Alkaline silicate

Keywords FTIR, Raman, alkaline, silicate, dissolved. 

IR and Raman spectroscopy can fulfill these requirements and they are also robust enough for in situ silicate analysis in plant reactors [7]. Both of these techniques have been used for identifying the symmetric (s) and asymmetric (as), stretching (va, vas) and bending (5a, 5as) O-Si-O vibrations in aqueous alkaline silicate solutions which are the cheapest hence most frequently used ingredients for zeolite synthesis [8, 9 and references herein]. However, this information has to be "translated" into siloxane ring... 

About one decade ago Bass et al. [13,14] proposed first that such approach could help in exploring the structure of water dissolved silicates. Following this initiative, recently we critically evaluated how the published FTIR and Raman assignments could be adopted for differentiating between the molecular structures of some commercially available sodium silicate solutions [7-9,15], In this paper we present comparative structural studies on aqueous lithium and potassium silicate solutions as well. According to some NMR studies, the nature of A+ alkaline ion and the A+/Si ratio barely affects the structural composition of dissolved silicate molecules [5], In contrast, various empirical observations like the tendency of K-silicate solutions to be less tacky and more viscous than their Na-silicate counterparts, the low solubility of silica films obtained from Li-silicate solutions compared to those made from other alkaline silicate solutions, or the dependence of some zeolite structures on the nature of A+ ions in the synthesis mixture hint on likely structural differences [16,17]. It will be shown that vibrational spectroscopy can indeed detect such differences. 

Table 1. Selected properties of the initial alkaline silicate solutions (more at www.pqcorp.com)...

Table 2 shows every measured value necessary to calculate the average molweight of silicates in various solutions. It also permits to follow the step by step calculation as detailed in our previous papers [8,9], It was found that, in contrast to the common belief, every dilute alkaline silicate dissociates only partly at the concentrations studied. The AMW, expressed as number of [Si04] tetrahedra per silicate ion in the last column of this table, clearly depends on the type of A+ ions, the A/Si ratios, and the concentration. In general AMW decreases with increasing dilution as one can expect and it is lower in the high A/Si ratio silicates (Kasil 1624 and Star) than in the other silicates at comparable concentrations. 

Table 2. Concentration, dissociation, ion size and other parameters of aqueous alkaline silicate solutions... 

Lime.—This substance, which forms an important constituent in flint-glass, maybe introduced either as a carbonate, or slaked or burned. Limestone, however, that contains proto-carbonate of iron, must be excluded from tha mixture for making white glass. The action of lima is to render the alkaline silicates insoluble, and when rightly balanced by the other ingredients, it promotes the fusion of the whole, and improves the quality, but when added in excess, the glass becomes hard and difficult to work, and subjoet to devitrification. 

ASBESTOS. The tenn asbestos is a generic designation referring usually to six types of naturally occurring mineral fibers which are or have been commercially exploited, These fibers are extracted from certain varieties of hydrated alkaline silicate minerals comprising two families seipe.ntin.es and amphiboles. The serpentine group contains a single fibrous variety chrysotile five fibrous forms of amphiboles are known anthophyllite, amosite, crocidolite. tremolite, and actinolite... 

Oxides of metals in Group 1 of the periodic table, such as potassium and sodium, are also highly reactive, though. It would not be safe to allow these chemicals to remain in the airbag, so the potassium and sodium oxides then react with silicon dioxide (Si02). This reaction forms an alkaline silicate powder. Alkaline silicate, a type of glass, will not burn and the resulting powder is harmless. 

The first part of the present paper is related to the alkaline silicate solutions and represents the main point of our work. The second part conoerns the alkaline aluminosilicate solutions which were studied less extensively. 

The model presented here alloas. in principle, the determination of the concentration of any oligomer species in an alkaline silicate solution provided that the monomeric silica concentration and the pH are knoon. Due to their greater complexity and experimental difficulty. the investigation of aluminosilicate solutions corresponds only to an extension of this model and it Has dealt with in a simplified say. 

Perhaps we have concentrated too much on the quaternary amines as templating agents. Another approach is suggested by Verdijn in the synthesis of zeolite L(17). As showing in Table VI, by addition of only trace amounts of alkaline earth cations, especially strontium, the gel composition range which produced the desired zeolite L product was widened, the formation rate increased, smaller crystallites were obtained, and stirred synthesis became possible. The alkaline earths were very probably present when natural faujasite was formed. But their solubility in alkaline silicate liquors is low 200 ppm Sr2 is near saturation in the synthesis slurry. 

The alkaline silicate species are commonly in dynamic equilibrium and on undergoing pH changes or dilution, equilibria may be quite rapidly established,... 

BURCO STABILIZER 35 eliminates the need for any form of alkaline silicates or chelates. 

Discussion of Experiment 140. — When silicon dioxide is fused with alkaline carbonates, an alkaline silicate is formed. The alkaline silicates are soluble in water, and when hydrochloric acid is added to such a solution, the gelatinous precipitate formed is a silicic acid having the formula H2Si03 (probably). This acid is decomposed by heat into silicon dioxide and water, thus —... 

Without tach as auxiliary ligand Cs2[Si(cj5 -InsH 3)2] (Cs298) [92] shows a bis-tridentate 1,3-diolate binding-cw-inositol complex. In contrast to the finding that a pyranoidic 1,2,3-triol like C4-Me- 8-D-Ribp, with its large torsional angles, is not so efficient an Si-chelator as a furanoidic diol, the significant enrichment of aqueous alkaline silicate solutions by hexaco-ordinate species on addition of cw-inositol is remarkable. 

Such a hybrid behavior has been noted on various materials amongst the most porous and is not peculiar to low density xerogels. It is the case of carbon black [6] and of some silica precipitated from alkaline silicates. The fumed silica synthesized in gas phase exhibits, depending on their bulk density, either a collapse behavior similar to the one of aerogels or a hybrid behavior similar to the one of low density xerogels [7]. 

The study of alkaline silicate and aluminosilicate solutions is of fundamental importance for a better understanding of the mechanism of zeolite synthesis (1,2). Real progress has been realized durinq the last fifteen years thanks to the use of new techniques such as the trimethylsilylation (3,4) of polysilicic acids (followed by a chromatographic separation of the derivatives) and, even more, 29Si and 27Ai NMR spectroscopy (5-11). The latter techniques have enabled the identification of about twenty types of oligomers in silicate solutions and in some cases estimates of their respective concentrations. The investigation of alkaline aluminosilicate solutions is... 

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