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Scandium: the story on HearLore | HearLore
Scandium
Scandium was the first element to be discovered that Mendeleev had predicted but never seen, existing in the gaps of his periodic table before anyone knew its name. In 1869, Dmitri Mendeleev published his periodic table and boldly predicted an element with an atomic mass between 40 and 48, which he called ekaboron, yet for a decade no one could find it. It was not until 1879 that Lars Fredrik Nilson, a Swedish chemist, finally isolated the element from the minerals euxenite and gadolinite, which he had obtained from Scandinavia. Nilson named the element scandium, derived from the Latin word Scandia, meaning Scandinavia, to honor his homeland, though he was initially unaware of Mendeleev's prediction. Per Teodor Cleve, a contemporary of Nilson, recognized the correspondence between the new discovery and Mendeleev's ekaboron and immediately notified the father of the periodic table, confirming that the missing piece of the puzzle had finally been found. Despite this triumph, the element remained a laboratory curiosity for decades because extracting pure metallic scandium proved to be an immense challenge. It was not until 1937 that scientists successfully produced metallic scandium for the first time through the electrolysis of a eutectic mixture of potassium, lithium, and scandium chlorides at temperatures between 700 and 800 degrees Celsius. The first pound of 99% pure scandium metal did not appear until 1960, and even then, it remained a rare and expensive substance with no practical use. The world's supply of scandium is so limited that global trade in scandium oxide amounts to only 15 to 20 tonnes per year, making it one of the rarest commercially available metals.
A Ghost In The Crust
Scandium is surprisingly abundant in the Earth's crust, ranking as the 35th most common element, yet it remains elusive because it is distributed sparsely and occurs in trace amounts in many minerals. Estimates place its concentration between 18 and 25 parts per million, which is comparable to the abundance of cobalt, but unlike cobalt, scandium does not form concentrated deposits that can be easily mined. The only known concentrated sources are rare minerals such as thortveitite, euxenite, and gadolinite, which are found in specific locations like Scandinavia, Madagascar, and the Kola Peninsula in Russia. Thortveitite can contain up to 45% scandium oxide, making it the richest source, but these minerals are often found in remote areas and are difficult to process. 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. Since then, other countries have built scandium-producing facilities, including operations in the Philippines by Nickel Asia Corporation and Sumitomo Metal Mining, which produce about 5 tonnes per year. Despite the abundance of scandium in the universe, where it is the 23rd most common element in the Sun and the 26th most abundant in stars, its scarcity on Earth is due to the fact that it is created in supernovae via the r-process and by cosmic ray spallation of iron-peak nuclei. The stable form of scandium is created in these cosmic events, but on Earth, it is locked away in minerals that are often byproducts of other mining operations. The absence of reliable, secure, and stable long-term production has limited the commercial applications of scandium, keeping it a niche material despite its potential. The mineral kolbeckite has a very high scandium content but is not available in any larger deposits, and the deposits in Madagascar and the Iveland-Evje region in Norway are not being exploited. In the United States, NioCorp Development hopes to raise $1 billion to open a niobium mine at its Elk Creek site in southeast Nebraska, which may be able to produce as much as 95 tonnes of scandium oxide annually, but this remains a future possibility. The price of scandium oxide has fluctuated, with the USGS reporting that from 2015 to 2019, the price of small quantities of scandium ingot ranged from $107 to $134 per gram, and that of scandium oxide from $4 to $5 per gram.
Scandium was discovered in 1879 by the Swedish chemist Lars Fredrik Nilson. Nilson isolated the element from the minerals euxenite and gadolinite obtained from Scandinavia and named it after the Latin word Scandia meaning Scandinavia.
When was pure metallic scandium first produced?
Scientists successfully produced metallic scandium for the first time in 1937 through the electrolysis of a eutectic mixture of potassium lithium and scandium chlorides. The process required temperatures between 700 and 800 degrees Celsius to create the pure metal.
Where are the main sources of scandium found on Earth?
The only known concentrated sources of scandium are rare minerals such as thortveitite euxenite and gadolinite found in locations like Scandinavia Madagascar and the Kola Peninsula in Russia. In 2003 the primary production came from mines in Zhovti Vody Ukraine Bayan Obo China and the Kola Peninsula Russia.
When did scandium become useful for aluminum alloys?
The discovery that scandium could strengthen aluminum alloys occurred in 1971 following a US patent issued on the 9th of November 1971. These alloys were first used in Russian military aircraft including the Mikoyan-Gurevich MiG-21 and MiG-29 to provide critical advantages in strength and weight reduction.
How much scandium is used globally each year?
Global trade in scandium oxide amounts to only 15 to 20 tonnes per year making it one of the rarest commercially available metals. Approximately 80 kg of scandium is used in metal-halide lamps and light bulbs globally per year while about 20 kg is used annually in the United States for these lamps.
What is the only stable isotope of scandium?
The stable form of scandium is found exclusively as the isotope 45Sc which has a nuclear spin of 7/2. All other known isotopes of scandium range from 37Sc to 63Sc and are radioactive with varying half-lives.
The discovery that scandium could strengthen aluminum alloys in 1971 transformed the element from a laboratory curiosity into a material of strategic importance, particularly for aerospace and military applications. The addition of as little as 0.5% scandium to aluminum limits the grain growth in the heat zone of welded aluminum components, creating a material that is as strong as titanium, light as aluminum, and hard as some ceramics. These alloys were first used in Russian military aircraft, specifically the Mikoyan-Gurevich MiG-21 and MiG-29, where they provided critical advantages in strength and weight reduction. The precipitated phase forms smaller crystals than in other aluminum alloys, and the volume of precipitate-free zones at the grain boundaries of age-hardening aluminum alloys is reduced, resulting in a coherent precipitate that strengthens the aluminum matrix by applying elastic strain fields that inhibit dislocation movement. Recent developments include the addition of transition metals such as zirconium and rare earth metals like erbium, which produce shells surrounding the spherical precipitate that reduce coarsening and lower the cost of the alloy. These innovations have made scandium-stabilized aluminum alloys somewhat competitive with titanium alloys, which are similar in lightness and strength but are cheaper and much more widely used. The alloy is as strong as titanium, light as aluminum, and hard as some ceramics, making it ideal for applications where weight and strength are paramount. Since 2013, Apworks GmbH, a spin-off of Airbus, has marketed a high-strength scandium-containing aluminum alloy processed using metal 3D printing under the trademark Scalmalloy, which claims very high strength and ductility. The alloy has found its way into sports equipment, including baseball bats, tent poles, bicycle frames, and lacrosse sticks, where lightweight high-performance materials are essential. 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, demonstrating the versatility of the material. Despite these advances, titanium alloys remain cheaper and more widely used, limiting the widespread adoption of scandium-aluminum alloys. The global trade of scandium oxide is 15 to 20 tonnes per year, and the demand is slightly higher, with both production and demand keeping increasing. The production of aluminum alloys began in 1971, following a US patent issued on the 9th of November 1971, and aluminum-scandium alloys were also developed in the USSR, highlighting the strategic importance of the material during the Cold War.
Light And Lasers
Scandium plays a crucial role in the development of high-intensity discharge lamps and laser crystals, providing light sources that closely resemble sunlight and enable advanced medical and defense technologies. The first scandium-based metal-halide lamps were patented by General Electric and made in North America, and approximately 20 kg of scandium is used annually in the United States for these lamps. One type of metal-halide lamp, similar to the mercury-vapor lamp, is made from scandium triiodide and sodium iodide, creating a white-light source with a high color rendering index that sufficiently resembles sunlight to allow good color reproduction with TV cameras. About 80 kg of scandium is used in metal-halide lamps and light bulbs globally per year, making it a significant component in the lighting industry. In the field of medicine, dentists use erbium-chromium-doped yttrium-scandium-gallium garnet lasers for cavity preparation and in endodontics, demonstrating the element's versatility beyond industrial applications. Laser crystals of gadolinium-scandium-gallium garnet were used in strategic defense applications developed for the Strategic Defense Initiative in the 1980s and 1990s, highlighting the element's importance in military technology. The radioactive isotope 46Sc is used in oil refineries as a tracing agent, and scandium triflate is a catalytic Lewis acid used in organic chemistry, further expanding the element's applications. 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, suggesting potential future uses in precision timing. Scandium has been proposed for use in solid oxide fuel cells as a dopant in the electrolyte material, typically zirconia, to enhance ionic conductivity and improve the overall thermal stability, performance, and efficiency of the fuel cell. This application would be particularly valuable in clean energy technologies, as solid oxide fuel cells can utilize a variety of fuels and have high energy conversion efficiencies. The scandium-stabilized zirconia enjoys a growing market demand for use as a high-efficiency electrolyte in solid oxide fuel cells, indicating a promising future for the element in the renewable energy sector.
The Chemical Enigma
Scandium's chemical behavior is a unique blend of properties that place it between aluminum and yttrium, creating a diagonal relationship with magnesium that is as significant as the relationship between beryllium and aluminum. The chemical properties of scandium ions have more in common with yttrium ions than with aluminum ions, and in part because of this similarity, scandium is often classified as a lanthanide-like element. The radii of M3+ ions indicate that scandium's chemical properties are intermediate, with an ionic radius of 74.5 pm, compared to 53.5 pm for aluminum and 90.0 pm for yttrium. The oxide and hydroxide of scandium are amphoteric, meaning they can react with both acids and bases, and solutions of scandium oxide in water are acidic due to hydrolysis. The halides of scandium, where X equals chlorine, bromine, or iodine, are very soluble in water, but fluoride is insoluble, and in all four halides, the scandium is 6-coordinated. The halides are Lewis acids, and scandium triflate is sometimes used as a Lewis acid catalyst in organic chemistry. Scandium forms a series of organometallic compounds with cyclopentadienyl ligands, similar to the behavior of the lanthanides, and one example is the chlorine-bridged dimer and related derivatives of pentamethylcyclopentadienyl ligands. Compounds that feature scandium in oxidation states other than +3 are rare but well characterized, such as the blue-black compound scandium(II) chloride, which adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers. Scandium hydride is not well understood, although it appears not to be a saline hydride of scandium(II), and as is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase. Scandium borides and carbides are non-stoichiometric, as is typical for neighboring elements, and lower oxidation states such as +2, +1, and 0 have also been observed in organoscandium compounds. The stable form of scandium is found exclusively as the isotope 45Sc, which has a nuclear spin of 7/2, and this is its only stable isotope. The known isotopes of scandium range from 37Sc to 63Sc, 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 a half-life of 58.6 hours, which is the lightest isotope with a long-lived isomer. 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.