Incorporation Of Silica Research Articles

Silica incorporated cellulose fibres as green concept for textiles with reduced flammability

Safety requirements led to widespread use of textile products with reduced flammability. The global production of nearly 3 million tons of flame retardants generates a substantial environmental burden both during synthesis of the chemicals and disposal of waste textiles. In this work a cleaner technology to impart reduced flammability to viscose fibres is presented, which bases on the incorporation of 20%wt of silica into the cellulose fibre matrix during the stage of fibre formation. Stabilisation of the silica against unwanted leaching during washing procedures was achieved by treatment with aluminate, which reacts with silica under formation of the less soluble aluminosilicate. This treatment successfully was combined with the reactive dyeing step where no precipitation of dyes, losses in colour depth or reduced fastness of the dyeings occurred. Substantial reduction in time of afterglowing (-82%) and in length of destroyed material (-90%) were observed in standard tests for ignitability of bedclothes. The incorporation of silica into regenerated cellulose fibres offers a green alternative to the rather polluting finishing processes used today. The use of these modified fibres is of particular value for textile products worn next to the skin, as leaching of irritating flame retardants to the skin can be avoided.

Understanding Variations in the Tracking and Erosion Performance of HTV-SR-Based Composites due to AC-Stressed Aging

Among the polymeric family, high-temperature-vulcanized silicone rubber (HTV-SR) is the most deployed material for high voltage insulation applications. However, in an outdoor environment, due to contamination and wetting-induced dry band arcing, consequently SR experiences surface tracking and erosion. From a practical standpoint, the tracking and erosion performance under multi-stress aging is required to be known. It is in that context that the present study was undertaken to measure and analyze the effect of multi-stress aging on tracking and erosion performance. Composite samples of SR having different filler concentrations of silica and alumina trihydroxide (ATH) were aged in a multi-stress chamber for a period of 5000 h, and after that their electrical tracking performance was studied. Simultaneously, unaged samples were also exposed to tracking test for comparison. To conduct this test, the inclined plane testing technique was used in accordance with IEC-60587. All samples exposed to tracking test were analyzed using different diagnostic and measuring techniques involving surface leakage current measurement, Fourier transform infrared spectroscopy (FTIR), thermal stability and hydrophobicity classification. Experimental results shown that the tracking lifetime increased through incorporation of silica and ATH fillers in the SR. Amongst all test samples, two samples designated as filled with 2% nano silica and 20% micro silica/ATH exhibited greater resistance to tracking. This was attributed to the optimum loading as well as better dispersion of the fillers in the polymer matrix. The presence of nano-silica enhanced time-to-tracking failure, owing to both improved thermal stability and enhanced shielding effect on the surface of nanocomposite insulators.

Synergistic Enhanced Thermal Conductivity and Dielectric Constant of Epoxy Composites with Mesoporous Silica Coated Carbon Nanotube and Boron Nitride Nanosheet.

Dielectric materials with high thermal conductivity and outstanding dielectric properties are highly desirable for advanced electronics. However, simultaneous integration of those superior properties for a material remains a daunting challenge. Here, a multifunctional epoxy composite is fulfilled by incorporation of boron nitride nanosheets (BNNSs) and mesoporous silica coated multi-walled carbon nanotubes (MWCNTs@mSiO2). Owing to the effective establishment of continuous thermal conductive network, the obtained BNNSs/MWCNTs@mSiO2/epoxy composite exhibits a high thermal conductivity of 0.68 W m−1 K−1, which is 187% higher than that of epoxy matrix. In addition, the introducing of mesoporous silica dielectric layer can screen charge movement to shut off leakage current between MWCNTs, which imparts BNNSs/MWCNTs@mSiO2/epoxy composite with high dielectric constant (8.10) and low dielectric loss (<0.01) simultaneously. It is believed that the BNNSs/MWCNTs@mSiO2/epoxy composites with admirable features have potential applications in modern electronics.

Investigation on the roles of solution-based alkali and silica in activated low-calcium fly ash and slag blends

An evaluation of strength-gain in binders with equal mass proportions of low-calcium fly ash and slag activated with alkaline solutions containing dissolved silica is conducted. The roles of Si and Na in the activating solution on compressive strength, reaction kinetics, and content and phase composition of reaction products are evaluated. The early reactions within the activated binder are due to the dissolution and hydration of slag. In the presence of silica, there is early precipitation of calcium silicate hydrate (CSH) before the hydration of slag. Silica in the activating solution delays the primary hydration of slag. The reactivity of silica depends on the SiO2/Na2O ratio in the activating solution. A less polymerized form of silica with higher reactivity is produced at a higher Na content in the activating solution. More reactive silica form produces a more rapid early precipitation of CSH following the initial dissolution of slag. Fly ash in the binder provides additional Si and Al to the calcium aluminosilicate hydrate (CASH) formed from the slag reaction. The Na identified in the reaction products is in a water-soluble form and not chemically bound to the CASH. The Na does not contribute directly to the compressive strength. In the long-term, the content and the silica incorporation in the CASH scales with the silica content in the activating solution and it does not depend on the form of silica. Increasing the activating solution silica content results in its larger incorporation in CASH and produces compressive strength enhancement. The form of silica has a negligible effect on the dissolution of fly ash in the binder and ultimate strength achieved.

High-voltage and high-safety nickel-rich layered cathode enabled by a self-reconstructive cathode/electrolyte interphase layer

To achieve widespread adoption of Ni-rich layered oxides in commercial applications, it is highly necessary to address their cyclic stabilities and safety aspects under prolonged and harsh operating conditions, which will aggravate the simultaneous degradation of the Ni-rich cathode and electrolyte due to the more serious interfacial side reactions between them. Herein, a self-reconstructive cathode/electrolyte interphase (CEI) layer with good interfacial stability was designed and constructed for Ni-rich cathode, through the incorporation of dendritic mesoporous silica (DMS) with rich surface silicon-hydroxyl groups as a multifunctional electrolyte additive. The DMS shows the ability to reconstruct the CEI layer in real time, i.e., endowing the CEI layer with defluorination function, spontaneously formed LiPO2F2, and in-situ formed anti-fluorination protective layer with enhanced electron and Li+ diffusion. As expected, the sample with a self-reconstructive CEI layer exhibits significantly superior cyclic stability compared to the pristine one under extended cut-off voltage (4.5 V) or elevated temperature (55°C). Notably, the flame-retardant effect of DMS additive can also contribute towards the thermal stability of the electrolyte and electrode, which will effectively improve the safety aspect of the battery. Thus, this work provides new insights into reducing undesired self-reinforced failure process in Ni-rich cathode and reconstructing a self-healing CEI layer for high-safety, high-voltage lithium-ion batteries.

Simultaneous Increase of Solvent Flux and Rejection of Thin-Film Composite Membranes by Incorporation of Dopamine-Modified Mesoporous Silica.

Thin-film nanocomposite membranes have shown great promise in organic solvent nanofiltration. However, it is challenging to acquire high permeation flux without severe swelling, which might do harm to rejection and long-term stability. In this study, we introduced dopamine-modified mesoporous silica nanoparticles into the polyamide (PA) matrix via interfacial polymerization to fabricate a series of thin-film nanocomposite membranes. By using polyethyleneimine (PEI) as the aqueous monomer, the modified nanoparticles are designed to be cross-linked within the PA network, which allows the penetration of PEI into the mesopores, and therefore, the membranes show better resistance to solvent-induced swelling and pressure-induced densification. More importantly, the mesopores of nanoparticles provide additional fast channels for solvents, resulting in an unusual enhancement of solvent flux under reduced membrane swelling. Along with the permeation flux, the rejection performance of the nanocomposite membranes is simultaneously improved, thanks to the controlled swelling arising from the strong interfacial adhesion. Thin-film nanocomposite membranes with optimal filler concentration exhibit a high isopropanol permeance of 8.47 L m–2 h–1 bar–1 as well as a quite low-molecular-weight cutoff of 281 Da.

Polyethylene glycol and silica sol penetration improves hydrophobicity and dimensional stability of wood after a short-time treatment

Polyethylene glycol (PEG) and silica sol were used to improve the dimension stability and hydrophobicity of wood with different moisture contents (MC after oven drying, air drying: 10–12% and steam conditioning: 38–40%) via 24 h immersion treatment. The water in wood served as a medium for helping PEG diffusion into cell wall, resulting in a better dimensional stability for 38–40% MC wood. PEG impregnation could improve the dimensional stability but decrease the surface hydrophobicity due to its moisture affinity. PEG concentration (10, 20, and 30 wt.%) showed little influence on water contact angles (WCA) of treated wood. Silica sol impregnation could improve the dimensional stability and WCA. It was ascribed to the -OH consumption and filling effect in wood caused by silica sol networks. After combination treatment (one-step or two-step method), PEG and silica sol could provide a synergistic effect on improving dimensional stability and hydrophobicity of wood owing to the bulking effect and filling effect, respectively. In one-step method, as a lubricant and bulking agent, PEG could improve the ductility of the film formed by stiff silica via Si–O–Si cross-linked sol in wood. Moreover, the decreased surface hardness and compression strength of PEG treated wood were compensated by silica incorporation.

Mechanical strength and microstructure of metakaolin/volcanic ash-based geopolymer composites reinforced with reactive silica from rice husk ash (RHA)

The physical, mechanical and microstructural properties of metakaolin/volcanic ash-based geopolymer composites were investigated, as well as the influence of the incorporation of a reactive silica from rice husk ash (RHA) in their performance. The geopolymer composites were designed by replacing metakaolin with volcanic ash, VA (10–30 wt%) and RHA (0–20 wt%). Physical and mechanical testing, FTIR, XRD, optical microscopic and SEM were used to characterize the geopolymer composites. The results showed that the mechanical strengths and physical properties were mostly affected by the VA content as well as RHA content where the optimal mechanical strengths (19.3 and 60.73 MPa for flexural and compressive strength, respectively) were obtained with the composite sample containing 20 wt% of VA and 10 wt% of RHA. This was due to the additive that enhances the compactness and microstructure of geopolymer matrices obtained and also the increase of SiO2/Al2O3 ratio with the addition of RHA. Synergistic use of metakaolin, volcanic ash, and rice husk ash for construction materials through alkaline activation looks like the upcoming trend to valorize these materials.

Cellulosic wood fibre‐dual functional (Janus) mineral filler networks

AbstractThe incorporation of Janus silica and titanium dioxide fillers in wood fibre networks (handsheets) with 10, 20, and 40 wt% loading by filtration and layer‐by‐layer (LBL) deposition was demonstrated. The effect of filler's dual functionality on the wettability and water vapour transmission rate of handsheets loaded with the Janus fillers was investigated. Without silanization, the handsheets with silica filler are hydrophilic except when prepared by LBL and 40 wt% Janus silica filler. It was also found that silanization of the handsheets in conjunction with Janus fillers results in the formation of superhydrophobic handsheets with minimal liquid water absorption. Only the silanized handsheets prepared at 40 wt% Janus TiO2 filler loading were found to be hydrophobic. The lowest values of 231 and 237 g · m−2 · day−1 for the water vapour transmission rate was obtained for silanized handsheets with a Janus silica and titanium dioxide filler at 10 wt% loading, respectively.

PORE STRUCTURAL AND FRACTAL ANALYSIS OF THE INFLUENCE OF FLY ASH AND SILICA FUME ON THE MECHANICAL PROPERTY AND ABRASION RESISTANCE OF CONCRETE

Dam concrete suffers from serious abrasion damages in southwestern China, the abrasion resistance of concrete is therefore one of the most important factors determining the reliability even the safety of the dams. In the present work, the effects of fly and/or silica fume on the mechanical properties, drying shrinkage, as well the cracking and abrasion resistance of concrete were investigated, then the pore structures of concrete added with fly ash and silica fume and the pore surface fractal dimensions ([Formula: see text]) were determined by the mercury intrusion porosimetry (MIP) method and a fractal model, respectively. Finally, the relationships between the abrasion resistance of concrete and the porosity as well as the [Formula: see text] were revealed and discussed. The results indicate that silica fume significantly increases the drying shrinkage especially at early age, while the incorporation of fly ash and silica fume together can decrease the early plastic shrinkage-induced cracking risk and the final shrinkage to some degrees. Besides, the utilization of 5[Formula: see text]wt.% silica fume and 20[Formula: see text]wt.% fly ash together increases the abrasion resistance and mechanical property by about 4–9% at various ages. In addition, the compressive strength and the abrasion resistance of concrete are linearly correlated with the concrete porosity and the [Formula: see text]. Both the fly ash and silica fume could decrease the porosity of concrete and increase the [Formula: see text], therefore the concrete containing fly ash and silica fume have desired mechanical property and abrasion resistance. Moreover, [Formula: see text] has a more profound effect on the abrasion resistance of concrete than the concrete porosity. The addition of 5[Formula: see text]wt.% silica fume and 20[Formula: see text]wt.% fly ash together is suitable for the concretes used for wearing surfaces in terms of mechanical property, cracking and abrasion resistance.

A comparison of the degradation behaviour of 3D printed PDLGA scaffolds incorporating bioglass or biosilica

Silica incorporation into biomaterials, such as Bioglass and Si-substituted calcium phosphate ceramics has received significant attention in bone tissue engineering over the last few decades. This study aims to explore the dissolution behaviour of natural biosilica isolated from a freshwater diatom, Cyclotella meneghiniana, that has been incorporated into 3D printed poly (DL-lactide -co – glycolide) (PDLGA) scaffolds using extrusion and additive manufacturing. In the study, two different dry weight percentage (1 wt% & 5 wt%) of diatom-silica were incorporated into PDLGA scaffolds that were then degraded in phosphate buffered saline (PBS) cell free media. In addition, pure PDLGA scaffolds and 5 wt% Bioglass scaffolds were used as control groups. The degradation study was performed over 26-weeks. The release rate of Si4+ ions from diatom-PDLGA scaffolds was found to increase exponentially with respect to time. The compressive strength of scaffolds was also measured with the Diatom–PDLGA scaffolds found to maintain their strength for longer than either pure PDLGA scaffolds or 5 wt% Bioglass scaffolds. 13C NMR data showed that diatom biosilica containing scaffolds had less degradation than pure or bioglass-containing scaffolds at comparable time-points. Overall, the Diatom-PDLGA scaffolds were found to have more desirable physiochemical properties for bone repair compared to Bioglass.

Phenotypic trait variability as an indication of adaptive capacity in a cosmopolitan marine diatom.

Determining the adaptive capacity of marine phytoplankton is important in predicting changes in phytoplankton responses to ocean warming. Phytoplankton may consist of high levels of standing phenotypic and genetic variability, the basis of rapid evolution; however, few studies have quantified trait variability within and amongst closely related diatom species. Using 35 clonal cultures of the ubiquitous marine diatom Leptocylindrus isolated from six locations, spanning 2000 km of the south-eastern Australian coastline, we found evidence of significant intraspecific morphological and metabolic trait variability, which for 8 of 9 traits (growth rate, biovolume, C:N, silica deposition, silica incorporation rate, chl-a, and photosynthetic efficiency under dark adapted, growth irradiance, and high-light adaptation) were greater within a species than between species. Moreover, only two traits revealed a latitudinal trend with strains isolated from lower latitudes showing significantly higher silicification rates and protein:lipid content compared to their higher latitude counterparts. These data mirror recent studies on diatom intraspecific genetic diversity, which has found comparable levels of genetic diversity at a single site to those thousands of kilometres apart, and provide evidence of a functional role of diatom diversity that will allow for rapid adaptation via ecological selection on standing variation in response to changing conditions.

Enhanced HDS and HYD activity of sulfide Co-PMo catalyst supported on alumina and structured mesoporous silica composite

Co-PMo catalysts were prepared from the 12-molybdophosphoric heteropolyacid and cobalt citrate on the base of freshly-synthesized alumina and mixed MCM-41-Al2O3 material. Carriers and catalysts were characterized by the following techniques: X-ray powder diffraction, low-temperature N2 adsorption, NH3-TPD, Raman spectroscopy, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Prepared catalysts were tested in hydrodesulfurization of dibenzothiophene and hydrogenation of naphthalene. It has been shown that mesoporous silica incorporation into alumina can improve morphological properties of the CoMoS active phase as well as the overall HDT activity.

The effect of incorporation of hybrid silica and cobalt ferrite nanofillers on the mechanical characteristics of glass fiber‐reinforced polymeric composites

AbstractRecently, hybrid nanofillers loading has been utilized to fabricate multifunctional composites. In this study, silica (SiO2) and cobalt ferrite (CoFe2O4) nanoparticles were combined to form a new hybrid composite structure. Nanofilled glass/epoxy hybrid composite laminates were fabricated using hand lay‐up technique. SiO2/CoFe2O4hybrid fillers were dispersed in epoxy matrix with sonication. The effect of incorporating SiO2/CoFe2O4hybrid nanoparticles on the mechanical properties of glass fiber/epoxy composites was investigated. The resultant SiO2/CoFe2O4hybrid nanocomposites showed good mechanical properties as compared to hybrid nanocomposites fabricated by individually loading SiO2or CoFe2O4nanoparticles as well as pristine glass fiber/epoxy composite. A visible improvement in the mechanical properties was observed with hybrid nanocomposite that consisted of CoFe2O4/epoxy core layers and SiO2/epoxy skin layers detached with intermediate layers of hybrid SiO2 + CoFe2O4/epoxy. Scanning electron microscopic (SEM) images of tensile and flexural fractured surfaces reveal a good fiber/matrix interfacial bonding.

An experimental study on one-step and two-step foaming of natural rubber/silica nanocomposites

AbstractThe curing and cellular structure of natural rubber (NR)/silica composite foams were investigated. The presence of an activator in the rubber formulation significantly lowered the decomposition temperature of the azodicarbonamide foaming agent, which allowed foaming before NR curing. Therefore, two foam methods were designed: foaming initially at 90°C and then curing at 140°C, and foaming and curing simultaneously at 140°C. Two-step foaming generated a lower cell density and higher cell size. Incorporation of nano silica into NR increased the foam density, but decreased the cell size. The higher foaming temperature restricted the bubble growth because of a higher curing rate and inhibited cell coalescence.

Influence of Incorporation of Silica and Zirconia Nanoparticles on Some Physical and Mechanical Properties of Thermoplastic Resin Material

Abstract: Objective: This study was aimed to evaluate the effect of incorporation of two-different nanoparticles; silica (SiO2), and zirconia (ZrO2) on flexural strength, impact strength, as well as, water sorption and solubility of thermoplastic resin material. Materials and Methods: Two nanoparticles SiO2-NPs, and ZrO2-NPs (Nano-gate Company, Egypt) were incorporated into thermoplastic resin (Bre-flex, Bredenttm, Germany) with different concentration (1.5 and 7 wt.%). This study was divided into five main groups; unmodified “control group” and four modified groups according to the type and concentration of the incorporated nanoparticles. Results: The results of this study revealed that; the incorporation of 1.5 wt.% SiO2-NPs significantly improve the flexural strength of thermoplastic resin. While, the incorporation of SiO2-NPs, and ZrO2-NPs nanoparticles insignificantly decrease its impact strength. However, they significantly increase water sorption and solubility of thermoplastic resin. Conclusion: The incorporation of nanoparticles into thermoplastic resin at different concentrations could negatively affects its flexural strength, impact strength, as well as its water sorption and solubility. Key Wards: Silica Nanoparticles, Mechanical properties, Thermoplastic resin, Zirconia.

Spectroscopic studies of silica-incorporated lanthanum β-diketonate complexes for application in optoelectronic devices

In the present research work, silica-incorporated complexes of lanthanum β-diketonate were synthesized. Structural characterization of the prepared complexes was made on the basis of FTIR and FESEM studies. Shifting of peaks in the FTIR spectra are discussed in relation with the complexation, also incorporation of silica in complexes was confirmed by the FTIR spectra. FESEM and EDX studies were performed to know the surface morphology as well as elemental composition of the prepared complexes. The optical properties such as diffuse reflectance and photoluminescence were studied to get the idea about the possible transitions among the energy levels of the complexes as well as to know the emission peaks. The assignment of luminescence band is determined from excited state lifetime. The variation in luminescence intensity with time was measured by recording decay curves at fixed emission wavelength. The life time for all the three complexes was measured in micro-second (µs) order. Color coordinates of the complexes lie in the blue region. Thermal stability of the complexes was checked by measuring the loss in weight as a function of temperature.

In-vitro corrosion assessment of silicate-coated AZ31 Mg alloy in Earle’s solution

Magnesium alloys are promising materials for biodegradable implants. In the present investigation, AZ31 Mg alloy was anodized in alkaline silicate electrolyte and anodization time period was optimized. From the current transient (i–t) curve and corrosion analysis, it was confirmed that 60-min anodization was sufficient to obtain a silicate coating with a better corrosion resistance of 37.05 kΩ. The hydrophilic nature of the coating was confirmed by the contact angle measurement. XRD results revealed the formation of MgO (periclase) and biocompatible Mg2SiO4 (forsterite) phases. Hydrogen evolution studies showed that the degradation rate of the anodized sample correlated with the real-time corrosion behavior. At the end of 7 days of immersion in Earle’s solution, bone-like apatite was precipitated with Ca/P ratio at 1.39 indicating the incorporation of silica in the apatite. From scanning electrochemical microscopic studies, the current density of anodized sample was found to be minimum and uniform over the entire surface. Increase in immersion time resulted in fluctuation in current density signifying the coating’s interaction with Earle’s solution and initiation of apatite formation.

Study on improvement of the selectivity of proton exchange membrane via incorporation of silicotungstic acid-doped silica into SPEEK

Nafion based proton exchange membrane (PEM) has long been used as conventional PEM in direct methanol fuel cell (DMFC) industry. However, the high cost of Nafion membrane and other drawbacks like high methanol crossover hinder the advancement of this industry. This study aims to develop a low cost membrane using sulfonated poly ether ether ketone (SPEEK) polymer. Silica and silicotungstic acid (SiWA) were incorporated into the membrane matrix using solution casting method. The optimum loading of the additives was tuned and it is discovered that the SPEEK membrane containing 10 wt% of silica and 5 wt% of SiWA has the best performance due to its high proton conductivity and moderately low methanol permeability. The performance of the membrane can further be enhanced by adding (3-aminopropyl)triethoxysilane (APTES) and carbonyldiimidazole (CDI) as coupling agents. Inclusion of APTES and CDI in SPEEK could not only improve the compatibility between organic SPEEK and inorganic additives, but also improve the homogeneity and dispersity of the additives. As a result, the resultant membrane with a better dimensional stability achieves high selectivity (10.60 × 104 S.s/cm3) up to 6.5 times more than pristine SPEEK membrane and 1.3 times higher than the commercial Nafion 117 membrane.

Enhancing the properties of gelatin–chitosan bionanocomposite films by incorporation of silica nanoparticles

AbstractFunctional enhancement of biopolymer was attempted in this work for food packaging application. Incorporation of chitosan (0–9%) and silica (0–10%) nanoparticles (NP's) into gelatin film (Gel) has been tried and their effects on moisture content, tensile strength (TS), elongation at break (%E), wettability, water vapor permeability (WVP), and antimicrobial activities were studied. Morphology of nanoparticles was studied using scanning electron microscopy and transmission electron microscopy. Chitosan NP's showed agglomeration at higher concentration which leads to lower the mechanical as well as barrier properties of the film. However, silica NP's enhanced the properties of bionanocomposite film. TS was increased from 6.05 MPa of pure gelatin film to a maximum value of 38.91 MPa at CS NP's of 5.8% and Si NP's of 7%; however, %E decreased with addition of nanoparticles resulting in brittleness of film. WVP for pure gelatin film was 25.21 g mm/kPa m2 day, which reduced to 3.30 g mm/kPa m2 day after incorporation of 10% Si NP's. Antimicrobial activity was observed against E. coli and S. aureus. Incorporation of CS NP's improved the antimicrobial activity of gelatin film. Si NP's showed improvement in mechanical and barrier properties of Gel–CS films, however, had no effect on antimicrobial activities.Practical ApplicationResearchers community are more concerned of natural biopolymers to reduce the use of synthetic polymers, especially in food packaging. Gelatin is one of the natural biopolymer and have potential to be used as food packaging material. Problem with gelatin and many other biopolymer based film is their poor mechanical and barrier properties. Present study was framed to overcome these problems by incorporating silica and chitosan nanoparticles in gelatin film. The results observed would be useful to develop a biopolymer based nanocomposite film with improved mechanical, barrier and antimicrobial properties, which can be used for active food packaging.