Cyclic polysilicates

Silicate Modifications. A method has been described in which silicate minerals are simultaneously acid-leached and trimethylsilyl end-blocked to yield specific trimethylsilyl silicates having the same silicate structure as the mineral from which these were derived (12). Olivine, hemimorphite, sodalite, natrolite, laumontite, and sodium silicates are converted to TMS derivatives of orthosilicates, pyrosilicates, cyclic polysilicates, etc, making it possible to classify the minerals according to their silicate structure. The same technique is used to analyze the siloxanol structure of aqueous solutions of vinyltrimethoxysilane (13). Certain anionic siliconates stabilize solutions of alkali silicates to give stable solutions in water or alcohols at any pH (14). Such silicate—siliconate mixtures are used as corrosion inhibitors in glycol antifreeze (15) (see Antifreezes and deicing fluids Corrosion and CORROSION CONTROL). 

Figure 15. Partial charge distributions in cyclic polysilicates found in minerals, (a) muirite BajQ(Ca,Mn,Ti)4Sig024(Cl,OH,0)i2.4H2o (P /mmm with R = 6.5%) and (b) eudialyte. Naj2CagFe3Zr3Si2406g(Cl,0H)g (Rim with R = 15%). Charges given are those on the network-extraeted oligomers.

From the various cyclic polysilicate ions that exist in small amounts in solution as the Si02 Na20 ratio exceeds 2 1, similar polycyclic oligomers appear as the first three-dimensional particulate colloid species. These then serve as nuclei as still larger colloid-ion species are formed at higher Si02 Na20 ratios. 

Regardless of the t)q)e of soluble metal silicates used, they are subject to the same molecular speciation in aqueous solution resulting in a mixture of monomeric tetrahedral ions, oligomeric linear or cyclic silicate ions, and polysilicate ions. Sodium metasilicate, an example of a soluble metal silicate, can be prepared in anhydrous form or in the presence of water of crystallization as the penta- or nona-hydrate. It is readily soluble in water [8]. 

It is well known that primary, aliphatic amines react with CO2 to form carbamic acids this eliminates CO2 as a candidate fractionation solvent. Supercritical ethane was used instead to process the amine-terminated polysil-oxanes. Many parent polymers were synthesized ranging in average molecular weight from 2,000 to 10,000 with polydispersities of 2 to 3 they were all first stripped of cyclics using ethane at 80°C then fractionated with ethane at 80°C with increasing pressure profiling from 55 bar to 275 bar. 

Figure 12 Partial charge distributions in cyclic trimers [SD Os] " found in polysilicates minerals, (a) Benitoite BaTiSi 09. (b) Wollastonite 03381309 (charges given are those on the Fl la network-extracted trimer). (c) Wadeite K2ZrSi309.

An alkoxysiloxane precursor or mix (usually the methyl or ethyl ester) is partially or completely hydrolyzed to produce a sol composed of linear, branched and/or cyclic polysiloxane and/or polysilicate species. Acidic prehydrolysis, fol-... 

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