SiO2 Particle Size Research Articles

Features of Fischer–Tropsch synthesis in the presence of an iron-containing catalyst supported on the surface of spherical nanosilica

Features of Fischer–Tropsch synthesis in the presence of an iron-containing catalyst supported on spherical nanosilica (the average sizes of spherical SiO2 and iron-containing particles on the silica surface are 250 and 14 nm, respectively) are studied. The catalyst exhibits high activity in the conversion of syngas, viz., 7.6 times higher than the activity of a 20% Fe/silica gel catalyst. A distinctive feature of a catalyst supported on spherical silica is higher selectivity for liquid products, which decreases only slightly with increasing temperature. Reduction characteristics are studied using the temperature-programmed reduction method; the specific surface area is measured and the phase composition of the synthesized catalyst systems is determined by X-ray diffraction analysis.

The synergy effect of Graphene/SiO2 hybrid materials on reinforcing and toughening epoxy resin

Based on the situ preparation of silica nanoparticles (SiO2) on the surface of Graphene nanoplatelets (GNPs) in the previous work, these unique three dimensional (3D) materials were introduced into epoxy resin to study the reinforcing and toughening synergy effect on the composites. Firstly, the tensile tests showed that Graphene/SiO2 hybrid materials attached with different size of SiO2 particles exhibited different reinforcing and toughening effect on the composites. With the increasing of the diameter of SiO2 particles, the toughness and strength properties of the composites firstly improved and then decreased, and when the average diameter was 0.14 μm, the elongation reached the max.. Meanwhile, the fractured surfaces presented on SEM images were consistent with the results of the tensile tests, which further explained the hybrid materials increased the interfacial adhesion between the fillers and matrix, leading to significant improvement in mechanical properties. Moreover, the DSC curves demonstrated that Graphene/SiO2 hybrid materials accelerated the curing process of epoxy resin due to the cross-link structure between fillers and matrix. Lastly, the crack propagation modes were built to clarify the synergy effect mechanism of reinforcing and toughening on nanoparticles/epoxy resin composites.

Scattering effect of SiO2 particles on correlated color temperature uniformity of multi-chip white light LEDs

This study proposes the addition of SiO2 scattering particles into the phosphor layer of a multi-chip white light LED (MCW-LED) for enhancing its performance. It is demonstrated by computer simulations that SiO2 particles can bring significant effects on the correlated color temperature (CCT) uniformity and luminous flux. Through the simulation experiments, it was found that the MCW-LED with hybrid SiO2 structure with SiO2 particle size around 1 μm can achieve higher color uniformity than other package structures. We investigated the influence of SiO2 (quartz) concentration on the CCT and the output flux of the MCW-LED with CCTs 7000, 7700, and 8500 K, respectively. Compared to an LED package without SiO2, SiO2 packages can shrink the CCT deviation about 48%. In this study, it was demonstrated that the inclusion of about 5–10% SiO2 can produce an MCW-LED with higher CCT uniformity and optimal lumen output.

Characteristics of Silicon Dioxide Particles in PCVD Synthesizing Silica Glass Process

SiO2nanoparticles in PCVD process were investigated by SEM, TEM, and optical emission spectra (OES). There are large spherical SiO2particles with diameter of 50–200 nm and more small particles about 10–50 nm in PCVD process. Size of SiO2particles is influenced by distance and feeding speed but not electron temperature. The amount of large spherical SiO2particles decreases with the increase of distance and decrease of feeding speed due to lower concentration. In addition, the evolution of SiO2particles was inferred from the experimental results.

The effect of SiO2 particle size on iron based F–T synthesis catalysts

The effect of particle size of silica, as catalyst binder, on the chemical and mechanical properties of iron based FT catalyst was studied in this work. The samples were characterized using XRD, BET, TEM, FT-IR, and H2-TPR, respectively. The attrition resistance and the FT activity were tested. Si-8–Si-15 catalysts prepared with 8–15nm silica sol show good attrition resistance (attrition loss<4%), especially Si-13 with an attrition loss of 1.89%. Hematite appeared in XRD patterns when silica sol above 15nm is used. TEM micrographs show that no obvious SiO2 particles appear when silica sol particle with size less than 8nm was used, but SiO2 particles coated with small ferrihydrite particles appear when silica sol above 8nm was used. Si–O–Si vibration peak in FT-IR spectra increases with increasing silica sol size. Samples prepared with silica sol show good stability of FT reactions, and the average molecular weight of FT products increases with the increase of SiO2 particle.

An efficient way to prepare hydrophobic antireflective SiO2 film by sol–gel method

A single-layer hydrophobic antireflective SiO2 film was prepared by sol–gel method. High transmittance (97%) and large static water contact angle (130.6°) were realized simultaneously through a simple and efficient way. Tetraethoxysilane (TEOS) was used as a precursor to prepare SiO2 sol. A dip-pulling method was used to prepare the thin film. We controlled the film thickness by regulating pulling speed for making the transmittance of the film to reach a peak at about 550nm. The surface of the film was covered with uniform particles of 20–30nm and pores of 50–60nm as shown in the SEM images. 1H, 1H, 2H, 2H-perfluorodecyltrichoxy silane (PFDS) was introduced to replace the hydroxyl (–OH) groups and decrease the surface energy of the film. The appropriate SiO2 particle size and porosity in the film and low surface energy give the hydrophobic antireflective SiO2 film with high transmittance and large static water contact angle.

Effect of matrix temperature and powder size on the infiltration height of SiO2-reinforced Al 7075 matrix composites produced by vacuum infiltration

Abstract In this study, the effect powder size and matrix temperature on the physical and mechanical properties of SiO2-reinforced Al 7075 matrix composites were investigated. It was observed that with increasing powder size and temperature, infiltration height was increased. Optimum parameters of full infiltration that were determined for particle size and temperature were d50=150 μm and 800°C, respectively. It was also observed that the porosity of the produced composites changed in the range of 3.2–14.6%, and the lowest porosity was obtained from the composite having 105 μm SiO2 particle size. The highest fracture strength (263 MPa) was obtained from the composite produced at a matrix temperature of 800°C and a particle size of 420 μm. It was concluded that particle size and temperature are effective parameters to reach full infiltration, and this method is more suitable for producing the composites that have high reinforcement volume fractions than conventional casting methods.

Processing and crystallographic structure of non-equilibrium Si-doped HfO2

Si-doped HfO2 was confirmed to exist as a non-equilibrium state. The crystallographic structures of Si-doped HfO2 were studied using high-resolution synchrotron X-ray diffraction and the Rietveld refinement method. Incorporation of Si into HfO2 and diffusion of Si out of (Hf,Si)O2 were determined as a function of calcination temperature. Higher thermal energy input at elevated calcination temperatures resulted in the formation of HfSiO4, which is the expected major secondary phase in Si-doped HfO2. The effect of SiO2 particle size (nano- and micron-sized) on the formation of Si-doped HfO2 was also determined. Nano-crystalline SiO2 was found to incorporate into HfO2 more readily.

Co-effects of graphene oxide sheets and single wall carbon nanotubes on mechanical properties of cement

The enhancement of mechanical properties of cement composites by a carbon nanomaterial is an important topic. However, the co-effect of two (or more) carbon nanomaterials on the mechanical properties of cement has not been explored. In this paper, it was found that the mixture of graphene oxide (GO) sheets and single-walled carbon nanotubes (SWCNTs) exhibited an excellent co-effect, leading to 72.7% increase in bending strength of cement, which is much larger than the strength enhancements of 51.2% by GO and 26.3% by SWCNTs. Furthermore, it was demonstrated that the bending strength of cement composite materials with GO and SWCNTs is proportional to the sizes of crystal SiO2 particles.

Identification of nanoscale ingredients in commercial food products and their induction of mitochondrially mediated cytotoxic effects on human mesenchymal stem cells.

Titanium dioxide (E171) and silicon dioxide (E551) are common additives found in food products, personal-care products, and many other consumer products used in daily life. Recent studies have reported that these food additives (manufactured E171 and E551) contain nanosized particles of less than 100 nm. However, the particle size distribution and morphology of added TiO2 and SiO2 particles are not typically stated on the package label. Furthermore, there is an increasing debate regarding health and safety concerns related to the use of synthetic food additives containing nanosized ingredients in consumer products. In this study, we identified the size and morphology of TiO2 and SiO2 particles in commercially available food products by using transmission electron microscope (TEM). In addition, the in vitro toxicological effects of E171 and E551 on human mesenchymal stem cells (hMSCs), an adult stem cell-based model, were assessed using the MTT assay and a flow cytometry-based JC-1 assay. Our TEM results confirmed the presence of nanoscale ingredients in food products, and the in vitro toxicology results indicated that the nanoscale E171 and E551 ingredients induced dose-dependent cytotoxicity, changes in cellular morphology, and the loss of mitochondrial trans-membrane potential in hMSCs. These preliminary results clearly demonstrated that the nanoscale E171 and E551 particles had adverse effects on hMSCs by inducing oxidative stress-mediated cell death. Accordingly, further studies are needed to identify the specific pathway involved, with an emphasis on differential gene expression in hMSCs.

Mechanism of GaN CMP Based on H2O2 Slurry Combined with UV Light

Chemical mechanical polishing (CMP) of GaN(0001) with a H2O2-SiO2-based slurry is investigated in this paper. The result shows that an atomically flat surface with a roughness of 0.065 nm is obtained after polishing. Compared with a SiO2-based slurry, the H2O2-SiO2-based slurry can realize a higher material removal rate (MRR) and a better surface quality with less scratches. The pH value mainly affects the mean particle size of SiO2 and the chemical environment of the corrosion reaction with H2O2, resulting in different MRRs. An off-site auxiliary polishing method is employed along with the H2O2-SiO2-based polishing system using ultraviolet light to shine the outlet of slurry in order to catalyze the production of substance for oxidation, and it is proved to be efficient by improving the MRR to 103 nm/h. Physical and mathematic removal models are proposed to describe the removal mechanism of GaN CMP.

Preperation of monodispersed SiO2 particles for electrostatic self-assembly of SiO2/PEI thin film with structural colors on polyester fabrics

The monodispersed SiO2 particles with perfect sphericity and desired particle sizes were synthesized by an improved Stober method. The particle sizes and size distribution of colloidal silica could be regulated by adjusting reaction temperature, reaction time, and the concentrations of NH4OH, H2O and TEOS. Dynamic light scattering particle size analysis and SEM analysis confirmed a narrowly distributed particle size and good sphericity of the synthesized SiO2 nanoparticles. The structural colors of silica/polyethyleneimine (SiO2/PEI) thin film fabricated on polyester fabrics were governed by SiO2 particle size, assembly cycles and viewing angles, and the origin mechanism of the structural colors was based on the thin film interference theory. The resultant polyester fabrics showed vivid structural colors changing with the change in viewing angles, displaying a biomimetic variable coloration effect on textiles.

Structural colors of the SiO2/polyethyleneimine thin films on poly(ethylene terephthalate) substrates

The SiO2/polyethyleneimine (PEI) films with structural colors on poly(ethylene terephthalate) (PET) substrates were fabricated by an electrostatic self-assembly method. The morphology of the films was characterized by Scanning Electron Microscopy. The results showed that there was no distinguishable multilayered structure found of SiO2/PEI films. The optical behaviors of the films were investigated through the color photos captured by a digital camera and the color measurement by a multi-angle spectrophotometer. Different hue and brightness were observed at various viewing angles. The structural colors were dependent on the SiO2 particle size and the number of assembly cycles. The mechanism of the structural colors generated from the assembled films was elucidated. The morphological structures and the optical properties proved that the SiO2/PEI film fabricated on PET substrate formed a homogeneous inorganic/organic SiO2/PEI composite layer, and the structural colors were originated from single thin film interference.

Preparation of silane-functionalized silica films via two-step dip coating sol–gel and evaluation of their superhydrophobic properties

In this paper, we study the two-step dip coating via a sol–gel process to prepare superhydrophobic silica films on the glass substrate. The water repellency of the silica films was controlled by surface silylation method using isooctyltrimethoxysilane (iso-OTMS) as a surface modifying agent. Silica alcosol was synthesized by keeping the molar ratio of ethyltriethoxysilane (ETES) precursor, ethanol (EtOH) solvent, water (H2O) was kept constant at 1:36:6.6 respectively, with 6M NH4OH throughout the experiment and the percentages of hydrophobic agent in hexane bath was varied from 0 to 15vol.%. The static water contact angle values of the silica films increased from 108° to 160° with an increase in the vol.% of iso-OTMS. At 15vol%. of iso-OTMS, the silica film shows static water contact angle as high as 160°. The superhydrophobic silica films are thermally stable up to 440°C and above this temperature, the silica films lose superhydrophobicity. By controlling the primer particle size of SiO2 about 26nm, leading to decrease the final size of silica nanoparticles after modification of nanoparticles by isooctyltrimethoxysilane about 42nm. The films are transparent and have uniform size on the surface. The silica films have been characterized by atomic force microscopy (AFM), fourier transform infrared spectroscopy (FT-IR), transparency, contact angle measurement (CA), Zeta-potential, Thermal stability by TG–DTA analysis.

Investigation on the Morphology and Dielectric Properties of PI/SiO&lt;sub&gt;2&lt;/sub&gt; Nanocomposite Films

Polyimide nanocomposite insulating materials are widely used in electrical and electron engineering owing to their outstanding electrical, mechanical, thermal, and wear-resistance properties. Polyimide/silica (PI/SiO2) nanocomposites have been prepared by the polymerization process of adding tetraethoxysilane (TEOS) and the coupling agent isocyanatopropyltriethoxysilane (ICTOS) in polyimide. The effects of SiO2addition on the microstructure and the dielectric property of nanocomposite films were investigated. It was found that the silica particles were well dispersed in PI matrix and the sizes of SiO2particles in the hybrid films range from 20 nm to 30 nm for 5-15 wt% SiO2loading in the matrix. The dielectric constant and the dielectric loss (tan δ) of these films increased with the increase of the content of silica particles.

The situ preparation of silica nanoparticles on the surface of functionalized graphene nanoplatelets

A method for situ preparing a hybrid material consisting of silica nanoparticles (SiO2) attached onto the surface of functionalized graphene nanoplatelets (f-GNPs) is proposed. Firstly, polyacrylic acid (PAA) was grafted to the surface of f-GNPs to increase reacting sites, and then 3-aminopropyltriethoxysilane (APTES) KH550 reacted with abovementioned product PAA-GNPs to obtain siloxane-GNPs, thus providing reaction sites for the growth of SiO2 on the surface of GNPs. Finally, the SiO2/graphene nanoplatelets (SiO2/GNPs) hybrid material is obtained through introducing siloxane-GNPs into a solution of tetraethyl orthosilicate, ammonia and ethanol for hours' reaction. The results from Fourier transform infrared spectroscopy (FTIR) showed that SiO2 particles have situ grown on the surface of GNPs through chemical bonds as Si-O-Si. And the nanostructure of hybrid materials was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All the images indicated that SiO2 particles with similar sizes were grafted on the surface of graphene nanoplatelets successfully. And TEM images also showed the whole growth process of SiO2 particles on the surface of graphene as time grows. Moreover, TGA traces suggested the SiO2/GNPs hybrid material had stable thermal stability. And at 900°C, the residual weight fraction of polymer on siloxane-GNPs was about 94.2% and that of SiO2 particles on hybrid materials was about 75.0%. However, the result of Raman spectroscopy showed that carbon atoms of graphene nanoplatelets became much more disordered, due to the destroyed carbon domains during the process of chemical drafting. Through orthogonal experiments, hybrid materials with various sizes of SiO2 particles were prepared, thus achieving the particle sizes controllable. And the factors’ level of significance is as follows: the quantity of ammonia > the quantity of tetraethyl orthosilicate (TEOS) > the reaction time.

Monodisperse macroporous poly(glycidyl methacrylate) microspheres coated with silica: Design, preparation and characterization

Monosized macroporous poly(glycidyl methacrylate) (PGMA) microspheres that were 9.3μm in size were synthesized by multistep swelling polymerization using a modified Ugelstad technique. The PGMA microspheres and their hydrolyzed analogs derived from poly(2,3-dihydroxypropyl methacrylate) (PDHPMA) were coated by silanization with tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES), respectively. The particles were characterized by elemental and thermogravimetric (TGA) analysis, scanning and transmission electron microscopy (SEM and TEM) coupled with an energy dispersive X-ray analysis (EDAX) and FT-IR spectroscopy to determine the SiO2 content, morphology, particle size, polydispersity and structure. These types of particles are expected to have improved biocompatibility relative to their starting polymers.

Preparation and Surface Modification of SiO&lt;sub&gt;2 &lt;/sub&gt;Particles Used in Electronic Ink

In order to improve the surface properties of SiO2 particles, SiO2 particles were modified by vinyl triethoxysilane, SiO2 particles and vinyl triethoxysilane modified SiO2 particles were characterized by FTIR, SEM and XRD techniques. The results showed that vinyl triethoxysilane has been successfully grafted onto SiO2 particles and basically there are no changes in the size of SiO2 particles before and after the modification by vinyl triethoxysilane. XRD results show that the synthesized SiO2 particles have certain crystallinity.

A study on superhydrophobic coating in anti-icing of glass/porcelain insulator

This paper focuses on the preparation of a superhydrophobic coating on glass/porcelain insulators which possess anti-icing property below freezing temperature. Inspired by lotus-effect, the fabrication of a superhydrophobic coating has two steps: the first step is to construct a hierarchical SiO2 coating on the substrate surface, and the second step is the chemical modification of the SiO2 coating with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (PDTS). The precursor for the hierarchical SiO2 coating is a suspension of SiO2 sol particles and dispersible SiO2 powder particles. According to the TEM testing, SiO2 sol particles prepared by sol–gel method has an average particle size about 2–5 nm, while the size of the dispersible SiO2 particles is ca. 20 nm. The precursor was sprayed on glass/porcelain insulators, and then dried at ambient condition, finally heat-treated at 773 K for 2 h. The morphology of the superhydrophobic coating was characterized by TEM and AFM, and experimental results indicated that the coating featured [hierarchical structure consisting of both large bumps with micron-sized height (0.8 μm) and tiny papillae with the size about 30 nm] micron-sized roughness (0.8 μm) combined with nano-sized roughness (about 2 nm). Moreover, the scratch test showed that the coating tightly adhered to the surface of the glass/porcelain insulators. The superhydrophobic property of the coating was examined by a contact angle measurement, and the results demonstrated that the static water contact angle is high up to 163.6°, and the sliding angle is 1.4°. The superhydrophobic property of the coating was also confirmed by the outdoor tests in winter, and it was found that the superhydrophobic coating had the function in anti-icing, based on which the anti-icing mechanism underlying was discussed in terms of the interaction between impacting droplets and superhydrophobic surface.

In Situ Observation of the Dissolution of SiO2 Particles in CaO–Al2O3–SiO2 Slags and Mathematical Analysis of its Dissolution Pattern

The dissolution of amorphous SiO2 particles in CaO–Al2O3–SiO2 slags was investigated at 1450°C by high‐temperature confocal scanning laser microscopy (HT‐CSLM) and thermodynamic/kinetic analyses. The SiO2 particles used in this experimental study had a spherical form so that any rotation of the particle did not cause errors in the determination of the particle size during the dissolution. Moreover, a wide composition range of the slag could be chosen without forming any solid reaction layer which could distort the evaluation of the dissolution mechanism. The evolution of the diameter of the spherical SiO2 particle was measured by image analysis of pictures obtained from the HT‐CSLM. It was found that the dissolution curve of the SiO2 particle (size as a function of time) exhibited either a parabolic‐like curve or an S‐shaped curve depending on the slag composition. The patterns were compared with a well‐known shrinking core model (SCM), and it was shown that the SCM could not represent the dissolution behavior of the SiO2 particle observed in this study. It was experimentally found that the shape of the dissolution curves varies as a function of the slag composition. The curve exhibited a parabolic‐like shape for low SiO2‐containing slags and changed to an S‐type shape with increasing SiO2 concentration in the slag. To elucidate the dissolution mechanism, a model based on approximations for the diffusion near the particle was proposed by modifying the previously available model [M. J. Whelan, Met. Sci. J., 3, 95–97 (1969)]. From the experimental data and the model calculations, the viscosity of the slag was shown to be the major factor affecting both dissolution rate and mechanism. Effective binary diffusion coefficients were estimated using the model and experimental data. Those were shown to be in the range of literature data.