SiO2 Nanopowder Research Articles

Microstructure and Mechanical Properties of Friction Stir Welded and Processed Joints with the Addition of Nanoparticles: A Review

Background: Friction Stir Welding (FSW) is an efficient process for solid-state joining of two different material without melting by using a non-consumable tool. FSW process was developed for the modification of metallic material microstructure. FSW requires a precise investigation of the process, microstructure, and the welds mechanical properties in order to be used in the fabrication of high- quality engineering components. Through the efforts of improving the weld's mechanical and microstructural properties and conveying the current knowledge of the friction stir to other applications, multiple new technologies have been developed over the time. One of the latest methods to fabricate high performance joints or Nanocomposites alloys is the addition of nano- reinforcements to the joint in Friction Stir Welding (FSW) or the metal matrix in Friction Stir Processing (FSP). Objective: In this study, an overview of effect of nanoparticles on mn this study, an overview of the effect of nanoparticles on microstructural and mechanical properties of the FSW/ FSP joints is presented. The review revealed that the most widely employed additions are SiC, SiO2, Al2O3, and graphite nano-powders. Microstructural evolutions, such as grain size, second phase particles, and reinforcement distribution, usually are investigated using optical methods and Scanning Electron Microscopy (SEM). Furthermore, the mechanical properties of the joints, such as tensile strength, hardness, and wear performance, are also investigated. Based on most of the researches, microstructural evolution associated with adding nanoparticles led to improve the joints mechanical properties.icrostructural and mechanical properties of the FSW/ FSP joints is presented. The review revealed that the most widely employed additions are SiC, SiO2, Al2O3, and graphite nano-powders. Microstructural evolutions such as grain size, second phase particles and reinforcement distribution usually are investigated using optical methods and scanning electron microscopy (SEM). Furthermore, the mechanical properties of the joints, such as tensile strength, hardness, and wear performance, are also investigated Based on most of researches, microstructural evolution associated with adding nanoparticles led to improve the joints’ mechanical properties.

Low temperature synthesis of highly pure cordierite materials by spark plasma sintering nano-oxide powders

The development of cordierite ceramics, using traditional materials and conventional methods, remains a key challenge because of the high and narrow sintering temperature range. In this work, single-phase cordierite ceramics were produced by spark plasma sintering nano-oxide powders, at low temperatures. A starting mixture of Al2O3, SiO2, and MgO nano-powders with the composition of stoichiometric cordierite was first sonicated, then, sintered in the temperature range 900–1200 °C. The raw powders, sonicated powder mixture, phase transformations, and fracture surface of sintered specimens were characterized by using an x-ray diffractometer and a field emission scanning electron microscope (FE-SEM). The hardness and fracture toughness were measured using the indentation technique. The influence of testing conditions, process parameters, characterization technique, and calculation method on hardness and fracture toughness was investigated. The FE-SEM images, x-ray maps, and EDS results revealed the homogeneity and stoichiometry of the sonicated powder and sintered samples. Highly pure α-cordierite was formed at 1150 °C. Samples that were sintered at 1150 and 1200 °C had bulk density of 2.58 g/cm3 (relative density of 100%), and maintained low average grain sizes of 28.68 and 34.95 nm, respectively. With the decrease in the temperature from 1200 to 1150 °C, the hardness of cordierite was slightly increased from 8.25 ± 0.158 to 8.46 ± 0.188 GPa, the fracture toughness was marginally improved from 2.2 ± 0.158 to 2.25 ± 0.238 MPa mm1/2, and the critical strain energy release rate was raised from 32.46 to 33.95 J/m2.

Hydrothermal SiO2 Nanopowders: Obtaining Them and Their Characteristics.

The technological mode of obtaining amorphous SiO2 nanopowders based on hydrothermal solutions is proposed in this study. Polycondensation of orthosilicic acid as well as ultrafiltration membrane separation, and cryochemical vacuum sublimation were used. The characteristics of nanopowders were determined by tunneling electron microscopy, low-temperature nitrogen adsorption, X-ray diffraction, and small-angle X-ray scattering. The scheme allows to adjust density, particle diameters of nanopowders, specific surface area, as well as diameters, area and volume of the pore. Thus, the structure of nanopowders is regulated—the volume fraction of the packing of spherical particles in aggregates and agglomerates, the size of agglomerates, and the number of particles in agglomerates. The pour densities of the nanopowders depend on the SiO2 content in sols, which were 0.02 to 0.3 g/cm3. Nanoparticles specific surface area was brought to 500 m2/g by low temperature polycondensation. Nanoparticle aggregates specific pore volume (0.2–0.3 g/cm3) weakly depend on powders density. The volume fraction of the packing of SiO2 nanoparticles in aggregates was 0.6–0.7. Solid samples of compacted nanopowders had a compressive strength of up to 337 MPa. Possible applications of hydrothermal SiO2 nanopowders are considered.

Efficient photocatalytic degradation of acrylonitrile by Sulfur-Bismuth co-doped F-TiO2/SiO2 nanopowder

In this study, a simple sol-gel method was applied for preparing effectual photocatalyst of S-Bi co-doped F-TiO2/SiO2 (S-Bi-F-TiO2/SiO2) nanopowder. Optimal preparation conditions were obtained by optimizing the calcination temperature and the ratio of S and Bi. The synthesized powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), brunauer-emmett-teller (BET), UV–Visible diffuse-reflectance spectroscopy (UV–Vis DRS), photoluminescence spectroscopy (PL) and ammonia adsorption and temperature-programmed desorption (NH3-TPD). The photocatalytic activity was evaluated by the degradation of acrylonitrile under simulated visible light irradiation. S-Bi-F-TiO2/SiO2 nanopowder possess excellent photocatalytic properties under visible light for the degradation of acrylonitrile, when the calcination temperature was 450 °C for 2 h and the ratio of S and Bi was 0.02: 0.007. The degradation efficiency of acrylonitrile reached to 81.9% within 6 min of visible light irradiation. Compared with F-TiO2/SiO2 sample, NH3-TPD and PL results revealed the higher photocatalytic activity for S-Bi-F-TiO2/SiO2, which is mainly due to the increase strength and number of surface acid site with S doping. The co-doping with S & Bi improved the separation of electron-hole pairs and enhanced the photocatalytic oxidizing species. The UV–Vis DRS showed stronger absorption in S-Bi co-doped F-TiO2/SiO2 catalyst as compared to F-TiO2/SiO2 catalyst. XPS results demonstrated the presence of various surface species viz. oxygen vacancies, Ti3+, Ti4+, O2− and OH group.

Study of SiO2 nanopowder produced by plasma arc method

The work is devoted to the study of the plasma arc method of obtaining nanosized silicon oxide from natural raw materials from Russian fields, such as diatomite of Kamyshlovsk deposit (Sverdlovsk region), the quartzite of Chupinsk deposit (Republic of Karelia), quartz sand of Tugansk deposit (Tomsk region). The method of transmission electron microscopy was used to study the morphology. Brunauer-Emmett-Teller method was used to study the surface. The main structural and morphological characteristics of the obtained nanoparticles were determined. The particles of nanoscale SiO2 obtained by the plasma arc method spherical shape, the size distribution 10–300 nm, the specific surface area 37–71 m2·g−1.

Bacterial Compatibility/Toxicity of Biogenic Silica (b-SiO2) Nanoparticles Synthesized from Biomass Rice Husk Ash.

Biogenic silica (b-SiO2) nanopowders from rice husk ash (RHA) were prepared by chemical method and their bacterial compatibility/toxicity was analyzed. The X-ray diffractometry (XRD) patterns of the b-SiO2 nanopowders indicated an amorphous feature due to the absence of any sharp peaks. Micrographs of the b-SiO2 revealed that sticky RHA synthesized SiO2 nanopowder (S1) had clustered spherical nanoparticles (70 nm diameter), while b-SiO2 nanopowder synthesized from red RHA (S2) and b-SiO2 nanopowder synthesized from brown RHA (S3) were purely spherical (20 nm and 10 nm diameter, respectively). Compared to the S1 (11.36 m2g−1) and S2 (234.93 m2g−1) nanopowders, the S3 nanopowders showed the highest surface area (280.16 m2g−1) due to the small particle size and high porosity. The core level of the X-ray photoelectron spectroscopy (XPS) spectra showed that Si was constituted by two components, Si 2p (102.2 eV) and Si 2s (153.8 eV), while Oxygen 1s was observed at 531.8 eV, confirming the formation of SiO2. The anti-bacterial activity of the b-SiO2 nanopowders was investigated using both gram-positive (Escherichia coli) and gram-negative (Staphylococcus aureus) microorganisms. Compared to S2 and S3 silica nanopowders, S1 demonstrated enhanced antibacterial activity. This study signifies the medical, biomedical, clinical, and biological importance and application of RHA-mediated synthesized b-SiO2.

Effect of Tin Dioxide Modified F-TiO2/SiO2 Nano-Powder Catalysts on Photocatalytic Degradation of Acrylonitrile

In this study, tin dioxide (SnO2) modified F-TiO2/SiO2 catalysts (F-TiO2/SnO2/SiO2) was prepared by two steps method. The prepared powders were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Ernmett-Teller (BET), ultraviolet-visible absorption spectroscopy (UV-vis), photoluminescence spectroscopy (PL). The photocatalytic activities was evaluated by degradation ratio of acrylonitrile, which reached 74.0%, that was higher than that of F-TiO2/SiO2 catalysts 60.5 % after irradiation under simulated sunlight for 6 min. A series of characterization showed that the SnO2 modified photocatalysts had small crystal size, large specific surface area, and were easily dispersed uniformly in the reaction system. The photoluminescence (PL) spectra were also slightly weakened, implying that SnO2 modification well inhibited the recombination of electron hole pairs. A red shift of absorption edge occurred implying that the utilization of visible light was effective.

Recycling of Waste Paraffin Wax by the Addition of SiO2 Nano-Powders to Improve Thermal Conductivity

Paraffin wax is an important material used in thermal energy storage (TES) systems. The thermal conductivity of the material is an important parameter that decides the degree of exploitation of the paraffin wax in TES systems. The thermal conductivity is improved by the addition of silicon oxide nanoparticles (1%, 2%, 4%, and 6%) to the paraffin wax. The average size of the SiO2 particles is equal to 38 nm. The addition of SiO2 nano-particles at very small ratios was found to enhance the thermal conductivity of the paraffin wax considerably. SiO2 nanoparticles, add to paraffin wax, have a significant effect in enhancing the thermal storage characteristics of paraffin Paraffin wax is an important material used in thermal energy storage (TES) systems. The thermal conductivity of the material is an important parameter that decides the degree of exploitation of the paraffin wax in TES systems. The thermal conductivity is improved by the addition of silicon oxide nanoparticles (1%, 2%, 4 %, and 6%) to the paraffin wax. The average size of the SiO 2 particles is equal to 38 nm. The a ddition of SiO 2 nano -particles at very small ratios was found to enhance the thermal conductivi ty of the paraffin wax considerably. SiO 2 nanoparticles, add to paraffin wax, have a significant effect in enhancing the thermal storage characteristics of paraffin

Retrieval of dielectric and structural properties of amorphous SiO2 nanopowder based on optical measurements and Bergman's spectral representation theory

The dielectric and structural properties of an amorphous SiO2 nanopowder have been characterized in the framework of Bergman's spectral representation. The methodology used in this paper is based on the acquisition of reflectivity spectra from a set of nanopowder pellets with different levels of porosity and the measurement of the transmittance spectra of KBr pellets containing low levels of silica nanoparticles. The fit of the spectra was performed with a dielectric function model through the solution of a nonlinear optimization problem including all the experimental data. In addition to the optical properties, the complete analysis also provided an accurate estimate of the total porosity of pellets and evaluated the percolation of the silica agglomerates in the porous matrix. A comparison with the predictions obtained by other mixing formulas clearly demonstrates that Bergman's theory is the most appropriate for treating this type of powder.

Citrate-nitrate gel combustion synthesis of micro/nanostructured SiOx/C composite as high-performance lithium-ion battery anode

A facile and low-cost citrate-nitrate gel combustion route was conceived to synthesize micro/nanostructured SiOx/C composite. Auto combustion process generated ultrafine and chemically active SiO2 nanopowders with a loose and porous structure. A simple carbon coating process was continuously adopted to carbothermally reduce the O/Si atomic ratio of the combustion synthesized SiO2 precursor, and simultaneously create a carbon outer layer on secondary particles. The obtained SiOx/C composite has a micro-sized loose particle structure, composing of a great deal of primary nanoparticles. The micro/nanostructured SiOx/C composite exhibits a high and stable reversible capacity of ca. 740 mAh g−1, and excellent good rate capability. The low O/Si atomic ratio, unique micro/nanostructure and sufficient carbon component ensure the excellent electrochemical performance of the combustion synthesized micro/nanostructured SiOx/C.

Specific Features of Ion Transport in New Nanocomposite Gel Electrolytes Based on Cross-Linked Polymers and Silica Nanoparicles

The spesific features of ion transport are studied in the nanocomposite system based on a network matrix synthesized by radical polymerization of polyethylene glycol diacrylate in the presence of liquid aprotic electrolyte containing 1 M LiBF4 in γ-butyrolactone and SiO2 nanopowder. The self-diffusion coefficients measured by 7Li NMR spectroscopy with pulsed field gradient have a maximum at 2 wt % SiO2 nanoparticles. Nanocomposites of the latter composition exhibit the highest cation transport numbers (0.49) and the maximum of conductivity in the temperature interval under study (from –70 to 100°С): 4 mS/cm at 20°С and 1 mS/cm at –70°С. The second conductivity maximum at 6 wt % is characterized merely by the low effective activation energy of conduction. Possible mechanisms are invoked to explain the increase in conductivity. The first mechanism is based on the increase in the number of mobile charge carriers which may be a result of salt dissociation to ions, the second mechanism is associated with the development of a large number of favorable pathways for ion transport.

Effect of nano-AlN addition on thermal diffusivity and mechanical strength of porous AL2O3 ceramic composites

Abstract In a properly made porous abrasive composite, the vitrified bond should ideally cover the grains and form a continuous network of bridges, and thus part of the heat energy from the grinding process is also transferred to the vitrified bond. Until recently, most studies on the design of composite properties have focused mainly on improving their mechanical strength and wear resistance, but increasingly the very important aspect of their thermal properties is noticed. The vitrified Al2O3 composites were made from Al2O3 grains, vitrified bond of Na2O K2O Al2O B2O3 SiO2 and AlN nanopowder. The increase in porosity in the tested composites is the effect of the AlN decomposition reaction. Crystalline phases were identified in both composites - α-Al2O3 and NaAl11O17, but with a different percentage share in individual composites. In composites doped with AlN nanopowder, the proportion of NaAl11O17 crystalline phase decreases, due to its high susceptibility to reduction by Al, obtained from the AlN decomposition reaction. The product of the redox reaction is also Na+ ions, which may participate in the formation of the glass phase and thus increasing the fraction of the residual glass phase. As a result of the partial reduction of NaAl11O17 phase, an increase in α-Al2O3 content is observed. A higher proportion of α-Al2O3 phase with high thermal conductivity can be a factor that increases the rate of heat removal from the work zone.

Mass transfer performance enhancement by nanoabsorbents during CO2 absorption process

A fluid in which nano-sized particles are dispersed is called nanofluids. It has been actively studied in the field of heat and mass transfer because of its attractive thermophysical properties. Since methanol is mainly used as a physical CO2 absorbent, methanol-based nanofluids (nanoabsorbents) are tested for mass transfer performance enhancement. Al2O3 and SiO2 nanopowders are used, and the nanoabsorbents are manufactured by the ultrasonication method. Thermal conductivity (0.005–1.0 vol%, 24–40 °C), viscosity (0.005–1.0 vol%, 20 °C), surface tension (0.005–0.1 vol%, 20 °C) and average cluster size (0.005–1.0 vol%, 20 °C) are measured to analyze the combined heat and mass transfer and the dispersion characteristics of the nanofluids. Also, the mass transfer characteristics between CO2 and nanoabsorbents is evaluated using the Schlieren visualization experiment. It is found that the thermal conductivity and viscosity of the nanoabsorbents increase with increasing the volume concentration of nanoparticles. At 1.0 vol%, the thermal conductivities of Al2O3/methanol and SiO2/methanol nanoabsorbents are 4.6% and 5.5% higher than that of pure methanol, respectively, while the viscosities are also increased by 21% and 11%, respectively. The average cluster sizes of Al2O3 and SiO2 nanoabsorbents are not vary depending on the volume concentration, and they range 267–288 nm and 496–507 nm, respectively. It is concluded that the mass diffusivities of nanoabsorbents are significantly higher than that of pure methanol, and the enhancement mechanism of mass transfer is newly proposed.

Evolution of particle interactions between accidentally released aerosol particles generated from powdered engineered nanomaterials into a simulated workplace atmosphere

The evaluation of aerosol processes which alter the size distribution of accidentally released nanomaterial particles in an indoor environment can provide size resolved exposure estimations, and subsequently contribute to a more comprehensive risk analysis on engineered nanomaterials (ENMs). In this work processed suspensions of TiO2 and SiO2 nanopowders were introduced into the reservoir of a nebuliser, and injected continuously as nano-aerosols into a room-size dispersion facility for a fixed release time. Following injection, the concentration of the dispersed aerosols was allowed to naturally decay for a prolonged period. Airborne particle number concentration (PNC) and particle size distributions (PSD) were continuously measured at a point within the breathing zone near to the source, while deposited particles were collected for transmission electron microscopy (TEM) analysis. A log10-normal fitting program was used to determine the evolution of the modal groups present within the measured PSDs. A modelling approach that considered the experimentally determined particle decay rate as a sum of the pair to pair coagulation and deposition rates was employed to estimate the relative importance of size-resolved deposition compared to coagulation. Results indicated that the variation of PNC with time was accurately modelled, providing size-dependent insights into the contribution of the two particle removal mechanisms to the change of PNC over time. The deposition patterns obtained from the TEM images qualitatively supported the model results. Since a limited set of input parameters were used, we concluded that the proposed model could be an effective tool for a reasonable quantification of worker's exposure to aerosols originating from the accidental release of diffuse ENM in real workplaces.

Role of Ceria Nanocrystals on Morphology and Luminescence of Eu3+ doped SiO2 nanopowder

Ceria nanocrystals embedded in Eu3+ doped in silica were prepared by sol-gel method. The evolution of cubic fluorite structure of ceria (CeO2) nanocrystal has been occurred in prepared nanopowder at a relatively low temperature (~300 °C). Effect of annealing and role of CeO2 nanocrystals were further confirmed by XRD, FTIR and the elemental compositions were examined by SEM-EDS. It has been observed that the average size of nanocrystallites and their morphology would be tailored by varying the annealing temperature and CeO2 content. The incorporation of Eu3+ ions and CeO2 nanocrystal in silica were revealed by intense PL excitation and emission spectra. We have shown the efficient excitation process of Eu3+ ions through CeO2 nanocrystal in the material. The characteristic emission due to Eu3+ ions has been observed by all direct and indirect excitation wavelengths. It is observed that PL intensity at λex = 325 nm has been increased tremendously by heat treatment due to removal of hydroxyl groups and remains almost same at λex = 394 nm. The MD transition (5D0--7F1) dominated in as prepared sample by indirect excitation while ED transition (5D0--7F2) was pronounced in annealed samples after the formation of CeO2 nanocrystals. Impressively, enhancement in PL intensity via indirect excitation has been demonstrated via a schematic diagram of energy transfer mechanism from CeO2 nanocrystals to the Eu3+ ions.

Embedding CuO Nanoparticles in PDMS-SiO2 Coating to Improve Antibacterial Characteristic and Corrosion Resistance

The purpose of this paper was to develop the hydrophobic nanocomposite coatings of polydimethylsiloxane (PDMS)-SiO2-CuO to improve biocompatibility, corrosion resistance and antibacterial property of 316 L stainless. In this research, after synthesize of CuO and SiO2 nanopowders using wet-chemical approaches, PDMS-SiO2-CuO coatings consisting of various amounts of CuO nanoparticles were developed using dip-coating process. The nanocomposite coatings were characterized with regard to the structural and physical properties, corrosion resistance, antibacterial activity and cellular interactive responses. The results showed that incorporation of CuO nanoparticles <2 wt% improved the corrosion resistance of 316 L stainless steel. At higher CuO nanoparticle contents (>1 wt%), the agglomeration of nanoparticles and their cytotoxic effects resulted in reduced antibacterial characteristics and MG63 cell viability and proliferation. In summary, PDMS-SiO2-CuO nanocomposite coating with significant antibacterial and anticorrosion behavior could be a promising coating for biomedical implants.

An IR Spectroscopic Study of the Effect of Gamma Radiation on the Nano-ZrO2 + Nano-SiO2 + H2O Systems

Using the method of IR Fourier-transform spectroscopy, the radiation decomposition of water in the nano-ZrO2 + nano-SiO2 + H2O system at room temperature (T = 300 K) under the influence of γ-quanta is studied. It is shown that the adsorption of water by the zirconium and silicon nanooxides proceeds by the molecular and dissociative mechanisms. The following intermediate active products of the radiation-heterogeneous decomposition of water are registered: Zr and Si hydrides, and hydroxyl OH groups. It is shown that a change in the ratio of the ZrO2 and SiO2 nanopowders gives rise to a change in the surface profile and in the radiation-chemical yield of molecular hydrogen.

Protective properties of SiO2 with SiO2 and Al2O3 nanoparticles sol-gel coatings deposited on FeCrAl alloys

Five layer SiO2 coatings containing SiO2 or Al2O3 nanopowders were deposited on FeCrAl alloy support by sol-gel method. Studies of protective properties of the coatings were carried out during high temperature cyclic oxidation. Changes in surface topography, structure and chemical composition of the surface layer of FeCrAl alloy were investigated. It has been shown that the type of nanofillers present in the SiO2 coating (about 2.5 wt%) affects morphology of Al2O3 growing scale and determines the heat resistance of FeCrAl alloy. The lowest relative mass change (approx. 1.3%) after 10 oxidation cycles in air at 900 °C (one cycle = 12 h) was measured for the samples with coatings containing hydrophilic nanosilica (Aerosil 380) as filler. The protective efficiency of the coatings in the process of high-temperature oxidation is from 66% to 85%. The thickness of the formed scale and the value of the parabolic rate constant depend on the type of nanopowder in the coating.

Adsorption Performance of DNA onto Magnetic Core-Shell Structure (1-x)Ni0.5Zn0.5Fe₂O₄/xSiO₂ Nanopowders Prepared via Methanol Combustion Process.

Magnetic core-shell structure (1-x)Ni0.5Zn0.5Fe2O4/xSiO2 (x = 0-0.2) nanopowders were successfully prepared via the methanol combustion process, the as-prepared magnetic core-shell structure nanopowders were characterized by XRD, SEM, TEM, HRTEM, BET, and VSM techniques, and the adsorption performance of DNA onto them was investigated. The results showed that the magnetic core-shell structure 0.9Ni0.5Zn0.5Fe2O4/0.1SiO2 nanopowders exhibited a good adsorption capacity of DNA, and the adsorbance of DNA for magnetic core-shell structure 0.9Ni0.5Zn0.5Fe2O4/0.1SiO2 nanopowders was enhanced to 2.8 times for Ni0.5Zn0.5Fe2O4 nanoparticles. The adsorption kinetics of DNA in aqueous solution onto the magnetic core-shell structure 0.9Ni0.5Zn0.5Fe2O4/0.1SiO2 nanopowders at room temperature were investigated, and the kinetics data were in good agreement with the pseudo-first-order kinetic model in the initial DNA concentration of 50 μg/mL.

Fourier Transform IR Spectroscopic Study of Nano-ZrO2 + Nano-SiO2 + Nano-H2O Systems Upon the Action of Gamma Radiation

The radiation decomposition of water in a nano-ZrO2 + nano-SiO2 + H2O system at 300 K by the action of gamma radiation has been studied by Fourier transform IR spectroscopy. Water adsorption in the zirconium and silicon nanooxides is attributed to molecular and dissociative mechanisms. Active intermediates in this radiation-induced heterogeneous decomposition of water were detected including zirconium and silicon hydrides and hydroxyl groups. Variation in the ratio of ZrO2 and SiO2 nanopowders was shown to lead to change in their radiation catalytic activity compared to initial ZrO2.