Showing papers on "Sodium silicate published in 2003"

Chemical optimisation of the compressive strength of aluminosilicate geopolymers synthesised by sodium silicate activation of metakaolinite

Abstract: High strength cements can be synthesised by alkali activation of materials rich in Al2O3 and SiO2. In this study, amorphous aluminosilicate polymers produced by sodium silicate activation of metakaolinite were studied, with particular reference to chemical optimisation of the compressive strength according to the relative concentrations of Si, Al and Na in the polymer. The sodium silicate was manufactured from silica fume and sodium hydroxide. The compressive strengths of polymers with Si∶Al molar ratios of 1.0–3.0 and Na∶Al molar ratios of 0.5–2.0 were considered. The polymers were cured at 75 °C for 24 h and their compressive strengths measured after aging for 7 days. The strength was found to depend systematically on the relative amounts of Si, Al and Na, with the maximum being 64 ± 3 MPa for an Si∶Al∶Na molar ratio of 2.5∶1∶1.3. X-Ray diffraction/scattering data indicate qualitatively that the bonding network in the amorphous aluminosilicate alters systematically with composition.

Hydration Products and Reactivity of Blast‐Furnace Slag Activated by Various Alkalis

Abstract: Pastes of blast-furnace slag were cured for up to 90 d using sodium silicate (waterglass), NaOH, and three different mixtures of Na2CO3–Na2SO4–Ca(OH)2 to activate reactions. The highest slag reactivity was observed for NaOH activation and the least for waterglass, although nonevaporable water indicated similar amounts of hydration products formed. The main hydration products found using X-ray diffractometry in all systems were calcium silicate hydrate (C-S-H) and a hydrotalcite-type phase. Microanalysis was performed on pastes activated using 50% Na2CO325% Na2SO425% Ca(OH)2, NaOH, and waterglass; the chemical composition of the C-S-H in the waterglass case was different relative to the other two alkalis. For all alkaline agents used, the C-S-H seemed finely intermixed with a hydrotalcitetype phase of Mg/Al 1.82, on average.

The Formation of Well-Defined Hollow Silica Spheres with Multilamellar Shell Structure

Abstract: Hollow mesoporous silica spheres that are highly defined in shape and size are prepd. using a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) [PEO-PPO-PEO] block copolymer based emulsion as the template, and sodium silicate as the silica source. The wall structure of the particles depends on the reaction temp. and can be monitored using small-angle X-ray scattering, solid-state NMR spectroscopy, and cryo-transmission electron microscopy.

Synthesis of sub-200 nm silsesquioxane particles using a modified Stöber sol–gel route

Abstract: A range of silsesquioxane nanoparticles has been synthesised by a modified Stober method. An aqueous sodium silicate solution was used as a seed for further growth of methyl-, ethyl-, phenyl- and vinyl-modified silica spheres. Particles with diameters in the range 60–180 nm were prepared by hydrolysis and condensation reactions of organotrimethoxysilane precursors in a mixture of water, ammonia and ethanol at room temperature. The materials prepared in this study have relatively low specific surface areas and average pore diameters typical of mesoporous solids. The results suggest that the mechanism for the formation of the particles is primarily aggregation and monomer addition.

Synthesis of Mesoporous Silica Nanoparticles from a Low-concentration CnTMAX–Sodium Silicate Components

Abstract: The 30–100 nm primary particles of mesoporous silica have been conveniently synthesized from a highly dilute aqueous solution of CnTAMX–sodium silicate.

Characterization by Multinuclear High-Resolution NMR of Hydration Products in Activated Blast-Furnace Slag Pastes

Abstract: The effect of activators on the hydration of granulated blast-furnace slag (gbfs) was studied through compressive strength measurements, 29Si, 27Al, and 23Na high-resolution nuclear magnetic resonance, and X-ray diffraction. Four different activations containing sodium hydroxide, sodium silicate, and/or calcium hydroxide (CH) were considered, at fixed amounts of alkali: 5% Na2O, 5% Na2O-2.5% CH, 5% Na2O-7.5% SiO2, and 5% Na2O-2.5% CH-7.5% SiO2. Silicate-activated gbfs cements have greater compressive strength than Portland cements over the whole period of study (1 yr). Also, silicate-free activated gbfs cements have poorer mechanical strength than silicate-activated cements. In fact, substantial structural differences were observed between hydration products in both kinds of activations. In silicate-activated pastes there exists an intimate mixture of C-S-H layers and AFm-like arrangements containing Al in octahedral sites bonded to the silicate layers, originated either from phase intergrowths or from a high density of Ca-Al incorporation in the interlayer spaces of C-S-H. In pastes obtained from silicate-free activation of gbfs there is a better chemical and structural definition among C-S-H and calcium aluminate hydrate domains (AFm and hydrogarnet).

Structure and magnetic properties of vanadium-sodium silicate glasses

Abstract: Vanadium–sodium silicate glasses with the chemical composition [(V2O5)x(Na2O)0.30(SiO2)0.70−x] (0.0⩽x⩽0.10) have been studied by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The core-level binding energies of O 1s, V 2p and Si 2p in these glasses have been measured for surfaces produced by in vacuo fracture. The peak position and width of the V 2p3/2 peak are independent of the V2O5 content while the O 1s core-level spectra show significant composition-dependent changes. Two distinct peaks are resolvable arising from the bridging oxygen and non-bridging oxygen (NBO) atoms in the silicate glasses. The fraction of NBO, determined from these spectra is found to increase with increasing V2O5 content in the glass and are consistent with the formation of predominantly alkali metavanadate species. The magnetic susceptibility data of these glasses indicate a large, temperature-independent diamagnetic contribution arising from the glass matrix as well as small paramagnetic contribution from the V4+ ions. The V4+ content deduced from the magnetization results (∼2%) is below the detection limit of XPS analysis.

Supercritical CO2-based formation of silica nanoparticles using water-in-oil microemulsions

Abstract: A novel method is proposed for the precipitation of silica nanoparticles using supercritical CO2, in which supercritical CO2 acts both as the antisolvent and as a reactant. A water-in-oil microemulsion of an aqueous sodium silicate solution in n-heptane or isooctane is injected into supercritical CO2 by means of a micronozzle, forming small droplets. Supercritical CO2 rapidly extracts the solvent from the droplets and reacts with the exposed surfactant-supported aqueous sodium silicate reverse micelles, forming silica nanoparticles sodium carbonate, byproduct and water. The precipitated silica nanoparticles are washed with water and the surfactant and sodium carbonate free particles are obtained using ultrafiltration. Process parameters affecting silica nanoparticle size such as water and surfactant concentrations, the type of solvent used in the microemulsion, and the CO2 pressure are investigated. Microstructure and size analyses of the precipitated silica nanoparticles are carried out using transmissio...

Silicate Thermal Insulation Material from Rice Hull Ash

Abstract: Silicate blocks were produced from rice hull ash (RHA) derived sodium silicate, and physical properties and thermal conductivity of the blocks were investigated. A Sodium silicate solution was produced from RHA by solublizing the silica in 1 M NaOH at 100 °C, followed by filtering to remove the carbon residue. The silicate solution was then boiled at different heating rates to evaporate the water and produce highly porous thermal insulation blocks with varying densities. X-ray diffraction patterns demonstrated the amorphous nature of silicate blocks. FTIR spectra demonstrated the presence of the silicate network in the silicate. Block density, mechanical strength (the compressive force per unit area required to break the block), and thermal conductivity decreased with increasing heating rate. The block density, mechanical strength, and thermal conductivity of silicate blocks were 0.33−0.42 g·cm-3, 145−196 N·cm-2, and 0.103−0.128 W·m-1·K-1, respectively. Data suggested that RHA could be used to produce the...

Water-borne non-toxic high-performance inorganic silicate coatings

Abstract: Silicate coatings are reactive inorganic coatings These provide weather-, chemical- and temperature-resistance coatings with lasting decoration and protection of steel against corrosion Properties of these coatings depend on the ratio of silica to alkali metal oxide The drying rate and chemical resistance properties of the film increase with increasing ratio of silica to alkali metal oxide However, water miscibility of the system decreases Their curing mechanism shows an explicit difference between the curing on masonry and iron substrates These coatings exhibit a unique property, namely their chemical reaction with the substrate, which accounts for their excellent abrasion resistance, thus making them a permanent part of the system

Preparation of Porous and Nonporous Silica Nanofilms from Aqueous Sodium Silicate

Abstract: Ultrathin SiO2 films in the range of 2−50-nm thickness were readily fabricated from inexpensive sodium silicate as starting material by its alternate adsorption with cationic polymer and subsequent treatment with O2 plasma and calcination. Film thickness can be controlled by adjusting the number of adsorption cycles and the pH value of silicate solution. Film surface is generally smooth (small roughness) and remains unchanged after O2 plasma treatment or calcination. Whereas a nanoporous thin film is obtained by O2 plasma treatment, a dense silica film is produced through calcination at 450 °C. These preparative methods prove that inexpensive sodium silicates are converted to advanced silica-based materials, such as functional ultrathin films, coatings, capsules, and catalysts, by simple procedures.

Composite nanoparticle and process for producing the same

Abstract: Composite nanoparticles which are nanocrystal particles independently dispersed stably in a suspension in a high concentration while being prevented from agglomerating. A given amount of pure water or deionized water is introduced into a reaction vessel. Nitrogen gas is passed through the vessel at a nitrogen flow rate of 300 cm3/min for a given period while stirring the contents with a stirrer to remove the oxygen dissolved in the pure water. Thereafter, the water is allowed to stand in a nitrogen atmosphere. Subsequently, while the nitrogen atmosphere inside the reaction vessel is maintained, sodium citrate as a dispersion stabilizer, an aqueous MPS solution as a surfactant, and an aqueous anion solution and aqueous cation solution which are to be coprecipitated as nanocrystals are added in this order with stirring. Thereto is added an aqueous sodium silicate solution. The resultant mixture is stirred and allowed to stand in the dark in the nitrogen atmosphere. A vitrification inhibitor may be added to control the growth of a vitreous surface layer.

Mechanical loss associated with silicate bonding of fused silica

Abstract: We report on mechanical loss associated with hydroxy-catalysis (or 'silicate') bonding between fused silica substrates in the presence of potassium hydroxide or sodium silicate. We measured the mechanical quality factor of three fused silica samples, each composed of two half-rods bonded together on their flat surfaces and compared them to that of an unbonded half-rod. The measurements show a significant reduction of quality factor due to mechanical loss associated with the silicate bonds. We calculate the loss factor of the bonded region bond and estimate that the effect of silicate bonding on thermal noise in the Advanced LIGO interferometers will be small.

Matrix-controlled channel diffusion of sodium in amorphous silica

Abstract: To find the origin of the diffusion channels observed in sodium silicate glasses, we have performed classical molecular dynamics simulations of Na2O–4SiO2 during which the mass of the Si and O atoms has been multiplied by a tuning coefficient. We observe that the channels disappear and that the diffusive motion of the sodium atoms vanishes if this coefficient is larger than a threshold value. Above this threshold the vibrational states of the matrix are not compatible with those of the sodium ions. We thus interpret the decrease of the diffusion by the absence of resonance conditions.

Water-based, fire retarding coating composition

Abstract: A water-based, fire-retarding coating composition comprising a water soluble alkali metal silicate, preferably sodium silicate or potassium silicate; a plasticiser and/or an adhesion promoter which may be an organic polymer or resin; a particulate formed of a refractory material i.e. a glass or ceramic, for example, silica, pumice, perlite; and water. Also disclosed is a water-based primer composition and a method of forming a surface coating or facing on a substrate using the water-based, fire-retarding coating composition and/or water-based primer composition.

Evolution of Sodium Silicate Sols through the Sol-to-Gel Transition Assessed by the Fluorescence-Based Nanoparticle Metrology Approach

Abstract: The fluorescence-based nanosize metrology approach, proposed recently by Geddes and Birch (Geddes, C. D.; Birch, D. J. S. J. Non-Cryst. Solids 2000, 270, 191), was used to characterize the evolution of primary silica particles through the sol-to-gel transition and during aging of sodium silicate (SS) derived silica. In this study, the evolution of silica particles within SS derived silica was examined as a function of pH and glycerol doping through the sol-to-gel transition and up to 10 months after gelation. Time-resolved anisotropy decays were measured for the cationic dye rhodamine 6G, which was strongly adsorbed to the silica nanoparticles, and for the anionic probe pyranine, which provided accurate data on the microviscosity of the internal aqueous solution within sols and gels. The data provide evidence for the presence of nonaggregated primary particles far beyond the gelation point and even after prolonged aging of the resulting silica when aging is done either at low pH or in the presence of glyc...

Lithium and sodium yttrium orthosilicate oxyapatite, LiY9(SiO4)6O2 and NaY9(SiO4)6O2, at both 100 K and near room temperature.

Abstract: Lithium yttrium orthosilicate oxyapatite [lithium nonayttrium hexakis(silicate) dioxide], LiY(9)(SiO(4))(6)O(2), crystallizes in the centrosymmetric space group P6(3)/m at both 295 and 100 K. The structure closely resembles those of fluorine apatite and sodium yttrium orthosilicate oxyapatite [sodium nonayttrium hexakis(silicate) dioxide], NaY(9)(SiO(4))(6)O(2), which was also investigated, at 270 and 100 K, in this study. There are two different crystallographic sites for the Y(3+) ion, which are coordinated by seven and nine O atoms. One-fourth of the nine-coordinated site is occupied by Li or Na atoms, thus maintaining charge balance. The Si atom occupies a tetrahedral site. The two compounds show no symmetry change between room temperature and 100 K, and the alterations in structural parameters are small.

Preparation method of polysilicon-aluminium flocculant

Abstract: The preparation method of polysilicoaluminium flocculant includes the following steps: (1). adding the solution containing sodium silicate into inorganic acid, making mixed solution pH value be 1-4, stirring, standing still and curing to produce polymerized silicic acid solution; and (2). adding the aqueous solution of inorganic aluminium salt into the above-mentioned polymerized silicic acid solution, stirring, standing still and curing so as to obtain the invented product. It is extensive in application range, its application condition is moderate, 2-10 ppm of said invented flocculant is added in water quality containing various suspension impurities of diatomaceous earth, channel living beings, organics and oil, etc., it can obtain good flocculating effect.