Showing papers on "Sodium silicate published in 1999"

Energetically favored formation of MCM-48 from cationic-neutral surfactant mixtures

Abstract: The cubic mesoporous silica molecular sieves MCM-48 have been obtained as an energetically favorable mesophase via a synthesis route using the surfactant mixtures between alkyltrimethylammonium bromides and polyoxyethylene alkyl ethers, with sodium silicate as the silica source. The MCM-48 mesophase was stable under the synthesis conditions for longer than a month, preventing a subsequent transformation to lamellar phases. Metal sources and salts could be added to the synthesis mixture during this period to incorporate metallic elements within the siliceous framework and to increase hydrothermal stability. The product yield amounted to 4.2 mol of SiO2 per surfactant, which was 5 times that of the previously reported synthesis procedure using hexadecyltrimethylammonium bromide and tetraethyl orthosilicate. The present synthesis results demonstrate that the use of mixed surfactants is emerging as a new useful strategy for the synthesis of mesoporous molecular sieves.

Investigation on the Synthesis of Zeolite NaX from Kerala Kaolin

Abstract: The synthesis of zeolite NaX from a locally available kaolin has been studied. Two steps are involved in the reaction (1) thermal activation of the kaolin to get a dehydroxylated product called metakaolin (metakaolinisation) and (2) hydrothermal reaction (zeolitisation) of metakaolin in alkaline medium in presence of additional silica to crystallise the zeolite. The metakaolinisation temperature (400–1000°C) is found to have an important role in determining the type of zeolite formed during the hydrothermal reaction. Under specified conditions, the uncalcined kaolin is partially converted to hydroxy sodalite (HS), whereas the metakaolins prepared at 400, 500 and 600°C also change to HS but at a faster rate. Increasing the metakaolinisation temperature to ≥700°C, zeolite NaX is found to be the product (higher the temperature, faster the reaction). The quantity of additional silica which in turn determines the SiO2/Al2O3 ratio of the reaction mixture and the time given for zeolitisation were also found to influence the formation of zeolite NaX. When metakaolin alone was used in the reaction (SiO2/Al2O3 = 2), the product was X-ray amorphous. Higher ratios were obtained by the addition of sodium silicate. The ratios 3 and 5 gave phase pure NaX whereas 7 resulted in a mixture of NaA, NaP and HS zeolites. The optimum conditions to get phase pure zeolite NaX with good crystallinity from kaolin were found to be metakaolinisation of the clay at 900°C for 1 h, maintaining the mole ratios of SiO2/Al2O3 = 3; Na2O/SiO2 = 1.1 and H2O/Na2O = 40 in the reaction mixture, an ageing of the reactants at room temperature for 24 h and heating at 87 ± 2°C for 15 h under autogenous pressure. Seeding was not essential for the zeolite crystallisation. X-ray diffraction, electron microscopy, IR and solid state NMR spectral analysis, water adsorption and calcium/magnesium exchange or binding capacity measurements and chemical analysis of the selected products substantiated these findings.

Structural and dynamical properties of sodium silicate melts: An investigation by molecular dynamics computer simulation

Abstract: We present the results of large scale computer simulations in which we investigate the static and dynamic properties of sodium disilicate and sodium trisilicate melts. We study in detail the static properties of these systems, namely the coordination numbers, the temperature dependence of the Q^(n) species and the static structure factor, and compare them with experiments. We show that the structure is described by a partially destroyed tetrahedral SiO_4 network and the homogeneously distributed sodium atoms which are surrounded on average by 16 silicon and other sodium atoms as nearest neighbors. We compare the diffusion of the ions in the sodium silicate systems with that in pure silica and show that it is much slower in the latter. The sodium diffusion is characterized by an activated hopping through the Si-O matrix which is frozen with respect to the movement of the sodium atoms. We identify the elementary diffusion steps for the sodium and the oxygen diffusion and find that in the case of sodium they are related to the breaking of a Na-Na bond and in the case of oxygen to that of a Si-O bond. From the self part of the van Hove correlation function we recognize that at least two successive diffusion steps of a sodium atom are spatially highly correlated with each other. With the same quantity we show that at low temperatures also the oxygen diffusion is characterized by activated hopping events.

Hollow silica particles from microemulsion

Abstract: Silica particles were obtained by addition of diluted soluble sodium silicate in sodium 1,2 bis (2-ethylhexyloxycarbonyl)-1-ethenesulfonate reverse microemulsions, in which aqueous phase was nitric acid solution and the water/surfactant ratio ( W ) was 5 or 10. Products, whether washed or not, were dried at 100°C and suspended in different solvents: heptane, water, kerosene or pentane for making SEM measurements. Thermal treatments of washed silica samples were carried out at 900°C and 1200°C. Silica particles of sizes from 1 to 10 μm were obtained at room temperature without changing their shape due to thermal treatment and crystallization. SEM micrographs show hollow particles suggesting that silica preferably polymerizes on microemulsion droplet interface where ionic strength of nitric acid aqueous solution is favourable for silica polymerization reaction.

Fluorescence Probing Investigations of the Mechanism of Formation of Organized Mesoporous Silica

Abstract: Spectrofluorometry (pyrene and dipyrenylpropane emission spectra) and time-resolved fluorescence quenching have been used to study the effect of addition of a large excess of sodium hydroxide and sodium silicate on the properties of micelles of cetyltrimethylammonium bromide and chloride (CTAB and CTAC). The systems investigated had overall compositions similar to those used when preparing organized mesoporous silica. Our purpose was to test whether the surfactant counterions are effectively exchanged by silicate ions and micelles grow in the presence of silica. The results show the CTAC or CTAB micelle micropolarity is not affected by the presence of the additives. The pyrene lifetime measurements with the CTAB systems indicate that only a small fraction of micelle-bound bromide ions, about 16%, is exchanged by hydroxyl and silicate ions even when they are largely in excess. The presence of the two additives was found to increase very little the micelle aggregation number in CTAB- and CTAC-containing sys...

Atomistic structure of sodium and calcium silicate intergranular films in alumina

Abstract: Sodium silicate intergranular films (IGF) in contact with the [0001] basal plane of a-alumina were studied using the molecular dynamics computer simulation technique. The results were compared to previous simulations of calcium silicate and sol-gel silica IGF’s in contact with alumina. An ordered, cagelike structure was observed at the interface. Sodium ions segregated to the cages at the interfaces. Calcium and hydrogen ions were also observed to segregate to the cages in the previous simulations. The modifier ions were surrounded by more oxygen ions in the cages at the interface than in the bulk of the IGF. This explains the segregation of modifiers at the interface. Interface energy decreased as the sodium content of the IGF increased. Interface energy decreased faster as a function of Na2O content than as a function of CaO content. However, interface energy decreased slower as a function of Na 1 content than as a function of Ca 21 content.

The “silica garden’' as a Brønsted acid catalyst

Abstract: The “silica garden’', an amorphous aluminosilicate produced from a solution of sodium silicate seeded with crystalline aluminium nitrate, has been examined by FTIR, TGA, solid-state NMR and catalytic testing. The silica garden is a Bronsted acid catalyst and we characterize its porosity, acidity and catalytic activity. The as-synthesized (AS) and H+-exchanged (H-AS) samples have BET surface areas of 148 and 161 g-1, respectively, with corresponding pore volumes of 0.36 and 0.31 cm3 g-1 and a broad distribution of pore sizes (30–1000 A in diameter). The average pore size for AS and H-AS is 116 and 88 A, respectively. The presence of Bronsted sites in the H+-exchanged samples was confirmed by FTIR of adsorbed pyridine. The population of Bronsted acid sites in the H+-exchanged sample with Si/Al=5.3 is lower than in a commercial amorphous aluminosilicate (ASA) with Si/Al=12 because, as NMR reveals, H-AS has proportionally more non-acid generating 6-coordinate aluminium. Catalytic tests reveal that, despite this, the acid sites in H-AS are stronger than in ASA.

Modified water glass for casting and its preparing process

Abstract: A modified water glass for casting purpose contains such chemical components of xylitol as modifier (0.5-25 mass%), sodium silicate (25-55) and water (the rest), and is prepared through proportioningwater glass, residual liquid or mother liquid of xylitol, or other modifiers, mixing them, heating while stirring at 40-100 deg.C regulating water content to 40-70%, and cooling to lower than 50 deg.C. Its advantages are high strength and dispersity, low cost and the ability to improve quality of castings.

Thermal studies on paper treated with flame-retardant

Abstract: Sodium silicate and sodium berate mere tested as dame retardants on two types of paper sheet (100% rice straw pulp paper with a high silica content while the other consisted of 100% wood pulp paper). After addition of inorganic flame retardant salts (sodium silicate and sodium berate) on to the two samples of paper, the thermal behaviour of the treated paper sheets revealed differences in the course of the differential thermal analysis curves. The thermal analysis studies were carried out under an oxidizing atmosphere using differential thermal (DTA) and thermogravimetric (TGA) analysis, The flame retardants used in this study reduced the amount of volatile products formed during decomposition of the paper and increased the weight loss due to formation of char for the treated papers. The thermal degradation of paper can be considered as a first order degradation. Two stages of thermal degradation were kinetically differentiated, namely, a volatilization stage and a decarbonization stage, The activation energy for these two stages were calculated. The addition of flame-retarding salts decreased the activation energy for both stages, Sodium silicate salt showed more reduction of activation energy than sodium berate, especially for the rice straw paper.

Medium range order in sodium silicate glasses: role of the network modifier

Abstract: The effect of different concentrations of the network modifier Na2O on the position of the Boson peak, observed in the low frequency Raman scattering experiments, is analyzed. Glasses containing 25% Na2O (Na2O · 4SiO2) and 33% Na2O (Na2O · 2SiO2) are compared with pure SiO2 glass. The observed shift of the Boson peak is interpreted in terms of a change of a correlation length, l, corresponding to some medium range order. This length, l, decreases when the amount of sodium oxide increases.

Investigation of the systems silica and silica containing chromium in alcohol medium

Abstract: The purpose of this work is to obtain micrometer sized spherical particles of silica and silica–chromium from sodium silicate. Spherical particles were prepared by sol–gel method from hydrolysis to polycondensation of aqueous sodium silicate in alcohol medium. Chromium was added to the system for some samples. Compositions and morphologies were achieved by changing the precipitation agent. X-ray diffractometry, electrophoretic mobility, infrared spectroscopy and scanning electron microscopies were carried out on these particles to identify phases, determine particle mobility, morphology, particle sizes, shapes and order at short distance. Non-crystalline silica particles with spherical shapes and micrometric size were obtained. The surface potentials of the silica particles differed from that of the silica–chromium particles.

Preparation of anionic nanocomposites and their use as retention and drainage aids in papermaking

Abstract: Anionic nanocomposites for use as retention and drainage aids in papermaking are prepared by adding an anionic polyelectrolyte to a sodium silicate solution and then combining the sodium silicate and polyelectrolyte solution with silicic acid.

Lightweight non-sintered bricks made from coal cinders

Abstract: A fire-free light brick is made up of calcined garbage, powdered coal ash, slag or sandstone, cement, calcium oxide, calcium sulfate, sodium sulfate, sodium silicate, and sodium fluosilicate through press shaping. It features simple manufacture process, low cost and reducing environmental polution.

Process for the preparation, preferably from waste materials, of silicate foam with closed pores, and the product produced by the process

Abstract: The process of the invention characterised in that to 100 parts by weight of a silicate powder having 2000-8000 m2/g specific surface, 1-10 parts by weight of gas-forming material with particle size of 10-100 νm and 0.5-15 parts by weight of montmorillonite, 0.5-2 parts by weight of alkali hydrogen phosphate or alkali dihydrogen phosphate or a mixture of alkali metal phosphate and sodium silicate in form of aqueous solution, 0.01-5 parts by weight of rare earth metal oxide or a mixture of such oxides were added, then the mixture obtained is homogenised, pre-dried, coated with 1-5 parts by weight of titanium oxide and/or titanium oxide hydroxide and/or aluminium oxide hydroxide, then subjected to heat treatment at 720-1000°C, and the mixture obtained is moulded. The subject of the invention: also the product of the above process.

Method and apparatus for generating aqueous silica network particles

Abstract: An aqueous composition including silica particles with a particle size distribution and particle structure that improve the water retention and exchange characteristics of the aqueous composition is provided. The aqueous silica composition includes silica network particles and water. The silica network particles comprise main particles and bridging particles that form chains between adjacent main particles. The main particles have a particle size greater than the particle size of the bridging particles. Because of the presence of the silica network particles, the aqueous composition is capable of wetting a hydrophobic substrate more than pure liquid water. The silica network particles are generated in water by a method in which an aqueous sodium silicate solution is subjected to vigorous agitation in air, followed by periods of circulation through magnetic fields of alternating direction and further periodic agitation exposed to the air. An apparatus for carrying out the method is provided.

Formation of insulated film on silicon steel sheet

Abstract: PROBLEM TO BE SOLVED: To obtain insulated coating having high coating adhesion by subjecting a silicon steel sheet free from a finish annealed film to anode electrolyzing treatment in an aq. soln. of silicate to precipitate a siliceous film and thereafter applying an insulated film thereon. SOLUTION: The aq. soln. of silicate is preferably composed of at least one or more kinds among lithium silicate, sodium silicate, potassium silicate and ammonium silicate. The quantity of the siliceous film formed on the surface of the steel sheet is suitably regulated to >=2 mg/m expressed in terms of the weight of SiO2 per side of the steel sheet. Preferably, the silicon steel sheet is a grain oriented silicon steel sheet which does not have a finish annealed film, and the insulated film is a tension application type. As the tension application type insulated film coating soln., the one essentially consisting of any of colloidal silica and phosphate, an alumina sol and an alumina sol and boric acid is suitable. The grain oriented silicon steel sheet excellent in the flattening degree of the boundary of ferrite in the film, provided with strong tension and low in core loss can be produced.

Continuous production of silica via ion exchange

Abstract: The present invention provides a continuous process for the conversion of sodium silicate to silicic acid, wherein a moving bed of a protonated ion exchange resin is contacted with an inlet stream of sodium silicate to provide an outlet stream of silicic acid. The outlet stream of silicic acid produced thereby can be processed into a variety of silica products. The outlet moving bed of spent sodium-enriched ion-exchange resin is continuously regenerated into protonated ion-exchange resin by contacting the spent resin with an inlet stream of acid of sufficient strength to exchange the sodium ions in the spent resin with a proton. The regenerated protonated ion-exchange resin is continuously recycled back into the sodium silicate stream for further production of silicic acid.

Performance of concrete surface treatment systems

Abstract: This study was undertaken to evaluate the effect of thermal and moisture variations on the performance of selected concrete surface treatment materials. The data developed in this study will be useful in selecting surface treatment materials compatible with the exposure conditions. The performance of the following concrete surface treatment materials, under thermal and moisture variations, was investigated: (1) Sodium silicate; (2) Silicon resin solution; (3) Silane/siloxane; (4) Silane/siloxane with acrylic top coat; (5) Alkyl alkoxy silane; (6) Two component acrylic coating.

Anti-fogging mirror for bathroom

Abstract: PROBLEM TO BE SOLVED: To exhibit a sufficient anti-fogging function over a long period in the anti-fogging mirror for a bathroom by forming a layer containing an alkali metal silicate on the mirror surface having a reflection coat on its rear side. SOLUTION: A layer containing an alkali metal silicate is formed on the mirror surface having a reflection coat on its rear side. A sol coating method is the suitable one with which no constraint related to equipment is present with respect to the size and shape of the mirror. The coating layer is simply formed on the mirror surface without necessitating any special equipment. As the alkali metal silicate, sodium silicate, potassium silicate, lithium silicate or ammonium silicate is appropriately utilized. The coating layer is desirably formed with one or more kinds of inorganic oxide particles included in the layer containing the alkali metal silicate. Thereby desired projecting and recessing parts exhibiting high hydrophilicity are easily formed. In the case the sol coating method, a coating composition comprising 0.05-20 pts.wt. metal oxide and 99.95-80 pts.wt. solvent is preferably utilized.

High molecular weight, solid state active detergent

Abstract: A high molecular weight, solid state active detergent made by mixing two pilled materials at a predetermined ratio, the detergent containing sodium lauryl sulfate, fatty alcohol polyoxyetbylene (9) ether (AEO-9)!, CMC (carboxymethyl cellulose), EDTA (ethylene diamine tetra-acetic acid), fluorescent whitening agent, sodium silicate pentahydrate (Na2 Sio3 5H2 O), sodium carbonate (Na2 CO3), E-44 (epoxy resin), polyamide resin, red iron oxide, zeolite A, and fragrance.