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 chemi ...
with formula
Sc2 O3. It is one of several
oxides 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 si ...
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 depends ...
. 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 discovere ...
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, porcelai ...
s, and
glass
Glass is a non-Crystallinity, crystalline, often transparency and translucency, transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most ...
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 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 ...
: 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 cal ...
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
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 discovere ...
produced by the mining industry. Scandium-rich ores, such as
thortveitite (Sc,Y)
2(Si
2O
7) and
kolbeckite ScPO
4·2H
2O 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
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 discovere ...
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 NH
4Cl by
sublimation
Sublimation or sublimate may refer to:
* ''Sublimation'' (album), by Canvas Solaris, 2004
* Sublimation (phase transition), directly from the solid to the gas phase
* Sublimation (psychology), a mature type of defense mechanism
* Sublimate of mer ...
at 300-500 °C. The presence of NH
4Cl 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), ...
upon drying.
:Sc
2O
3 + 6
HCl + ''x'' H
2O → 2 ScCl
3·''n''H
2O + 3 H
2O
:ScCl
3·''n''H
2O + ''n''
NH4Cl → ScCl
3 + ''n'' H
2O + ''n''
NH4Cl
Likewise, it is converted into hydrated
scandium(III) triflate (Sc(OTf)
3·''n''H
2O) 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
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 t ...
. 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 Ti ...
for the production of metallic
titanium
Titanium is a chemical element with the Symbol (chemistry), 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, resista ...
.
Scandium oxide forms scandate salts with alkalis, unlike its higher homologues
yttrium oxide and
lanthanum oxide (but like
lutetium oxide), for example forming K
3Sc(OH)
6 with KOH. In this, scandium oxide shows more similarity with
aluminium oxide.
Natural occurrence
Natural scandia, although impure, occurs as mineral
kangite.
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References
{{Authority control
Scandium compounds
Sesquioxides
Transition metal oxides