Alkaline silicate solution

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

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. 

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. 

By means of Si NMR spectroscopy, it is established that the distribution of silicate anions in alkaline silicate solutions is a moderate function of base composition. At a fixed SiC concentration and silicate ratio, the proportion of Si present in oligomeric and cage-like structures increases in progressing from Li to Cs hydroxide. This trend is ascribed to cation-silicate anion pairing and to a higher selectivity for ion pairing by large silicate anions as cation size increases. 

The hardening of a silicate - ester sand proceeds through an intermediate step, which consists of the hydrolysis of the ester by the alkaline silicate solution. This hydrolysis produces glycerol and acetic acid, which precipitates a silicate gel to form the initial bond. Further strength develops as the residual silicate dries. 

Kirkpatrick, R. J. (1989) Oxygen-17 Nuclear Magnetic Resonance Spectroscopic Studies of Aqueous Alkaline Silicate Solutions, J. Chem. Soc. Dalton Trans., 275-281. 

McCormick, A. V., Bell, A. T., and Radke, C. J. 1989JEvidence from alkali metal NMR spectroscopy for ion pairing in alkaline silicate solutions. J. Phvs. Chem. 93t 1733-7. 

Precipitated siHcas are industrially produced by acidifying an alkaline silicate solution (waterglass) with sulfuric acid in a semi-batch stirred tank reactor. 

Silicon. Ionization of Cl from [0(CMe = NNMe2)2SiClPh] has been observed using Si NMR spectroscopy. Si NMR spectroscopy has been used to study the formation of [(MeO)Si(OH)3] in methanolic alkaline silicate solutions. The role of Na+ in the interaction mechanism of sodium silicate melt has been probed by and Na NMR spectroscopy. Si NMR spectroscopy has provided evidence of pentaoxosilicon complexes in dilute neutral aqueous silicate solutions. ... 

In-depth NMR studies have given us a better picture of the molecular forms present in alkaline silicate solutions. Most of these species are ring-shaped. Strictly linear molecules with more than four silicon atoms are nonexistent, except for anhydrous sodium metasilicate. The information collected by NMR deals mostly with the smaller species possessing less than 10 silicon atoms, called oligomers. There is little information available on the... 

In general the Si/AI ratio in geopolymer systems has an important influence on the structure and mechanical properties. Other researchers such as Palomo et al. showed that Al solubility is generally much higher than Si under alkaline conditions, thus aluminate anions are likely to react with silicate species from alkaline silicate solutions. A higher Al content assists in condensation occurring more feasibly, and tends to lead to a denser network structure due to the removal of more hydroxyl groups. 

The Al reaction remains a critical factor in the performance of these Si rich systems. Given that aluminate anions for the reaction are solely derived from the dissolution of mineral oxides under alkaline conditions, monomeric [Al(OH)4] ions are probably the only aluminate species existing under high alkaline conditions. On the other hand, silicate species come from both soluble alkaline silicates and the dissolution of mineral oxides. In the specific case of metakaolin systems, the silicate species from the dissolution of particles are difficult to predict because the hydrolysis process of amorphous silica is kinetically dependent on various factors, such as the reactivity of the particles, temperature, time, and the eoncentration and pH value of alkaline silicate solutions. 

Sample preparation. Samples were synthesized using an alkaline silicate solution and three metakaolins (namely Mkl, Mk2 and Mk3). The alkaline silicate solution was obtained by the dissolution of KOH pellets (85.2 % purity) and amorphous silica (99.9 % purity) in water at room temperature. Syntheses were performed by mixing the alkaline silicate solution and metakaolins. The samples were named Ml, M2 and M3. Other samples were realized with addition of ammonium molybdate (10 and 20% molar) to the alkaline solution before metakaolin. These samples were named Ml-20, M2-10, M2-20 and M3-20. 

---