Silicates orthosilicates

Dicalcium silicate is the orthosilicate with formula Ca lSiO ], and tricalcium silicate—orthosilicate with formula Caj[SiOJO. 

Normal and dibasic lead stearate have a stabilising effect but their main uses are as lubricants (see section 12.5.4). Lead silicate is sometimes used in leathercloth formulations but is today of little importance. Other lead compounds now of negligible importance are coprecipitated lead orthosilicates and lead salicylate. 

Silicate binders are used in conjunction with zinc powder to give paints of excellent corrosion resistance. The organo-silicates, e.g. ethyl orthosilicate, are most commonly used. The full potential of this type of binder has probably not yet been exploited. 

A. Determination of silica in a soluble silicate Discussion. Most of the silicates which come within the classification of soluble silicates are the orthosilicates formed from SiO units in combination with just one or two cations. More highly condensed silicate structures give rise to the insoluble silicates. 

Polysilicates are effective in potable HW systems and provide threshold effect protection against hardness destabilization and red water. They also function by laying down a protective calcium silicate film. Polysilicates used for this type of application typically require a dose rate of 8 to 15 ppm Si02 above that of the natural orthosilicate found in the MU water. Where polysilicates are employed for dualtemperature and LPHW systems, however, the silicate reserve required is higher and ranges from 50 to 150 ppm. 

The silicates which will occur are orthosilicates, R++2Si04, metasilicates, R++Si03, etc. This is verified by observation no basic silicates of such cations are known, although many normal silicates such as forsterite Mg2Si04, etc., exist. 

In our previous work, we reported that a new ALD precursor HfCl2[N(SiMe3)2]2, which contains Si in ligands, can be used to deposit hafhium silicate films using H2O as an oxidant but the Si content in the film was relatively low [4]. In the present work, two different approaches were performed to increase Si content and to improve the film properties. One is to use hydrogen peroxide as a stronger oxidant than water, and the other is to use tetra-n-butyl orthosilicate (TBOS, Si(0"Bu)4) as an additional Si source. 

Closely related to silica are the silicate minerals, all of which contain polyatomic anions made of silicon and oxygen. The simplest silicates, called orthosilicates, contain Si04 anions. The 8104 anion is tetrahedral, with a central silicon atom bonded to four outer oxygen atoms. 

Different minerals contain different metal cations to balance the -4 charge on the orthosilicate ion. Examples Include calcium silicate (Ca2 Si04), an important ingredient in cement, and zircon (ZrSi04), which is often sold as artificial diamond. One of the most prevalent minerals in the Earth s mantle is olivine, Af2(Si04), in which M is one or two of the abundant metal cations, Fe -, Mg -, and Mn +. 

Note carefully the sequence of intermediate reactions that have occurred, as depicted in this diagram. We see that the first solid state reaction involves formation of the orthosilicate. But this is very quickly transformed into meta- and pyro-sllicates. However, it is the metasilicate which predominates as the solid state reaction reaches its maturity. Finally, it predominates over all other forms of silicate present. 

It is helpful in the discussion to describe silicate structures using the Q nomenclature, where Q represents [SiOJ tetrahedra and the superscript n the number of Q units in the second coordination sphere. Thus, isolated [SiO ] " are represented as Q and those fully connected to other Q units as Q. In general, minerals based on Q , Q and units are decomposed by acids. Such minerals are those containing isolated silicate ions, the orthosilicates, SiO (Q ) the pyrosilicates, Si O " (Q ) ring and chain silicates, (SiOg) (Q ). Certain sheet and three-dimensional silicates can also yield gels with acids if they contain sites vulnerable to acid attack. This occurs with aluminosilicates provided the Al/Si ratio is at least 2 3 when attack occurs at A1 sites, with scission of the network (Murata, 1943). 

Island silicates containing discrete ions. Orthosilicates, SiO " (Q ) pyrosilicates, Si O " (Q ) and ring silicates, SigO,", SieOir (Q ). 

Silicates having an O Si ratio larger than or equal to 4 are orthosilicates, i.e. the Si04 tetrahedra do not share atoms with each other, but with the polyhedra about the other cations. Examples olivines, M2Si04 (M = Mg2+, Fe2+) and garnets, M3M2[Si04]3 (M = Mg2+, Ca2+, Fe2+ M = Al3+, Y3+, Cr3+, Fe3+). 

Phenylene-bridged periodic mesoporous organosilicas, with both amorphous and crystal-like walls, (referred to in the following as AW-Ph-HMM and CW-Ph-HMM, respectively) were synthesized and characterized as previously reported [6,7]. BTEB was used as a precursor for both solids the surfactant was Brij-76 (Ci8H37(OCH2CH2)nOH) in acidic media for AW-Ph-HMM and octadecyl-trimethylammonium bromide(ODTMA) in basic media for CW-Ph-HMM. A purely siliceous MCM-41 sample was also synthesised, the first step being the solution of octadecyltrimethylammonium bromide in a basic aqueous solution (NH3), kept a 333 K. Tetraethyl orthosilicate (TEOS) was then added in all cases dropwise, and the mixture stirred for 24h at room temperature (H20 34.2 g/ NH3 (15%) 8.52 g/ ODTMA 0.73 g TEOS 3.24 g). After further 24 hours in hydrothermal conditions at 368 K, the sample... 

Some non-silica sol-gel materials have also been developed to immobilize bioactive molecules for the construction of biosensors and to synthesize new catalysts for the functional devices. Liu et al. [33] proved that alumina sol-gel was a suitable matrix to improve the immobilization of tyrosinase for detection of trace phenols. Titania is another kind of non-silica material easily obtained from the sol-gel process [34, 35], Luckarift et al. [36] introduced a new method for enzyme immobilization in a bio-mimetic silica support. In this biosilicification process precipitation was catalyzed by the R5 peptide, the repeat unit of the silaffin, which was identified from the diatom Cylindrotheca fusiformis. During the enzyme immobilization in biosilicification the reaction mixture consisted of silicic acid (hydrolyzed tetramethyl orthosilicate) and R5 peptide and enzyme. In the process of precipitation the reaction enzyme was entrapped and nm-sized biosilica-immobilized spheres were formed. Carturan et al. [11] developed a biosil method for the encapsulation of plant and animal cells. 

The tetrahedral Si()44 ion is known as the orthosilicate ion. It can be regarded as the fundamental unit in the structures of most complex silicates. Several minerals including phenacite, Be2Si04, and willemite, Zn2Si04, contain this ion. Both of these minerals have tetrahedral coordination of Si044- units around the metal ion ... 

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The product of the fusion of silica with sodium carbonate, sodium silicate (strictly called sodium poly trioxosilicate but usually metasilicate), dissolves in water to give a clear, viscous solution known as waterglass . It hydrolyses slowly and silica is precipitated. Besides the metasilicate, other silicates of sodium are known, e.g. the poly-tetroxosilicate (orthosilicate), Na4Si04. Only the silicates of the alkali metals are soluble in water. Other silicates, many of which occur naturally, are insoluble, and in these substances the polysilicate anions can have highly complicated structures, all of which are constructed from a unit of one silicon and four oxygen atoms arranged tetrahedrally (cf. the structure of silica). Some of these contain aluminium (the aluminatesilicates) and some have import ant properties and uses. 

In the silicate crystal chemistry, compounds such as Mg3Al2Si30i2 are classified within the orthosilicates owing to the isolated Si044+ tetrahedra existing in their structure, and better described by a chemical formula such as Mg3Al2(Si04)3. 

Kieflfer S. W. (1980). Thermodynamics and lattice vibrations of minerals, 4 Application to chain and sheet silicates and orthosilicates. Rev. Geophys. Space Phys., 18 862-886. 

Synonyms Tetraethyl orthosilicate tetra-ethoxysilane ethyl orthosilicate silicic acid, tetraethyl ester... 

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