Aqueous Silicate Solutions Research Articles

Facile preparation of a water-based antireflective SiO2 film with high transmittance for perovskite solar cells.

The synthesis of anti-reflective (AR) films has been increasingly focused on environmental friendliness and cost efficiency in order to realize green and sustainable development. Herein, a novel strategy for preparing a nanoporous SiO2 AR film with high transmittance by a sol-gel process is proposed based on a sodium silicate aqueous solution. Sodium ions in the as-prepared SiO2 AR film can be effectively removed by a facile washing process, and thus its refractive index can be regulated. Moreover, the pH value of the sol has a huge effect on the structure and properties of the SiO2 AR film. As a result, the AR film exhibited a high transmittance increase of 4.10% at 550 nm and an average transmittance increase by 3.51% in the wavelength range of 380-1100 nm compared with blank glass. In addition, the obtained water-based SiO2 AR film exhibited hydrophilicity and the water contact angle (WCA) can be regulated from 61° to 8.4°. When the AR film was applied to the upper surface of perovskite solar cells, the photoelectric conversion efficiency (PCE) revealed an improvement of 1.44% compared with the PCE of perovskite solar cells without the AR film. Therefore, this work can provide a facile and effective method to prepare water-based antireflective films with high transmittance for solar cells.

Transformation of Cu(OH)2 to mesostructural copper-silicate in alkaline silicate solution

Mesoporous materials with high surface area, tunable pore size, and large pore volume have applications in catalysis, adsorption, and optical devices. While the templating method has been used widely to synthesize these materials, removing the organic template leads to energy and chemical waste, and the emission of CO2 greenhouse gas. Here, a new non-organic templating method, based on structural transformation, is proposed to prepare mesostructural copper silicate with a high surface area (425 m2g-1) and large pore volume. This mesostructural transformation is already achieved by hydrothermally treating the Cu(OH)2 crystalline precipitate in an alkaline silicate aqueous solution. The copper silicate platelets obtained from a 5-day hydrothermal treatment in silicate solution have mesopores of about 3.5 nm. For the applications in absorption and catalyst application, the copper silicate has a high absorption efficiency (∼67%) and a fast removal rate toward PH3 gas at 600 ppb and a high-performance catalyst (yield of phenol derivatives about 86%) for the C–O coupling reaction. The mesostructural copper silicate platelets offer a cost-effective and environmentally friendly production method due to their flexible and straightforward preparation process. The synthetic route provides a promising approach to preparing different mesoporous metal silicates.

Silica–Chitosan Composite Aerogels for Thermal Insulation and Adsorption

The dissipation of energy in the form of heat causes a huge energy loss across the globe. Thermal insulation materials which reduce heat loss can alleviate the energy crisis. Among many thermal insulation materials, silica aerogels (SAs) have attracted extensive attention due to their high surface area, low density and low thermal conductivity. However, the applications of SAs are restricted by their mechanical fragility. In this paper, a series of different ratios of silica–chitosan composite aerogels (SCAs) were prepared by mixing sodium silicate aqueous solution and chitosan solution followed by freeze drying. The surface morphology of SAs, CAs and SCAs was studied by scanning electron microscopy (SEM). The specific surface area, pore volume and pore size of the composite aerogels were studied by N2 adsorption–desorption isotherms. The thermal conductivities, chemical structures, thermal stabilities and hydrophobicities of SAs, CAs and SCAs were tested and analyzed. In addition, the adsorption properties of SCAs were measured using different organic solvents. The results reveal that when the proportion of sodium silicate aqueous solution and chitosan solution is 1:1, the obtained SCA−1/1 has the best performance, with a low thermal conductivity of 0.0369 W/m·K, a large specific surface area of 374.7 m2/g, and good thermal stability. In addition, the prepared SCAs also have good hydrophobicity and absorption properties, with adsorption capacities of 6.7–9.4 g/g, which show great application potential in the fields of insulation and adsorption.

Petrographic and Geochemical Inferences for Genesis of Terra Rossa: A Case Study from the Apulian Karst (Southern Italy)

Terra rossa is a reddish clay soil which is often present on the surface of limestone in regions with a Mediterranean-type climate. Its genesis is a controversial subject in terms of the origin of the parent material, from the residuum of underlying (carbonate/dolomite) bedrock in the absence/presence of an external silicate contribution (e.g., aeolian dust). Within this context the main goal of the present work was the understanding of the geochemical processes leading to the formation of the terra rossa starting from the carbonate bedrock. We report the results of a multi-method analysis on a terra rossa deposit occupying the bottom of a Quaternary karst depression on Mesozoic limestones exposed in the Murge area (Apulia Foreland, southern Italy). Geological, petrographic, textural, and chemical data were collected on karst products (reddish calcite incrustations and nodules, and fine-grained portion of terra rossa) by a detailed field mapping, optical microscopy, XRF and fusion ICP/MS analyses and by scanning electron microscope. New collected data show that the mineralogical composition of reddish incrustations and nodules is comparable, consisting of fibrous and impure calcite, detrital fragments of quartz, K-feldspar, zircon and authigenic minerals as (Mn, Ba, Ca) phases, (Al, Si, Mn, Fe, Mg, Ba, Ca) minerals, Fe-kaolinite and anatase. The prevailing minerals, instead, in the fine-grained portion of terra rossa are hematite, kaolinite, and goethite. Based on the chemical composition, and especially on REE patterns, a progressive interaction of silicate aqueous solutions (with Al, Si, Fe), containing pelite material, with the calcareous bedrock, as a source of carbonic acid, was the process driving the formation of terra rossa. Obtained results add new elements to the definition of the long-lasting question about the genetic processes responsible for the formation of terra rossa, corroborating their polygenetic origin, as result of limestone alteration in conjunction with the chemical interaction with allochthonous siliciclastic material.

Bubble formation phenomenon on the absorber column for CO2 absorption and to produce precipitated silica sodium carbonate.

CO2 absorption using sodium silicate aqueous solution in a bubble column has been studied. Sodium silicate aqueous solutions are classified as non-Newtonian fluids that can affect the bubble distribution. The goal of this research is to investigate the effect of a superficial gas velocity (0.85 cm s-1, 2.55 cm s-1, and 4.25 cm s-1) and sodium silicate concentration (0.2% v, 0.6% v, and 1.0% v) on the phenomenon formation of spherical-bubbles, ellipsoidal-bubble, and rod-shape bubbles in bubble column. The experiment was carried out in one minute interval during the five minutes operation. The CO2 absorption and the gel formation is influenced by the pH of the solution where the gas holdup plays an important role in changing the pH. The characterization of the precipitated particles showed that the trona phase (C2H5Na3O8) reached 88% in the preparation of 1% aqueous sodium silicate at a superficial gas velocity of 4.25 cm s-1. The superficial velocity of the gas and the concentration of the sodium silicate solution influence the formation of bubbles. Spherical bubbles and ellipsoidal bubbles were observed in CO2 absorption experiments using a plate sparger, while rod-shaped bubbles were observed in experiments using a ball sparger.

Preparation of molded biomass carbon from coffee grounds and its CH4/N2 separation performance

Coffee grounds are promising precursors for excellent porous carbon adsorbents. During the preparation of the porous carbons, sodium silicate was used as a binder and pore-forming agent, and extrusion molding technology was used to prepare them in a columnar form. After carbonization, steam activation and silica removal by alkaline washing, high-strength columnar porous carbon adsorbents (CGCs) were obtained. Their CH4/N2 separation performance was studied by multicomponent breakthrough experiments. The Brunauer-Emmett-Teller (BET) surface area of CGC-1.5 (where 1.5 is the mass ratio of a 9 wt% sodium silicate aqueous solution to the coffee grounds) is 527 m2·g-1. Both the N2 and CO2 adsorption isotherms show that the CGCs are rich in micropores and mesopores, with the micropores size mainly centered at about 0.48 nm. FT-IR results show that CGC-1.5 has abundant oxygen-containing functional groups. At 298 K and 0.1 MPa, its equilibrium adsorption capacity for CH4 is 0.87 mmol·g-1, and the separation selectivity for a CH4/N2 mixture (3/7, vol/vol) is 10.3, which is better than most biomass-based porous carbon adsorbents and crystalline materials. Dynamic breakthrough tests show that CGC-1.5 has an excellent CH4/N2 separation performance at both high and atmospheric pressures. The dynamic selectivities at 298 K, 0.11 and 0.5 MPa are 10.4 and 17.9, respectively. The adsorption capacity is unchanged after 10 adsorption-desorption cycles. The mechanical strength of CGC-1.5 is as high as 123 N·cm-1, which meets the criteria of industrial applications.

Preparation of spherical amorphous boron particles via a green silicothermic reduction method

Spherical amorphous boron with an average particle size of 380 nm have been successfully prepared by a novel silicothermic reduction method using silicon, alkali borate and silicate as raw materials. The low-viscosity R2O-B2O3-SiO2 melt that exist in the above reaction system could be used to facilitate the silicothermic reduction and absorption of silica, a water-insoluble by-product formed in conventional silicothermic reduction. In contrast to silica, the by-product of improved silicothermic reduction is alkali silicate which could be separate easily by washing. Besides, the alkali silicate aqueous solution is an important recyclable industrial material. The results reveal that this is a simple and environment-friendly way to prepare sub-micron amorphous boron particles with intact sphericity.

Influence of cetyltrimethylammonium bromide and hydroxide ions on the interfacial tension and stability of emulsions of dodecane in aqueous silicate solutions

This manuscript provides an understanding of the emulsification mechanisms of a model alkane (dodecane) in concentrated aqueous sodium silicate solutions, for e.g. formulating alkane/geopolymer composites for varied applications. To this purpose, we assume that silicate oligomers stabilize the emulsion by positioning themselves at the interface between alkane/aqueous solution. Moreover, the addition of an alkyltrimethylammonium, which interacts with silicate oligomers, is assumed to favor their positioning at the interface to increase the stability of the emulsion by Pickering effect. First, we study the influence of sodium silicate and hydroxide concentrations with up to 6 mol⋅L -1 (NaOH and SiO 2 ) on the interfacial tension (γ) between dodecane and water. Secondly, we study the effect of CetylTrimethyl Ammonium Bromide (CTAB) and DecylTrimethylAmmonium Bromide (DeTAB) on the interfacial tension and the stability of the emulsion. Adding CTAB surfactant leads to partial precipitation but significantly decreases the interfacial tension to less than 4 mN.m -1 . These effects that are not observed with DeTAB. The precipitate corresponds to CTAB-silicates and seems to contribute to the stabilization of the water/dodecane system, presumably through Pickering effect. Moreover, emulsion stability is shown to be related to the condensation/decondensation state of silicate species.

High performance cementless composites from alkali activated GGBFS

Some of the thermally activated minerals and pozzolans were generally preferred in the production of geopolymer and/or alkali-activated composites as unary, binary, and ternary mixtures. The general trend is to use Ground Granulated Blast Furnace Slag (GGBFS) as binary or ternary mixes in the production of alkali-activated composites. However, GGBFSs have preferred the only binder in this study. Alkali-Activated Concrete (AAC) specimens were produced by using sodium hydroxide and sodium silicate aqueous solutions in three different molarity values (8, 10, and 12 M) for the formation of activation. For each mixture, three different activation temperatures, 25 °C (ambient temperature), 60 °C and 90 °C for 18 h, were applied. After this process, the specimens were kept under laboratory conditions (25 ± 2.5 °C) for 90 days to gain strength. Then capillary water absorption, density, Dynamic Modulus of Elasticity (DMoE), compressive strength, splitting tensile strength, and abrasion resistance tests were performed on the specimens. Furthermore, microstructure analyses were performed on the selected specimens. In the conclusion, AAC production was able to achieve using 100% GGBFS. High strength cementless concretes with a compressive strength of 82.32 MPa could be obtained by using GGBFS, which is a waste material. Besides, AAC with an abrasion value of 3.86% by weight was obtained in the specimen coded M12T60.

Application of High Modulus Silica Sol Electrolyte in Lead-acid Battery

High modulus silica sol of n/m=52 sodium silicate aqueous sol was prepared by compressing and filtering sodium silicate aqueous solution without loss of SiO2 content. The SiO2 content can increase from 14.2% to 30%. The high modulus silica sol are mixed with acidic water to prepare a high modulus silica sol electrolyte, which is then produced into 6-DZM-20 Ah electric bicycle batteries. A combination of intermittent current-changing charging process, simple electrolyte production process, brings about reduced energy consumption and cost. The battery with the high modulus silica sol electrolyte shows enhanced stability, deep cycling performance, long service life, strong resistance to harsh environments, low self-discharge rate, low floating current, and excellent heat resistance.

Critical Review—Photostable Fluorescent Cd-Free Quantum Dots Transparently Embedded in Monolithic Silica

Fluorescent Cd-free quantum dots (QDs) such as InP/ZnS and CuInS2/ZnS have attracted attention for use as color converters for blue light emitting diodes. To protect QDs from oxygen, which degrades them by photo-oxidation during excitation, we fabricated a transparent monolithic silica composite containing the QDs using an aqueous solution of tetramethylammonium silicate (TMAS) as a silica source. The TMAS solution readily dispersed the negatively charged QDs prepared by ligand exchange of 1-dodecanethiol for 3-mercatopropionic acid (MPA). A highly transparent monolithic TMAS-derived silica composite containing the MPA-capped QDs was obtained from the QD dispersion through a sol–gel process. Improved photostability of QDs was explained by the TMAS-derived silica acting as a gas barrier to protect the embedded QDs from photo-oxidation by oxygen in air.

Effect of Type and Concentration of Aqueous Solutions on Corrosion Behaviour of Plasma Electrolytic Oxide Films on ZM21 Mg Alloy

Plasma electrolytic oxidation (PEO) is a technique employed to significantly enhance the corrosion and tribological properties of the materials by forming an oxide ceramic film on the surface of the material. In this investigation, ZM21 Mg alloy was subjected to PEO treatment in silicate and phosphate-based aqueous solutions of 5grams and 10 grams per liter concentrations. The oxide film was characterized using SEM, profilometer, thickness meter, and polarization test. Results showed that the oxide film obtained with 10g/L phosphate-based solution offers higher corrosion resistance than the oxide films formed with other solutions.

NONCONVENTIONAL TECHNIQUE FOR PRODUCING HIGH MECHANICAL STRENGTH GLASS FOAM FROM GLASS WASTE

In the work experimental results on the manufacture of glass foam with high mechanical strength from glass waste are presented. By replacing the usual conventional energy source with a nonconventional energy (electromagnetic waves) the heating efficiency allows a fast and economical manufacturing process. Calcium carbonate as a foaming agent and an addition of sodium silicate (aqueous solution) as a binder were used. By their physico-mechanical and morphological features (0.40-0.66 g/ cm<sup>3 </sup>the apparent density, 0.054-0113 W/ m·K the thermal conductivity, 2.2-6.3 MPa the compressive strength, below 1.2 % the water absorption and under 2 mm the pore size), the foams are appropriate for their use as replacer of existing similar building materials on the market.

NONCONVENTIONAL TECHNIQUE FOR PRODUCING HIGH MECHANICAL STRENGTH GLASS FOAM FROM GLASS WASTE

In the work experimental results on the manufacture of glass foam with high mechanical strength from glass waste are presented. By replacing the usual conventional energy source with a nonconventional energy (electromagnetic waves) the heating efficiency allows a fast and economical manufacturing process. Calcium carbonate as a foaming agent and an addition of sodium silicate (aqueous solution) as a binder were used. By their physico-mechanical and morphological features (0.40-0.66 g/ cm3 the apparent density, 0.054-0113 W/ m·K the thermal conductivity, 2.2-6.3 MPa the compressive strength, below 1.2 % the water absorption and under 2 mm the pore size), the foams are appropriate for their use as replacer of existing similar building materials on the market.

Crystallization of Polytetrafluoroethylene in a Wide Range of Cooling Rates: Nucleation and Diffusion in the Presence of Nanosilica Clusters.

Polytetrafluoroethylene (PTFE) is a polymer that displays exceptional properties. This synthetic fluoropolymer is also known to crystallize very fast upon cooling. The present work highlights for the first time the influence of nanosilica clusters on PTFE crystallization at fast cooling rates (up to 5000 K·s−1). The silica was synthesized from aqueous silicate solution and the surface modification was performed using TriEthoxyFluoroSilane (TEFS). In order to understand the crystallization behavior of PTFE/silica nanocomposite at a fast cooling rate, the measurements were carried out by Fast Scanning Calorimetry (FSC). The data were consequently combined with the measurements performed by conventional Differential Scanning Calorimetry (DSC). Interestingly, the results displayed variation of the crystallization behavior for the nanocomposite at fast cooling rates compared to slow cooling rates. The differences in crystal morphologies were then observed by Scanning Electron Microscopy (SEM) after slow and fast cooling rates. Finally, the effective activation energies (Eα) obtained from the crystallization under various cooling rates were combined in order to obtain one set of Hoffman-Lauritzen parameters. This procedure allowed us to show that the crystallization of PTFE in the presence of silica is promoted or hampered according to the cooling rates employed.

The effect of carbon fiber plasma treatment on the wettability and interlaminar shear strength of geopolymer composite

Interlaminar shear strength (ILSS) of composite depends on the adhesion between its reinforcement and matrix. To improve the mechanical properties of geopolymer composite reinforced with carbon fibers (CFs), the surface of the fibers was modified by plasma treatment in four types of argon atmosphere. The modification of the CFs was evaluated by contact angle measurement, scanning electron microscopy, and X-ray photoelectron spectroscopy. Geopolymer matrix was prepared by the dissolution of metakaolin and an amorphous silica in an aqueous solution of potassium silicate. Vacuum bagging technique was used to prepare the CF/geopolymer composite. The mechanical properties of the composites were determined by ILSS test. The results were compared to results obtained for untreated carbon fibers and their composites. A significant increase of the wettability of CFs was achieved for all plasma treatments and the increase of oxygen functional groups was detected on the CF surface. The results of the mechanical test confirmed improved adhesion for composite samples with CFs treated by plasma in argon atmosphere. Other samples exhibited low or no adhesion between the fibers and matrix. This leads to the conclusion that there are more effects influencing the adhesion than only the properties of CFs.

Microwave-Assisted Heating Method toward Multicolor Quantum Dot-Based Phosphors with Much Improved Luminescence.

Solid-state highly photoluminescent quantum dot (QD)-based phosphors attract great scientific interests as color converters because of an increasing demand for white-light-emitting devices. Herein, a microwave-assisted heating method is presented to fabricate multicolor QD-based phosphors within 30 s through microwave-assisted heating of the mixture of QDs and sodium silicate aqueous solution. In the composites, the formed cross-linked networks not only play as a matrix to prevent QD aggregation in solid state but also cause the variation of the refractive index around QDs and the QD surface optimization, which contributes to good stabilities and twice enhancement in photoluminescence quantum yields (69%) compared with the initial QD aqueous solution (33%). Using the QD-based phosphors as color conversion layers, white-light-emitting diodes were realized with controllable color temperature, high color purity, and high color-rendering index (90.3), which show a great potential in display and illumination. Furthermore, the luminescence lifetime of the QD-based phosphors is less than 25 ns. The potential application of the QD-based phosphors in visible light communication was also demonstrated, with the modulation bandwidth achieving 42 MHz.

Effect of Electrolyte on Micro Arc Oxidation Coating of Al-2014 Alloy

Micro Arc Oxidation (MAO) coating was performed on Al-2014 aluminium alloy in aqueous solution of silicate, phosphate and hybrid electrolytic environments. The MAO thickness was measured around 5-15 μm, in which significant thickness of both dense and porous layers were identified. A combination of nanocrystalline α-Al2O3and Υ-Al2O3 was identified in the MAO coating using X-ray diffraction analysis. The thickness and morphology of the coating, which is analyzed using SEM are different for different MAO process parameters and it was found that the MAO coating prepared in phosphate electrolyte is giving a better coating with higher coating thickness, minor pore size and better adherence.

Fire-proof silicate coatings with magnesium-containing fire retardant

A formula for an environmentally friendly and safe fire-proof paint was developed based on a potassium silicate aqueous solution with addition of a magnesium-containing fire retardant. The predominant use in paint of magnesium-containing fire retardant such as hydromagnesite compared to brucite and magnesite was demonstrated. It was established that a paint containing 5.5 wt% of hydromagnesite provides the first group of fire resistance for a wooden surface. The high fire resistance of the paint with this formula is proven by the high intumescence ratio (150%) and low weight losses (8.4%) after tests in a ceramic tube. When the paint is heated, a gradual loss of weight is detected, which is related to the characteristics of the hydromagnesite structure and helps to obtain an effectively foamed protective layer that prevents the diffusion of combustible gases and flame.

The rheological anomaly in water-silicate systems: a possible thermodynamic explanation

A rheological anomaly, consisting in the reversible increase in solution viscosity with increasing temperature, is a typical property of aqueous solutions of aminosilicates (polysilicates of aliphatic amines, amino alcohols and other amino compounds). To explain this anomaly, a simple mathematical model of interrelated acid-base and polycondesation equilibria in such solutions is proposed. The proposed calculation model assumes a direct dependence of the solution viscosity on the polymerization degree of silicate anions, as well as the independence of the dissociation constant of silanols and the polycondensation equilibrium constant on the degree of anions polymerization. Based on the assumptions made, a system of eight linear and nonlinear equations was constructed and solved. The results of calculations performed for concentrated solutions of aminosilicates (methylamine and piperidine silicates), as well as sodium and tetramethylammonium silicates, confirm the presence of a positive temperature dependence of the polymerization degree of silicate anions in the aminosilicate solutions, in contrast to the solutions of silicates of the strong bases. Thus, the proposed mathematical model of polymerization-hydrolysis equilibria in aqueous silicate solutions qualitatively explains the existence of the rheological anomaly in aqueous solutions of aminosilicates and its absence in solutions of alkali silicates and silicates of quaternary ammonium bases. In addition, this model correctly reproduces the displacements of the molecular mass distribution of silicate anions with changes in chemical composition and concentration of solutions. The proposed approach makes it possible to clarify the mechanism of the rheological anomaly, to understand the roles of various thermodynamic factors in its occurrence, and, as a consequence, to conduct a more meaningful search for new silicate and non-silicate systems with the same anomaly.