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A pyrosilicate is a type of
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...
; either an ionic compound that contains the pyrosilicate anion , or an organic compound with the
hexavalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of ...
≡-O-≡
group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...
. The anion is also called disilicate"Disilicate"
''Chemspider'' website, CSID:5257009, Accessed 2018-05-26
or diorthosilicate. Ionic pyrosilicates can be considered
salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...
of the unstable
pyrosilicic acid Pyrosilicic acid is the chemical compound with formula or . It is one of the silicic acids and has pyrosilicate as its conjugate base. It was synthesized, using nonaqueous solutions, in 2017. :H6Si2O7(aq) -> 2 SiO2(s) + 3 H2O Pyrosilicic acid m ...
, . Unlike the acid, the salts can be stable. Indeed, pyrosilicates occur widely in nature as a class of silicate minerals, specifically the
sorosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually co ...
s. Some notable synthetic pyrosilicates include *
sodium pyrosilicate Sodium pyrosilicate is the chemical compound . It is one of the sodium silicates, specifically a pyrosilicate, formally a salt of the unstable pyrosilicic acid .Myron C Waddell (1932): "Process of purifying technical sodium pyrosilicate hydrates ...
, a possible component of
water glass Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate , sodium orthosilicate , and sodium pyrosilicate . The anions are often polymeric. These compounds are generally colorless transparent ...
. * sodium iron(II) pyrosilicate , a potential
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
material for
batteries Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
.Abhishek Panigrahi, Shin-ichi Nishimura, Tatau Shimada, Eriko Watanabe, Wenwen Zhao, Gosuke Oyama, and Atsuo Yamada (2017): "Sodium Iron(II) Pyrosilicate : A Potential Cathode Material in the -- System". ''Chemistry of Materials'', volume 29, issue 10, pages 4361–4366. *
sodium manganese(II) pyrosilicate Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable i ...
, another potential
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
material.Viktor Renman, Mario Valvo, Cheuk-Wai Tai, and Cesar Pay Gómez (2017): "Manganese Pyrosilicates as Novel Positive Electrode Materials for Na-Ion Batteries". Uppsala University Publications, DIV
urn:nbn:se:uu:diva-334063
/ref>Viktor Renman (2017): "Structural and Electrochemical Relations in Electrode Materials for Rechargeable Batteries", Doctoral Thesis, Uppsala University, Department of Chemistry. ORCID: 0000-0001-8739-4054


Structure

The pyrosilicate anion can be described as two
tetrahedra In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all th ...
that share a vertex (an oxygen atom). The vertices that are not shared carry a negative charge each. The structure of solid sodium pyrosilicate was described by Volker Kahlenberg and others in 2010.Volker Kahlenberg, Thomas Langreiter, and Erik Arroyabe (2010): " – The Missing Structural Link among Alkali Pyrosilicates". ''Zeitschrift für anorganishe und allgemeine Chemie'' (''Journal for Inorganic and General Chemistry''), volume 636, issue 11, pages 1974-1979.
Yuri Smolin Yuri may refer to: People and fictional characters Given name *Yuri (Slavic name), the Slavic masculine form of the given name George, including a list of people with the given name Yuri, Yury, etc. * Yuri (Japanese name), also Yūri, feminine Ja ...
and Yuri Shepelev determined in 1970 the crystal structures of pyrosilicates 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 silve ...
s with generic formula , where "Ln" stands for either one of lanthanum,
cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
, neodymium, samarium, europium, gadolinium, dysprosium, holmium,
yttrium Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in co ...
,
erbium Erbium is a chemical element with the symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare-earth element, orig ...
, thulium, or ytterbium. They were found to belong to four distinct crystallographic classes, determined by the size of the
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
.Yu. I. Smolin and Yu. F. Shepelev (1970): "The crystal structures of the rare earth pyrosilicates". ''Acta Crystallographica Section B'', volume B26, pages 484-492. Other researchers also studied
yttrium pyrosilicate Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in com ...
.,Dias, H.W.; Glasser, F.P.; Gunwardane, R.P.; and Howie, R.A. (1990): "The crystal structure of δ-yttrium pyrosilicate, δ-". ''Zeitschrift für Kristallographie'', volume 191, issues 1/2, pages 117-123; ISSN 0044-2968 gadolinium pyrosilicate ., and scandium pyrosilicate .Anan'eva, G.V.; Karapetyan, V.E.; Korovkin, A.M.; Merkulyaeva, T.I.; Peschanskaya, I.A.; Savinova, I.P.; and Feofilov, P.P. (1982): "Strukturnye kharakteristiki i fizicheskie svojstva kristallov diorto(piro)silikatov lantanoidov, ittriya i skandiya, vyrashchennykh metodom Chokhral'skogo" ("Structural characteristics and physical properties of diortho(pyro)silicate crystals of lanthanides yttrium and scandium grown by the Czochralski technique"). ''Izv. Akad. Nauk SSSR, Neorg. Mater'' (translated in ''Inorganic Materials'', USA) volume 18, issue 3, pages 442-445. ISSN 0002-337X.


Preparation

Rare earth pyrosilicates can be obtained by fusing the corresponding oxide with silica in 1:2 molar ratio, Single crystals can be grown by the Verneuil process or the
Czochralski method The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platinum, silver, gol ...
.


References

{{reflist Oxyanions Sorosilicates