Silica Nanopowder Research Articles

Fluidization of Nanoparticle Agglomerates at Elevated Temperatures

The behavior of hydrophobic and hydrophilic nanoparticles was investigated. In a novel approach, the interparticle force (IPF) was altered by changing the temperature of the gas–solid fluidized bed in the range 25–110 °C. The hydrodynamic state of the bed was monitored by examining pressure fluctuations using coherent and incoherent analysis. Formation, coalescence, eruption, and mobility of bubbles in the fluidized bed were determined in addition to investigating the behavior of agglomerates. The diameter of the agglomerate was calculated from the incoherent output of the power spectral density of pressure fluctuations in the agglomerate particulate fluidization (APF) regime at various temperatures. No bubbles were detected in the bed of the silica nanopowder at low temperatures whereas small bubbles form at higher temperature. In contrast, hydrophilic titania nanopowder becomes fluidized in the ABF regime at lower temperatures and tends to fluidize at the APF regime with increasing bed temperature.

Examination of hot mix asphalt and binder performance modified with nano silica

The aim of the study is to evaluate the performance of Hot Mix Asphalt (HMA) and bitumen by modifying bitumen with nano materials according to Superpave™ mix design procedure. In this study, bitumen is modified by silica nanopowder (SiO2NP). Nano powders are mixed with base bitumen at contents of 0.1, 0.3 and 0.5% by weight. Rutting and fatigue performance of bitumens are determined. HMA is prepared with nano modified bitumens at optimum binder content (OBC). Moisture susceptibility of modified HMA is evaluated according to Modified Lottman test procedure. Nano modified bitumens are also evaluated by scanning electron microscopy (SEM) whether the modification is uniform or not. As a result, better performance is obtained by SiO2NP at a content of 0.3% modification. Performance Grades (PG) of all modified bitumens are determined as PG 64-22. OBCs are decreased by modification. HMA sample modified by SiO2NP at a content of 0.3% is determined 26.25% higher resistive to moisture compared to reference sample. Homogenous mixture is obtained according to SEM results. It is found that the agglomeration of nano materials is mostly lower than 4μm in the mixtures. As a result, SiO2NP 0.3% shows satisfying results.

In Russian

The problem of environmental purification from petroleum pollution today is becoming increasingly topical. To solve this problem, the bioremediation way based on the processes of petroleum products decomposition by means of microorganisms that are cap able to oxidize hydrocarbons is the most perspective method. The model composite system based on the mixture of nanosilica powders and Saccharomyces cerevisiae yeast cells was created by us to destruct the petroleum products. The purpose of our investigation was to improve the composition of the composite by adding the mineral compounds (KCl – 1.5 %, CuSO 4 – 0.3 %, ZnSO 4 – 0.4 %, (NH 2 ) 2 CO – 3.0 %, Ca(H 2 PO 4 ) 2 – 0.35 %) that can increase the efficiency of yeast cells in the destruction of motor oil hydrocarbons and to investigate the pH influence of aqueous media on the bioremediation. In this paper, it has been found that the presence of the mixture of hydrophilic (A-300) and hydrophobic (AM1-300) silicas increases vital activity of yeast cells without of nutrient medium. The results show when the additional source of mineral nutrition is added to the nanocomposite, the 1.4 to 1.2 times increase of yeast gas evolution as well as the 1.7 to 3.3 times biomass growth compared to the blank; and 1.3 to 2 times one compared to the mixture of nanosilica powders without additives was observed. The release of carbon dioxide gas by cells suspension at pH 4.0 was 2 times decreased and 1.5 – 2 times raised at pH 8.0 compared to the blank. Moreover , gas evolution in the alkaline medium was 3.5 times higher than that in the acidic one . It showed be noted that destruction of motor oil hydrocarbons can be visually observed as gradual destruction of the oil layer on the water surface. Consequently, t he experimental results obtained during this research are crucial for the development of new effective methods of water and soil purification from the motor oil pollutants.

Collection of Industrial Oil Using Nanoparticles and Porous Powders of Silica

AbstractIndustrial oil was collected using hydrophobic silica powders. Silica nanopowder was modified with octadecyltriethoxysilane (OTS) using spray pyrolysis reactor continuously. Besides nanoparticles, mesoporous silica powder synthesized using Pluronic P104 was adopted as another oil adsorbents. Spherical macroporous or meso-macroporous silica particles were prepared by self-assembly for the removal of oil. The effects of the amount of powder on the oil adsorption were studied and compared with the results of various silica powders. The meso-macroporous silica particles were found to be the most efficient, indicating that both specific surface area and porosity played crucial role.

A study of APC surfactant role on the surface characteristics, size and morphology improvements of synthesized mesoporous silica nanopowder through a sol-gel process

The synthesis of mono-sized silica nanoparticle with mesostructures via sol-gel method by employing ammonium polycarboxylate (APC) surfactant has investigated. The major aim of this paper is to introduce APC as an appropriate surfactant to control nucleation and growth of nanoparticles during hydration and condensation steps of the sol-gel process. Dynamic light scattering (DLS) results indicated that the particle in the sol containing APC had an average particle size about 10 nm. The bonds of prepared silica nanoparticles were studied by IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The result of scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) confirmed that applying APC could sufficiently induce the mass transfer during the synthesis process, this claim have also verified according to the particle size analysis. Resulting information also approved the synthesis of spherical and mono-sized nanoparticle with an average particle size of 25 nm. Furthermore, the synthesized nanoparticles possessed a mesostructured characteristic due to leaving of APC organic components during final heat treatment. N2 adsorption/desorption porosimetry indicated that the particles were comprised of mesopores with an average pore size of 2.5 nm and specific surface area of 1015 m2 g−1. This strategy could be readily applied to prepare an engineered product of silica nanoparticles with uniform spherical morphology and mesostructure.

Broad band (UV–VIS) photoluminescence from carbonized fumed silica: Emission, excitation and kinetic properties

Carbon incorporated silica nano-powder (SiO2:C) has been fabricated by chemical treatment of a fumed silica with tetramethoxysilane and subsequent annealing at 700°C in pure nitrogen ambient. Upon thermal treatment SiO2:C powder exhibits strong photoluminescence (PL) that spans in the range from near-ultraviolet to visible. Two characteristic broad bands, with their maxima at 2.5eV (Green-band) and 3.3eV (Violet-band), contribute to the observed broadband emission spectrum from SiO2:C. PL emission and PL excitation (PLE) studies in the temperature range of 10–300K revealed a different PL behavior pertaining to the change of the peak position of the green and violet bands with respect to temperature. The low-energy emission band showed a redshift in the peak position with decreasing temperature, in contrast to the blue-shift behavior of the violet-band. The latter PL behavior suggests a different origin for the observed emission bands. Complementary time-resolved PL analysis for both emission bands was carried out and yielded PL transients of a few nanoseconds. On the basis of PL/PLE studies and structural characterization by FTIR it is suggested that the origin of the broad band emission may be attributed to radiative recombination in carbon-related surface sites/clusters.

Influence of nano-silica and -metakaolin on the hydration characteristics and microstructure of air-cooled slag-blended cement mortar

This study aims at enhancing the hydration characteristics and microstructure of cement mortar (CM) containing ground air-cooled slag (ACS), using nano-silica (NS) and nano-metakaolin (NMK) powder. Firstly, ordinary Portland cement (OPC) was replaced by 0, 5, 10, 15, and 20 wt.% ground ACS. CM was designed at 3:1 of sand: OPC/ACS ratio. The water to cement (W/C) ratio was adapted at 0.47. It was found that the CM containing 5 wt.% ACS showed the highest compressive strength and free lime content at 90-day of hydration. Meanwhile, significant reduction in compressive strength and free lime values was observed in case of CM containing 20 wt.% ACS. Different NS and NMK percentages (2, 4, 6 and 8 wt.%) were individually added to CM containing 20 wt.% ACS, in order to enhance its chemical and physico-mechanical properties. The results showed that the addition of 6 wt.% NS and 4 wt.% NMK led to increase the compressive strength of ACS-blended CM by ~116 and 42%, respectively, compared to the control sample (without ACS). The hydration products were identified using X-ray diffraction, differential thermal analysis, thermogravimetric analysis, and scanning electron microscopy.

Effect of combining Al, Mg, Ce or La oxides to extracted rice husk nanosilica on the catalytic performance of NiO during COx-free hydrogen production via methane decomposition

Amorphous nanosilica powder was extracted from rice husk and used as a catalyst support as well as a starting material for the preparation of different binary oxides, i.e., SiO2Al2O3, SiO2MgO, SiO2CeO2 and SiO2La2O3. A series of supported nickel catalysts with the metal loading of 50 wt % were prepared by wet impregnation method and evaluated in methane decomposition to “COx-free” hydrogen production. The fresh and spent catalysts were extensively characterized by different techniques. Among the evaluated catalysts, both Ni/SiO2Al2O3 and Ni/SiO2La2O3 catalysts were the most active with an over-all H2 yield of ca. 80% at the initial period of the reaction. This distinguishable higher catalytic activity is mainly referred to the presence of free mobile surface NiO and/or that NiO fraction weakly interacted with the support easily reducible at low temperatures. The Ni/SiO2CeO2 catalyst has proven a great potential for application in the hydrogen production in terms of its catalytic stability. The formation of MgxNi(1−x)O solid solution caused the Ni/SiO2MgO catalyst to lose its activity and stability at a long reaction time. Various types of carbon materials were formed on the catalyst surface depending on the type of support used. TEM images of as-deposited carbon showed that multi-walled carbon nanotubes (MWCNTs) and graphene platelets were formed on Ni/SiO2, while only MWCNTs were deposited on all binary oxide supported Ni catalysts.

The Effects of Water on the Dielectric Properties of Silicon-Based Nanocomposites

A series of polyethylene-based nanocomposites was prepared, utilizing silicon nitride or silicon dioxide (silica) nanopowders, and the effect of filler loading and conditioning (i.e., water content) on their morphology and electrical properties was examined. The addition of nanosilicon nitride led to systems that were free of obvious nanoparticle aggregates, whereas the nanosilica-based systems showed evidence of aggregation up to the micrometer scale. While the nanosilicon nitride composites remained essentially dry under ambient conditions, the nanosilica-based composites absorbed appreciable quantities of water from the ambient environment, indicating that interactions with water are dependent on the nanoparticle surface chemistry. Dielectric spectroscopy showed a broad relaxation peak due to adsorbed water at nanoparticle surfaces, which shifted to higher frequencies with increased water content. Similarly, the electrical conductivity was found to be highly sensitive to the presence of absorbed water, particularly for systems containing well-dispersed nanoparticles. We conclude that, in nanodielectric applications, nanoparticle surface chemistry is important in determining macroscopic properties, and not just as a means of compatibilizing the filler and the matrix. Additional factors can be critical, here, as exemplified by interactions with water.

Optical properties of thin fibrous PVP/SiO2 composite mats prepared via the sol-gel and electrospinning methods

Abstract The aim of the research was to create thin, nanofibrous composite mats with a polyvinylpyrrolidone (PVP) matrix, with the reinforcing phase in the form of silicon oxide (SiO 2 ) nanoparticles. SiO 2 nanopowder was obtained using the zol-gel method with a mixture of tetraethyl orthosilicate (TEOS, Si (OC2H5)), hydrochloric acid (HCl), ethanol (C3H5OH) and distilled water. The produced colloidal suspension was subjected to a drying process and a calcination process at 550 °C, resulting in an amorphous silica nanopowder with an average particle diameter of 20 nm. The morphology and structure of the manufactured SiO 2 nanoparticles was tested using transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). Then, using the electrospinning method with a 15% (weight) solution of PVP in ethanol and a 15% solution of PVP/EtOH containing the produced nanoparticles equivalent to 5% of the mass concentration relative to the polymer matrix, polymer PVP nanofibres and PVP/SiO 2 composite nanofibres/SiO 2 nanoparticles were produced. The morphology and chemical composition of the produced polymer and composite nanofibres were tested using a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). The analysis of the impact of the reinforcing phase on the absorption of electromagnetic radiation was conducted on the basis of UV–vis spectra, based on which the rated values of band gaps of the produced thin fibrous mats were assessed.

Modeling the size distribution in a fluidized bed of nanopowder

Fluidization is a technique used to process large quantities of nanopowder with no solvent waste and a large gas–solid contact area. Nonetheless, nanoparticles in the gas phase form clusters, called agglomerates, due to the relatively large adhesion forces. The dynamics within the fluidized bed influence the mechanism of formation, and thus, the morphology of the agglomerates. There are many theoretical models to predict the average size of fluidized agglomerates; however, these estimates of the average lack information on the whole size range. Here, we predict the agglomerate size distribution within the fluidized bed by estimating the mode and width using a force balance model. The model was tested for titania (TiO2), alumina (Al2O3), and silica (SiO2) nanopowders, which were studied experimentally. An in-situ method was used to record the fluidized agglomerates for size analysis and model validation.

De-agglomeration of nanoparticles in a jet impactor-assisted fluidized bed

Nanoparticles in agglomerated state lose their outstanding properties; hence, it is essential to break them up prior to use and prevent their re-agglomeration. Even though there are several dry techniques to disperse nanopowders, none of them have been able to produce truly nanoscale aerosols so far. Here, we study de-agglomeration of dry silica nanopowder via a jet impactor-assisted fluidized bed (JIAFB). The particle size distribution of fragmented powders was characterized by in-line scanning mobility particle spectrometry (SMPS) and offline transmission electron microscopy (TEM). In order to ascertain the jet length and that the kinetic energy of particles is sufficient for de-agglomeration, a CFD simulation was carried out. Both SMPS and TEM measurements imply that at a certain fluidization velocity, increasing the jet velocity shifts the particle size distribution towards smaller diameters, and at higher velocities the mode value reduced from 113 130 to 55–60nm. However, the geometric standard deviation or degree of polydispersity rises from 1.5 to 2.0 by increasing the jet velocity up to 197m/s, as it will increase the total superficial velocity and consequently entrainment of larger particles from the bed. In addition, the TEM results indicate that the range of individual particle sizes in the supplied nanopowder is wide; hence, increasing the geometric standard deviation can be an indicator of a higher level of agglomerate dispersion.

Investigating the effects of calcination temperatures on the structure of modified nanosilica prepared by sol–gel

Modified nanosilica powder was prepared with a sol-gel method using a tetraethoxysilane (TEOS) and γ-amino propyltriethoxysilane (APTES) mixture as the starting materials and ethanol as solvent, followed by the addition of water. The xerogels obtained after drying at 125°C had an average particle size of 225nm and were calcinated in a furnace for 30min at 175°C, 250°C, 300°C, 350°C and 550°C. The primary particle size was gradually reduced to 109nm as the temperature reached 300°C, followed by reductions of 134nm and 151nm at 350°C and 550°C, respectively. The characteristic structural changes within the matrix of the silica powder as a function of the calcination temperatures were investigated by atomic force microscopy (AFM) and X-ray diffraction. The unstable structure of the dried, modified silica powder defines their characteristic changes as they are highly sensitive to the calcination process within two decoupled zones at 300°C, particle shrinkage by densification, and growth by particle coarsening behaviour. In addition, the modification was gradually lost between 300°C and 350°C. This is of interest to many composite systems where nanosilica have been widely used as filler materials.

A facile method for fabrication of superhydrophobic surface with controllable water adhesion and its applications

Abstract In this work, a simple alkaline etching method was presented to fabricate superhydrophobic surfaces. X-Ray Diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and atomic force microscope (AFM) were utilized to characterize the surfaces. The morphology of superhydrophobic surfaces shows hierarchical structures and the corresponding water contact angles (WCA) are more than 155°. The adhesion force between the water droplets and the surfaces were discussed in detail, the specimen etching for 40 min in NaOH solution shows the lowest adhesion. The applications of these superhydrophobic surfaces were exploited. For instance, the superhydrophobic surface with high adhesion can be used in drug delivery. In addition, the self-cleaning property of the superhydrophobic surface with low adhesion was also tested by applying nano-silica powder as dust on the surfaces. Importantly, the superhydrophobic surfaces show excellent anti-corrosion performance with an extremely low corrosion current density of 2.748 × 10−9 A/cm2, and the anti-corrosion mechanism was discussed comprehensively. The present method can also be used to fabricate large-scaled superhydrophobic surfaces and expand applications of metal materials.

Analysis and Alternate Selection of Nanopowder Modifiers to Improve a Special Protective Coating System

This paper presents a practical approach for rational choice of silica nanopowders as modifiers to control and improve the performance of protective coating systems operating in harsh environmental conditions. The approach is based on the multiparameter analysis of nanoparticle reactivity of similar silica synthesized by using chemical and physical methods. The analysis indicates distinct adsorption centers due to the differences in the particles formation; the features of the formation and adsorption mechanisms lead to higher diffusion capacity of the nanoparticles, synthesized by physical methods, into a paint material and finally result in stronger chemical bonds between the system elements. The approach allows reducing the consumption of paint materials by 30% or more, at least 2-3 times increasing of the coating adhesion and hence the system life. Validity of the approach is illustrated through the data obtained from comparative modeling, factory testing, and practical use of modified systems.

Mechanical Characteristics of Micro and Nano Silica, ZnO and Chitin Powder Filled Unsaturated Polyester Composites

Objectives: In this study stir processing method is used to increase the strength of polymer with the addition of reinforcements such as micro and nano silica, ZnO and chitin powder. Methods/Statistical Analysis: produced with this process are the production of parts having good resistance to solvents like HCl and H 2 SO 4 being environmental friendly. Silica (micro and nano), chitin and ZnO were added into polyester resin in different fractions as 2%,4%,6% and 10% through mechanical stirrer at 1000 rpm for 1 h. Accelerator and catalyst were added and stirred using a glass rod. The influence of ZnO nano particles with the addition of silica and chitin powder on the mechanical properties like tensile strength and hardness were investigated. The comparison of different weight fractions is also studied. Findings: By adding ZnO nano particles with micro silica and chitin the tensile property of polyester composite was increased. The hardness increased with the addition of Silica (micro and nano) and ZnO whereas, it decreased with the addition of chitin powder. Application/Improvements: Investigating the effect of Silica (micro and nano) and chitin in addition to the ZnO nano particles on the mechanical and micro structure of polyester composites.

Sono-assisted adsorption of a textile dye on milk vetch-derived charcoal supported by silica nanopowder

This study was performed to assess the efficiency of silica nanopowder (SNP)/milk vetch-derived charcoal (MVDC) nanocomposite coupled with the ultrasonic irradiation named sono-adsorption process for treating water-contained Basic Red 46 (BR46) dye. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and Fourier transform infrared spectroscopy (FT-IR) were performed for the characterization of as-prepared adsorbent. The sono-assisted adsorption process was optimized using response surface optimization on the basis of central composite design by the application of quadratic model. Accordingly, the color removal can be retained more than 93% by an initial BR46 concentration of 8 mg/L, sonication time of 31 min, adsorbent dosage of 1.2 g/L and initial pH of 9. The pseudo-second order kinetic model described the sono-assisted adsorption of BR46 reasonably well (R2 > 0.99). The intra-particular diffusion kinetic model pointed out that the sono-assisted adsorption of BR46 onto SNP/MVDC nanocomposite was diffusion controlled as well as that ultrasonication enhanced the diffusion rate.

Effect of filler loading, geometry, dispersion and temperature on thermal conductivity of polymer nanocomposites

Using a unidirectional heat transfer apparatus, the roles of nanoparticle geometry, loading, dispersion and temperature on the thermal conductivity of polymer nanocomposites are investigated. The polymer nanocomposites (PNC) consist of epoxy matrices filled with silica nanopowder and carbon nanotubes, respectively, as well as poly (2-vinylpyridine) (P2VP) matrices loaded with silica nanoparticles. First, it is shown that thermal conductivity generally increases with nanofiller loading. These results are also reasonably described by the three phase Lewis-Nielsen or Halpin-Tsai analytical models. More importantly, it has been also demonstrated that the thermal conductivity of the polymer nanocomposites greatly depends on the dispersion state of the nanofillers. Furthermore, the effect of temperature on the thermal behavior of PNCs is briefly discussed. These results emphasize the important role of nanoparticles content and dispersion state on the thermal characteristics of polymer nanocomposites, which can be used to design composite materials with tunable thermal behavior.

Production of Nano Amorphous SiO2 from Malatya Pyrophyllite

Pyrophyllite (Al4Si8O20(OH)4) is an important industrial clay mineral. In this paper, highly pure nano silica powder was synthesized by alkaline treatment method from the local pyrophyllite deposit which is in Malatya, Turkey. The morphologies, structures and properties of the raw pyrophyllite and the obtained nano amorphous SiO2 were determined by XRF, XRD, ATR, SEM and EDX. The results showed that the nano silica can be produced with a high purity (98%) and nano size (< 50 nm).

CoFe2O4-SiO2 Composites: Preparation and Magnetodielectric Properties

Cobalt ferrite (CoFe2O4) and silica (SiO2) nanopowders have been prepared by the microwave hydrothermal (M-H) method using metal nitrates as precursors of CoFe2O4 and tetraethyl orthosilicate as a precursor of SiO2. The synthesized powders were characterized by XRD and FESEM. The (100-x) (CoFe2O4) + xSiO2 (where x = 0%, 10%, 20%, and 30%) composites with different weight percentages have been prepared using ball mill method. The composite samples were sintered at 800°C/60 min using the microwave sintering method and then their structural and morphological studies were investigated using X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectra, and scanning electron microscopy (SEM), respectively. The effect of SiO2 content on the magnetic and electrical properties of CoFe2O4/SiO2 nanocomposites has been studied via the magnetic hysteresis loops, complex permeability, permittivity spectra, and DC resistivity measurements. The synthesized nanocomposites with adjustable grain sizes and controllable magnetic properties make the applicability of cobalt ferrite even more versatile.