Polymerization Of Silicic Acid Research Articles

Effects of pH and Metal Cations on Polymerization of Silicic Acid in Low Temperature Solutions

Effects of pH and Metal Cations on Polymerization of Silicic Acid in Low Temperature Solutions

Silicon: its manifold roles in plants

AbstractThe title of this essay declares that silicon does have roles in plants and all participants in this conference know that that is so. This knowledge, however, is not shared by the general community of plant biologists, who largely ignore the element. This baffling contrast is based on two sets of experience. First, higher plants can grow to maturity in nutrient solutions formulated without silicon. That has led to the conventional wisdom that silicon is not an essential element, or nutrient, and thus can be disregarded. Second, the world's plants do not grow in the benign environment of solution culture in plant biological research establishments. They grow in the field, under conditions that are often anything but benign. It is there, in the real world with its manifold stressful features, that the silicon status of plants can make a huge difference in their performance. The stresses that silicon alleviates range all the way from biotic, including diseases and pests, to abiotic such as gravity and metal toxicities. Silicon performs its functions in two ways: by the polymerization of silicic acid leading to the formation of solid amorphous, hydrated silica, and by being instrumental in the formation of organic defence compounds through alteration of gene expression. The silicon nutrition of plants is not only scientifically intriguing but also important in a world where more food will have to be wrung from a finite area of land, for that will put crops under stress.

Effect cf the Concentration of Sodium Chloride on the Polymerization of Silicic Acid

Effect cf the Concentration of Sodium Chloride on the Polymerization of Silicic Acid

Depolymerization of polysilicic acid by tiron

As a preliminary experiment for the development of an effective silica scale inhibitor at geothermal power plants, the effect of tiron, a ligand to monosilicic acid, on the polymerization of silicic acid was investigated by gel chromatographic method. The experiments were carried out at Si concentration of 400 ppm (14 mM) and at pH 8 where are a similar condition to geothermal water. The tiron concentration was varied (0–50 mM). At 30 mM of tiron, the polymerization of silicic acid occurred rapidly within first 1 h in spite of the presence of tiron, however, polysilicic acids were depolymerized by tiron. The depolymerization mechanism of polysilicic acids was discussed based on zeta potentials for silica gel particles in the absence and presence of tiron.

Occurrence of polymerized silicic acid and aluminum species in two forest soil solutions with different acidity

Silica species were determined in soil solutions from different soil horizons of acidic Dystric Cambisols in Austria and France. In general, more acid pH and elevated concentrations of Al, Si, and DOC were found in solutions of the upper soil horizons and in particular in the Austrian soil solutions. Aqueous Al speciation was dominated by complexes with respect to DOC and sulphate and by free Al 3+, whereas dissolved Si was dominated by monosilicic acid. The average proportion of low molecular weight polymerized silicic acid (PS) is about 10 mol% of total dissolved Si. However, PS proportions sporadically reached up to 23 mol%. The origin of polymers is most likely due to weathering of soil silicates and polymerization of silicic acid by freezing or evaporation events. We found a positive relationship between the occurrence of PS and the saturation degree with respect to secondary Al-silicates. Thus, we suggest that PS may even indicate precursors for the formation of secondary Al-silicates. In accordance with this concept, our results show that PS preferentially occurred in the upper B1 horizons, where low pH and high Al content may prevent its destruction.

Polymerization and Complexation Behavior of Silicic Acid: A Review

Polymerization and Complexation Behavior of Silicic Acid: A Review

Polymerization study of o-Si(OH) 4 and complexation with Am(III), Eu(III) and Cm(III)

The stability constants of Am +3, Cm 3+ and Eu 3+ with ortho silicate, o -Si ( OH ) 3 - were measured at pH 3.50 and in ionic strengths of 0.20–1.00 M (NaClO 4) by the solvent extraction method. The Am +3, Cm 3+ and Eu 3+ forms 1:1 complex with ortho silicate ion at pH 3.60 with the stability constant (log β 1) value of 8.02 ± 0.10, 7.78 ± 0.08 and 7.81 ± 0.11, respectively. The stability of these metal ions decrease with increased ionic strength from 0.20 to 1.00 M (NaClO 4) for silicic acid concentrations of 0.002–0.020 M. Increasing silicic acid concentration above 0.02 M increased the amount of M 3+ extracted into the organic phase, contrary to the trend usually observed for increased ligand concentration in solvent extraction. This reversed trend is likely due to the extraction of cationic species of silicic acid by HDEHP. Aging time (60–300 min) had no effect on the stability constant of these metal ions for 0.002–0.020 M silicic acid at pH 3.50 and I = 0.20 M (NaClO 4). The fraction of polymeric silicic acid present in solutions of 0.20–4.50 M NaClO 4 solutions at pH 3.0–10.0, T = 0–60 °C and aging time = 5–300 min was measured for determination of the silicomolybdate reaction to ascertain the proper conditions to study metal–silicate complexation.

Are Hydroxyl-Containing Biomolecules Important in Biosilicification? A Model Study

To understand the roles of hydroxyl-containing biomolecules in biosilicification, theoretical and experimental studies of silica formation utilizing biological and model organic additives have been undertaken. However, the role of hydroxyl functionalized biomolecules in silica formation is still not fully understood. To address this problem, we performed a systematic in vitro study of silica formation in the presence of two proteins rich in hydroxyl-containing amino acids (native sericin proteins extracted from Bombyx mori and a recombinant sericin precursor peptide) and a range of small alkanediols. The data obtained suggest the following hypotheses for the role of hydroxyl-containing organic molecules in silica formation. In the first case, hydroxyl-containing organic molecules are not at all involved chemically in the formation of silica. Instead, they may be only assisting in rendering stability and solubility to the organic molecules found occluded in silica. The second possibility is that if we assume that hydroxyl-containing organic molecules affect silica formation, then the environments of silicic acid polymerization could be highly deficient in water to increase the effects of hydroxyl functional groups of proteins in silica formation. These results and their implications are discussed in the context of biosilicification and biomineralization.

Sorption of europium(III) on polymeric silica in perchlorate media

Sorption of europium, Eu(III) with polymeric silicic acid has been studied under varying experimental conditions such as pH, ionic strength (I), concentration of silicic acid and of Eu(III), the presence of carbonate ions, and aging time. Sorption studies of Eu(III) at pH 7.50 ± 0.50) andI= 0.20 M NaClO4indicate 1.32 ± 0.06 × 10-5M Eu as the Critical Coagulation Concentration, CCC. Sorption of Eu(III) on colloidal silica increases with increased ionic strength from 80% (0.20 M NaClO4) to 93% (0.89 M NaClO4). The coagulation process is favored by an increase in silica concentration. The influence of CO32-(1.00 × 10-3M) on the reaction of Eu(III) with polysilicic acid was negligible in the pH range 7.0 to 9.0. Dissolved Eu3+binds more strongly to the silicate polymers than do Cs+and Cu2+.

Hydrometallurgical treatment of tailings with high zinc content

Zinc exists as smithsonite and hemimorphite in the lead flotation tailings from the Dandi mineral processing plant in north western Iran. In this research, zinc-rich tailings produced in the Dandi plant were characterized mineralogically and a leaching study was carried out to assess the effect of several parameters on the kinetics of zinc dissolution. Parameters studied included: sulfuric acid concentration, reaction time, temperature and slurry density. It was found that leaching is controlled by a single rate-controlling step with an activation energy of 23.5 kJ/mol. To overcome some of the filtration problems associated with polymerization of silicic acid, lime was added as a coagulant. The optimum pH, holding time and temperature required to maximize the filtration rate were determined.

An Experimental Approach on the Effect of Rock Alteration on Sorption Behavior

ABSTRACTIn the geological disposal of radioactive wastes, cement used for the repository construction alters the condition of groundwater to highly alkaline of pH about 13. Such alkaline groundwater around the repository would alter the surfaces of the rocks in the flow paths to the amorphous phase. Once the surface is altered, it takes a geological period (so much long time) to restore the surface to its former condition. This study examined the sorption behavior of europium (Eu-152 (tracer), Eu-151 (5×10-5 M, carrier) onto some silica minerals with polymeric silicic acid. Polymeric silicic acid also affects the alteration of the solid surface.The results showed that the kinds of silica minerals strongly affect the sorption behavior in the range of 5<pH<8. The main difference was due to the degree of crystallization of the solid phase, the specific surface area and the concentration of polymeric silicic acid. Since the amorphous silica or polymeric silicic acid takes a loose structure, the isoelectric point is high compared to the crystal ones such as opal-CT and cristobalite, which in turn decreases the sorption. The crystalline silica with polymeric silicic acid remarkably decreased the sorption of europium. This suggested that the surface of solid phase was altered by polymeric silicic acid.

Identification of the Silicon Form in Xylem Sap of Rice (Oryza sativa L.)

Rice (Oryza sativa L.) is a typical silicon (Si)-accumulating plant, but the mechanism responsible for the translocation from the root to the shoot is poorly understood. In this study, the form of Si in xylem sap was identified by (29)Si-nuclear magnetic resonance (NMR) spectroscopy. In rice (cv. Oochikara) cultured in a monosilicic acid solution containing 0.5 mM Si, the Si concentration in the xylem reached 6 mM within 30 min. In the (29)Si-NMR spectra of the xylem sap, only one signal was observed at a chemical shift of -72.6 ppm, which is consistent with that of monosilicic acid. A (1)H-NMR study of xylem sap did not show any significant difference between the wild-type rice and mutant rice defective in Si uptake, and the components of the xylem sap were not affected by the Si supply. The Si concentration in the xylem sap in vitro decreased from an initial 18 mM to 2.6 mM with time. Addition of xylem sap to a solution containing 8 mM Si did not prevent the polymerization of silicic acid. All these results indicate that Si is translocated in the form of monosilicic acid through the xylem and that the concentration of monosilicic acid is high in the xylem only transiently.

Molecular Dynamics Simulations of the Polymerization of Aqueous Silicic Acid and Analysis of the Effects of Concentration on Silica Polymorph Distributions, Growth Mechanisms, and Reaction Kinetics

We have performed large-scale molecular dynamics simulations of the polymerization of silicic acid in aqueous solution using the potential developed by Fueston and Garofalini [J. Phys. Chem. 1990, 94, 5351]. Seventeen simulations, with different water-to-silicon ratios and silicic acid concentrations, were each run for between 1.6 and 12.5 ns, at temperatures of 1500, 2000, and 2500 K. Water clearly acts as a catalyst in these simulations. When the water-to-silicon ratio is large, we find that the initial stages of the polymerization process are dominated by the conversion of monomers to dimers and addition of monomers to small clusters, while at longer times cluster−cluster aggregation is observed. Using data from simulations at different temperatures, the activation energies of condensation between silicic acid monomers were calculated at different water-to-silicon ratios and found to compare favorably with experimental results; an extrapolation (at constant density) of simulated reaction rates to ambient conditions (a temperature difference of more than 1200 K) agrees with experimental rates to within one order of magnitude.

Formation Process of Precursor Solution for Preparation of Transparent Mesoporous Silica Thin Film

Viscosity, conductivity, pH and concentration of silicic acid in a solution of tetraethylorthosilicate (TEOS)-cetyltrimethylammonium bromide (CTAB)-water (H2O)-nitric acid (HNO3) system have been measured, and the formation process of a precursor solution for preparing transparent mesoporous silica thin films was postulated. For the precursor solution of TEOS/CTAB/H2O=8/1/185 molar ratio, the relationship of viscosity vs. concentration of silica in a solution at aging times of 15 to 23 h showed good linearity with a slope which became steeper with time, while the viscosity of silica remained almost unchanged for aging times of 3 to 11 h. These results showed that the initial stage includes spherical polysilicate and the later stage a linear one. The concentration of silicic acid in precursor solutions showed the maximum at the aging time of about 1.6 h. The conductivity in the precursor solution of TEOS/CTAB/H2O=8/1/185 molar ratio was measured, and it slowly decreased with slight fluctuation, exhibiting a the maximum value at the aging time of about 2.5 h. This type of conductivity change suggested that silicic acid or polysilicate interacts with CTAB. The pH of the precursor solution remained unchanged at around 3 throughout the measurement. From these results, the formation process of a precursor solution was assumed as follows; 1st step: cationization of +H3O•Si(OH)3; 2nd step: complexation of silicic acid cation and CTAB micell; 3rd step: polymerization of silicic acid on CTAB micell; 4th step: separation of CTAB and polysilicate; 5th step: adsorption of CTAB on polysilicate; 6th step: complexation of CTAB and polysilicate; 7th step: formation of hexagonal structure.

In situ polymerization of silicic acid in polyethylene–octene elastomer: Properties and characterization of the hybrid nanocomposites

AbstractSilicic acid produced from sodium metasilicate hydrate and metallocene polyethylene–octene elastomer (POE) were chosen as the ceramic precursor and the continuous phase, respectively, for preparation of new hybrids by an in situ sol–gel process. To obtain a better hybrid, the acrylic acid‐grafted polyethylene–octene elastomer (POE‐g‐AA) prepared in our laboratory and used as the continuous phase was also investigated. Characterizations of POE/SiO2 and POE‐g‐AA/SiO2 composites were performed by Fourier transform infrared spectroscopy, 29Si solid‐state nuclear magnetic resonance (NMR) spectrometry, X‐ray diffractometry, differential scanning calorimetry, thermogravimetry analysis, and an Instron mechanical tester. The POE‐g‐AA/SiO2 hybrid could give the positive effect on the properties of POE/SiO2 hybrid because the carboxylic acid groups of acrylic acid should act as coordination sites for the silica phase to form chemical bonds. The result of 29Si solid‐state NMR spectra showed that Si atom coordination around SiO4 units is predominantly Q3 and Q4. Also, the POE‐g‐AA/SiO2 hybrid with 15 wt % SiO2 gave the maximum values of tensile strength and glass‐transition temperature because excess particles might cause the separation between the organic and inorganic phases when the silica content was beyond this point. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 351–359, 2003

Functional nanocomposites prepared by self-assembly and polymerization of diacetylene surfactants and silicic acid.

Conjugated polymer/silica nanocomposites with hexagonal, cubic, or lamellar mesoscopic order were synthesized by self-assembly using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. By tailoring the size of the oligo(ethylene glycol) headgroup of the diacetylene-containing surfactant, we varied the resulting self-assembled mesophases of the composite material. The nanostructured inorganic host altered the diacetylene polymerization behavior, and the resulting nanocomposites show unique thermo-, mechano-, and solvatochromic properties. Polymerization of the incorporated surfactants resulted in polydiacetylene (PDA)/silica nanocomposites that were optically transparent and mechanically robust. Molecular modeling and quantum calculations and (13)C spin-lattice relaxation times (T(1)) of the PDA/silica nanocomposites indicated that the surfactant monomers can be uniformly organized into precise spatial arrangements prior to polymerization. Nanoindentation and gas transport experiments showed that these nanocomposite films have increased hardness and reduced permeability as compared to pure PDA. Our work demonstrates polymerizable surfactant/silica self-assembly to be an efficient, general approach to the formation of nanostructured conjugated polymers. The nanostructured inorganic framework serves to protect, stabilize, and orient the polymer, mediate its performance, and provide sufficient mechanical and chemical stability to enable integration of conjugated polymers into devices and microsystems.

Formation Mechanism of Spherical Mesoporous Silica Prepared Using Dodecylamine.

Formation mechanism of spherical mesoporous silica particles prepared using dodecylamine (DDA) as a template was investigated by measuring surface tension, conductivity, pH and concentration of silicic acid in the mixed solutions. Porous structure of spherical mesoporous silica was found for irregular structure by means of X-ray diffraction and scanning electron microscopy. The fomation of DDA micell in DDA-H2O-C2H5OH system was confirmed by the presence of inflection points for tension and conductivity curves at about 0.5 mmol/l of DDA concentration. When tetraethyl orthsilicate was added in the solution, the conductivity raised suddenly, stayed the same for a few minutes, and decreased steadily while the concentration of silicic acid decreased largely. In addition, the value of pH shifted from about 11 to 9.8 at the same time. From these results, the formation mechanism of spherical mesoporous silica is considered to be as follows; 1st step: cationization(DDAH+) of DDA; 2nd step: formation of DDA H+ micell; 3rd step: hydrolysis of TEOS and polymerization of silicic acid; 4th step: complexation of DDAH+ and polysilicic acid; 5th step: nucleation and growth of the mesoporous silica; and 6th step: reconfiguration and growth of the mesoporous silica particles.

Combined in situ 29Si NMR and small-angle X-ray scattering study of precursors in MFI zeolite formation from silicic acid in TPAOH solutions

Silicic acid powder was dissolved and polymerized in a concentrated aqueous tetrapropylammonium (TPA) hydroxide solution at room temperature. Two complementary techniques were employed to follow this process leading to silicalite-1 zeolite upon heating. The formation of small silicates and specific oligomers involved in the assembly of silicalite-1 nanoprecursors was investigated using 29Si NMR. Small-angle X-ray scattering (SAXS) was used to follow processes at a colloidal level. Dissolution and polymerization of silicic acid could then be related to events occurring at both molecular and colloidal scales. The appearance of very well-defined colloidal particles was linked to a specific intermediate already observed in systems using an organic and monomeric silica source. In situ time-resolved ultra-small-angle X-ray scattering (USAXS) using synchrotron radiation showed a linear growth of the average crystal diameter, which was slower than of that encountered in Na+ containing synthesis mixtures. Using the results presented here, we propose a mechanism describing the TPA-mediated self-assembly of silicalite-1 from silicic acid powder as silica source. This model is in agreement with rising evidence of a common mechanism involving nanoblock aggregation for organic mediated crystallization of high-silica zeolites.

Self-Assembled Organic-Inorganic Silica Hybrids From Polyviologens

AbstractPolyviologens (bipyridinium polymers) are effective catalysts for the polymerisation of silicic acid at room temperature and neutral pH. Variations in the alkylene spacer length and the associated counter ion appear to have little, if any, effect upon the rate of polymerisation as measured by the colorimetric molybdosilicate method. The resultant hybrid materials are amorphous aggregates of roughly spherical particles typically less than 0.1μm in diameter.

Ultrastructural effects of silicic acid on primary lung fibroblasts in tissue culture

Transmission and scanning electron microscopic examination of primary lung fibroblasts exposed in tissue culture to polymeric silicic acid (PSA) revealed profound cellular changes in the cell surface membranes, resulting in rapid endocytosis of affected membranes and formation of multivesicular bodies. Exposure to monomeric silicic acid did not appear to exhibit any immediate adverse effects. Appearance of numerous cytoplasmic vacuoles within 1h of PSA exposure was easily visible by light microscopy. Electron microscopy revealed that PSA exposure caused formation of an ‘osmiophilic’ cell surface membrane. Numerous osmiophilic cytoplasmic blebs on the surface and subsequent endocytotic vesicles appeared to collapse and aggregate into multivesicular bodies. This study provides ultrastructural evidence of the direct interaction between lung fibroblasts and polymeric silicic acid, which has a dramatic effect the surface membrane, its subsequent internalization and cytoplasmic processing. This interaction could be one of the key steps in the damaging effects of silica containing dust.