Effect Of Silica Concentration Research Articles

The Effect of Silica Concentration on The Absorption Properties of Silica-Based Ceramic Membrane

Water pollution is currently an increasingly widespread environmental problem. Methylene blue is a synthetic dye used in the textile industry which pollutes the aquatic environment. The absorption of Methylene Blue textile dye which pollutes the environment uses silica precipitate as a filler in ceramic membranes with a clay matrix. Silica precipitate added to the ceramic membrane varies with a concentration of 0.3 %, 1.01 %, 1.68 %, 2.34 % and 2.99 %. The membrane will be characterized using Fourier Transform Infrared (FTIR) testing to determine the functional groups of the components it contains. Testing the absorption of methylene blue contaminant content from artificial wastewater using the UV-Vis Spectrophotometry test. The FTIR test carried out compared the functional groups of membrane samples before and after sintering. The results obtained from the FTIR test were that the membrane after sintering contained silica and some PEG, while the membrane before sintering contained other components such as PVA, PEG, water molecules and silica. The UV-Vis test carried out on the membrane gave results that the membrane was 0.3 %, 1.01 %, 1.68 %, 2.34 % and 2.99 % respectively has a removal efficiency of 58.0 %, 54.0 %, 59.3 %, 64.0 % and 66.4 %, where the best removal efficiency of methylene blue was on a membrane filled with 2.99 % of silica. Tests on the membrane showed that an increase in silica concentration was in line with an increase in the quality of the membrane’s performance in rejecting methylene blue contaminants.

Effect of silica concentration on degree of sintering of chromite-silica ladle well filler sand based on South African raw materials

During steelmaking, one important factor for production efficiency is the free opening of the ladle nozzle during continuous casting. Free opening occurs when the well filler sand and the steel flow freely when the slide gate is opened. Well filler sands are used for the slide gate of a ladle to separate the slide gate refractory and the molten steel. The well filler sand is partially sintered by the heat of the molten metal, which can result in the ladle nozzle failing to open if the sand is not sintered to an appropriate extent. It is therefore of great importance that the sintering behaviour of well filler sand is understood. We studied the effect of the well filler sand chemistry on its sintering properties. Samples of well filler sand with various chemical compositions were sintered in a high-temperature chamber furnace. Quantitative X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), and wavelength dispersive spectrometry (WDS) by electron microprobe analysis (EMPA) were used to analyse the various well filler sand mixes. Points of analysis were indicated on backscattered electron (BSE) micrographs. Quantitative element mapping was undertaken by energy dispersive spectrometry (EDS). Thermodynamic calculations in FactSage predicted the percentage liquid phase present for the various well filler sand compositions at equilibrium conditions. The results of this work show that the degree of sintering of chromite-silica well filler sand depends strongly on the silica content. The amount of liquid phase formed increases with increasing silica content.

Synthesis of PVA/SiO2 Nanofibers by Electrospinning Method for Supercapacitor Separators

In this research, polyvinyl alcohol (PVA)/silica nanofibers have been synthesized using electrospinning technique. Solutions of sodium silicate (Na2SiO3) in water and PVA flakes were blended and then processed by electrospinning method to obtain PVA/silica nanofibers. The effect of silica concentration on the resulting morphology and diameter of as-spun nanofibers were investigated by using scanning electron microscopy (SEM). The electrolyte uptake and retention of the as-spun nanofibers were measured. The silica concentration has an effect on the resulting nanofibers, where an increase in silica concentration resulted in a decrease on the diameter of the fibers. The manufactured nanofibers have an average diameter of 200-300 nm. The electrolyte uptake and retention values are also affected by the concentration of the silica in the electrospun solution, with the electrolyte uptake and retention values decreasing with the increase in silica concentration. The best values obtained are 151% for electrolyte uptake and 60% for electrolyte retention, which shows potential for PVA/silica nanofibers as an alternative material for supercapacitor separators.

Aerogel Spring‐Back Correlates with Strain Recovery: Effect of Silica Concentration and Aging

Silica aerogels display exceptional properties and great application potential, with a mature market in thermal insulation. Both supercritical drying (SCD) and ambient pressure drying (APD) routes are implemented industrially. Herein, how aging and silica content affect the mechanical properties, and how these in turn determine the shrinkage, spring back, and density during APD are systematically investigated. The APD densities display a U‐shaped dependence of density w.r.t. silica concentration. At low silica concentrations, the gels cannot withstand the capillary forces during APD and dense xerogels are obtained. At intermediate to high concentrations, APD shrinkage is strongly reduced and density increases with silica concentration. A series of cylinders are prepared by SCD and investigated by uniaxial compression and their strain recovery is determined systematically. The mechanical responses are plastic, viscoelastic, and brittle in nature for low, intermediate, and high silica concentrations, respectively. The strain recovery of the SCD cylinders correlates to the degree of spring back during APD. The viscoelastic response of SCD aerogels having 6 wt% corresponds to the silica concentration where a minimum in APD aerogel density is observed. The importance of gel mechanics for silica aerogel spring back during APD, in addition to surface modification and hydrophobization is highlighted.

Synthesis and characterization of Fe3O4/SiO2 Nanocomposite from Kaolin Bangka Island

Magnetite is widely used in various fields of separation and adsorbent. Various studies have also reported that magnetite without modification have low thermal stability, low water solubility and may undergo reactions forming a FeOOH intermediate phase. The use of silica templates is done in such a way that the magnetite produced is not easily agglomerated. The source of silica can easily be found in nature, one of which is kaolin. Synthesis of Fe3O4/SiO2 nanocomposites from Kaolin Bangka Island was carried out. The source of silica used is sodium silicate which is made from kaolin. The parameter observed in this study is the effect of silica concentration on the formation of Fe3O4/SiO2 nanocomposites. The SiO2 concentrations used were 5%, 15% and 30%. Based on the XRD analysis results, it appears that the three samples have typical diffraction peaks from Fe3O4/SiO2 nanocomposites at 2θ 24°, 26° and 35°. The average particle size of each composite for 5%, 15% and 30% SiO2 concentrations is 50.05 nm, 43.21 nm and 41.68 nm. It can be concluded that nanocomposite with SiO2 concentration of 30% has the potential to be applied further as a heavy metal adsorbent. FTIR analysis showed an absorption peak indicating the silica has coated the magnetite material from Fe3O4.

Precipitated Silica from Sodium Silicate by CO<sub>2</sub> on Fixed Bed Column

The precipitated silica prepared by reaction of sodium silicate and gas CO2 on fixed bed column have been production successfully. In this study, silica from bagasse was extraction by sodium hydroxide 2N solution to produce sodium silicate solution. The sodium silicate solution was dilute by demineralize water to produce some concentration in the range of 0.33-0.98 %SiO2. Fixed bed column has a diameter of 7.5 cm with a height of 50 cm and a pH control apparatus. CO2 gas and sodium silicate liquid are both flowed from under of the column with a specified flow rate. The precipitate process was carried out on a fixed bed column with high of bed in the range of 10-30 cm. The effect of silica concentration and the high of the bed on the characterize of the precipitated silica product have been studied. The precipitated silica product characterized by XRF, XRD, SEM-EDX and BET. The quality of precipitated silica produced in the range concentration of 95-98 w% SiO2, surface area (BET) in the range of 46.1 – 58.8 m2/g.

Effect of Silica Nanoparticles on Dry Water Gas Hydrate Formation and Self-Preservation Efficiency

The effect of silica concentration in dry water microdispersion on the kinetics of formation of methane hydrates and efficiency of their self-preservation was studied beyond the range of thermodynamic stability of hydrates below 273 K. For dry water used for the formation of gas hydrates, there is a certain concentration of silica that provides an optimum combination of high rate of formation and self-preservation efficiency of hydrates during their dissociation. Below this concentration, the rate of formation of methane hydrates in dry water significantly decreases with the silica content, while the self-preservation efficiency remains almost constant. Above this concentration, the formation rate changes insignificantly when the silica concentration increases, and the self-preservation efficiency abruptly decreases. Possible reasons for this behavior of hydrates were considered. It was found that the specific surface area of silica used to form dry water can significantly affect the formation rate of gas hydrates and their self-preservation efficiency.

Silica scaling and scaling control in pressure retarded osmosis processes

The performance of pressure retarded osmosis (PRO) processes is significantly limited by membrane fouling. This study systematically investigated PRO scaling by silica, which is one of the most common salts causing membrane scaling. In particular, the effect of silica concentration, the initial water flux, the chemistry of feed solution (FS) /draw solution (DS), and the type of membrane were studied in the PRO mode of operation. It has been observed that a low silica concentration (e.g., 10mg/L SiO2) could even cause membrane scaling during a PRO process. The rate and extent of the scaling was mainly governed by the internal concentration of silica in the membrane support layer and the solution chemistry of the FS/DS. The results suggested that the scaling could be mitigated by decreasing the internal concentration through the reduction of bulk silica concentration, the optimization of operating water flux, and the decrease in membrane structural parameter. The structural parameter seems to play a dominant role in PRO scaling by silica than the membrane materials and other physico-chemical properties. In addition, silica scaling can be controlled by lowering the pH of the FS and/or DS. For the first time, it has been demonstrated that utilizing an acidic DS was highly effective in controlling PRO scaling, which can be attributed to the low local pH in the membrane support layer as a result of the internal concentration polarization (ICP) of the reversely diffused H+. This method opens a new dimension for PRO scaling/fouling control.

Carbon-silica nanocomposite with negative differential resistance for high voltage negatronic devices: Effect of silica concentration

In this work, carbon-silica nanocomposites have been elaborated by sol-gel technique. SiO2 nanoparticles were added to resorcinol-formaldehyde (RF) carbon precursor solution with different silica weight percentages. The XRD investigations carried out on these samples outline that the material has amorphous phase. The transmission electron microscopy (TEM) images show the presence of nanostructures in RF-30% SiO2 and RF-50% SiO2 samples. The electrical conductivity was investigated in the temperature range 80–300 K and in the frequency range 100 Hz–1 MHz. The dc and ac conductivity can be explained by hopping conduction model. Current-Voltage characteristics exhibit nonlinear and symmetric behavior for all measurement temperatures between 80 K and 300 K. In addition, a negative differential resistance (NDR) phase has been detected even at room temperature in RF-50% SiO2 non dispersive sample. These investigations will contribute to the fabrication of thermal and high voltage negatronic devices working at room temperature where NDR plays an important role.

Fumed silica/polyurethane nanocomposites: effect of silica concentration and its surface modification on rheology and mechanical properties

The effects of nanosilica type and its content on microstructure, mechanical properties, and rheology of thermoplastic polyurethane (TPU) nanocomposites were investigated. Three different types of silica which included: unmodified (Si-Un) and commercially modified with octylsilane (Si-OS) and polydimethylsiloxane (Si-PDMS) with 5, 10, and 15 wt% of all fillers, were prepared by solution casting method. Scanning electron microscopy (SEM) showed that surface treatment of nanosilica with OS and PDMS reduced the aggregation of particles and improved their dispersion at microlevel. The effect of adding nanoparticles on microdomain morphology of TPU was studied by transmission electron microscopy (TEM), infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results demonstrated a relatively good interaction between the hard and soft segments in the presence of treated nanosilica that hindered the crystallization of hard segments in TPU. Thermogravimetric analysis (TGA) and tensile test showed that nanocomposites with treated nanosilica have better thermal stability and mechanical properties. The dynamic rheological studies indicated that nanocomposites containing Si-OS and Si-PDMS (with better dispersion and higher interface between the soft and hard domains in TPU) have improved viscoelastic properties in comparison with nanocomposites with untreated silica. In this study, dynamic frequency sweep data were correlated by a generalized Maxwell model and found that elastic constants of TPU chains were improved in the presence of modified silica nanoparticles.

Intermolecular cooperativity and entanglement network in a miscible PLA/PMMA blend in the presence of nanosilica

Nanosilica filled polylactide (PLA)/Poly(methyl methacrylate) (PMMA) 50/50 blends with varying silica concentrations were prepared by melt mixing. In this work, the effects of silica concentration and the preferential adsorption between silica and the component on the thermo-mechanical and rheological properties of PLA/PMMA blends were systematically investigated. The results of DSC indicate the miscibility of PLA/PMMA/silica nanocomposites in the solid state, and the incorporation of nanosilica does not only increase the glass transition temperature but also extend the broadness of glass transition. Local nanoscale heterogeneities in the miscible blends are proposed due to the self-concentration of the components, and the presence of nanosilica increased the concentration fluctuation and dynamic heterogeneity of the PLA/PMMA blends. A distinct “crater” structure can be observed in the fractured surfaces of the blend nanocomposites. According to the results of SEM and rheological measurements, it was proposed that PLA molecules were selectively adsorbed on the surface of nanosilica, and the preferential adsorption of PLA changed the blend composition in the “crater” structure and the bulk matrix. The phase separation temperature of the filled PLA/PMMA blends was also improved by the incorporation of nanosilica, implying a potential role of nanosilica in improving the phase stability of PLA/PMMA blends. In addition, nanosilica could increase and entanglement density and decrease the entanglement molar mass of the blends in a concentration-dependent manner.

A facile method for the production of high-surface-area mesoporous silica gels from geothermal sludge

Mesoporous silica gels were successfully produced from geothermal sludge by alkali extraction followed by acidification. The silica in the geothermal sludge was dissolved by NaOH solution to produce a sodium silicate solution, which was then reacted with HCl or tartaric acid to produce silica gels. The effects of silica concentration and pH on the silica gel properties were investigated. In addition, an improved method was proposed by incorporating two-step aging. The first aging step, which was conducted at pH 10, was used to induce Ostwald ripening to increase the size of the primary particles, and the second step was used to strengthen the gel network. Decreasing the silica concentration by diluting the as-prepared sodium silicate solution tended to increase the surface area and pore volume of the prepared silica gels. The silica gels produced by tartaric acid possessed higher surface area and pore volume than those by HCl. The surface area and pore volume reached approximately 450m2g−1 and 0.8cm3g−1, respectively. When the gelation pH was decreased to 6, the surface area exceeded 600m2g−1. The first aging process increased the size and uniformity of the primary particles, which in turn increased the surface area of the particles. The pore diameter for all cases was greater than 5nm, indicating that the silica gels were mesoporous.

Investigation of Fouling of Membranes of a Reverse Osmosis Unit by Silica

A reverse osmosis unit to treat ground water in Saboura/Syria has been in operation for several years. It suffered frequently from severe fouling of membranes. This led to frequent stoppages and losses of flow. Operators of the unit reported the formation of white solid scales on the membranes. It is well known that membranes treating ground water suffer from precipitates such as CaCO3, CaSO4, Fe, Al, Silica compounds, colloidal matters, bacteria and others. In this study analysis of the solid scales on the membranes showed that silica is the main scaling component. So experiments were carried out to investigate the effect of silica concentration in ground water and other variables such as pressure, pH, metal cations and type of membrane on fouling. The results obtained showed that silica has a direct effect on fouling of membranes. This is influenced by many parameters. Increasing pressure leads to increase in flow rates of water through the membranes. Reduction of pH causes less scaling of silica on the membranes. Cations present in water such as calcium and magnesium help in forming polymeric silicates which cause fouling.

The effect of silica concentration on the biosorption of Cu<sup>2+</sup> and Co<sup>2+</sup> from aqueous solutions mediated by strains of <i>Bacillus</i>

Bacillus strains were isolated from a mine tailings dump in Nigel town, south-east of Johannesburg. These were then grown at 37(±0.5)°C in a trace element-agitated liquid media. The effects of pH, contact time, initial ion concentration and the presence of co-cations were studied to ascertain the optimal conditions for biosorption to take place. Test solutions contained 0.002 M, 0.07 M and 0.2 M of either copper or cobalt ions. The Bacillus strains removed the copper and cobalt more efficiently from solutions of low concentration (0.002 M and 0.07 M) than from solutions of high concentration (0.2 M) over a 48 h period. Maximum biosorption was obtained at pH 6.5 and 5.5 for copper and cobalt solutions, respectively. The presence of silica led to an initial increase in both copper and cobalt biosorption, though higher concentrations of silica resulted in a decrease in metal uptake by Bacillus strains.Keywords: biosorption, Bacillus, silica, copper, cobalt

The size and polydispersity of silica nanoparticles under simulated hot spring conditions

AbstractThe nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33°C) and the addition of glucose restricted particle growth to sizes <20 nm, while varying [SiO2] or ISdid not affect the size (30—35 nm) and polydispersity (±9 nm) observed at 58°C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation.

Understanding the Generation of Dissolved Silica in Thermal Projects: Theoretical Progress

Abstract The production of silica in thermal petroleum recovery projects is a well-known phenomenon, and considerable efforts for its control are a common feature of facilities engineering in such projects. Recent work related to the generation of silica in SAGD projects has shown that the largest effect on silica production in SAGD is the steam zone pressure. Silica levels in produced water tend to increase with temperature. However, a significant suppressive effect of silica dissolution from quartz sands is provided by the presence of carbon dioxide dissolved in steam condensate. Lesser effects of silica concentration are due to ionic strength of the condensate. The carbon dioxide concentration in the steam condensate is amenable to theoretical prediction, available from recent progress in gas dissolution thermodynamics, and this allows the estimation of one of the major factors responsible for the suppression of produced water silica concentration. Other effects may be due to pH and fluid alkalinity, which are not independent of CO2 concentration. This paper is intended to provide an overview of the progress in obtaining a predictive capability, and to highlight the issues related to appropriate sampling and analytical methods that hinder simple correlations to date. Introduction The effect of temperature on silica dissolution from quartz has been known for a long time. Cowan and Weintritt(1) in their well-known treatise on water-formed scale deposits, cite Kennedy's work(2) and provide convenient tabulations and graphs of silica solubility and temperature. The experimental data for the solubility of silica from quartz are shown in Figure 1. By comparison, the data generated by the SOLMINEQ program of the Alberta Research Council are quite similar (Figure 2), with slightly increased solubilities at lower temperatures, and a slight reduction at higher temperatures. The SOLMINEQ program is a program based on the solution thermodynamic database of the U.S. National Bureau of Standards (now NIST), and operates by a free energy minimization algorithm. Data such as these usually make it mandatory that silica concentrations be reduced in produced water treatment in SAGD schemes, whether the water is recycled for steam generation or injected into a disposal well. Common methods in use are warm or hot lime softeners, MagOx units or acidification schemes. One would expect that apart from temperature, some aspects of produced water chemistry, such as dissolved acid gas content, pH, alkalinity and ionic strength, play a part in controlling the silica content of produced water from SAGD operations, so that the simple solubility curves published by Cowan and Weintritt cannot be used to correctly predict silica concentrations in any given scheme. Temperature Effect The magnitude of the temperature effect has already been shown. The use of the SOLMINEQ program produces results consistent with original experimental data. The use of this program to FIGURE 1: Experimental quartz solubility(2). Available in Full Paper. FIGURE 2: Equilibrium silica, mg/L, as function of steam zone temperature. Available in Full Paper. generate silica solubilities for any given produced water composition is a simple trial and error procedure, as follows:

Electrical conductivity of epoxy resin–carbon black–silica nanocomposites: Effect of silica concentration and analysis of polymer curing reaction by FTIR

Electrical properties of epoxy resin–carbon black–silica nanocomposites are determined by conductive paths imparted by carbon black and influenced by a “network” of silica. Fractures are observed in nanocomposites with a high solids content, contributing to low conductivity. At these concentrations, the space occupied by the silica and carbon black particles causes the distance between reactants to be relatively large and the extent of cross-linking in the nucleophilic addition reaction between epoxy resin polymer and isophorone diisocyanate is reduced.

Effect of silica concentration on electrical conductivity of epoxy resin–carbon black–silica nanocomposites

Electrical properties of nanocomposites are determined by the conductive paths of carbon black and influenced by a “network” of silica. With increasing content of silica, carbon black (CB) particles are optimally dispersed, contributing to the generation of a conductive network between CB particles via direct particle contact and a tunneling effect; maximum conductivity for the epoxy resin–CB–silica nanocomposite described herein occurs at a ratio of 0.6:1.0 (SiO 2 :CB). As a non-conductive component, excessive silica will prevent electron flow, giving rise to low conductivity.

Performance of RO membranes in silica bearing waters

Performance of two types of reverse osmosis membranes in silica bearing waters were investigated. The experiments were carried out using the Osmonics SEPA CF membrane flat sheet unit. The membranes investigated were polyamide (MS19) and thin film (DS11); their rejection, compaction, concentration polarization, fouling propensity and ease of cleaning were examined. In addition, the effect of silica concentration and polyvalent ions were investigated. The average silica rejections on DS11 and MS19 membrane were found to be 96.2% and 93.8%, respectively. The thin film (DS11) membrane was found to be easier to foul by silica than polyamide (MS19) membrane, but more easily cleaned. Both membranes underwent compaction; however MS19 was more prone to compaction (15–30%) than DS11 (0–15%). The concentration polarization ranged between 2 and 3 for the runs. Increases in Ca, Mg and total hardness for runs with given silica feed concentration increased fouling penalties. Analysis of the deposit by EDS indicated that Ca and Mg did not partake in chemical structure of the deposit; it appears that they catalyzed polymerization and were minutely adsorbed by the silica deposit. The results indicated that keeping low feed silica concentration might not, under all conditions, be effective in minimizing fouling. For Ca to Mg ratio of 1.5, the optimum initial silica feed concentration was found to be 100 ppm, not the lowest concentration of 50 ppm. The emphasis should be put to understand the mechanism of silica fouling (i.e. crystallization or particulate fouling) in order to mitigate this problem. Further experiments are needed to investigate the effects of other parameters on silica fouling in dynamic systems and to understand the mechanism of silica fouling.

Effect of grazing history, experimental defoliation, and genotype on patterns of silicification in Agrostis tenuis Sibth.

We examined the effect of grazing exclosures in reducing the concentration of silica, the effect of experimental defoliation on silica accumulation, and the existence of genotypic variability in silica content in plants of Agrostis tenuis. Silica content of plants was higher in heavily grazed areas than within exclosures during the summer, but no significant differences in content were found in winter. Laboratory experiments indicated that there were significant differences among genotypes in their silica content. Some genotypes increased their silica content after clipping at intervals of 14 days but most of them reduced their silica content when clipped weekly. The existence of a significant genotype-clipping treatment interaction term showed that silica accumulation as a response to clipping varied among genotypes, and may provide the basis for microevolutionary changes in natural populations of A. tenuis. However, the possibility of silica acting as a defence was not supported when caterpillars of the graminivorous Lepidoptera, Pararge aegeria, fed on plants. The caterpillars fed more extensively on plants from grazed areas, which had a higher silica content. We conclude that there is some genetic variation in patterns of silica accumulation in plants of A. tenuis and that different grazing histories lead to differences in silica content of plants. Although the effect of silica concentration on large herbivores remains uncertain, herbivores can exert an effect on the silica content of the leaf blades of A. tenuis.