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 elements 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: tetrahedral (T_h), space group: Ia) containing 6-coordinate metal centres. Powder diffraction 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 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 hydrated 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. Metallic scandium is produced industrially by the reduction of scandium oxide; this proceeds via conversion to scandium fluoride followed by a reduction with metallic calcium. This process is in some ways similar to the Kroll process for the production of metallic titanium. Scandium oxide forms scandate salts with alkalis, unlike its higher homologues yttrium oxide and lanthanum oxide (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