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Scandium

physical science Maturity 7-9 Next article →

Scandium is a silvery-white metallic element with the chemical symbol Sc and atomic number 21. It is located in the d-block of the periodic table. Scientists often classify it as a rare-earth element. This grouping includes yttrium and the lanthanide series. While it is not actually rare in the Earth's crust, it is distributed very sparsely. It exists in trace amounts within many different minerals. This makes it difficult to collect in large, concentrated quantities.

Mig-29 on landing
Mig-29 on landing

In nature, scandium is found exclusively as the stable isotope 45Sc. Other known isotopes exist, but they are not stable. These isotopes range from 37Sc to 63Sc. Many of these are radioisotopes with short half-lives. For example, 46Sc has a half-life of 83.76 days. Others, like 43Sc, last for only about 3.891 hours. The lightest isotopes undergo a process called proton emission. This process produces calcium isotopes. Heavier isotopes usually undergo beta emission to produce titanium isotopes. The stable form of scandium is created in space through the r-process in supernovae. It is also created by cosmic ray spallation of iron-peak nuclei.

Scandium has unique chemical characteristics. It is a soft metal with a silvery appearance. When it is oxidized by air, it develops a yellowish or pinkish cast. It is susceptible to weathering and dissolves slowly in most dilute acids. Interestingly, it does not dissolve in a specific mixture of nitric acid and hydrofluoric acid. This is likely due to the formation of an impermeable passive layer. If scandium turnings are ignited in the air, they produce a brilliant yellow flame. This reaction forms scandium oxide. Most scandium chemistry is dominated by the trivalent ion, Sc3+. This ion has properties that are intermediate between aluminium and yttrium.

Mig-29 on landing
Mig-29 on landing

Producing metallic scandium is a complex industrial process. Most scandium is currently sold as scandium oxide. To create the pure metal, the oxide must first be converted into scandium fluoride. This fluoride is then reduced using metallic calcium. Because of the difficulties in preparation, practical applications were not developed until the 1970s. The global trade of scandium oxide is relatively small. It is estimated at only 15 to 20 tonnes per year. In 2003, only three mines produced the element. These were located in Ukraine, China, and Russia. Today, production has expanded to include facilities in the Philippines. In the United States, a project in Nebraska aims to produce 95 tonnes of scandium oxide annually.

History shows that scandium was a predicted discovery. In 1869, Dmitri Mendeleev predicted an element called ekaboron. He estimated its atomic mass would be between 40 and 48. In 1879, Lars Fredrik Nilson detected the element using spectral analysis. He found it in the minerals euxenite and gadolinite from Scandinavia. He named it scandium after the Latin word for Scandinavia. Nilson prepared 2 grams of high-purity scandium oxide. Later, in 1937, the first metallic scandium was produced via electrolysis. The first pound of 99% pure scandium metal was produced in 1960.

Mig-29 on landing
Mig-29 on landing

The most significant use of scandium is in aluminium alloys. Adding just 0.1% to 0.5% scandium to aluminium creates a very strong material. This addition limits grain growth in the heat zones of welded parts. It creates a fine dispersion of nanoscale precipitates. These precipitates strengthen the aluminium matrix by inhibiting dislocation movement. This makes the alloy as strong as titanium but as light as aluminium. These alloys are used in Russian military aircraft like the MiG-21 and MiG-29.

Mig-29 on landing
Mig-29 on landing

High-performance sports equipment also uses these alloys. Examples include bicycle frames, baseball bats, and lacrosse sticks. Even some semi-automatic pistols from Smith & Wesson use scandium alloys.

Scandium also plays a role in lighting and advanced technology. It is used in metal-halide lamps to create high-intensity discharge light. In the United States alone, about 20 kg of scandium is used for these lamps every year. Scandium-stabilized zirconia is also used as an electrolyte in solid oxide fuel cells. In the 1980s and 1990s, gadolinium-scandium-gallium garnet crystals were used in strategic defense applications. Modern manufacturing also uses scandium in 3D-printed metal parts. This technology is known as Laser Powder Bed Fusion. These diverse uses show how a small amount of scandium can change the properties of other materials.

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