ScCl₃) administered intraperitoneally to mice is 755 mg/kg, while the oral LD50 exceeds 4 g/kg, indicating minimal risk from ingestion or injection under typical exposure scenarios. Chronic exposure studies in have shown no significant changes in body weight, organ function, or histopathological effects at doses up to 100 mg/kg over extended periods, suggesting limited potential for long-term harm. data remain sparse due to scandium's rarity and low industrial exposure levels, but it is classified as non-toxic in material safety assessments and has been safely used as a nutritional absorption marker in both humans and animals without adverse effects. In terms of biological interactions, scandium ions demonstrate lower toxicity to microorganisms compared to other transition metals; for instance, they inhibit bacterial growth in and at concentrations higher than those of or ions, with minimal disruption to cellular processes. Scandium lacks a known essential biological role and is poorly absorbed in the , with most ingested forms excreted via rather than accumulating in tissues. In a toxicokinetic study of scandium oxide nanoparticles in rats, intravenous administration led to primary accumulation in the lungs and liver, followed by fecal excretion, with negligible urinary output and no observed organ toxicity over 28 days. The environmental impact of scandium primarily arises from its extraction and processing, often as a of (REE) mining, which generates substantial waste. Life cycle assessments of scandium oxide production from REE tailings, such as those at China's Bayan Obo mine, reveal that beneficiation and leaching stages account for over 88% of total impacts, including high energy consumption, greenhouse gas emissions, and acidification from use. from scandium recovery can contaminate soil and water with residual acids and , potentially affecting local ecosystems, though scandium concentrations in ores are low (typically <100 ppm), limiting its direct contribution to compared to co-extracted elements like . Recovery methods, such as solvent extraction or with fluoride-based agents, introduce additional risks; for example, scandium (ScF₃) stripping generates fluoride-laden effluents that pose to aquatic life if not properly managed. Emerging sustainable approaches, including recycling from industrial wastes like production residues, can reduce impacts by up to 23% in categories like and human health risks, emphasizing the value of secondary sourcing to minimize mining-related environmental burdens. Overall, scandium's environmental footprint is modest due to its small-scale production (global output around 30–40 tons annually as of 2024), with projections for significant growth in the coming decade, but scaling for applications in alloys and ceramics necessitates stricter to prevent localized .

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