Aqueous Sodium Silicate Solution Research Articles

Semi-micro preparation and characterization of mesoporous silica microspheres from rice husk sodium silicate using a non-ionic surfactant as a template: application in normal phase HPLC columns

A simple and low-cost process has been developed for the production of mesoporous silica microspheres using a non-ionic surfactant as a template in an aqueous acidic sodium silicate solution prepared from rice husk. The influences of synthesis parameters such as the sodium silicate concentration, hydrochloric acid concentration, temperature and aging time on the morphology and on particle size range are described. The product’s physical and normal phase chromatographic properties are reported.

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

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 NH(4)HCO(3) and NH(4)Cl. 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.

Double helical formation of cobalt silicate tubes under magnetic fields

Magnetic field effect on the growth of cobalt silicate tubes in aqueous solution of sodium silicate is studied. Cobalt silicate tubes grown from CoCl2 powders in 10wt.% sodium silicate solution under a horizontal magnetic field of 2.2 T and a field gradient of 20.3 T/m are found to tilt toward the higher field direction, which is attributed to the paramagnetic property of the Co2+ion. In addition, twisted structures are recognized on the tube walls. The direction of the twist is right-handed in the case that the higher field direction is parallel to the field direction and left-handed in the anti-parallel case. Observing the growth of the tubes in situ under magnetic fields has revealed that two cusps of silicate proceed revolving around at the growing end to form a tube wall double-helically. We have proposed a model for the mechanism of the helix formation that Lorentz force exerted on anions (Cl−) flowing through and out of the tubes would cause vortex around the growing ends and the vortex could strand the two cusps, which explains the twist direction with respect to the field direction reasonably.

Preparation of sodium borosilicates using sodium silicate and boric acid

The gelling behaviour of an aqueous sodium silicate solution with boric acid was investigated for different initial compositions and solid sodium borosilicate samples were obtained by drying the gels at 100°C, 225°C and 450°C. The chemical composition, dissolution, pH, loose-packed bulk density, B.E.T. surface area, moisture, size distribution and XRD/IR patterns of the sodium borosilicate particles were determined. The minimum gelling times were observed at pH values between 9–10 and although no gels were obtained using HCl at pH = 11, the silicate solution was gelled with boric acid suggesting borate ions promote the formation of siloxane network and behave as a crosslinking agent.

Development of an Electroless Method to Deposit Corrosion-Resistant Silicate Layers on Metallic Substrates

A novel electroless method for depositing corrosion-resistant silicate layers on metallic substrates from aqueous solutions has been developed. The silicate layer was deposited from an aqueous solution of sodium silicate (3.22 weight ratio sodium silicate, 37.5% solution in water from PQ Corporation) and sodium borohydride. The technique is demonstrated by forming a passive film on galvanized steel. Deposition parameters such as concentration of the bath, temperature, and pH have been optimized based on the corrosion characteristics of the final coating. Studies on the coating reveal the formation of a very thin zinc disilicate layer followed by a much thicker silica layer. Accelerated corrosion tests showed that the silicate coatings have higher corrosion resistance and better stability when compared to chrome passivates. Silica coatings developed by this method show promise as an alternative to chrome passivation for corrosion protection.

Synthesis of fine sodium-free silica powder from sodium silicate using w/o emulsion

Fine silica powders were synthesized from sodium silicate at room temperature using w/o emulsion containing water, nonionic surfactant of Triton N-57, and cyclohexane. Submicron and sodium-free silica particles could be prepared at low cost using inexpensive starting material of aqueous sodium silicate solution and ion exchange of ammonium sulfate. The particle size and size distribution of the silica powders were affected by the factors of reaction time, and concentrations of surfactant and sodium silicate solutions. The particle size of silica powders could be controlled by the same factors to be ranged from submicron to micron sizes. The particle size of SiO 2 decreased with reaction time and concentration of surfactant, but increased with concentration of sodium silicate. The preparation conditions were experimentally determined for obtaining the silica powder with submicron size, narrow size distribution, sphere in shape, and high purity without sodium contamination.

Ormosil Nanocomposite Materials as Modifiers for Acrylic Coating Systems

Organically modified silica (ormosil) particles were prepared using hydrolytic sol-gel methods and the miniemulsion polymerisation approach. Methyl-, ethyl-, and phenylsilsesquioxane nanoparticles with diameters in the range 50-180 nm were obtained using the modified Stöber method with an aqueous sodium silicate solution used as a seed for further growth of the particles. Methyl- and phenylsilsesquioxane particles were prepared by a sol-gel method in the presence of benzethonium chloride used as a surfactant. The miniemulsion polymerisation approach has been extended to the production of methacrylate-modified silica nanoparticles with vinylpyridine or lauryl methacrylate used as comonomers both in the presence and in the absence of a surfactant. Styryl-modified silica particles with diameters in the range 300-800 nm were obtained by the Stöber method using pre-formed SiO2 nanoparticles as the seeds for silsesquioxane nanoparticle formation. The effect of incorporation of the particles produced using different synthetic methods on hardness and water resistance of acrylic coating systems was studied here.

A simple and inexpensive route to synthesize porous silica microflowers by supercritical CO 2

In this work, a simple and inexpensive route to synthesize porous silica microflowers has been developed. By adding supercritical CO 2 into the sodium silicate aqueous solutions, the porous silica microflowers were obtained. The results of scanning electron microscopy, transmission electron microscopy and nitrogen adsorption isotherms show that through the easy control of CO 2 pressure, the morphologies and porosity properties of the obtained silica can be tuned. During this process, supercritical CO 2 works not only as a reactant but also as a modifier to the morphology and porosity of silica. Moreover, the growth of silica microflowers was investigated by changing the reaction time. The silica microflowers show optical properties in the wavelength range of 340–480 nm.

Gelatine thin films as biomimetic surfaces for silica particles formation

The formation of silica nanostructures by several living organisms, such as diatoms or sponges, involves specific macromolecules that control the growth and the organization of silica nanoparticles. In order to investigate if a single molecular system could perform both particle size control and morphological template, gelatine thin films of various concentration and strength were prepared as biomimetic models and their reactivity towards sodium silicate aqueous solutions was studied. Simultaneous formation of silica particles in the nanometric and micrometric size range was observed. The former corresponds to colloids grown at the surface of the gelatine films and the latter to particles induced by gelatine chain brushes formed at the film/water interface. These results are in good agreement with well-known principles of biomineralization and suggest that multi-molecular systems, rather than single components, are responsible for biogenic silica nanostructure formation.

Compressibility of hydrated and anhydrous Na2O‐2SiO2 liquid and also glass to 8 GPa using Brillouin scattering

Brillouin scattering measurements have been carried out on an aqueous solution of Na2O‐2SiO2 and anhydrous Na2O‐2SiO2 glass and liquid under in situ pressures to 8 GPa in the temperature range from 300 to 850 K. This temperature range spans through the glass transition of both the hydrous and anhydrous forms of Na2O‐2SiO2. The “modified” platelet scattering geometry has allowed us for the first time to determine VP independently from refractive index and hence the adiabatic compressibility and density of liquids as a function of pressure and temperature. The observed increase in density of the melt and glass phases formed at high‐pressure‐temperature conditions is likely associated with structural effects. There is a marked change in pressure derivative of adiabatic bulk modulus (K′S = dKS/dP) between the two phases. The large values of K′S of the liquid phase illustrate that the means of compaction of the liquid differ substantially from those of the glass and that the liquid is able to access a wider range of compaction mechanisms. The measured bulk modulus of the aqueous sodium silicate solution is highly temperature‐dependent but is much more similar to values of silicate melts than to that of end‐member water, particularly at high pressures. Thus water‐rich silica‐bearing solutions present at depth are likely to be difficult to seismically distinguish from anhydrous silicate melts solely on the basis of their sound velocities. The data on water‐bearing compounds allow the pressure dependence of the partial molar volume of water to be assessed to upper mantle depths. These results are in excellent agreement with prior determinations and illustrate the utility of Brillouin experiments coupled with the externally heated diamond anvil cell in determining partial molar properties of liquids at high pressures.

Three-Dimensional Morphological Chirality Induction Using High Magnetic Fields in Membrane Tubes Prepared by a Silicate Garden Reaction

Using a vertical superconducting magnet (max. 15 T), we studied magnetic field effects on membrane tube morphology prepared by a silicate garden reaction. At zero field, semipermeable membrane tubes grew upward when metal salts were added to a sodium silicate aqueous solution. In the presence of a magnetic field (15 T, downward) right-handed helical membrane tubes grew along a glass vessel's inner surface when magnesium chloride and copper sulfate were added. Referring to membrane tubes by the names of metal cations used in their preparation, in the case of Mg(II) and Zn(II) membrane tubes, the left-handed helical tubes grew when the field direction was reversed upward. The left-handed helical Mg(II) membrane tubes grew in the magnetic field when a glass rod was placed in a vessel. Mg(II) and Zn(II) tubes, separate from a vessel wall, grew in a twisted shape in the magnetic field. In situ observation of the solution's motion during the reaction revealed that the Lorentz force on the outflow from the opened top of the hollow membrane tube induced convection of the solution near the tube exit, engendering chiral growth of the membrane tubes. Relative orientation of the outflow and a boundary (a vessel wall or glass rod surface) helped to determine the convection's direction.

Supercritical CO2 Based Silica Coating of Gold Nanoparticles Using Water-in-Oil Microemulsions

A method is developed for the formation of a silica coating on 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 an organic solvent is injected into supercritical CO2 by means of a micronozzle, forming small droplets. Supercritical CO2 rapidly extracts the solvent from the droplet and reacts with the exposed surfactant-supported aqueous sodium silicate, forming silica. When gold nanoparticles are suspended in the sodium silicate solution, a silica coating on those nanoparticles is obtained. The particle size is controlled by controlling the coagulation process, i.e., how fast the “sticky” sodium silicate is reacted into “hard” silica. The reaction rate is simply controlled by adjusting the CO2 concentration. Particles in the size range 30−300 nm were obtained by changing the CO2 pressure from subcritical to supercritical with a coating thickness of as low as 20 nm. The particle size increases linearly with the CO2 molar volume. The water-to-surfactant mole ratio in the microemulsion also influences the silica coating.

Final Report on the Safety Assessment of Potassium Silicate, Sodium Metasilicate, and Sodium Silicate1

Potassium Silicate, Sodium Metasilicate, and Sodium Silicate combine metal cations with silica to form inorganic salts used as corrosion inhibitors in cosmetics. Sodium Metasilicate also functions as a chelating agent and Sodium Silicate as a buffering and pH adjuster. Sodium Metasilicate is currently used in 168 formulations at concentrations ranging from 13% to 18%. Sodium Silicate is currently used in 24 formulations at concentrations ranging from 0.3% to 55%. Potassium Silicate and Sodium Silicate have been reported as being used in industrial cleaners and detergents. Sodium Metasilicate is a GRAS (generally regarded as safe) food ingredient. Aqueous solutions of Sodium Silicate species are a part of a chemical continuum of silicates based on an equilibrium of alkali, water, and silica. pH determines the solubility of silica and, together with concentration, determines the degree of polymerization. Sodium Silicate administered orally is readily absorbed from the alimentary canal and excreted in the urine. The toxicity of these silicates has been related to the molar ratio of SiO2/Na2O and the concentration being used. The Sodium Metasilicate acute oral LD50 ranged from 847 mg/kg in male rats to 1349.3 mg/kg in female rats and from 770 mg/kg in female mice to 820 mg/kg in male mice. Gross lesions of variable severity were found in the oral cavity, pharynx, esophagus, stomach, larynx, lungs, and kidneys of dogs receiving 0.25 g/kg or more of a commercial detergent containing Sodium Metasilicate; similar lesions were also seen in pigs administered the same detergent and dose. Male rats orally administered 464 mg/kg of a 20% solution containing either 2.0 or 2.4 to 1.0 ratio of sodium oxide showed no signs of toxicity, whereas doses of 1000 and 2150 mg/kg produced gasping, dypsnea, and acute depression. Dogs fed 2.4 g/kg/day of Sodium Silicate for 4 weeks had gross renal lesions but no impairment of renal function. Dermal irritation of Potassium Silicate, Sodium Metasilicate, and Sodium Silicate ranged from negligible to severe, depending on the species tested and the molar ratio and concentration tested. Sodium Metasilicate was negative in the local lymph node assay (LLNA), but a delayed-type hypersensitivity response was observed in mice. Potassium Silicate was nonirritating in two acute eye irritation studies in rabbits. Sodium Metasilicate (42.4% H2O) was corrosive to the rabbit eye. Sodium Silicate was a severe eye irritant in some eye irritation studies, but was irritating or nonirritating in others. A skin freshener containing Sodium Silicate was nonirritating. Sodium Metasilicate was nonmutagenic in bacterial cells. Rats given Sodium Silicate (600 and 1200 ppm of added silica) in the drinking water in reproductive studies produced a reduced number of offspring: to 67% of controls at 600 ppm and to 80% of controls at 1200 ppm. Three adult rats injected intratesticularly and subcutaneously with 0.8 mM/kg of Sodium Silicate showed no morphological changes in the testes and no effect on the residual spermatozoa in the ductus deferens. Sodium Metasilicate (37% in a detergent) mixed with water was a severe skin irritant when tested on intact and abraded human skin, but 6%, 7%, and 13% Sodium Silicate were negligible skin irritants to intact and abraded human skin. Sodium Silicate (10% of a 40% aqueous solution) was negative in a repeat-insult predictive patch test in humans. The same aqueous solution of Sodium Silicate was considered a mild irritant under normal use conditions in a study of cumulative irritant properties. The Cosmetic Ingredient Review (CIR) Expert Panel recognized the irritation potential of these ingredients, especially in leave-on products. However, because these ingredients have limited dermal absorption and Sodium Metasilicate is a GRAS direct food substance, the Panel deemed the ingredients safe for use in cosmetic products in the practices of use and concentration described in this safety assessment, when formulated to avoid irritation.

Preparation and Formation Mechanism of Silica Microcapsules (Hollow Sphere) by Water/Oil/Water Interfacial Reaction

Silica microcapsules (hollow spheres) were readily prepared by an interfacial reaction using a water/oil/water (W/O/W) emulsion system. A W/O emulsion consisting of an aqueous solution of sodium silicate (WP-1) and an n-hexane solution of Tween 80 and Span 80 (OP) was added to another aqueous solution of a precipitant (WP-2). The reaction of sodium silicate with a precipitant to form silica on this W/O/W emulsion system (WP-1/OP/WP-2) forms the hollow structure spontaneously. Therefore, no core material often utilized in silica hollow sphere fabrication was required in this process. The formation and the particle size of the silica microcapsule depended on the precipitant employed. When NH4HCO3 was used as precipitant, the particle size of the silica microcapsule was successfully controlled by the volume ratio of WP-1/OP/WP-2, the rotation number of the homogenizer, and the concentration of sodium silicate in WP-1. However, this control of the particle size was not achieved when other precipitants such as...

Advantageous features of sodium silicate as the plasticizer for low-cement refractory castables

The plasticizing effect of an aqueous sodium silicate solution of low concentration (0.3 – 0.4%) on the properties of a low-cement refractory castable is studied. The merits of using sodium silicate, rather than the conventional sodium tripolyphosphate, for plasticizing sintered refractory castables are emphasized.

Preparation and Properties of Organic-Inorganic Hybrid Materials from Sodium Silicate

In this study, organic-inorganic hybrid monomer, poly silicic acid urethane methacrylate (PSUMA), was prepared by reaction of poly silicic acid extracted from sodium silicate aqueous solution with THF and 2-(methacryloyloxy)ethyl isocyanate. The PSUMA was copolymerized with methyl methacrylate to obtain hybrid copolymers. The material properties such as mechanical properties, thermal properties, Vickers hardness, transparency and so on were evaluated. The PMMA-PSUMA hybrid copolymers kept high transparency and showed higher elastic modulus and Vickers hardness than those of raw PMMA. Moreover, in comparison with PMMA, the hybrid copolymers had greater heat-resistance and lower volume contraction.

Gelatine/silicate interactions: from nanoparticles to composite gels

The possibility to design new composites associating biopolymers with mineral phases relies on the understanding and control of their mutual interactions. In this work, aqueous solutions of gelatine and sodium silicate were mixed at pH 5, 37 °C and left to stand at 20 °C for 1 day. At low gelatine and high silicate contents, precipitates were obtained, containing a fixed silicon/polymer molar ratio. Scanning electron microscopy (SEM) reveals that they are formed of large aggregates of platelets, constituted of closely-packed nanoparticles. For high gelatine contents, composite gels were formed consisting of silica particles dispersed in the biopolymer matrix. Swelling studies indicate that the addition of silica decreases the stability of the gels by inducing gelatine depletion in solution. Similar experiments conducted at pH 7 show that at this pH, silicates are more effective at precipitating gelatine. A model is proposed for the formation of the composites, based on the electrostatic interactions arising between silicates and polymer chains. These results are discussed in the context of hybrid biomaterials design and biosilicification processes.

Size distribution of colloidal silica in sodium silicate solutions investigated by dynamic light scattering and viscosity measurements

Three types of aqueous sodium silicate solutions characterized by molar SiO 2:Na 2O ratios of 2.2, 3.3, and 3.9 were investigated by dynamic light scattering and viscosity measurements. The solutions were prepared by diluting concentrated commercial products to SiO 2 content between 0.5 and 15 wt%. Dynamic light scattering (DLS) was used for the investigation of size distributions of colloids immediately after dilution. At least three size classes of colloidal particles were detected, which exist in parallel in the solutions. The respective radii are 0.4 to 0.6 nm, 2.5 to 13 nm, and 75 to 85 nm. The larger colloids dominate the mass distribution, whereas the smaller colloids control the surface area of the colloidal fraction. Material properties such as pH, viscosity, refractive index, and density were measured as a function of dilution. The evaluation of the viscosity data indicated that the colloids have a lower density than dense amorphous silica. Aging effects could be suppressed by measuring within 1 h after dilution.

Synthesis of Al-containing mesoporous silica (KSW-2) with semi-squared channels by incorporation of Al into the framework of kanemiteElectronic supplementary information (ESI) available: powder XRD patterns and 29Si MAS NMR spectra of kanemite and Al-kanemite, N2 adsorption isotherm of Al-KSW-2, TEM images of Al-KSW-2. See http://www.rsc.org/suppdata/jm/b2/b211073c/

Incorporation of Al into the framework of single-layered silicate kanemite and the formation of Al-containing mesoporous silica (Al-KSW-2) with semi-squared one-dimensional channels were surveyed. Al-containing δ-Na2Si2O5 was successfully obtained by thermal treatment of an aqueous sodium silicate solution (Na2O/SiO2 = 1 ∶ 2) containing NaAlO2 up to 785–810 °C, depending on the amount of NaAlO2 added. After Al-containing δ-Na2Si2O5 was dispersed in distilled water, Al-containing kanemite (Al-kanemite) was obtained with tetrahedrally coordinated Al. The reaction of Al-kanemite with an aqueous solution of hexadecyltrimethylammonium (C16TMA) surfactant yielded a layered C16TMA–Al-kanemite complex which was converted to a mesostructured precursor of Al-KSW-2 by mild acid treatment. Tetrahedral coordination of Al was retained in the framework of Al-KSW-2 with high surface area (830 m2 g−1) and uniform semi-squared mesopores (2.7 nm), which increased the adsorption ability for cationic dye molecules.

Supercritical CO2-Based Formation of Silica Nanoparticles Using Water-in-Oil Microemulsions

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...