Characterizing the Infrared Bands of Aqueous Soluble Silicates

Abstract

A systematic study of the transition in silicate solutions from a solution containing a highly complex mixture of silicate species to one dominated by a single symmetric cubic octamer has been completed. Infrared and NMR results have been analyzed and compared with each other and literature values. The FT-IR band locations are dependent on many factors, particularly the dominant band near 1000 cm(-1). The analysis supports Dent Glasser's hypothesis that silica polymerization results from changes in distribution between the larger colloidal silica and intermediate sized anionic fraction rather than the continuous stepwise growth seen with organic polymerization. A constant value of silica monomer seen in all solutions independent of the complexity of the species or their distribution suggests equilibrium between the monomeric form and larger anions and polymers that is independent of their structure. No evidence is uncovered for specific silicate species dependent IR band assignments.

The rheological anomaly in water-silicate systems: a possible thermodynamic explanation

“…The state of the problem of theoretical modeling aqueous solutions of silicates at the end of the 1970s is described in monograph [4], where the dissociation constants of a mono-, oligo-and polysilicic acids and the polycondensation constant of monosilicate ions, are given. This line of research was further developed in a number of works, the authors of which created theoretical models based on the results of potentiometric [18], NMR [18,19], rheological [20], FTIR [21] and other experiments. In all these studies, the equilibrium between monomeric and individual oligomeric SOA was studied with the use of experimental or calculated data on the corresponding equilibrium constants.…”

Recent Trends in Operando and In Situ Characterization: Techniques for Rational Design of Catalysts

“…Three possible mechanisms, as shown in Figure 12.2a [16], are distinguished and the crucial differences lie in two points: the size range in which the first ordered units are formed and the size range in which particles aggregate to form larger structures. The parameters that influence the mechanism and thus the final structure are reaction mixture pH [25] and synthesis and crystallization temperatures [21,23].…”

“…29 Si NMR is one of the most used techniques for the analysis of these compounds. It is especially capable of analyzing silicate structures in solution [25,32]. However, all NMR studies on silicalite-1 synthesis until now have been performed ex situ [21,22,25,27], mostly as a complementary technique to in situ scattering techniques.…”

“…It is especially capable of analyzing silicate structures in solution [25,32]. However, all NMR studies on silicalite-1 synthesis until now have been performed ex situ [21,22,25,27], mostly as a complementary technique to in situ scattering techniques. As in situ NMR has been used in the study of catalytic reactions over a catalytic solid [33] (see the subsequent text), it might only be a matter of time before these studies are expanded to 29 Si NMR of actual silicalite-1 synthesis.…”

“…However, in the case of silicalite-1 synthesis, they have not yet been used [35]. Attenuated total reflectance infrared (ATR-IR) spectroscopy has however been used to study soluble silicates and shown to be able to characterize various structures [25,[35][36][37]. It is likely only a matter of time before we see ATR-IR used under in situ conditions.…”