Fumed Silica Particles Research Articles

Overcoming coffee-stain effect by particle suspension marble evaporation

One disadvantage of using the hydrophobic surface technique to suppress coffee-stain effect is that it requires hydrophobization of a relatively large area of hydrophilic surface. The opposite technique, which involves coating a particle suspension with powdered hydrophobic particles can perhaps be used to overcome this limitation, but has not been explored. Herein, we explored this technique by evaporating hydrophobic particle-coated aqueous suspensions of hydrophilic 100% SiOH fumed silica particles on hydrophilic glass slides and examining the particle films left. Various suspensions (1–5 wt%) of hydrophilic 100% SiOH silica particles were coated with either hydrophobic Aerosil® R 202 fumed silica or PF-12 fluorinated sericite clay particles and then allowed to evaporate on hydrophilic glass slides. The particle films left after complete evaporation were compared with those left by the corresponding uncoated particle suspensions. Visual observation and optical microscopy revealed that evaporation of the uncoated particle suspensions produced the so-called “coffee-stain” while that from the coated suspensions did not produce the effect, but rather gave a spot-like particle deposit. This shows that encapsulating particle suspensions in hydrophobic particles before evaporation prevents coffee-stain formation.

The Effect of Incorporating Ultra-Fine Spherical Particles on Rheology and Engineering Properties of Commercial Ultra-High-Performance Grout

In this study, ultra-fine spherical particles of silica fume and reactive ultra-fine fly ash were added to a mixture of commercial ultra-high-performance grout (UHPG) with the aim of enhancing the rheological properties, compressive strength, compactness, and permeability. This commercial UHPG study was conducted in collaboration with Triaxis Corporation (Changsha city, Hunan province, China). A water-to-binder ratio of 0.21 and a binder-to-fine aggregates ratio of 1.17 were used as fixed parameters, and the binders were a combination of type-II Portland cement, sulphoaluminate cement, silica fume, and reactive ultra-fine fly ash (RUFA). Polycarboxylate superplasticizer powder was used to control the rheology. The results revealed excellent compressive strength, volume stability, and resistance to chloride penetration. Mercury intrusion porosimetry and scanning electron microscopy tests revealed that the medium-sized RUFA particles with small silica fume particles completely filled the spaces between large cement particles to achieve optimal densification. This mixture also produced dense hydration and calcium-silicate-hydrates colloids, which filled the microstructures of the UHPG resulting in excellent engineering properties and durability. This commercially available UHPG mix responded to excellent compressive strengths approaching 120 MPa and exhibited good workability with a loss of slump-flow rate up to 33% after 60 min. It also exhibited very low abrasion resistance (0.5%), stable shrinkage and expansion rates (stabilization over 10 days), very low chloride diffusion coefficient (less than 0.1 × 10−14 m2/s) with a denser microstructure. This commercial UHPG (UHPG-120) has been developed to meet the needs of the market.

Enhancing Thermo-Mechanical Properties of Epoxy Composites Using Fumed Silica with Different Surface Treatment.

The objectives of this study are to improve the thermal and mechanical properties of epoxy/fumed silica composite with different surface treatments of fumed silica. The addition of silica nanoparticles improved the thermal stability of the composite and slowed down the pyrolysis process. The crosslinking density and Tg of the epoxy/fumed silica composites increased because of the interfacial interaction between the PDMS-treated fumed silica particles and the epoxy matrix. The flexural strength of the epoxy nanocomposite was very high even at a low silica content because of the strong interactions between the PDMS-treated fillers and the epoxy matrix. These strong interfacial interactions originate from the attractive forces between the polymer and the filler. Therefore, the polymer nanocomposite containing the PDMS-treated fumed silica is shown to be sufficiently commercially promising.

Development of magnesium oxychloride cement with enhanced water resistance by adding silica fume and hybrid fly ash-silica fume

In this paper, a water-resistant magnesium oxychloride cement (MOC), an environment friendly cementitious material, was developed by incorporating silica fume and the hybrid of silica fume and fly ash. The effects of these admixtures on the water repellence of MOC were investigated via comprehensive macroscopic physical and mechanical tests and micro-scale studies. A formula design of MOC blended with 15% silica fume and 15% fly ash retained the compressive strength as high as 100% and 95% after 28 days' and 56 days’ immersion in water, respectively. Micro-scale studies, including XRD, FTIR, SEM, MIP, TG/DSC and XRM, were conducted to discover the mechanism of the enhanced water resistance of the new MOC. Besides, a clear and precise distribution of the hydration products in well-cured MOC specimens was demonstrated with the X-ray mapping (XRM) technique. It was found that adding silica fume or the hybrid of silica fume and fly ash optimised the porous structure of MOC and thereby increased the density and compressive strength leading to the enhanced water resistance. The filling effect of fine silica fume and fly ash particles, as well as the formation of Mg–Cl–Si–H gel, was found to be the main reason for the densified microstructure of MOC. The fractional contribution of phase 5, i.e. the main phase of MOC, decreased with the combined silica fume and fly ash, and this helped to relieve the internal stress and improve the stability of MOC, leading to enhanced water repellence.

N-Doped Graphene Oxide as Additive for Fumed Silica Based Gel Electrolyte of Valve Regulated Lead Acid Batteries

In this work, nitrogen doped graphene oxide powder (N-GrOP) was used as an additive for fumed silica based gelled electrolyte of valve regulated lead acid (VRLA) batteries for the first time in the literature. Optimum amount of additive was determined as 0.4 wt% N-GrOP by using of electrochemical methods and corrosion tests. The structural features of fumed silica based gelled electrolyte with and without N-GrOP was investigated by SEM analysis. Then, the effects of agitation time and stirring rate on the formation and structure of the fumed silica based gelled electrolyte were optimized as 180 min and 1250 rpm, respectively, by using of electrochemical technics. Corrosion tendency of the electrodes were determined by Tafel curves. Cyclic charge/discharge tests were also carried out to determine the discharge capacity of the electrolytes. The discharge capacities of fumed silica based gelled electrolyte with and without N-GrOP and non-gelled electrolyte were determined as 33 mAh·cm−2, 16 mAh·cm−2 and 0.70 mAh·cm−2 at 20 mA·cm−2 charge/discharge current densities, respectively. The interaction of N-GrOP with hydrolyzed fumed silica particles occurred and the discharge capacities of the fumed silica-based gel electrolyte increased in VRLA batteries.

Correlation between the Compressive Strength and Ultrasonic Pulse Velocity of Cement Mortars Blended with Silica Fume: An Analysis of Microstructure and Hydration Kinetics.

The effect of the replacement rate of silica fume (SF) on the correlation between the compressive strength and ultrasonic pulse velocity (UPV) of cement mortar was experimentally analyzed. Specimens were fabricated with different replacement rates of SF, the compressive strength and UPV were measured, and isothermal calorimetry and mercury intrusion porosimetry tests were conducted to analyze the effects of replacement on the hydration kinetics and microstructures on these properties. Field emission scanning electron microscopy analysis was performed to observe SF particles and microstructure. The substitution of SF changed the cement mortar’s hydration kinetics and microstructures, resulting in different strengths and UPVs depending on the replacement rate. The compressive strength and UPV for cement mortars blended with SF also showed a different exponential relationship depending on the SF replacement rate.

Effect of Silica Fume on the Shear Strength of Cohesionless Soil

Utilization of waste materials in geotechnical applications reduces the environmental problems of factories wastes. Silica fume is a by-product of the extraction of silicon or ferrosilicon manufacturing. Using silica fume as an additive to the soil can significantly increase the strength and decrease the permeability of the mixture. In this study silica fume is used to improve the mechanical properties of cohesionless soil, with special attention when used as backfill material for reinforced earth retaining walls. Biaxial geogrid prototype was used as reinforcement sheets in prepared bed of sand-silica fume mixture. The effect of adding silica fume was evaluated based on the results of Pull-out tests under various overburden pressures. From this study it was concluded that, adding silica fume to the sand had reduced the pull-out displacement of the geogrid by about 30 to 91% depending on the applied overburden pressure. That interlocking between the sand and silica fume particles is the main cause of densifying the sand by minimizing the lateral movement of the particles. Reduction in geogrid elongation reflects the increase in shear resistance interaction of the geogrid-backfill, and consequently the increase in the stability of the reinforced earth retaining walls under static and earthquake actions.

Sensorized tissue analogues enabled by a 3D-printed conductive organogel

State-of-the-art tissue analogues used in high-fidelity, hands-on medical simulation modules can deliver lifelike appearance and feel but lack the capability to provide quantified, real-time assessment of practitioner performance. The monolithic fabrication of hybrid printed/textile piezoresistive strain sensors in a realistic Y/V plasty suture training pad is demonstrated. A class of 3D-printable organogels comprised of inexpensive and nonhazardous feedstocks is used as the sensing medium, and conductive composite threads are used as the electrodes. These organogels are comprised of a glycol-based deep-eutectic solvent (DES) serving as the ionic conductor and 3-trimethoxysilylmethacrylate-capped fumed silica particles serving as the gelating agent. Rheology measurements reveal the influence of fumed silica particle capping group on the mixture rheology. Freestanding strain sensors demonstrate a maximum strain amplitude of 300%, negligible signal drift, a monotonic sensor response, a low degree of hysteresis, and excellent cyclic stability. The increased contact resistance of the conductive thread electrodes used in place of wire electrodes do not make a significant impact on sensor performance. This work showcases the potential of these organogels utilized in sensorized tissue analogues and freestanding strain sensors for widespread applications in medical simulation and education.

Influence of different fumed silica as thixotropic additive on carbonyl particles magnetorheological fluids for sedimentation effects

The present work reports the influence of different types of surface area, hydrophobic, and hydrophilic fumed silica mixed in silicone oil as a thixotropic additive on carbonyl particles based magnetorheological fluids (MRFs) were prepared. Scanning electron microscopy analysis confirms the fumed silica particles attached to the surfaces of CIPs. The vibrating sample magnetometer result shows the MRF4 and 5 have a better magnetic saturation value of 30.12 emu/gm and 40.12 emu/gm, respectively. The experimental rheological flow curve behaviours are investigated using the magnetorheometer. The Herschel–Bulkley rheological model is found to be in good agreement with the experimental curves and suggested shear thinning property is observed. The results showed that the hydrophilic silica with larger surface area type presented (i.e.MRF 4 and 5) better magnetorheological fluid characteristics in terms of shear stress, with a high value of dynamic yield stress, and have much-improved sedimentation ratio up to seven days.

Effect of carrier fluid and particle size distribution on the rheology of shear thickening suspensions

We present a systematic rheological study on the fumed silica suspensions to understand the effect of particle and fluid parameters on the critical shear rate and shear thickening ratio. It was observed that removal of air bubbles and water contamination is crucial to prepare good shear thickening fluids. A careful sample preparation method was adopted to properly disperse the fumed silica particles in polyethylene glycol solution, and we achieved discontinuous shear thickening at low particle concentration. It was observed that the critical shear rate in shear thickening suspension is strongly influenced by both carrier fluid and particle concentration. However, the shear thickening ratio is mainly influenced by the particle parameters and the frictional forces between the particles. Increasing the amount of smaller particles in the suspension significantly decreases the maximum viscosity and shifts the onset of shear thickening to higher values of critical shear rates with much smaller shear thickening ratio. Further, a possible mechanism has been proposed based on the influence of carrier fluid and particle size distribution to explain the rheological behaviour of shear thickening suspension. Our study supports the theory of particle-particle frictional contacts as the main reason for the discontinuous shear thickening.

Preparation and Rheology of Magnetorheological Fluid Using Six Kinds of Fumed Silica as Stabilizing Additives

In this study, magnetorheological fluid (MRF) was prepared with several kinds of hydrophobic fumed silica in order to improve MRF stability while maintaining desirable fluidity. We conducted steady flow measurements and oil separation tests under gravity and centrifugal conditions. The linkage of fumed silica particles was also observed morphologically by transmission electron microscopy. We found that the MRF sedimentation stability correlated with viscosity in the lower shear rate range. The oil separation ratio improved with the addition of the fumed silicas examined in this study. The surface characteristics of the silica particles affected the stabilization ability. The addition of hydrophobic fumed silica can desirably increase MRF magnetic properties.

Water diffusivity transition in fumed silica-filled polydimethylsiloxane composite: Correlation with the interfacial free volumes characterized by positron annihilation lifetime spectroscopy

Fumed silica (FS)-filled polydimethylsiloxane (PDMS) composite is widely used as the external insulating material in power grid. The function of PDMS composite is to keep the core of an insulation device being dry by preventing the permeation of outside water. To study water diffusion in PDMS composite helps to shed light upon the failure mechanism of the insulation devices. In this paper, positron annihilation lifetime spectroscopy (PALS) and electrochemical impedance spectroscopy (EIS) were applied to study the FS/PDMS interface structure and water diffusion in PDMS composite. It is found that the FS has two basic existing states in PDMS matrix: dispersed state and percolated state, and the percolation threshold of FS is fitted to be 6.0 wt.%. In the dispersed state, the FS particles are randomly dispersed in PDMS matrix. The values of $$\tau _3$$ remain stable, being approximately 1.0 ns, indicating no overlaps of the FS/PDMS interfaces. Moreover, water cannot diffuse through the sample after corona aging. In the percolated state, the FS particles are tightly packed in the PDMS matrix. The values of $$\tau _3$$ decrease with the weight fraction of FS, suggesting the overlapping of the FS/PDMS interfaces. As the FS percolates in sample bulk, these overlapped FS/PDMS interfaces provide continuous diffusion tunnels for water, thus resulting in failure of the composite after corona aging. It is found that polarization and discharge of the electrons at FS/PDMS interface under corona discharge is the main mechanism that leads to the failure of the composite bulk.

Structuring Edible Oils With Fumed Silica Particles

Organogels are often made from solutions of proteins, polymers or fatty acids in oil. The macromolecular species crystallise, or assemble, into mesh structures that inhibit oil flow. This review focuses on using fumed silica nanoparticles as an alternative structuring agent. Fumed silica particles have a unique, branched morphology that means the particles aggregate into three-dimensional, interconnected networks. Two key aspects for formulating edible oleogels are addressed. Advances in our understanding of fumed silica particle aggregation in oil that point towards strategies for tuning the rheological properties of oleogels are examined. Secondly, the factors likely to affect the lipolysis of oils structured used fumed silica particles, and hence the bioavailability of ingredients loaded into the gels, are discussed. The next challenge for these promising materials is to target suitable applications for their use as fat replacement in foods.

Effects of functionalized fumed-silica on the three-point bending and sliding wear properties of woven basalt fabric-epoxy composites

In this work, the effects of fumed-silica functionalization and functionalized fumed-silica content on the three-point bending and sliding wear properties of woven basalt fabric/epoxy composites were investigated. The functionalized fumed-silica particles were evaluated by Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The multiscale composites were prepared by impregnating basalt fabrics into epoxy resin incorporated with various functionalized fumed-silica contents (0.5, 1, 3, and 5 wt%). The results of the 3-point bending test showed that a maximum improvement of 50% was gained with the addition of 1 wt% functionalized fumed-silica. Besides, the wear rate and friction coefficient of the basalt fiber/epoxy composite were decreased by 90% and 36%, respectively when 3 wt% functionalized fumed-silica was incorporated. It was also found that the fumed-silica after surface-functionalization improved the flexural properties and wear resistance of basalt fiber/epoxy composite more remarkably than the un-treated fumed-silica. Scanning electron microscope was also utilized to evaluate the fracture and wear mechanisms of the specimens.

Performance Comparison between Densified and Undensified Silica Fume in Ultra-High Performance Fiber-Reinforced Concrete.

Silica fume (SF) is a key ingredient in the production of ultra-high performance fiber-reinforced concrete (UHPFRC). The use of undensified SF may have an advantage in the dispersion efficiency inside cement-based materials, but it also carries a practical burden such as high material costs and fine dust generation in the workplace. This study reports that a high strength of 200 MPa can be achieved by using densified SF in UHPFRC with Portland limestone cement. Additionally, it was experimentally confirmed that there was no difference between densified and undensified SFs in terms of workability, compressive and flexural tensile strengths, and hydration reaction of the concrete, regardless of heat treatment, because of a unique mix proportion as well as mixing method for dispersing agglomerated SF particles. It was experimentally validated that the densified SF can be used for both precast and field casting UHPFRCs with economic and practical benefits and without negative effects on the material performance of the UHPFRC.

A Novel Organic-Inorganic Hybrid Admixture for Increasing Flowability and Reducing Viscosity of Ultra-High Performance Paste.

The low flowability and high viscosity of ultra-high performance concrete (UHPC), which is mainly caused by the silica fume (SF) agglomeration and low water–binder ratio, is a severe defect in its engineering applications. Herein, a novel organic–inorganic hybrid (OIH) admixture was synthesized by grafting comb-like polycarboxylate ether (PCE) onto the surface of SF. On the one hand, PCE-grafting could effectively prevent SF agglomeration and improve the dispersion of SF core. The reason being the consumption of polar silicon hydroxyl (Si-OH) groups on the surface of SF and the steric hindrance effect generated from PCE arms. On the other hand, OIH admixture could adsorb onto the surface of cement and SF particles by electrostatic interaction, exhibiting stronger steric hindrance effect than traditional comb-like PCE. As a result, UHPC system with this star-like OIH admixture presented high flowability and low viscosity at low water–binder ratio (0.18).

A non-fluorinated mechanochemically robust volumetric superhydrophobic nanocomposite

The widespread use of water-repellent superhydrophobic surfaces is limited by the inherent fragility of their micro- and nanoscale roughness, which is prone to damage and degradation. Here, we report a non-fluorinated volumetric superhydrophobic nanocomposites that demonstrate mechanochemical robustness. The nanocomposites are produced through the addition of microscale diatomaceous earth and nanoscale fumed silica particles to high-temperature vulcanized silicone rubber. The water-repellency of the surface and bulk of nanocomposites having 120 phr of filler was determined based on the water contact angle and contact angle hysteresis. We compared the water-repellency of nanocomposites of differing diatomaceous earth to fumed silica mass ratios. Increasing the amount of diatomaceous earth enhanced the water-repellency of the nanocomposite surface, whereas an increased amount of fumed silica improved the water-repellency of the bulk material. Moreover, increasing the diatomaceous earth/fumed silica mass ratio improved the cross-linking density and hardness values of the nanocomposite. Despite being subjected to a range of mechanical durability tests, including sandpaper abrasion, knife scratching, tape peeling, water jet impact, and sandblasting, the nanocomposite maintained a water contact angle of 163° and contact angle hysteresis of 2°. When the water-repellency of the prepared nanocomposites eventually deteriorated, we restored their superhydrophobicity by removing the upper surface of the nanocomposite. This extraordinary robustness stems from the embedded low surface energy micro/nanostructures distributed throughout the nanocomposite. We also demonstrated the chemical stability, UV resistance, and self-cleaning abilities of the nanocomposite to illustrate the potential for real-life applications of this material.

Influence of Silica Fume on the Geotechnical Characteristics of Cemented Sand

It is well recognized that the addition of cement to sand is one of the environmental and economic techniques in soil stabilization. However, with respect to silica fume, its impact on the characteristics of cemented sand has not been comprehensively investigated. For this purpose, a series of standard Proctor compaction, unconfined compression, pH and microstructure tests including field emission scanning electron microscope, X-ray diffraction and atomic force microscopy tests were carried out in this research to explore the influence of silica fume on the geotechnical characteristics of cemented sand. Cement in percentages of 3, 5 and 7% and silica fume in percentages of 0, 0.25, 0.5 and 1% by dry weight of sand were utilized. For unconfined compression and pH tests, samples were cured for different curing times of 3, 7, 14, 28, 42 and 56 days. The results indicated that silica fume particles increase maximum dry unit weight of sand–cement mixtures and reduce their optimum moisture content. Moreover, silica fume improves unconfined compressive strength of cemented sand which the impact of this improvement is more obvious for samples with longer curing time. According to the results obtained by unconfined compression and pH tests, it was detected that there are optimum values of curing time and silica fume amount at which strength of silica fume–cemented sand enhances significantly. Furthermore, some relations were proposed between stiffness and unconfined compressive strength of silica fume–cemented sand. Finally, the results of microstructure analysis confirmed the results found through unconfined compression tests.

Influence of magnetic field treated water on the compressive strength and bond strength of concrete containing silica fume

The overall objective of this study is to investigate the effect of magnetic field treated water and silica fume content on the compressive strength and bond strength of concrete. A total of ninety specimens were cast and tested under compression and pullout tests. In order to fully understand the concrete strength development, both tests were carried out at 7 and 28 days of concrete age. Normal water and magnetic water were used in the mix using different silica fume content. The results showed significant increase in the compression strength when magnetic water was used regardless of the silica fume content. Specimens prepared with magnetized water showed an increase in the bond strength compared to those prepared with normal water at all silica fume contents. The results also showed the use of high content of silica fume reduces the bond strength due to the reduction in adhesive properties between steel and concrete. The ultimate pullout load for 16 mm diameter bar was larger than that for use of larger than that for the 12 mm bar size but the bond strength of the larger diameter bar size is smaller since it has larger surface embedded area. The effect of silica fume on bar size illustrated that for a smaller bar size a lower development of bond strength is recorded because the distribution of silica fume particles around the small surface area reduces the adhesion forces between concrete and steel bars. Finally, as expected, the results showed that age of concrete has significant influence on the bond strength. The main contribution of this work is to prove that magnetic field treated water can enhance not only the compressive strength of concrete but also the bond strength between steel bar and concrete.

Dual modified nanosilica particles as reinforcing fillers for dental adhesives: Synthesis, characterization, and properties

A facile procedure has been devised to develop a novel dentin bonding system containing poly (acrylic acid)-grafted-silanized fumed silica particles as reinforcing filler, with high stability of nanoparticle dispersion and enhanced bond strength and mechanical properties. In the first step, the silanization of fumed silica nanoparticles was performed in the following conditions: (i) ethanol-water solution with a pH of 5 and (ii) cyclohexane with a pH of 9 using trimethoxysilylpropyl methacrylate (γ–MPS) as a reactive silane coupling agent. FTIR and TGA analyses confirmed the presence of silane in the resultant structure and enhanced dispersion stability of modified particles was proved by a separation analyzer and also zeta potential analyses. In the second step, free radical polymerization of acrylic acid monomers in the presence of silanized nanoparticles was carried out and poly (acrylic acid) -grafted- silanized fumed silica were acquired. The flexural strength and fracture toughness of the adhesive containing 0.2 wt.% of the dual modified filler reached maximum of 70.4 MPa and 1.34 MPa m1/2, respectively, showing average improvements of 74% and 179%, respectively, in comparison with the adhesive without filler. Flexural modulus values did not significantly change with increasing the filler content except the adhesive containing 5 wt.% having the lowest flexural modulus. The highest microtensile bond strength was also observed at 0.2 wt.% filler content showing the average improvements of 197% as compared with the neat adhesive. Energy dispersive X-ray (EDX) mapping confirmed a homogenous and uniform distribution of the fillers in the adhesive matrix containing 0.2 wt.% and 0.5 wt.% of filler while incorporation of 5 wt.% led to large particle aggregates. SEM images of the fracture surface of the adhesive with different filler contents subjected to fracture toughness test showed rougher surface and longer crack path by increasing filler concentration. The adhesive containing 0.2 wt.% of filler perfectly penetrated into the dentin tubules proved by the SEM micrographs in microtensile bond strength test.