Aqueous solutions silicate solution, kinetics

A more economical route to MQ resin uses low cost sodium silicate and trimethylchlorosilane as inputs (eq. 35) (395). The sodium silicate process is initiated by acidifying an aqueous sodium silicate solution to a pH of 2. The resulting hydrosol quickly builds molecular weight. The rate of this increase is moderated by the addition of an alcohol such as 2-propanol. The hydrosol is subsequently silylated by the addition of trimethylchlorosilane. This process, which is kinetically sensitive and limited to synthesizing M/Q ratios of 1 or less, is preferred when MQ resins having high (>1%) OH content are required... 

Boyd GE, Adamson AW, Myers LS (1947) The exchange adsorption of ions from aqueous solutions by organic zeolites II. Kinetics. J Am Chem Soc 69 2836-2848 Brindley GW, MacEwan DMC (1953) Structural aspects of the mineralogy of clays and related silicates. In Green AT, Stewart GH (eds) Ceramics—A Symposium. The British Ceramic Society, Stoke-on-Trent UK, pp 15-59... 

The scope of kinetics includes (i) the rates and mechanisms of homogeneous chemical reactions (reactions that occur in one single phase, such as ionic and molecular reactions in aqueous solutions, radioactive decay, many reactions in silicate melts, and cation distribution reactions in minerals), (ii) diffusion (owing to random motion of particles) and convection (both are parts of mass transport diffusion is often referred to as kinetics and convection and other motions are often referred to as dynamics), and (iii) the kinetics of phase transformations and heterogeneous reactions (including nucleation, crystal growth, crystal dissolution, and bubble growth). 

Experimental investigations will continue to play a critical role in understanding heterogeneous reaction kinetics, such as mineral dissolution rates in silicate melts and in aqueous solutions, the melting rates at the interfaces of two... 

Helgeson, H. C. Kinetics of mass transfer among silicates and aqueous solutions, Geochim. Cosmochim. Acta 35,... 

The above concept describes very well the real behaviour of silicate glasses in contact with water and aqueous solutions, in spite of its considerable simplification, in particular as regards the assumption of linear distribution of concentration in the leached layer. In fact, the concentration distribution is very complex and also depends on total glass composition. This question on the mechanism and kinetics involved in the decomposition of glass by aqueous solutions has recently been paid considerable attention in the literature. An up to date review is presented, for example, in the survey paper by Hench (1977),... 

Helgeson, H. C. (1972), Kinetics of Mass Transfer Among Silicates and Aqueous Solutions Correction and Clarification, Geochim. Cosmochim. Acta 36, 1067-1070. Holdren, G. R., Jr., and R. A. Berner (1979), Mechanism of Feldspar Weathering—I. 

O-P linkages as in silicates. These linkages are kinetically stable in aqueous solution and are... 

Frolov, Shabanova, and co-workers (37-39) studied the transition of a sol into a gel and the aggregate stability of colloidal silica. Their aim was to develop a technology for the production of highly-concentrated silica sols and to use them as binders, catalyst supports, polymer fillers, adsorbents, and so forth. Kinetic studies were made of polycondensation and gel formation in aqueous solutions of silicic acids. At the stage of particle growth, poly condensation proceeds in the diffusion-kinetic region. With changes in pH, temperature, concentration, and the nature of electrolytes,... 

So, NMR spectra of 4,4 -bipyridyl, pyrazine, and ethylenediamine coordinated to undecatungstocobalto(III)silicate and -borate anions. Identification of 1 1 and dumbbell-shaped 12 complexes, Bull. Korean Chem. Soc, 14 759 (1993) (c) J.L. Samonte and M.T. Pope, Derivatization of polyoxotungstates in aqueous solution. Exploration of the kinetic stability ofcobalt(II)- and cobalt(III) derivatives of lacunary anions with pyridine and pyridine-type ligands. Can. J. Chem.. In press... 

The use of Si NMR to obtain definitive information about the chemical structure and kinetics of aqueous silicate solutions is discussed. Special techniques such as enrichment in si are required. Some typical spectra are shown and results presented. 

In spite of the low inherent sensitivity of Si NMR, it is a very valuable tool for the study of the species present in aqueous silicate solutions. Firm deductions about the chemical structure of such species can only be made using systems enriched in si. With the methodology described above, we have positively identified twelve species in an alkaline potassium silicate solution. Kinetic information is available in acid silicate solutions. Our experimental procedures are outlined in references ( - , 20). This article is not intended as a comprehensive review of the area, but the list of references, including ref. (22) (hitherto unmentioned), covers all currently published work. 

In the course of synthesis, the template molecules act as structure-directing agents. Size and shape of the template determines the geometry of the pore. During crystallization, the amphiphilic nature of the template (mainly organic amines) allows for molecular interaction between the aqueous silicate solution and the growing hydrophobic silica framework. Thermodynamic analyses suggest that the kinetics of nucleation are the most important factors in the crystallization process. 

Kinrade, S.D., and Swaddle, T.W. (1988) SiUcon-29 NMR Studies of Aqueous Silicate Solutions. 2. Transverse 29si Relaxation and the Kinetics and Mechanism of SiUcate Polymerization, Inorg. Chem., 27,4259-4264. 

The synthesis of imogolite occurs in mild conditions and in aqueous solution. However, its mechanism of formation is rather complex and involves self assembly. The AP+ ions in solution rapidly hydrolyze forming polynuclear species (Bi et ah, 2004). It has been pointed out that the thermodynamic equilibrium is not achieved rapadly and the kinetics is very slow (Casey, 2006). The silicates in solution are a very complicated system forming many polynuclear intermediates (Exley et ah, 2002 Schneider et ah, 2004). The imogolite formation... 

Assuming a constant surface area, dissolution at a solution-solid interface (Case I) results in linear kinetics in which the rate of mass transfer is constant with time (equation 1). Analytical solutions to the diffusion equation result in parabolic rates of mass transfer (, 16) (equation 2). This result is obtained whether the boundary conditions are defined so diffusion occurs across a progressively thickening, leached layer within the silicate phase (Case II), or across a growing precipitate layer forming on the silicate surface (Case III). Another case of linear kinetics (equation 1) may occur when the rate of formation of a metastable product or leached layer at the fresh silicate surface becomes equal to the rate at which this layer is destroyed at the aqueous... 

White, A. F., and Claassen, H. C. Dissolution kinetics of silicate rocks, application to solute modeling, JjL Jenne, E.A., ed., Chemical Modeling—Speciation, Sorption, Solubility, and Kinetics in Aqueous Systems, Am. Chem. Soc., 1978 (this volume). 

---