Showing papers on "Sodium silicate published in 2001"

Mechanism of biomineralization of apatite on a sodium silicate glass: TEM-EDX study in vitro

Abstract: The mechanism of biomineralization of apatite on a Na2O−SiO2 glass was investigated in vitro, in which the glass surface was surveyed by transmission electron microscopy and energy-dispersive X-ray spectrometry as a function of soaking time in simulated body fluid (SBF), complemented with Fourier transform infrared reflection spectroscopy of the glass surface and atomic emission spectroscopy of the fluid. The glass was found to exchange Na+ ions with H3O+ ions in the SBF to form silanol (Si−OH) groups on its surface at an early stage of soaking. Immediately after they were formed, the Si−OH groups incorporated calcium ions in the fluid to form an amorphous calcium silicate. After a long soaking time, the calcium silicate incorporated phosphate ions and further calcium ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.43. The amorphous calcium phosphate was eventually converted into crystalline apatite, which contained small amounts of Na, Mg, and Cl and had a Ca/P ...

Control over Microporosity of Ordered Microporous−Mesoporous Silica SBA-15 Framework under Microwave-Hydrothermal Conditions: Effect of Salt Addition

Abstract: The crystallization of ordered microporous−mesoporous silica, SBA-15, has been investigated in the presence of an ionic salt, such as sodium chloride, under microwave-hydrothermal conditions. The crystallization was performed by templating a silica precursor (tetraethyl orthosilicate or sodium silicate) with pluronic123 copolymer (EO20PO70EO20; MW 5800) with varied amounts of salt content at 373 K. The crystallized samples were characterized by means of powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and nitrogen adsorption−desorption measurements at 77 K. The textural properties of the SBA-15 samples, such as pore volume, pore size, and specific surface area, were found to decrease with an increase in salt concentration. Furthermore, the microporosity of the crystallized samples was found to be a function of the added salt concentration, that is, micropore volume has been found to decrease with an increase in salt concentration. Interestingly, SBA-15 samples crystallized in the presenc...

Local structures of MD-modeled vitreous silica and sodium silicate glasses

Abstract: Structures of vitreous silica and sodium silicate glasses have been simulated using different potential models and compared with the neutron diffraction data, with good agreement. The environments of O, Si and Na have been thoroughly examined and compared with those in both crystalline structures and experimental glasses. Considerable similarities in local structures exist between crystalline and simulated glass structures in terms of bond length, coordination number and bond angle distribution (BAD). No significant environment changes were found, except for the coordination number (CN) variation due to composition changes. Further analysis suggests that a weaker interaction between Na and non-bridging oxygen (NBO) exists in the modeled glass structures, perhaps due to use of the same charge for both the bridging and non-bridging oxygens. On the other hand, the existence of fivefold silicon sites in sodium silicate glasses implies that these glasses more resemble high-pressure structures. In addition, the observation of neighboring Na around the fivefold silicons suggests that these fivefold silicons are transition state complexes. Examination of 2- and 3-rings reveals that these smallest rings are closely associated with the fivefold silicons, and are only intermediate states where oxygens transfer from one silicon site to another.

Uptake of 85Sr, 134Cs and 57Co by antimony silicates doped with Ti4+, Nb5+, Mo6+ and W6+

Abstract: Antimony silicate ion exchangers were prepared by precipitation using two different procedures. A crystalline product with a pyrochlore structure (SbSi) was obtained by mixing SbCl5 in HCl with sodium silicate solution (pHfinal < 1) and heating it at 60 °C overnight. An amorphous material (KSbSi) formed when KSb(OH)6 was mixed with tetraethylorthosilicate (TEOS) in acidic conditions and heated overnight at 77 °C. In both cases the Sb∶Si molar ratio was 1∶1 in the starting mixture. The products showed high 85Sr selectivity in acidic conditions, distribution coefficients (KD) being 35 500 mL g−1 for SbSi and 19 700 mL g−1 for amorphous KSbSi in 0.1 M HNO3. They are very selective for 85Sr over a wide pH range, making them superior to other strontium selective ion exchangers such as zeolites, sodium titanates and silicotitanates, which function effectively only in neutral or alkaline conditions. The antimony silicate products had also a high or reasonable selectivity for 57Co, 59Fe and 63Ni, but the selectivity for 134Cs was low. An attempt was made to increase the selectivity for 134Cs by doping the antimony silicates with Ti4+, Nb5+, Mo6+ or W6+. The best results were obtained by doping SbSi with W, which resulted in a 10-fold increase in caesium selectivity. The original pyrochlore structure was retained in the W-doped SbSi.

Formation of silver particles and periodic precipitate layers in silicate glass induced by thermally assisted hydrogen permeation

Abstract: Nanoscale silver particles embedded in sodium silicate glass were produced by Na/Ag ion exchange and subsequent thermal treatment in a hydrogen atmosphere. Their structure and spatial distribution were studied by conventional and high-resolution electron microscopy (HREM). Two different mechanisms of particle formation could be identified: (i) reduction of ionic silver by hydrogen and formation of mostly defective particles (twinned) within a near-surface region; and (ii) formation of single-crystalline particles in the interior of the glass resulting from reduction by means of polyvalent iron ions. Electron microscopy investigation revealed the completion of periodic layers of silver particles in near-surface regions with high silver concentration induced by thermally assisted hydrogen permeation. The self-organized periodic layer formation may be explained in terms of Ostwald's supersaturation theory, assuming interdiffusion of two mobile species. Analysis of lattice plane spacings from HREM images of silver particles revealed the typical size-dependent lattice contraction. The extent of this, however, was found to be different for particles formed by hydrogen permeation and those formed by interaction with polyvalent iron ions. These differences reflect different influences of the surrounding glass matrix, probably originating from the conditions of particle formation (thermal history).

Cesium and Strontium Ion Exchange on the Framework Titanium Silicate M2Ti2O3SiO4·nH2O (M = H, Na)

Abstract: The ion exchange properties of the titanium silicate, M2Ti2O3SiO4.nH2O (M = H, Na), toward stable and radioactive 137Cs+ and 89Sr2+, have been examined. By studying the cesium and strontium uptake in the presence of NaNO3, CaCl2, NaOH, and HNO3 (in the range of 0.01-6 M) the sodium titanium silicate was found to be an efficient Cs+ ion exchanger in acid, neutral, and alkaline media and an efficient Sr2+ ion exchanger in neutral and alkaline media, which makes it promising for treatment of contaminated environmental media and biological systems.

Synthesis and structural characterization of zirconium silicates

Abstract: A zirconosilicate (Na0.2K1.8ZrSi3O9·H2O) analogue of the small-pore mineral kostylevite (AV-8) has been prepared via hydrothermal synthesis. The thermal transformation of microporous zirconosilicat...

Method for pretreatment of filler, modified filler with a hydrophobic polymer and use of the hydrophobic polymer

Abstract: A modified filler used in the making of paper or the like, preparation of the filler and its use. The modified filler comprises a filler known as such, e.g. calcium carbonate, kaolin, talc, titanium dioxide, sodium silicate and aluminiumtrihydrate or their mixture, and a hydrophobic polymer made of polymerisable monomers, which is added to the filler as a polymer dispersion or a polymer solution.

Calcium phosphate cements prepared from silicate solutions

Abstract: Methods are provided for producing flowable compositions, e.g. pastes, that set into calcium phosphate products. In the subject methods, dry reactants that include a calcium source and a phosphate source are combined with a solution of a soluble silicate, e.g. sodium silicate, and the combined liquids and solids are mixed to produce the flowable composition. Also provided are the compositions themselves as well as kits for preparing the same. The subject methods and compositions produced thereby find use in a variety of applications, including the repair of hard tissue defects, e.g. bone defects.

Chapter 12 Silicon sources for agriculture

Abstract: Characteristics of an acceptable silicon (Si) source are: a high content of soluble-Si, physical properties conducive to mechanized application, ready availability, and low cost. Since Si is the second most abundant element in the earth's crust, finding sources of Si is easy. But, Si is always combined with other elements and most sources are insoluble. Responses of crops to soluble-Si applications in sands (largely SiO 2 ) provide an example of the insolubility of one source. Slags, by-products from the processing of iron and alloy industries, have been utilized quite extensively. Their concentrations and solubility of Si and their contents of other elements vary widely. For a given source, solubility is indirectly related to particle size. A few sources are soluble, but too costly for general use. Potassium silicate is used in nutriculture for disease control in some high value crops. Sodium silicate and silica gel have also been used to supply Si in research and high value crops. Calcium silicates have emerged as the most important sources for soil applications. Of those, calcium meta -silicate (wollasonite, CaSiO 3 ) has been the most effective source in many locations with low concentrations of soluble-Si in soils. Such a material, supplied as a slag by-product from the high temperature electric furnace production of elemental P, is applied extensively to Everglades mucks and associated sands planted to sugarcane and rice. Thermo-phosphate, a commercial fertilizer used in Brazil to supply P, Ca, and Mg, also supplies soluble-Si due to high temperature manufacturing process effects on its magnesium silicate ingredient.

Fire-resistant material and method of manufacture

Abstract: The present invention provides a building material derived from straw, such as rice straw, that has significantly improved fire-resistance properties over traditional cellulose-based materials. In one embodiment, the invention provides a method of fabricating a board from milled rice straw. The milled rice straw is blended with a binder to form a mixture. The mixture is then formed into a mat with sufficient size to achieve a predetermined board thickness and density. The mat is then pressed into the board. In another embodiment, the present invention provides a fire resistant board that includes milled rice straw, a resin binder, and a fire retardant material such as an organic phosphate, zinc borate, aluminum trihydrate, sodium silicate, or even rice hulls.

Crystallization behavior and characteristics of mullites formed from alumina–silica gels prepared by the geopolymer technique in acidic conditions

Abstract: Mullites were prepared by the geopolymer technique to obtain nanometer sized mullite polycrystals. Sodium silicate solutions prepared from Na 2 O·SiO 2 ·9H 2 O (A-series) and Na 2 O·2SiO 2 ·aq (B-series) were applied as host solutions. Then, Al-nitrate guest solution was added drop by drop into the host solutions to obtain precipitates, which were filtrated and washed by deionized water. The air-dried precursor gels thus obtained were fired at elevated temperature up to 1400°C and were examined by XRD, DTA and ICP techniques. The XRD results showed that the A-series gels began to crystallize mullite at about 1000°C, while the B-series at about 1100°C. According to the DTA, a sharp exothermic peak appeared at about 1000°C in the A-series gels indicating polymer character of the gels, while no such a peak in the B-series gels indicating nonpolymer character of the gels. Chemical analysis by ICP revealed low concentration of Al 2 O 3 -component in the gels, and this caused the gels consisted of mullite and silica potentials. Na-contaminations were extremely low. The process of mullite generation was also discussed on the basis of cell-parameters measured.

Thermogravimetric Investigations During the Synthesis of Silica-based MCM-41

Abstract: MCM-41 material was synthesized starting from hydrogel containing colloidal fumed silica, sodium silicate, cetyltetramethylammonium bromide(CTMABr) as surfactant, and distilled water as solvent. These reactants were mixed to obtain a gel with the following composition: 4SiO2:1Na2O:1CTMABr:200H2O. The hydrogel with pH=14 was hydrothermally treated at100°C, for 4 days. Each day, the pH was measured, and then adjusted to 9.5–10 by using 30%acetic acid solution. Thermogravimetry was the main technique, which was used to monitor the participation of the surfactant on the MCM-41 nanophase, being possible to determine the temperature ranges relative to water desorption as well as the surfactant decomposition and silanol condensation.

Sodium silicate glass as an inorganic binder in foundry industry

Abstract: Mixtures of sand, sodium silicate, some additives such as iron oxide, pitch or sugar and an ester can form a temporary mould . Sodium silicate is used in foundries to bind sand grains by means of anappropriateacid, either directly such as CO2, or indirectly with an organic ester, which hydrolyzes and subsequently gels the silicate sand mass . A gel network is prepared by acidifying concentrated sodium silicate (3 .3 ratio of SiO2 :Na2O) solution. Sodium silicate solution, under acidic conditions is polymerized to silica and acts as an inorganic binder. In other word, lowering the pH of an alkali silicate solution below about 10.9 causes the polymerization to occur, thus leading to high molecular weight aggregates of hydrated silica. The produced hydrated silica namely silica gel is responsible for giving the necessary strength to the mould. Concentration of the sodium silicate solution is adjusted to 55%(wlw) in water. The viscosity of this solution is adjusted on 500 cp by addition of sugar in an amount of 1 .0—2 .0% based on weight of sodium silicate . The sugar or pitch is used as a thickening agent, to concentrate the binder solution at a desirable limit Sodium silicate solution as an inorganic binder is of particular importance mainly because, the necessary time for curing the silicate is low, and it is environmentally extremely beneficial.

Structural evolution of sodium silicate solutions dried to amorphous solids

Abstract: Sodium silicate solutions with a molar SiO 2 :Na 2 O ratio of 3.3 were dried at temperatures up to 100 °C to solid, amorphous and transparent materials with water contents between 45 and 12 wt%. A time–temperature-transition diagram of the specific drying process was established. The dried materials were investigated by optical microscopy, X-ray diffraction, electron microscopy, and thermal analysis. Materials with higher water contents had structural units with sizes of 50–100 nm, whereas materials with lower water contents did not show a structure in this size range. At least two thermal effects were detected and are discussed with respect to composition, glass transition and structure of the materials. Hot stage microscopy was applied to correlate these effects to a liquid–solid transition. A model of the structural evolution of the materials during drying is discussed.

Chemical durability of commercial silicate glasses. I. Material characterization

Abstract: Six commercial silicate glasses; silica, sodalime silicate, two fiberglass compositions and two Bioglass® compositions were subjected to three solutions: distilled water, Dulbecco's phosphate buffered saline solution and Ham's F-12 1x cell culture media under the exact experimental conditions that would be encountered during a cell culture study. For companion, a binary sodium silicate glass was also exposed. Weight loss, diffuse reflectance infrared spectroscopy (DRIFTS) and potentiometric titration were used to determine the chemical evolution of the substrates during a typical period for cell culturing. The silica, sodalime silicate and high-silica fiberglass material showed only small changes in all cases except for differences in OH active site concentration. The bioglass compositions and the low-silica fiberglass exhibited solution-dependent dynamic surface chemistry. The sodium silicate was too dynamic for even the most aggressive buffering system. The purpose of this study was to elucidate cell behavior to be reported in a later paper.

The arrangement of fractal clusters dependent on the pH value in silica gels from sodium silicate solutions

Abstract: Structural features and thus, optical transparency of silica hydro- and aerogels from sodium silicate solution strongly depend on the preparation parameters. This study is focused on the effect of pH, for values higher than the isoelectric point of silica acid (pH ∼ 2). Previous studies have presented SAXS data characterizing the primary particles and fractal properties in silica gels from a sodium silicate solution. This study presents an analysis focusing on the structural units >50 nm, which is the relevant structure for the process of gelation and for optical transparency. UV–vis–NIR spectra revealed that hydrogel transmission increases with rising pH and decreases with the fraction of SiO2. Scanning electron microscopy (SEM) analyses of the inner structure of the supercritical dried gels showed that the mean cluster size along with the deviation dropped substantially with rising pH. An equation which agrees with the experimental results and describes the correlation between cluster size, fractal dimension, and packing index in mass fractal cluster packages is provided.

Fluid catalytic cracking catalyst manufacturing process

Abstract: An in situ process for making improved zeolitic fluid cracking catalysts by spray drying a mixture of (i) hydrous kaolin and/or metakaolin, and (ii) calcined aluminum source, said calcined aluminum source being derived from a pulverized, ultrafine kaolin, calcining the resulting microspheres to convert hydrous kaolin to metakaolin, and reacting microspheres composed of a mixture of metakaolin and calcined aluminum source with an alkaline sodium silicate solution. The weight percent of metakaolin in the calcined microspheres is greater than the calcined aluminum source content.

29Si T1 relaxation in alkali silicate glasses: a method for detecting glass-in-glass phase separation

Abstract: High resolution nuclear magnetic resonance (NMR) has been used to measure relaxation times, T 1 , in alkali silicate glasses. Two-component relaxation was observed in lithium silicate glasses. In glasses close to the sodium disilicate composition, the relaxation was one component but, with decreasing sodium content, this becomes two component. In heat-treated sodium silicate glasses two components appear to grow from the single component and the extent of growth depends upon the heat-treatment temperature and time. The results for all systems are explained in terms of phase separation and an insight into the Q n distribution is also presented.

Diene-based rubber/inorganic compound complexes, methods for producing the same and rubber compositions containing the same

Abstract: The object of the present invention is to provide a method for producing a diene-based rubber/inorganic compound complex capable of allowing a silicic acid compound including silica and the like to be dispersed uniformly and allowing a reinforcing effect to be exerted sufficiently, as well as a complex produced by said method and a rubber composition containing said complex. A latex comprising a diene-based rubber such as styrene-butadiene copolymeric rubber, butadienestyrene-isoprene copolymeric rubber and the like is mixed with an aqueous solution of a silicate in which an alkaline salt of silicic acid such as sodium silicate, potassium silicate and the like is dissolved, and then the resultant mixture is further mixed with an aqueous solution of electrolytes containing [1] a cationic substance which has an affinity to the diene-based rubber including a cationic polymer coagulating agent such as poly(meth)acrylic ester or the like and a cationic surfactant such as alkylamine acetate or the like and [2] a salt of an acid such as hydrochloric acid, nitric acid and the like with a multivalent metal such as calcium, magnesium and the like, to form a co-coagulated material, which is followed by a drying, whereby obtaining a diene-based rubber/inorganic compound complex.

Aqueous black enamel composition for glass substrate

Abstract: A water-based black enamel composition capable of being deposited on a glass substrate, especially on a glass sheet. The enamel composition includes: 20 to 40% by weight of water-soluble sodium silicate and/or potassium silicate; a water-soluble base, in an amount sufficient for the pH of the composition to be at least 10.5; 5 to 25% by weight of water; 40 to 60% by weight of a metal oxide chosen from the group consisting of copper oxides, iron oxides, cobalt oxides, mixtures of these oxides, and mixtures of at least one of the oxides with chromium oxide(s); less than 10% by weight of zinc oxide; at least 10% by weight of a glass frit having a melting point below 680° C.; and less than 10% by weight of a glass frit having a Littleton point above 700° C. A glazing, especially an automobile glazing, including at least one glass sheet can have at least one of the faces of the glass sheet coated at least partially with the enamel composition.

Process for producing silica particles suitable for use as filler for paper

Abstract: The present invention relates to a process for easily and efficiently producing silica particles having a narrow particle size distribution and a high porosity from inexpensive starting materials such as sodium silicate. The silica particles of the present invention can be obtained in the form of a slurry containing them by (1) forming a slurry by mixing first particles difficultly soluble in an alkali and soluble in an acid, with an aqueous alkali silicate solution to form a first slurry containing the first particles, (2) neutralizing the first slurry with a mineral acid to prepare a second slurry containing second particles wherein silica is deposited on the first particles, and (3) adding a mineral acid to the second slurry to dissolve the first particles from the second particles, to prepare a third slurry containing silica particles. When the silica particles of the present invention are used as a filler even in a small amount for paper making, the resultant papers have excellent brightness, opacity, opacity-after-printing, etc.

Options for Bleaching Mechanical Pulp with Lower COD Load

Abstract: Peroxide bleaching requires alkaline conditions. In mechanical pulp bleaching this results in an increased solubilisation of wood substances, visible in an increase of the effluent COD. Because bleaching to very high brightness requires a high input of caustic soda for the activation, the resulting COD load becomes very high. As an alternative for the application of caustic soda other compounds like sodium carbonate (soda ash) and magnesium oxide have been recommended. Within a narrow range, sodium carbonate is capable to replace caustic soda by weight in equivalent amounts. Similar brightness is achieved at a COD level about 20 % lower. The buffering effect of soda ash results in a lower turnover of the H{2}O{2} added. However, it is impossible to make use of the higher residual. Thermal activation, retention time increases or an initially higher soda ash input are not resulting in a higher brightness. The reason for this is the decomposition of the intermediately generated percarbonic acid at the normal bleaching temperature. This is verified by a comparison of the stability of buffered peroxide solutions in the presence or absence of carbonate or bicarbonate. This side reaction is a limitation for the application of carbonates at the 'normal' (60 C to 70 C) temperature level in mechanical pulp bleaching. The application of sodium bicarbonate at low temperature (40 C) results in very moderate COD values, however, it requires days to reach the top brightness. Magnesium oxide and magnesium hydroxide are alternatives to caustic soda. Their disadvantage in the first place is their poor solubility. This requires very effective mixing to guarantee an even distribution and in addition a low particle size. Mg(OH){2} not only replaces NaOH but in addition most of the sodium silicate. The COD is between 30% and 40% lower. For very high brightness, a slightly higher peroxide charge is needed.