Scandium

Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic element found in the d-block of the periodic table. Usually, it is classified as a rare-earth element, together with yttrium and the lanthanides. It was discovered in 1879 by looking at the minerals euxenite and gadolinite from Scandinavia.

Scandium is present in most deposits of rare-earth and uranium compounds, but it is only taken from these ores in a few mines around the world. Because it was hard to prepare metallic scandium, which was first done in 1937, people did not find many uses for it until the 1970s. That is when they learned that scandium could improve aluminium alloys. Today, this is its main use. The world trade of scandium oxide is only about 15 to 20 tonnes per year.

The properties of scandium compounds are similar to those of aluminium and yttrium. There is also a special relationship between how magnesium and scandium behave, just like there is between beryllium and aluminium. In chemical compounds of elements in group 3, scandium usually shows an oxidation state of +3.

Properties

Scandium is a soft, silvery metal that can change color slightly when it meets air. It slowly dissolves in many common acids but does not dissolve in a special mix of two particular acids. Tiny pieces of scandium can catch fire in air and burn with a bright yellow flame.

Scandium is most commonly found as one type called ⁴⁵Sc. Scientists have discovered many other types of scandium, but they are not stable and break down over time. In the Earth’s crust, scandium is not rare but is spread out and found only in small amounts in various minerals. Some minerals from places like Scandinavia and Madagascar contain more scandium, but these are also sources of other rare elements.

Production

The world makes about 15 to 20 tonnes of scandium each year, mostly as scandium oxide. Both how much we make and how much we need are growing. Scandium is usually a byproduct when we mine other elements like uranium, iron, or rare earth metals.

To get pure scandium metal, we first change the oxide into scandium fluoride and then use calcium metal to turn it into scandium.

Madagascar and a region in Norway have minerals with a lot of scandium, but we don’t mine them much yet. Even though we don’t use much scandium, adding a tiny amount to aluminium can make it stronger. Scandium is also used in special cells that can produce energy very well.

Compounds

See also the categories Scandium compounds and Scandium minerals

Scandium mostly forms compounds where it has a +3 charge. Because of this, scandium behaves more like yttrium than aluminium. This is why scandium is often grouped with elements called lanthanides.

Oxides and hydroxides

The oxide Sc₂O₃ and the hydroxide Sc(OH)₃ can react with both acids and bases. When mixed with a base, they form a scandate ion. When mixed with an acid, they form another compound.

Halides and pseudohalides

The compounds ScX₃, where X stands for chlorine, bromine, or iodine, dissolve easily in water. However, ScF₃ does not dissolve. These compounds can act as Lewis acids.

Organic derivatives

Main article: Organoscandium chemistry

Scandium can form compounds with organic molecules, similar to lanthanides. One example is a compound with cyclopentadienyl ligands.

Uncommon oxidation states

It is rare, but scandium can form compounds with charges other than +3. For example, there is a compound called CsScCl₃ where scandium has a +2 charge. Scandium can also form compounds with hydrogen and other elements in different charges.

History

Dmitri Mendeleev, known for creating the periodic table, guessed that an element called ekaboron might exist between elements with an atomic mass of 40 and 48, back in 1869. Later, in 1879, Lars Fredrik Nilson and his team found this element in minerals called euxenite and gadolinite. Nilson made 2 grams of pure scandium oxide and named the element scandium after Scandinavia. Another scientist, Per Teodor Cleve, noticed that Nilson's discovery matched Mendeleev’s prediction and told Mendeleev about it.

In 1937, people made metallic scandium for the first time using a special process called electrolysis. The first pound of very pure scandium metal was made in 1960. In 1971, people started mixing scandium with aluminium to make strong alloys, first in the USSR. Later, in the 1980s and 1990s, special crystals made from scandium were used for important defense projects.

Applications

Aluminium alloys

Main article: Aluminium–scandium alloys

Scandium is mainly used to make special kinds of aluminium alloys, which are important for aircraft parts. These alloys contain a tiny amount of scandium, between 0.1% and 0.5%. They have been used in Russian military planes like the Mikoyan-Gurevich MiG-21 and MiG-29.

Adding scandium to aluminium helps to make the metal stronger, especially when it is welded. It forms tiny crystals that make the aluminium harder without making it heavier. This makes the alloys strong and light, useful for aircraft and other special parts.

Some sports gear, like baseball bats, tent poles, bicycle frames, and components, are made from these alloys. Lacrosse sticks also use scandium. A company called Smith & Wesson makes guns with parts made from scandium alloys.

Light sources

Scandium is used to make bright lights called metal-halide lamps. These lamps look very much like sunlight and are good for TV cameras. Dentists also use special lasers that contain scandium for treating teeth.

Other

A special kind of scandium can be used to track oil in refineries. Scandium is also used in chemistry for certain reactions. It has been studied for use in very accurate clocks and in energy cells that can use many different fuels.

Health and safety

Elemental scandium is not known to be harmful, but we don’t have a lot of tests to know for sure. Scientists have studied scandium chloride and found that large amounts can be harmful to rats. Because of this, we should treat scandium compounds as somewhat dangerous. The body handles scandium in a way that is similar to gallium, which can also cause problems if it is not dissolved well.