Scandium(III) oxide or scandia is a

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

with formula Sc₂ O₃. It is one of several

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

s of

rare earth element The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous sil ...

s with a high

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

. It is used in the preparation of other

scandium Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the Lanthanides. It was discovered in ...

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

thermal shock Thermal shock is a type of rapidly transient mechanical load. By definition, it is a mechanical load caused by a rapid change of temperature of a certain point. It can be also extended to the case of a thermal gradient, which makes different pa ...

), 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, porcelain, ...

s, and

glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...

composition (as a helper material).

Structure and physical properties

Scandium(III) oxide adopts a cubic crystal structure (

point group In geometry, a point group is a mathematical group of symmetry operations ( isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every ...

: tetrahedral (T_h),

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

: 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 call ...

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, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...

of 6.0 eV.

Production

Scandium oxide is the primary form of refined

produced by the mining industry. Scandium-rich ores, such as

thortveitite Thortveitite is a rare mineral consisting of scandium yttrium silicate (Sc,Y)2Si2O7. It is the primary source of scandium. Occurrence is in granitic pegmatites. It was named after Olaus Thortveit, a Norwegian engineer. It is grayish-green, bla ...

(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 fo ...

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 HCL may refer to: Science and medicine * Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia * Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development * Hollow-cathode lamp, a s ...

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 In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula , where X = fluorine (F), chlor ...

upon drying. :Sc₂O₃ + 6

+ ''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 Scandium trifluoromethanesulfonate, commonly called scandium triflate, is a chemical compound with formula Sc(SO3CF3)3, a salt consisting of scandium cations Sc3+ and triflate anions. Scandium triflate is used as a reagent in organic chemistr ...

(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 with the 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 ...

. 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. The Kroll process replaced the Hunter process for almost all commercial production. Process In the Kroll process, the TiCl ...

for the production of metallic

titanium Titanium is a chemical element with the 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 i ...

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

yttrium oxide Yttrium oxide may refer to: * Yttrium(II) oxide, YO, a dark brown solid * Yttrium(III) oxide Yttrium oxide, also known as yttria, is Y2 O3. It is an air-stable, white solid substance. The thermal conductivity of yttrium oxide is 27 W/(m·K). ...

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.

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