Showing papers on "Silicic acid published in 2009"

Synthesis of nanoporous silica aerogel by ambient pressure drying

Abstract: A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol, which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 °C under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to the silica sol and aged in a 70%EtOH/30%TEOS solution.

Sorption of selenium(IV) onto magnetite in the presence of silicic acid

Abstract: Sorption of selenium(IV) and silicic acid onto magnetite (Fe(3)O(4)) was investigated in binary systems, with concentrations of silicic acid under the solubility limit of amorphous silica. Using the double diffuse layer model (DDLM), surface complexation constants of selenium(IV) and H(4)SiO(4) onto magnetite were extracted using Fiteql 4.0. Then, prediction curves of the sorption of selenium(IV) in the presence of silicic acid onto magnetite were obtained, using the calculated surface complexation constants. Finally, laboratory experiments were performed and showed a competition between selenium(IV) and silicic acid for the surface sites of magnetite. Experimental results matched the model predictions, confirming its ability to model qualitatively and quantitatively the ternary system.

Effects of silicon levels on growth and yield of wheat in silty loam soil

Abstract: Silicon is the abundant mineral in soil, present exclusively in the form of silicic acid (H4SiO4). It is absorbed by plants in the form of silicic acid. The different levels of silicic acid were tested in a pot experiment to assess their effects on improvement of growth and yield in wheat. In a complete randomized block design the seeds of three varieties viz., Mehran, Abadgar and Kiran-95 were sown in pots filled with 2 kg of silty loam soil. The silicic acid was added to soil in a concentration of no silicic acid (T1), 0.25% silicic acid (T2), 0.50% silicic acid (T3) and 0.75% silicic acid (T4). The silicic acid concentrations affected crop positively as well as negatively as all the varieties produced highest plant growth and yield at 0.25% and 0.50% silicic acid application while the lowest plant growth and yield was found under 0.75% silicic acid. The highest plant growth and yield was observed in Abadgar followed by Mehran wheat variety.

Preparation and properties investigation of PMMA/silica composites derived from silicic acid

Abstract: Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6 M HCI. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright (C) 2008 John Wiley & Sons, Ltd.

No limit? The multiphasic uptake of silicic acid by benthic diatoms

Abstract: Silicic-acid ; uptake kinetics for a field population of benthic diatoms were examined using a radioisotope tracer over a concentration range of 0–300 mmol L21. The microphytobenthos half saturation constant (54 mmol L21) and specific uptake rates (0.096 h21) for silicic acid were well above those usually found in the pelagic environment. Silicic-acid kinetics were hyperbolic only at low concentrations (,60 mmol L21). At higher concentrations, a second mechanism that did not suggest saturation was activated. Many benthic diatoms are motile and migrate vertically in the upper few centimeters of sediment where there are strong gradients of nutrient concentrations. The multiphasic uptake may allow them to take maximum advantage of the high silicic-acid concentrations found at depth.

Calcium silicate and silicon dioxide/silicic acid gel added for nutritional purposes to food supplements 1 Scientific Opinion of the Panel on Food Additives and Nutrient Sources added to Food

Abstract: SUMMARY Following a request from the European Commission to the European Food Safety Authority, the Scientific Panel on Food Additives and Nutrient Sources added to Food has been asked to deliver a scientific opinion on calcium silicate, silicon dioxide and silicic acid gel added for nutritional purposes to food supplements. The present opinion deals only with the safety of calcium silicate, silicon dioxide, silicic acid gel as sources of silicon, and with the bioavailability of silicon from these sources. The Panel notes that one petitioner also applied for the use of calcium silicate as a source of calcium. The safety of silicon and calcium itself, in terms of amounts that may be consumed, and the consideration of silicon as a nutrient, are outside the remit of this Panel. Silicon occurs naturally in foods as silicon dioxide (SiO2, silica) and silicates. High levels of silicon are found in foods derived from plants, and particularly cereals, whereas silicon levels are lower in foods from animal sources.

Imidazole catalyzed silica synthesis: Progress toward understanding the role of histidine in (bio)silicification

Abstract: Histidine is an amino acid present in proteins involved in biosilica formation and often found in peptides identified during phage display studies but its role(s) and the extent of its involvement in the silica precipitation process is not fully understood. In this contribution we describe results from an in vitro silicification study conducted using poly-histidine (P-His) and a series of different molecular weight synthetic polymers containing the imidazole functionality (polyvinylimidazole, PVI) for comparison. We show that the presence of imidazole from PVI or P-His is able to catalyze silicic acid condensation; the effect being greater for P-His. The catalytic mechanism is proposed to involve the dual features of the imidazole group—its ability to form hydrogen bonds with silicic acid and electrostatic attraction toward oligomeric silicic acid species.

On the Bimodal Effects of Silicic Acids on Calcite Growth

Abstract: The effects of silicic acids on calcite growth are a model for the effects of partially polymerized additives on crystal growth. At alkaline pH, silicic acid polymers coexist with small mono- and oligomers. Atomic force microscopy (AFM) showed that large polymers promote two-dimensional nucleation, while mono- and oligomers have a bimodal promoter/inhibitor effect on step propagation. This bimodality can be interpreted as the result of attachment of mono- and oligomers along the steps along with a modification of the kinetics of kink generation and/or propagation. The bimodal step kinematic effect is accompanied by a single morphologic effect: growth islands transform from a rhombus into an ellipse. This effect has been reported for other additives, indicating that many additives generate few morphologies. Such a convergence limits the versatility of chemical control on biomorphogenesis. Contrarily, the strong kinetic effect of silicic acids may make them very efficient controllers of biomorphogenesis, if coupled with a physical shape control, for example, by templates. Thus, silicic acids show a unique bimodality as a controller of calcite biomineralisation and as an abundant biomineral.

Simple and mild preparation of silica-enzyme composites from silicic acid solution

Abstract: Silica-enzyme composite materials including nanoparticles are formed readily from silicic acid and some hydrolase enzymes under mild conditions when the enzyme pI is greater than about 10.

Mechanisms of the Formation of Silica Particles from Precursors with Different Volatilities by Flame Spray Pyrolysis

Abstract: The flame spray pyrolysis (FSP) synthesis of silica particles from two different precursors, tetraethylorthosilicate (TEOS) and silicic acid which have significantly different volatilities, was investigated. The size and morphology of the particles produced using various concentrations of precursors and flame temperatures were examined. Significantly different volatilities of the precursors affected the particle formation mechanism. Two different particle formation mechanisms, vapor phase reaction (VPR) and intradroplet reaction (IDR), are proposed based on the relative time scale for the evaporation of sprayed precursor droplets and for particle formation at the same process conditions. VPR resulted in silica agglomerates with small primary particles of around 10 nm sizes. IDR resulted in isolated and spherical silica particles with the sizes of around 650 nm from silicic acid.

Effect of silica polymerization on the oxalate-promoted dissolution of goethite

Abstract: Numerous studies have investigated the ligand-promoted dissolution of Fe (oxyhydr)oxides. In natural environments, inorganic ligands can compete with organic ligands for surface sites on (oxyhydr)oxides which may influence dissolution rates. Published research of this interaction and its effect on the dissolution of (oxyhydr)oxides is rare. The objective of the present study was to examine the extent to which silica, as a naturally occurring competitive ligand added in the form of silicic acid, impacts the oxalate-promoted dissolution of the common soil Fe (oxyhydr)oxide goethite. Sorbed silica reduced the oxalate-promoted dissolution rate of goethite at all surface coverages investigated. As initial silica solution concentrations increased from 0.50 mM to 5.0 mM, relatively little change in the dissolution rate was observed. Fourier-transform infrared (FTIR) spectra indicated that, as silica-surface coverages increased, the silica underwent polymerization on the goethite surface. Initially, silicate was associated with surface functional groups, but as polymerization occurred some of the silica appeared to desorb from the goethite surface without being released into the bulk solution, suggesting that silica polymers formed discrete islands or surface clusters that grew away from the goethite surface rather than expanding epitaxially across the surface. Minimal changes were observed in the quantity of reactive goethite surface, which is responsible for the observed dissolution rates, as silica-surface coverages increased.

Aplicação do silício para aumentar a resistência do arroz à mancha-parda

Abstract: The aim of this study was to evaluate sources and methods of silicon application to improve silicon uptake and the resistance of rice plants (Oryza sativa), cultivar Metica-1, to brown spot (Bipolaris oryzae). Two experiments were carried out in a greenhouse, with an Oxisol soil, in a completely randomized design with eight repetitions. The treatments were wollastonite (calcium silicate) applied via soil and potassium silicate and silicic acid applied to the leaves. The soil-applied silicon increased the foliar silicon content and reduced the severity of brown spot, in contrast to the results observed in the foliar-applied silicon treatments.

Stimulation of expression of a silica-induced protein (Sip) in Thermus thermophilus by supersaturated silicic acid.

Abstract: The effects of silicic acid on the growth of Thermus thermophilus TMY, an extreme thermophile isolated from a siliceous deposit formed from geothermal water at a geothermal power plant in Japan, were examined at 75°C. At concentrations higher than the solubility of amorphous silica (400 to 700 ppm SiO2), a silica-induced protein (Sip) was isolated from the cell envelope fraction of log-phase TMY cells grown in the presence of supersaturated silicic acid. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the molecular mass and pI of Sip to be about 35 kDa and 9.5, respectively. Induction of Sip expression occurred within 1 h after the addition of a supersaturating concentration of silicic acid to TM broth. Expression of Sip-like proteins was also observed in other thermophiles, including T. thermophilus HB8 and Thermus aquaticus YT-1. The amino acid sequence of Sip was similar to that of the predicted solute-binding protein of the Fe 3 ABC transporter in T. thermophilus HB8 (locus tag, TTHA1628; GenBank accession no. NC_006461; GeneID, 3169376). The sip gene (987-bp) product showed 87% identity with the TTHA1628 product and the presumed Fe 3 -binding protein of T. thermophilus HB27 (locus tag TTC1264; GenBank accession no. NC_005835; GeneID, 2774619). Within the genome, sip is situated as a component of the Fbp-type ABC transporter operon, which contains a palindromic structure immediately downstream of sip. This structure is conserved in other T. thermophilus genomes and may function as a terminator that causes definitive Sip expression in response to silica stress.

Functional substance-releasing agent

Abstract: The present invention relates to a functional substance-releasing agent containing a silicic acid ester compound represented by formula (1) below, a process for producing the functional substance-releasing agent, and a composition containing the functional substance-releasing agent. wherein R1 represents a residue of an alcohol which results from removal of one hydroxyl group therefrom, the alcohol being selected from a functional alcohol having a log P value of 2.0 or less and an alcohol having a log P value of 2.1 or more, a plurality of R1s may be the same or different, provided that the silicic acid ester compound has, in one molecule, at least one residue resulting from removal of one hydroxyl group from a functional alcohol having a log P value of 2.0 or less and at least one residue resulting from removal of one hydroxyl group from an alcohol having a log P value of 2.1 or more.

Anisotropic silicon etchant composition

Abstract: An etchant composition contains (a) an alkaline compound mixture of an organic alkaline compound and inorganic alkaline compound and (b) a silicon-containing compound. The organic alkaline compound is composed of one or more ingredients from quaternary ammonium hydroxide and ethylenediamine. The inorganic alkaline compound is composed of one or more ingredients from sodium hydroxide, potassium hydroxide, ammonia and hydrazine. The silicon-containing inorganic compound is composed of one or more ingredients from metal silicon, fumed silica, colloidal silica, silica gel, silica sol, diatomaceous earth, acid clay and activated clay, and the silicon-containing organic compound is composed of one or more ingredients from quaternary ammonium salts of alkyl silicate and quaternary ammonium salts of alkyl silicic acid.

Foliarly applicable silicon nutrition compositions & methods

Abstract: A foliarly applicable plant nutrient composition comprises, in aqueous solution, (a) a first component comprising an agriculturally acceptable source of foliarly absorbable silicon; (b) a second component selected from agriculturally acceptable sources of thiosulfate ions, agents effective to inhibit polymerization of silicic acid or silicate ions, and mixtures thereof; and (c) as a third component, an agriculturally acceptable mixture of compounds selected from the group consisting of organic acids, organic compounds having functional groups capable of reversibly binding or complexing with inorganic anions, and mixtures thereof. The composition is useful for silicon nutrition of a plant and for reducing susceptibility of a plant to fungal or bacterial disease.

Diurnal heterogeneity in silicic acid fluxes in shallow coastal sites: Causes and implications

Abstract: In shallow coastal areas the amplitude and range of benthic silicic acid fluxes can have a significantinfluence on benthic–pelagic coupling and the functioning of the pelagic system. To explore the oscil-lation in fluxes over the diurnal cycle and in particular the influence of microphytobenthos (MPB), anexperiment was carried out in a shallow subtidal site in the Bay of Brest (France). Benthic chambers wereemployed over a 48 h period to measure the variability in silicic acid and oxygen fluxes; MPB migrationwas investigated using a diving Pulse Amplitude Modulated (PAM) fluorometer and uptake rhythms ofsilicic acid by natural MPB populations were measured using the 32 Si isotope. It was discovered thatsilicic acid fluxes fluctuated greatly throughout the diurnal period resulting in an oscillation in theavailability of this nutrient for phytoplankton communities. The uptake of silicic acid by the MPB wasquantified for the first time and highlighted a 2-fold increase in the demand from night to afternoonperiods. The combined silicic acid uptake and the concentration of cells at the sediment–water interface,forming a dense biofilm of MPB, were postulated to be the main processes reducing effluxes at midday.Our work highlighted the many processes which influence silicic acid effluxes in shallow coastal areasand the possible interaction between uptake and dissolution processes. The variations in benthic fluxesover the diurnal period were comparable to observations reported at the seasonal scale. Therefore, up-scaling hourly flux observations to daily and annual estimates should be undertaken with caution.Further we suggest that the main processes influencing flux oscillations over the diurnal period shouldbe considered when planning sampling strategies and extrapolating to larger time scales. 2009 Elsevier Ltd. All rights reserved.

Method for preparing inorganic chemical product using waste produced by polycrystalline silicon

Abstract: A method using polysilicon production waste for preparing inorganic chemical products is disclosed. The wastes which are generated in the process of producing polysilicon by an improved Siemens method mainly comprise silicon tetrachloride, trichlorosilane, dichloro-dihydro-silicon, and the like; the method using polysilicon production waste for preparing inorganic chemical products comprises two steps: firstly, polysilicon production waste is hydrolyzed; when the polysilicon production waste is put into the water, the hydrolysis reaction is carried out on the silicon tetrachloride, the trichlorosilane, and the dichloro-dihydro-silicon, thereby generating silicic acid and hydrochloric acid; secondly, the silicic acid and hydrochloric acid are used; the hydrochloric acid is used for being reacted with carbonate to prepare chloride, or the hydrochloric acid is used for being reacted with phosphate to prepare phosphoric acid or acid phosphate; the silicic acid is used for being reacted with alkali to prepare silicate or metasilicate, or the silicic acid is used for preparing silicon dioxide or silica gel by heating and dehydration. The invention has the advantages that by the hydrolysis, silicon tetrachloride becomes 'harmlessness'; by the reuse of the silicic acid and the hydrochloric acid, inorganic chemical products which are needed urgently by the market are prepared, thereby changing the silicon tetrachloride into 'resource' and changing the waster into valuables. The production process achieves 'zero emissions'; the obtained inorganic products have stable quality and high purity; large-scale production can be easily realized; the invention also has the advantages of low energy consumption, low production cost, can be conducive to solve the pollution problem in the polysilicon industry, and has great economic and social benefits.