Scandium

Scandium is a chemical element on the periodic table whose symbol is Sc and its atomic number is 21. It is a transition metal found in ores from Scandinavia and is often classified among the lanthanides because of its similarities to them.

It is a silvery-white metallic D-block element, historically classified as a rare earth element, along with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.

Scandium is present in most uranium and rare earth compound deposits, but it is extracted from these ores in only a few mines worldwide. Due to the low availability and difficulties in the preparation of metallic scandium, which was first performed in 1937, applications of scandium did not develop until the 1970s, when the positive effects of scandium in aluminum alloys were discovered. and its use in said alloys. It remains its only major application. World trade in scandium oxide is 15 to 20 tons per year.

The properties of scandium compounds are intermediate between those of aluminum and yttrium. There is a diagonal relationship between the behavior of magnesium and scandium, just as there is between beryllium and aluminum. In chemical compounds of group 3 elements, the predominant oxidation state is +3.

Main features

Chemical characteristics

Scandium is a soft metal with a silvery appearance. Develops a slightly yellowish or pinkish hue when oxidized in air. It is weatherable and dissolves slowly in most dilute acids. Does not react with a 1:1 mixture of nitric acid (HNO
3) and hydrofluoric acid (HF) to 48.0% possibly due to the formation of an impermeable passive layer. Scandium shavings ignite in air with a bright yellow flame to form scandium oxide.

It is a soft, very light metal, resistant to attack by nitric and hydrofluoric acids, whose silver color tarnishes when exposed to air, adopting a slightly pink color. Its most common oxidation state is +3 and its salts are colorless. Its properties are more similar to those of yttrium and lanthanides than to those of titanium, which is why it is often included among the rare earths.

Applications

Scandium oxide Sc₂O₃, is used in high-intensity lights and adding scandium iodide in mercury vapor lamps produces sunlight very high quality artificial The radioactive isotope Sc-46 is used in the oil industry as a tracer.

The main application of scandium by weight is in aluminum-scandium alloys for minor components in the aerospace industry. These alloys contain between 0.1% and 0.5% of scandium. These were used in the Russian Mig 21 and Mig 29 military aircraft. However, titanium alloys, which are similar in lightness and strength, are cheaper and much more widely used.

The addition of scandium to aluminum limits grain growth in the heat zone of welded aluminum components. This has two beneficial effects: the Al
3Sc precipitate forms smaller crystals than in other aluminum alloys, and reduces the volume of the precipitate-free zones at grain boundaries of age-hardenable aluminum alloys. Both effects increase the utility of the alloy. The precipitate of Al
3Sc is a coherent precipitate that strengthens the aluminum matrix by applying elastic strain fields that inhibit dislocation motion (i.e. plastic deformation).The Al
3Sc has an L1₂ balance of unique supergrid structure of this system. A fine dispersion of nanoscale precipitate can be achieved by heat treatment which can also strengthen alloys through order hardening.

Recent developments include the addition of transition metals such as Zr and rare earth metals such as Er, which produce shells surrounding the spherical precipitate Al
3Sc which reduce thickening. These shells are dictated by the diffusivity of the alloying element and reduce the cost of the alloy because less Sc is replaced in part by Zr while maintaining stability and less Sc is needed to form the precipitate. These have made Al
3Sc somewhat competitive with titanium alloys along with a wide range of applications. However, titanium alloys, which are similar in lightness and strength, are cheaper and are widely used.

The alloy Al
20Li
20Mg
10Sc
20 Ti
30 is as strong as titanium, light as aluminum and as hard as some ceramics.

History

Scandium (from the scientific Latin scandĭum, and this one from Scandio, Scandinavia) was discovered by Lars Fredrick Nilson in 1879 while working with his team in the search for metals rare earths by spectral analysis of the minerals euxenite and gadolinite. To isolate the element, he processed 10 kg of exenite with other rare earth residues, obtaining approximately 2 grams of oxide (Sc ₂ O ₃ ) of high purity.

In 1869 Dmitri Mendeleyev predicted, based on periodic laws, that this metal should have properties similar to those of boron, which is why he named the element yet to be discovered ekaboro (symbol Eb). At about the same time as Nilson, Per Theodor Cleve discovered scandium oxide and confirmed that it was ekaboro.

In 1937, the metal was isolated for the first time by electrolysis of a eutectic solution of potassium, lithium and scandium chlorides at 700-800 °C using a tungsten filament and a bath of liquid zinc in a graphite crucible as electrodes. The first pound of 99% pure scandium was made in 1960.

Abundance and obtaining

The only known concentrated sources of the metal, which is not found in a native state, are rare minerals from Scandinavia and Madagascar such as euxenite, gadolinite, and thortveitite. In the earth's crust, scandium is not rare. Estimates vary from 18 to 25 ppm, which is comparable to the abundance of cobalt (20 to 30 ppm). Scandium is only the 50th most common element on Earth (35th most abundant in the crust). Scandium, however, is sparsely distributed and is found in trace amounts in many minerals. Rare Minerals from Scandinavia and Madagascar as thortveitite, euxenite, and gadolinite are the only known concentrated sources of this element. Thortveitite can contain up to 45% scandium in the form of scandium oxide.

It is more abundant on the Sun and similar stars (23rd in abundance) than on Earth (50th) where it is widely distributed, with traces of the metal appearing in more than 800 minerals. The blue color of aquamarine, a variety of beryl, is believed to be due to the presence of scandium and appears among tungsten residues after tungsten extraction.

Thortveitite is the main scandium ore, another important source being the residues from uranium extraction where it is obtained as a by-product. The metal is obtained industrially by reduction of scandium fluoride with calcium.

The stable form of scandium is created in supernovae through the R process. Additionally, scandium is created by cosmic ray spallation of the more abundant iron nuclei.

• ²⁸Yes + 17n → ⁴⁵Sc (Process-R)
• ⁵⁶Fe + p → ⁴⁵Sc + ¹¹C + n (Cosmic beaming)

Production

World production of scandium is in the order of 15-20 tons per year, in the form of scandium oxide. Demand is about 50% higher and both production and demand continue to increase. As of 2003, only three mines were producing scandium: the uranium and iron mines at Zhovti Vody in Ukraine, the rare earth mines at Bayan Obo, China, and the apatite mines on the Kola Peninsula, Russia; since then many other countries have built scandium production facilities, including 5 t/y (7.5 t/y Sc 2 O 3) by Nickel Asia Corporation and Sumitomo Metal in the Philippines.

In the United States, NioCorp Development expects to raise $1 billion soon to open a niobium mine at its Elk Creek site in southeastern Nebraska which can produce up to 95 tons of scandium oxide annually. In each case, scandium is a by-product of mining other elements and is sold as scandium oxide.

Price

The United States Geological Survey reports that from 2015 to 2019 in the US, the price of small quantities of scandium bullion has been $107 to $134 per gram, and that of scandium oxide of $4 to $5 per gram.

Isotopes

Natural scandium has a single stable isotope, Sc-45. 13 radioactive isotopes are known, of which the most stable are Sc-46 with a half-life of 83.79 days, Sc-47 (3.3492 days) and Sc-48 (43.67 hours); the other radioactive isotopes have half-lives of less than 4 hours and most less than 2 minutes. In addition, 5 metastable states are known, the most stable being Scm-44 (half-life of 58.6 hours).

The atomic mass of scandium isotopes ranges from 39.978 amu for Sc-40 to 53.963 amu for Sc-54. The main decay mode of isotopes lighter than stable (Sc-45) is electronic capture, giving rise to calcium isotopes, while isotopes heavier than stable decay mainly by beta emission, giving rise to titanium isotopes.

Precautions

Scandium metal powder is flammable. Elemental scandium is considered non-toxic, although extensive testing of scandium compounds in animals has not been performed. Median lethal dose (LD₅₀) levels of scandium chloride for rats have been determined as 755 mg/kg intraperitoneally and 4 g/kg for oral administration. In light of these results, scandium compounds should be handled as compounds of moderate toxicity. The body appears to handle scandium in a similar way to gallium, its full D-block counterpart, with similar dangers associated with its poorly soluble hydroxide.^{[citation needed]}