Scandium(III) oxide or scandia is a

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with formula Sc₂ O₃. It is one of several

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

s of

rare earth element The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set o ...

s with a high

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

. It is used in the preparation of other

scandium Scandium is a chemical element; it has Symbol (chemistry), symbol Sc and atomic number 21. It is a silvery-white metallic d-block, d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the lantha ...

compounds as well as in high-temperature systems (for its resistance to heat and

thermal shock Thermal shock is a phenomenon characterized by a rapid change in temperature that results in a transient mechanical load on an object. The load is caused by the differential expansion of different parts of the object due to the temperature chang ...

), electronic

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

s, and

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

composition (as a helper material).

Structure and physical properties

Scandium(III) oxide adopts a

cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

crystal structure (

point group In geometry, a point group is a group (mathematics), mathematical group of symmetry operations (isometry, isometries in a Euclidean space) that have a Fixed point (mathematics), fixed point in common. The Origin (mathematics), coordinate origin o ...

: tetrahedral (T_h),

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

: Ia) containing 6-coordinate metal centres.

Powder diffraction Powder diffraction is a scientific technique using X-ray, neutron, or electron diffraction on powder or microcrystalline samples for structural characterization of materials. An instrument dedicated to performing such powder measurements is ca ...

analysis shows Sc−O bond distances of 2.159–2.071 Å. Scandium oxide is an insulator with a

band gap In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...

of 6.0 eV.

Production

Scandium oxide is the primary form of refined

produced by the mining industry. Scandium-rich ores, such as thortveitite (Sc,Y)₂(Si₂O₇) and

kolbeckite Kolbeckite (scandium phosphate dihydrate) is a mineral with formula: ScPO4·2H2O. It was discovered originally at Schmiedeberg, Saxony, Germany in 1926 and is named after Friedrich L. W. Kolbeck, a German mineralogist. Kolbeckite is usually found ...

ScPO₄·2H₂O are rare, however trace amounts of scandium are present in many other minerals. Scandium oxide is therefore predominantly produced as a by-product from the extraction of other elements.

Reactions

Scandium oxide is the primary form of refined

produced by the mining industry, making it the start point for all scandium chemistry. Scandium oxide reacts with most acids upon heating, to produce the expected

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

d product. For example, heating in excess aqueous HCl produces hydrated ScCl₃·''n''H₂O. This can be rendered anhydrous by evaporation to dryness in the presence of NH₄Cl, with the mixture then being purified by removal of NH₄Cl by sublimation at 300-500 °C. The presence of NH₄Cl is required, as the hydrated ScCl₃·''n''H₂O would otherwise form a mixed oxychloride upon drying. :Sc₂O₃ + 6 HCl + ''x'' H₂O → 2 ScCl₃·''n''H₂O + 3 H₂O :ScCl₃·''n''H₂O + ''n'' NH₄Cl → ScCl₃ + ''n'' H₂O + ''n'' NH₄Cl Likewise, it is converted into hydrated scandium(III) triflate (Sc(OTf)₃·''n''H₂O) by a reaction with

triflic acid Triflic acid, the short name for trifluoromethanesulfonic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CF3SO3H. It is one of the strongest known acids. Triflic acid is mainly used in research as a catalyst for este ...

. Metallic scandium is produced industrially by the reduction of scandium oxide; this proceeds via conversion to

scandium fluoride Scandium(III) fluoride, ScF3, is an ionic compound. This salt is slightly soluble in water but dissolves in the presence of excess fluoride to form the ScF63− anion. Production ScF3 can be produced by reacting scandium and fluorine.S.A.Cotton, ...

followed by a reduction with metallic

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

. This process is in some ways similar to the

Kroll process The Kroll process is a pyrometallurgical industrial process used to produce metallic titanium from titanium tetrachloride. As of 2001 William Justin Kroll's process replaced the Hunter process for almost all commercial production. Process In the ...

for the production of metallic

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

. Scandium oxide forms scandate salts with alkalis, unlike its higher homologues

yttrium oxide Yttrium oxide may refer to: * Yttrium(II) oxide Yttrium(II) oxide or yttrium monoxide is a chemical compound with the formula YO. This chemical compound was first created in its solid form by pulsed laser deposition, using yttrium(III) oxide as ...

and

lanthanum oxide Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock ...

(but like lutetium oxide), for example forming K₃Sc(OH)₆ with KOH. In this, scandium oxide shows more similarity with

aluminium oxide Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as alum ...

Natural occurrence

Natural scandia, although impure, occurs as mineral kangite.Mindat, http://www.mindat.org/min-42879.html

References

{{Authority control Scandium compounds Sesquioxides Transition metal oxides Crystals in space group 206