Showing papers on "Sodium silicate published in 2007"

Workability and strength of coarse high calcium fly ash geopolymer

Abstract: In this paper, the basic properties viz., workability and strength of geopolymer mortar made from coarse lignite high calcium fly ash were investigated. The geopolymer was activated with sodium hydroxide (NaOH), sodium silicate and heat. The results revealed that the workable flow of geopolymer mortar was in the range of 110 ± 5%–135 ± 5% and was dependent on the ratio by mass of sodium silicate to NaOH and the concentration of NaOH. The obtained compressive strength was in the range of 10–65 MPa. The optimum sodium silicate to NaOH ratio to produce high strength geopolymer was 0.67–1.0. The concentration variation of NaOH between 10 M and 20 M was found to have a small effect on the strength. The geopolymer samples with high strength were obtained with the following practices: the delay time after moulding and before subjecting the sample to heat was 1 h and the optimum curing temperature in the oven was 75 °C with the curing duration of not less than two days.

Attenuated Total Reflectance Fourier Transform Infrared Analysis of Fly Ash Geopolymer Gel Aging

Abstract: Structural changes in fly ash geopolymers activated with different sodium hydroxide and silicate concentrations are investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy over a period of 200 days. A strong correlation is found between the concentration of silicate monomer in the activating solution and the position of the main Si−O−T stretching band in the FTIR spectrum, which gives an indication of the relative changes in the gel Si/Al ratio. The FTIR spectra of geopolymer samples with activating solution concentrations of up to 1.2 M SiO2 indicate that an Al-rich gel forms before the final gel composition is reached. The time required for the system to reach a steady gel composition depends on the silicate activating solution concentration and speciation. Geopolymers activated with solutions containing predominantly high-order silicate species rapidly reach a steady gel composition without first forming an Al-rich gel. A minimum silicate monomer concentration...

Layer-by-Layer Deposition of Poly(diallyldimethylammonium chloride) and Sodium Silicate Multilayers on Silica-Sphere-Coated Substrate—Facile Method to Prepare a Superhydrophobic Surface

Abstract: A facile method for preparing a superhydrophobic surface was developed by layer-by-layer (LbL) deposition of poly(diallyldimethylammonium chloride) (PDDA)/sodium silicate multilayer films on a silica-sphere-coated substrate followed with a fluorination treatment. First, a silica-sphere-coated substrate that contains loosely stacked silica spheres of 600 and 220 nm was prepared and cross-linked with SiCl4. PDDA was then alternately assembled with sodium silicate on the silica-sphere-coated surface to prepare a micro- and nanostructured hierarchical surface. Scanning electron microscopy (SEM) images verify that the deposition of a 5-bilayer PDDA/sodium silicate multilayer film leads to the formation of a micro- and nanostructured hierarchical surface. After chemical vapor deposition of a layer of fluoroalkylsilane, a superhydrophobic surface with a water contact angle of 157.1° and sliding angle of 3.1° was successfully fabricated. The easy availability of the materials and simplicity of this method might m...

Preparation, structure and hydrothermal stability of alternative (sodium silicate-free) geopolymers

Abstract: In this contribution, we present the preparation and structural characterization of a new type of alternative (sodium silicate-free) geopolymer system. A new procedure of geopolymer synthesis based on the preparation of a reactive geopolymer precursor by direct calcinations of low-quality kaolin with Na/K hydroxides is introduced. The subsequent formation of geopolymer matrix does not require activation by alkaline silicate solution. The compact and hardened material was prepared only by adding a small amount of water. Besides the introduction of a new synthetic procedure, we focused also on the systematic study of chemical structure, mineralogical composition and hydrothermal stability of the prepared geopolymer systems as seen by solid-state NMR spectroscopy and powder X-ray diffraction (XRD). An important part of our contribution is the demonstration of structural and mineralogical changes induced by hydrothermal treatment and long-term aging of the prepared geopolymers. It was found that redistribution of basic structural units (SiO44− and AlO45−) and gradual formation of zeolite fractions can be related to the observed changes in mechanical properties. Up to a certain level, the presence of zeolites enhances the mechanical properties of the prepared geopolymer systems. However, the additional formation of a new generation of zeolite fractions, occurring over the long-term period causes an inversion of this trend and a dramatic reduction of mechanical strength. Nevertheless, formation of the geopolymer matrix by alkaline and thermal activation of low-quality kaolin has the potential to be used in ecological problems solving (solidification of powdered and dangerous waste materials).

Hydration of alkali-activated slag: thermodynamic modelling

Abstract: The composition of solid and liquid phases of alkali-activated slag systems was investigated by thermodynamic modelling. The calculations predict the formation of C(–A)–S–H, stratlingite and hydrotalcite in different alkali-activated slag systems, which agrees well with experimental findings. In addition traces of FeS and ettringite are predicted to precipitate. The type of alkaline activator (Na-silicate, NaOH) has no influence on the type of hydrates formed but influences the Ca/Si ratio of the C–S–H. The addition of sodium silicate leads to the formation of C–S–H with a higher Ca/Si ratio (1.1–1.2), whereas NaOH results in a Ca/Si ratio of 0.8to1.1. In contrast, the kind and concentration of the activator has strong influence on the composition of the pore solution. Low concentrations of the alkaline activator result in lower Na, Si and Al concentrations and lower pH values. In all pore solutions a high concentration of sulphide (HS–) is expected to be present.

Geopolymer synthesis using silica fume and sodium aluminate

Abstract: Monoliths that set rapidly and harden at ambient temperature have been prepared by exploiting sol–gel type condensation reactions between sodium silicate, formed in-situ by alkaline dissolution of silica fume, and a solution of sodium aluminate. Structural characterisation of the product was carried out by XRD, 27Al and 29Si MAS NMR spectroscopy) and the samples showed reproducibly good compressive strengths, indicating that the products display all the characteristics of typical aluminosilicate geopolymers.

Tailored Core−Shell−Shell Nanostructures: Sandwiching Gold Nanoparticles between Silica Cores and Tunable Silica Shells

Abstract: Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.

Formation of aluminosilicate geopolymers from 1:1 layer-lattice minerals pre-treated by various methods: a comparative study

Abstract: Materials resembling aluminosilicate geopolymers have been prepared from the kaolinitic 1:1 layer lattice aluminosilicate clay mineral halloysite by reaction with sodium silicate solution under alkaline conditions. The effect on geopolymer formation of pretreating the clay mineral reactant by heating, high-energy grinding or exposure to acid or alkali was monitored by the ability of the samples to cure and harden, and by XRD, 27Al and 29Si solid-state MAS NMR spectroscopy. Only samples prepared from the fully thermally dehydroxylated clay showed the typical XRD and NMR geopolymer characteristics. Less complete reaction was found in samples pretreated by highly energetic grinding, whereas samples exposed to chemical pretreatment with dilute acid did not react to form viable geopolymers. Pretreatment with dilute alkali produced a zeolite which reacted with sodium silicate, but the hardened sample was not X-ray amorphous and showed subtle differences in its NMR spectra. These results are discussed in terms of the vital role played in the early stages of the reaction sequence by the presence of labile aluminium. The efficacy of the various pretreatment methods is related to their ability to render the aluminium source (the solid aluminosilicate clay) sufficiently soluble in alkali.

Direct encapsulation of BSA and DNA into silica microcapsules (hollow spheres).

Abstract: We reported before that silica hollow spheres (microcapsules) are prepared by interfacial reaction method that W/O emulsion with the aqueous solution of sodium silicate and n-hexane solution of Tween 80 and Span 80 is combined with another aqueous solution of silica precipitant such as NH4HCO3 and NH4Cl. This procedure using W/O/W emulsion fabricates the hollow structures of silica particles directly, and additional steps such as the removal of core parts, that are often essential for the preparation of hollow particles via core-shell materials, are not required. When biomacromolecules such as protein and nucleic acid are mixed in the aqueous solution of sodium silicate, these macromolecules can be encapsulated into the microcapsules. We succeeded the direct encapsulation of bovine serum albumin (BSA) and duplex DNA. Most of encapsulated BSA and DNA cannot be released from the microcapsules without the destruction of microcapsule shell. These microcapsule materials encapsulating biomacromolecules will be applied to biotechnologies such as immobilized enzyme and so on. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2007

Use of silicon oxide and sodium silicate for controlling Trichothecium roseum postharvest rot in Chinese cantaloupe (Cucumis melo L.)

Abstract: Summary Silicon oxide and sodium silicate were investigated as potential agents for the control of postharvest pink rot in Chinese cantaloupe (cultivar Yujingxing) caused by Trichothecium roseum. In vitro tests showed that sodium silicate, when added to potato dextrose agar, was effective in suppressing the radial growth of the pathogen on the medium, whereas silicon oxide was ineffective. The effectiveness of sodium silicate increased with concentration, and the growth of the fungus was completely inhibited at 100 mm. When melons were dipped in the solutions, both silicon oxide and sodium silicate significantly (P < 0.01) reduced the severity of pink rot of the cantaloupe with lesion diameters reduced by up to fivefold when compared with the controls. Scanning electron microscopy-energy dispersive X-ray analysis showed that silicon (Si)-treated melons had a smoother surface feature and higher Si levels in the epidermis, especially at the stomata and along the junction between the exocarp and mesocarp. Enhanced peroxidase and phenylalanine ammonia lyase activities were observed in sodium-silicate-treated melons but not in those treated with silicon oxide. The results indicate that different mechanisms might be involved in sodium silicate and silicon-oxide-initiated reduction of postharvest pink rot in Chinese cantaloupe.

Effect of solvent exchanging process on the preparation of the hydrophobic silica aerogels by ambient pressure drying method using sodium silicate precursor

Abstract: Experimental results obtained on the preparation of hydrophobic silica aerogels by ambient pressure drying method using the sodium silicate precursor with the variation of solvent exchanging process, are reported The silica hydrogel was prepared by passing the 112 specific gravity sodium silicate through the Amberlite (TM) 120 Na+ resin and addition of 1 M ammonium hydroxide to silicic acid The gel was kept in an oven for 3 h to strengthen the gel Solvent exchange was carried out with ethanol and hexane for 36 h each followed by 24 h silylation using 20% hexamethyldisilazane (HMDZ) in hexane Unreacted HMDZ was washed with hexane by keeping the gel in hexane for 24 h Solvent was decanted and the gel was dried for 24 h by keeping the gel at 50 °C for 6 h, at 150 °C for 12 h and at 200 °C for 6 h The low density (006 g/cm3), highly porous (969%), highly hydrophobic (contact angle of 160°), low thermal conductivity (007 W/m K) aerogels were obtained for the process of three times exchange with ethanol and three times exchange with hexane in 36 h each, followed by silylation with 20% HMDZ in hexane and two times washing with hexane in 24 h FTIR studies showed the increase in the intensity of the Si–H and C–H bands of the aerogels with the increase of solvent exchanging times because of increase in silylation for more times of solvent exchange processes It was found from the TG–DTA studies that the hydrophobicity of the aerogels retained up to the temperature of 325 °C Water absorption studies show that the aerogels were remained hydrophobic up to 4 months when the aerogels were placed over the water as well as for up to 60 h in a 90% humid atmosphere SEMs of the aerogels reveal that the pore sizes of the silica network increased, so the percentage of optical transparency decreased with the increase in exchange times with ethanol and hexane

Tube Formation in Reverse Silica Gardens

Abstract: The flow injection of sodium silicate solution into a large reservoir of lighter cupric sulfate solution creates single, downward growing precipitation tubes. These hollow structures have diameters in the range of 0.8−2.4 mm and can grow several centimeters in length. Four distinct growth regimes are observed, and their stability in terms of flow rate and cupric sulfate concentration is investigated. Three of these growth regimes resemble behavior reported earlier for the injection of cupric sulfate into silicate solution. However the “reverse” conditions studied here reveal one distinctly different regime in which tube growth is limited by repetitive fracturing. The lengths of the broken-off tube segments and the times between subsequent break-off events can be described by log−normal distributions.

Effect of silicon fertilizers on silicon accumulation in wheat

Abstract: The effect of fertilization with silicon (Si) compounds on accumulation of Si in wheat (Triticum aestivum L.) has been studied. Wheat plants were grown under identical growing conditions, but subjected to fertilization with various Si compounds (pyrolitic fine silica particles [aerosil®], sodium silicate, silica gel), and the Si content of the above ground plants was analyzed via X-ray microanalysis (EDX) and atomic-absorption spectroscopy (AAS). Silicon was predominantly deposited in the epidermis cells of the leaves and their cell walls. The efficiency of the Si compounds used as fertilizers to augment the Si content of the plants increased in the order sodium silicate > silica gel > aerosil® and thus seemed to correlate with the ease of formation of orthosilicic acid from these compounds.

Utilizing Colloidal Silica and Aluminum-Doped Colloidal Silica as a Binder in FCC Catalysts: Effects on Porosity, Acidity, and Microactivity

Abstract: This paper reports on the synthesis and characterization of fluid catalytic cracking (FCC) catalysts using two different colloidal silica materials as binders, where one was doped with 2 wt % Al2O3 and the other was without any dopant. The physicochemical properties such as attrition resistance, particle size distribution, surface areas, porosity, morphology, chemical environment, and acidity were investigated employing various analytical and spectroscopic techniques such as N2 sorption, scanning electron microscopy, transmission electron microscopy, 29Si and 27Al MAS NMR, and temperature programmed desorption of ammonia (NH3-TPD). It was observed that the FCC catalysts synthesized using colloidal silica have larger particle sizes than that synthesized using sodium silicate (baseline catalyst) as a binder and lower than that of a commercial FCC catalyst. They also exhibit relatively lower attrition resistance than the commercial and the baseline FCC catalysts; however, they exhibit higher BET and matrix s...

Studies on sodium silicate solutions by the method of trimethylsilylation

Abstract: The method of trimethylsilylation was used to study anion distributions in sodium silicate solutions with Na2O: SiO2 ratios of 1:1 and 1:3.41 at various concentrations. The polysiloxanes produced were characterised, mainly by g.l.c., g.p.c. and C and H analyses, to give a picture of the anion distribution in the original solution. The results were compared with those from previous studies. The observations of earlier workers—that the degree of polymerisation increases with increasing concentration and decreasing soda:silica ratio—were confirmed.

The local environment of trivalent lanthanide ions in sodium silicate glasses: A neutron diffraction study using isotopic substitution

Abstract: Neutron diffraction data on lanthanide-bearing sodium silicate glasses were collected using the glass, liquid and amorphous materials diffractometer (GLAD) at the intense pulsed neutron source (IPNS), Argonne. Measurements were made on four glass samples; a sodium silicate base glass with no added lanthanide, a sample with 6 mol% La2O3 added to the base composition, and two isotopically-distinct samples containing 6 mol% Dy2O3. Of the Dy-bearing samples, one contained natural enrichment Dy, and the other a ‘null scattering’ mixture of natural and 162Dy isotopes. The first-order isotope difference of the scattering from the Dy-bearing samples revealed a Dy–O nearest-neighbor distance of 2.3 A and a mean coordination number of 5.9 oxygen atoms around each dysprosium ion; the latter is in good agreement with the coordination number derived from bond–valence theory. The results for the La-bearing glass were also consistent with a sixfold coordination of oxygen atoms around the rare earth. The diffraction data are used in combination with Reverse Monte Carlo modeling techniques to interpreter the structural role of the rare earth ions. From these models, it is apparent that there is competition between monovalent sodium ions and the rare earth ions for the same non-bridging oxygen atoms. As a result the addition of rare earth ions appears to cause disruption of the Na-rich percolation domains characteristic of the sodium silicate base glass. These neutron results are consistent with the formation of a specific lanthanide Q3 as suggested by NMR and Raman spectroscopy, but offer no direct evidence for the formation of ‘oxide-like’ lanthanide clusters.

Method for preparing permanently hydrophobic aerogel and permanently hydrophobic aerogel prepared by using the method

Abstract: A method for preparing permanently hydrophobic aerogel and permanently hydrophobic aerogel prepared by the method. The method comprises adding sodium silicate to HCl at 30 to 90° C. until an acidity reaches pH 3-5, to form silica hydrogel under acidic conditions of pH 3-5, washing the silica hydrogel with distilled water using a mixer, followed by filtering, adding the silica hydrogel to a silylating solution of silylating agent in n-butanol at pH 1-5 using an acid selected from hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid, to simultaneously conduct silylation and solvent replacement, and drying the silica hydrogel; The method has the following advantages; i) silylation and solvent replacement can be simultaneously conducted, ii) n-butanol is used as a reaction solvent instead of methanol upon silylation, thus obtaining a thermal conductivity comparable to conventional aerogel powders, iii) silylation is conducted under improved conditions, i.e., strong acidic conditions of pH 1-5, and as a result, all of the aerogel powders can be reacted with a silylating agent, thereby obtaining permanently hydrophobic aerogel, iv) the washing with a mixer makes the amount of removed sodium ions uniform, thus it is suitable for mass-production, and v) the method provides a relatively simplified procedure and the use of the silylating agent in a small amount enables low costs and mass-production.

The surface properties of silica gels. I. Importance of pH in the preparation from sodium silicate and sulphuric acid

Abstract: Gels were prepared by adding sodium silicate solution to sulphuric acid until a certain pH was reached, and then the products were aged, washed and dried under controlled conditions. The surface properties of the dry gels were studied by measuring adsorption isotherms of nitrogen at – 195·8° and nitrous oxide at — 78·5°. The pH reached came within the range 3·7–5·8, as this corresponded to a decrease in setting time from over an hour to a few seconds. For gels prepared over this pH range, the isotherms of the two gases also changed profoundly, both sets showing the same general pattern. In one preparation the temperature was varied, and in another the ageing period was reduced to the minimum; in neither case could any difference in the adsorption of nitrous oxide be detected. Activation, by soaking in very dilute sulphuric acid, was shown to be more important for a gel prepared at the higher-pH end of the range. Surface areas have been calculated from both sets of isotherms by the Brunauer, Emmett and Teller (B.E.T.) method. Good agreement is obtained, in some cases, by assuming that each nitrous oxide molecule occupies an area of 20·4 A2 in the close-packed monolayer, and taking the usual value of 16·2 A2 for the nitrogen molecule. The values of residual water content and B.E.T. surface area both decreased substantially over the pH range, but there appears to be no simple relationship between them.