Polymerization Of Silicic Acid Research Articles

Polymerization of Silicic Acid A Review

Etude generale: utilisation de la spectrophotometrie, de la chromatographie gaz-liquide des derives obtenus par trimethylsilylation, et de la chromatographie pour etudier la reaction. Mecanisme en 3 etapes: formation de l'acide polysilicique par reaction des acides molybdosiliciques reactifs, croissance des particules d'acide polysilicique par reaction des acides molybdosiliciques avec l'acide polysilicique, et par reaction entre acides polysiliciques. Influence du pH et de l'ion fluorure sur la vitesse de ces 3 processus

Preparation of monolithic gels SiO 2M xO y (M = Al, Zr) by the reaction of silicic acid with metal chelate compounds

Preparation and thermal treatment of monolithic gels SiO 2M x O y (M = Al, Zr) were investigated. The gels were prepared via polymetalloxane compounds formed by condensation polymerization of silicic acid with metal chelate compounds. The reaction gave a homogeneous solution of the polymer which underwent further condensation to form transparent monolithic gels of 3.0–89 mol% Al 2O 3 and 5.7–94 mol% ZrO 2. Thermal treatment of gels provided oxide glasses. The X-ray analysis showed that SiO 2Al 2O 3 gels heated up to 1000°C were amorphous regardless of composition while SiO 2ZrO 2 gels showed crystallization due to ZrO 2 depending on the thermal treatment temperature and their composition.

Effect of aluminium on the polymerization silicic acid in aqueous solution and the deposition of silica of silica

The effect of aluminium on the polymerization of silicic acid was studied at pH 7, 8 and 9 in the aluminium concentration range of 0–26 ppm (Al) by spectrophotometry, gel chromatography and 27Al NMR. Retarding and accelerating effects of aluminium on the growth of polysilicic acid particles and on the reaction between monosilicic acid and polysilicic acid were observed by changing the pH. It is suggested that the accelerating effect on the reaction between polysilicic acid particles is due to the formation of aluminium hydroxide on the surface of polysilicic acid. The rate of decrease in the monosilicic acid concentration in the presence of aluminium was faster than that in the absence of aluminium at pH 9, because monosilicic acid could be adsorbed rapidly on the aluminium hydroxide. From the results it was presumed that the formation of aluminium hydroxide on the solid surface may accelerate the deposition of silicic acid from geothermal water.

Preparation of monolithic SiO 2TiO 2 gels by condensation polymerization of silicic acid and titanium chelates

The preparation of monolithic gels as a precursor for SiO 2TiO 2 glasses via polytitanosiloxanes was investigated. The gels were obtained from polytitanosiloxanes formed by condensation polymerization of titanium chelates and silicic acid. Silicic acid was extracted with tetrahydrofuran from an aqueous sodium metasilicate solution neutralized with hydrochloric acid. Titanium chelates used were bis(acetylacetonato)titanium diisopropoxide (ATP) and bis(ethyl acetoacetato)titanium diisopropoxide (ETP). Monolithic gels with a TiO 2 content of less than 20 mol% were formed by the reaction of silicic acid with ATP, whereas the reaction with ETP provided transparent monolithic SiO 2TiO 2 gels of 5.7–94 mol% TiO 2. Heat treatment of the gels gave monolithic SiO 2TiO 2 glasses.

A study of mechanism of silica fouling of anion exchange resins

The relationship between silica fouling of a strong-base anion exchange resin and polymerization of silicic acid or size of polysilicic acid molecules was studied. The amount of silica adsorbed by the resin increases with the concentration of low-molecular weight polysilicic acids. The SiO 2 content of the resin reaches a maximum at an aggregation number of 3.3.

Preparation of A Gel-Like Silica Glass by the Condensation of Silicic Acid in Organic Solvents

The preparation of a gel-like silica glass from silicic acid was investigated. This method requires the processes: (1) Extraction of silicic acid with tetrahydrofuran from an aqueous sodium metasilicate solution neutralized with hydrochloric acid, followed by concentration of an extracted solution to give “concentrated silicic acid”, (2) Preparation of silicic acid solutions with various concentrations and solvents to allow a moderate condensation, and (3) Formation of a gel plate by condensation polymerization of silicic acid with evaporation of solvent. Since gels are formed by the condensation which is highly dependent on the evaporation of solvent. Alcohols, acetone, methyl ethyl ketone, THF, formamide, dimethyl formamide, acetonitrile and water were used as solvent. Pieces of silica gels were obtained easily, but plate was not obtainable unless condensation was controlled. Gel plates without cracks were obtained when the solutions with the molar ratio (solvent/SiO2) of 1-5 were aged.

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.

Study of the Polymerization of Silicic Acid Adsorbed on Iron(III) Hydroxide by Trimethylsilylation-Gas Chromatography

Abstract Polymerization of silicic acid adsorbed on iron (III) hydroxide from dilute monosilicic acid solutions in the concentration range 5–40ppm (SiO2) was studied over the pH range 6–12. Silicic acid species formed on the hydroxide were trimethylsilylated and trimethylsilyl derivatives were detected by gas chromatography. Monosilicic acid adsorbed polymerized, and dimer (Si2O76−), linear trimer (Si2O108−) and tetramer (Si4O1310−), and cyclic tetramer (Si4O128−) were found as polymeric species.

Study of the polymerization of silicic acid in aqueous solution by trimethylsilylation—gas chromatography

The effects of pH, concentration of monosilicic acid and temperature on the formation of low-molecular-weight silicic acid species in the early stages of polymerization were studied by trimethylsilylation—gas chromatography (TMS—GC). The change with time in the distribution of silicic acid species up to the hexamer was measured. The results obtained by TMS—GC are compared with those obtained by colorimetry. In solutions of initial monosilicic acid concentration of 600 ppm SiO 2 at pH 1.8, 20°C and at pH 8.5, 90°C, it was found that a temporary equilibrium is set up among ▪, ▪ and ▪ during the induction period. On the other hand, for 2500 and 5000 ppm SiO 2 solutions at pH 1.8, 20°C, higher-molecular-weight silicic acid species than ▪ were formed during the induction period, and the distribution of these species changed with time. All of the silicic acid species formed during the induction period, and the distribution of these species changed with time. All of the silicic acid species formed during the induction period were determined by colorimetry.

Gel chromatographic study of the polymerization of silicic acid in the presence of fluoride

The effect of fluoride on the polymerization of silicic acid was studied in the pH range 2.5–0. The polymerization of silicic acid was accelerated by fluoride. The rate of reaction between monosilicic acids was most rapid at an F/Si atomic ratio of about 0 5. In silicic acid solutions containing fluoride up to an F/Si atomic ratio of 2 0 the growth rate of polysilicic acid particles increased with increasing fluoride concentration and was most rapid at about pH 1. It Is suggested that the growth of polysilicic acid particles is due mainly to the reaction between monosilicic and polysilicic acids, because the reaction between polyslllclc acids is relatively slow.

Polymerization of Silicic Acid Adsorbed on Aluminium Hydroxide

Abstract Factors controlling the absorption of silicic acid on aluminium hydroxide from aqueous solution and the polymerization of adsorbed silicic acid were studied. Measurements included the amount of silicic acid adsorbed on aluminium hydroxide, the amount and size distribution of the polysilicic acid formed, and the differential thermal analysis curve of aluminium hydroxide which had adsorbed silicic acid. The adsorption and the polymerization of silicic acid are affected by pH, the relative amounts of silicic acid and aluminium hydroxide, the reaction time between monosilicic acid and aluminium hydroxide, and the formation of amorphous aluminosilicate. The amount of adsorbed silicic acid and the rate of its polymerization are maximum at pH 9.0–9.5. A part of adsorbed monosilicic acid reacts with aluminium hydroxide to form an aluminosilicate. In an early stage of the polymerization of the adsorbed silicic acid, the polymerization mainly proceeds by the reactions between monosilicic acids and between monosilicic and polysilicic acids; the particle sizes of polysilicic acids gradually increase with time. When the polymer particles grow large enough to touch neighboring polymers, the growth rate of polymer particles becomes faster due to the polymer-polymer reactions.

Kinetics of silica polymerization

The polymerization of silicic acid in dilute aqueous solutions was studied experimentally and theoretically. Two basic processes were studied: the formation of colloidal particles by homogeneous nucleation, and their further growth by deposition of dissolved silica upon them. It was found that the state of ionization of the silica surface controls the rate of polymerization. The rate of deposition of dissolved silica on the surface of amorphous silica is proportional to the surface density of ionized silanol groups. The extent of surface ionization also determines the value of the surface tension, and thus also the rate of homogeneous nucleation. Added salts accelerate both molecular deposition and homogeneous nucleation by increasing the extent of surface ionization and decreasing the solubility of silica. Except for fluoride, salt ions were found not to have any specific catalytic effect. Fluoride was confirmed to be a powerful catalyst. Aluminum and boron were found to inhibit the reaction at pH 8. A successful quantitative theory of the homogeneous nucleation of colloidal silica particles was developed. The Lothe-Pound factor was shown to be about 3.34 × 10 25 (kg H 2O) −1. The nucleation model and results of our data analysis are incorporated in a computer code which models the homogeneous nucleation and growth of colloidal silica particles. This code is able to reproduce much of our data to within experimental error, and may be used to generate useful predictions for conditions that are typical of geothermal brines. The concentration of “adsorbed silica” on the surface of amorphous silica was determined, and was found to increase with the concentration of dissolved silica in the ambient solution. It is probably a reaction intermediate between dissolved silica and solid amorphous silica.

ChemInform Abstract: THE KINETICS OF THE POLYMERIZATION OF SILICIC ACID

AbstractDer Polymerisationsprozeß der Kieselsäure läßt sich in 3 Stufen unterteilen: 1. Reaktion zwischen monomeren Kiesel‐ Säuren; 2. zwischen Mono‐ und Polykieselsäuren und 3. zwischen Polykieselsäuren.

Phospholipid monolayers

The action of polymerized silicic acid on lecithin and cephalin monolayers brings about changes in its physical state, molecular area, and pressure of collapse. These changes are more notable in the case of lecithins, varying not only with the substrate pH, but also with the length of the hydrocarbon chains of the fatty acids that esterify glycerol in the molecules of these substances. The different actions observed between silicic acid and the lecithin and cephalin monolayers are explained with the help of different models. © 1981 Dr. Dietrich Steinkopff Verlag.

Polymerization and polymers of silicic acid

Polymerization and polymers of silicic acid

The Kinetics of the Polymerization of Silicic Acid

Abstract The process of the polymerization of silicic acid can be divided into three steps: (1) a reaction between monosilicic acids, (2) a reaction between monosilicic and polysilicic acids, and (3) a reaction between polysilicic acids. The rates of the reactions between monomer-monomer, monomer-polymer and polymer-polymer are most rapid at pH values around 9.3, 8.5, and 6.8 respectively. It is concluded that, above about pH 4, the polymerization due to Reactions 1, 2, and 3 proceeds mainly by a reaction between ionized and un-ionized silanol groups.

Gel chromatographic study of the polymerization of silicic acid in acid solutions

The polymerization of silicic acid in hydrochloric, nitric, perchloric and sulphuric acid solutions has been studied by gel chromatography. The rate of polymerization of silicic acid is in the order of HClO 4 > HCl ≈ HNO 3 > H 2SO 4. A mechanism for the growth of particles of polysilicic acids is proposed. The growth in 1 N acid solutions is due mainly to the reaction between monosilicic and polysilicic acids, whereas that in 3 N and 5 N acid solutions is due mainly to the reaction between polymer species.

Polymerization and polymers of silicic acid

AbstractLinear relationships among molecular weight, polymerization time, and gelation for the condensation of any monomer, including those of unknown size and functionality, are developed and applied to data on soluble silicic acids generated from tetraethyl silicate and from sodium silicate. The results suggest the formation of monomers containing ca. 12–15 OSi units with functionality of ca. 2.05 that condense with a rate constant of ca. 10−4 liter/mole sec and an activation energy of 40–70 kJ/mole. One model compatible with these characteristics and the stoichiometry involved is a ladder polymer ca. 3 SiO units wide. Polymer isolation was achieved by replacing residual OH with (CH3)3Sio, as well as by freezing of of aqueous solutions, which yielded fibers under special conditions. Solutions of the uncapped and capped polymers and melts of the latter had low viscosity even for fractions with M̄n ∼100,000. This implies a coiled or globular nature for the polymers, which is supported by their limited propensity for film and fiber formation. Attemps to improve this situation by copolymerization, the use of other capping agents, and by the polymerization of precapped monomers were unsuccessful.

Isolation and characterization of particle nuclei during the polymerization of silicic acid to colloidal silica

The polymerization of silicic acid through the stages of oligomers, nucleation, and growth of silica particles was investigated in 0.1 M silica solution at pH 1.75 and 25°C. The nuclei and larger polymer particles were separated from monomer and oligomers by extraction with tetrahydrofuran from samples of solution saturated with sodium chloride. The nuclei and larger particles dissolve in molybdic acid solution to form the yellow silicomolybdate ion as a first-order reaction for which rate constants were calculated. Based on data available in the literature, particle size was estimated from the rate constant. At an early stage, the particle size was confirmed by ultrafiltration. The nuclei appear in about 2 hr and are about 1 nm in diameter. These grow first at the expense of monomer and oligomers and after 40 hr mainly by Ostwald ripening, reaching about 4 nm in size in 20 days. During this period, the concentration of monomer, Si(OH) 4, decreases as particle size increases. According to the Ostwald-Freundlich equation, the interfacial energy appears to be about 100 erg cm −2 which is double that reported for particles formed above pH 7.

Polymerization of Silicic Acid Adsorbed on Iron(III) Hydroxide

Abstract Adsorption of silicic acid on iron(III) hydroxide from aqueous solution and polymerization of adsorbed silicic acid were affected by pH, concentration of silicic acid before and after adsorption, or the relative amount of silicic acid and iron(III) hydroxide. The amount of adsorbed silicic acid and the rate of its polymerization were maximum at pH 9. The polymerization reaction of silicic acid on the surface of iron(III) hydroxide was found to consist of two steps: (1) polymerization of adsorbed monosilicic acid and (2) polymerization between monosilicic acid in the solution and silicic acid species already present on the surface of iron(III) hydroxide, giving a three-dimensional gel structure.