Showing papers on "Silicon dioxide published in 2021"

Hydrophobic nanosilica-stabilized graphite particles for improving thermal conductivity of paraffin wax-based phase-change materials

Abstract: Phase change materials based on paraffin wax are characterized with low thermal conductivity, which could be improved by the addition of particles of a heat-conducting material, for example, graphite. However, graphite particles agglomerate in molten paraffin wax matrix and settle. In this study, the use of hydrophobic nano-sized silicon dioxide as a stabilizer was considered to obtain stable dispersions of graphite in paraffin wax. Rheological and thermophysical properties of paraffin-based mixtures containing from 1 to 5 vol. % of hydrophobic silica and from 1 to 15 vol. % of graphite were investigated. At the concentration of 3 vol. %, silica nanoparticles form a percolation structure, which is expressed in the emergence of the yield stress that is capable to prevent the sedimentation of graphite particles introduced into the mixture. It allows obtaining dispersions that are stable both in time and at passage of cooling–heating cycles. The joint influence of silica and graphite fillers on the ability of paraffin wax to accumulate and conduct heat was investigated. Thermal conductivity of dispersions at the introduction of graphite increases according to the Maxwell's model, which allows improving the thermal conductivity on 33 % from initial value at the introduction of 15 vol. % of graphite.

Investigation of oxidation mechanism of SiC single crystal for plasma electrochemical oxidation

Abstract: Silicon carbide (SiC) is a hard-to-machine material due to its high hardness and chemical stability, and usually an essential step in chemical mechanical polishing (CMP) is to modify the SiC surface without introducing damage or other elements, then to polish the modified surface. For high quality and high efficiency surface modification of SiC, a green and promising oxidation approach named plasma electrochemical oxidation (PECO) is proposed. Experiments were conducted to investigate the oxidation mechanism of PECO to enable its application for CMP. The oxidized surface was detected by scanning electron microscope (SEM) and atomic force microscopy (AFM), many atomic-scale protuberances were confirmed to be introduced in the PECO process. Through the analysis of energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), it is proved that the SiC surface has been oxidized into SiO2 and a transition layer (silicon oxycarbide) is formed between SiO2 and SiC. Based on the analysis of the cross section image of the oxidized layer, electrolyte–SiC interface chemical reaction and oxidation layer formation mechanism are illustrated to explain the oxidation mechanism. Silicon dioxide growth process model is proposed and illustrated that the phrase of protuberances growth change from charge transfer to diffusion. The present work offers an alternative approach to modify SiC surface, and provides a reference for chemical and mechanical synergetic effect applied in CMP.

Photocatalytic Phenol Degradation by Silica-Modified Titanium Dioxide

Abstract: Titanium dioxide (TiO2) has been widely applied as a photocatalyst for wastewater treatment due to its high photocatalytic activity and it can remove various harmful organic pollutants effectively. Under heated system, however, TiO2 is prone to agglomeration that decrease its abilities as a photocatalyst. In order to overcome the agglomeration and increase its thermal resistance, addition of silica (SiO2) as supporting material is proposed in this research. Silica or silicon dioxide can be extracted from natural resources such as beach sand. Here, we report the application of a composite photocatalyst of TiO2/SiO2 to remove phenolic compounds in wastewater. The photocatalyst was synthesized by adding SiO2 from beach sand onto TiO2 through impregnation methods. The results of the X-ray diffraction (XRD) showed that TiO2 was present in the anatase phase. The highest crystallinity was obtained by TiO2/SiO2 ratios of 7:1. SEM results showed that the shape of the particles was spherical. Further characterizations were conducted using Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis, and a particle size analyzer (PSA). By using the optimized condition, 96.05% phenol was degraded by the synthesized photocatalyst of TiO2/SiO2, under UV irradiation for 120 min. The efficiency of the TiO2/SiO2 is 3.5 times better than commercial TiO2 P25 for the Langmuir–Hinshelwood first-order kinetic model.

Signaling Pathways Regulated by Silica Nanoparticles

Abstract: Silica nanoparticles are a class of molecules commonly used in drug or gene delivery systems that either facilitate the delivery of therapeutics to specific drug targets or enable the efficient delivery of constructed gene products into biological systems. Some in vivo or in vitro studies have demonstrated the toxic effects of silica nanoparticles. Despite the availability of risk management tools in response to the growing use of synthetic silica in commercial products, the molecular mechanism of toxicity induced by silica nanoparticles is not well characterized. The purpose of this study was to elucidate the effects of silica nanoparticle exposure in three types of cells including human aortic endothelial cells, mouse-derived macrophages, and A549 non-small cell lung cancer cells using toxicogenomic analysis. The results indicated that among all three cell types, the TNF and MAPK signaling pathways were the common pathways upregulated by silica nanoparticles. These findings may provide insight into the effects of silica nanoparticle exposure in the human body and the possible mechanism of toxicity.

Realization of a Graphene/PMMA Acoustic Capacitive Sensor Released by Silicon Dioxide Sacrificial Layer.

Abstract: We report the realization of an acoustic capacitive microphone formed by graphene/poly(methyl methacrylate) (PMMA). It is the first time that the ultra-large graphene/PMMA membrane suspended fully over the cavity has been fabricated by releasing the silicon dioxide sacrificial layer underneath the membrane. The novelty in the fabrication method is that the silicon dioxide layer has been etched by hydrogen fluoride vapor from the back of the partly etched silicon substrate. Using the new process, the ultra-large graphene/PMMA membrane, with a diameter to thickness ratio of 7800, has been suspended over the cavity with a 2 μm air gap. The spacing of 2 μm is the minimum gap over the graphene-based acoustic capacitive microphones which have been reported so far. The static deformation of the suspended graphene/PMMA membrane after silicon dioxide has been etched is estimated to be 270 nm. The aspect ratio of the membrane's diameter over its static deformation is around 13,000, which shows that the graphene/PMMA membrane with a diameter of a few millimeters can be transferred and suspended over the substrate with relatively small deformation by releasing the sacrificial silicon dioxide layer. The dynamic behavior of the device under electrostatic actuation has been characterized. The acoustic response of the graphene/PMMA capacitive microphone has been measured, and the sensitivity has been observed to be -47.5 dB V (4.22 mV/Pa) ± 10%. The strain in the graphene/PMMA membrane is estimated to be 0.034%.

Application of Silicon Dioxide as the Inert Component or Oxide Component Enhancer in ANFO

Abstract: Non-ideal explosives with differing contents of silicon dioxide (silica or dioxosilane) added in the form of powder and gel were tested. Measurements of structure, crystallinity and morphology were performed by means of infrared spectroscopy (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). IR and XRD analysis revealed a lack of SiO2 influence on the non-ideal explosive structure. SEM analysis indicated that all the surface deformations of ammonium nitrate(V) prill were filled by a thin fuel film layer on which SiO2 was present. The additional calculations of selected theoretical properties of non-ideal compositions were made using ZMWCyw software. Based on this, it was established that the optimum semimetal content was 1.0 wt.%. Blasting tests confirmed that the addition of 1.0 wt.% SiO2 to the Ammonium Nitrate Fuel Oil (ANFO) resulted in the lowest volume of post-blast fumes. Moreover, it was established that finer SiO2 powder cannot be used as the oxide component enhancer due to the inhibition of detonation reaction. SiO2 should be used only as an inert component.

Amorphous silica nanoparticles induced spleen and liver toxicity after acute intravenous exposure in male and female rats

Abstract: Synthetic amorphous silica (SAS) nanomaterial – consisting of aggregates and agglomerates of primary silicon dioxide (SiO2) particles in the nanorange (<100 nm) – is commonly used as excipient in p...

Graphene sheet-encased silica/sulfur composite cathode for improved cyclability of lithium-sulfur batteries

Abstract: The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To inhibit the shuttle effect, a combination of graphene oxide and silica has been adopted in this work. Here, two different ratios of sulfur/silicon dioxide/partially reduced graphene oxide (S/SiO2/prGO - 70:20:10 and 70:10:20) composite materials were prepared via a melt diffusion method and were used as a cathode for a Li-S battery. The wrinkled sheets of partially reduced graphene oxide not only provide a conductive network for electron transport, but also ease the volume changes of active material during cycling. The 20 wt% of prGO present in the S/SiO2/prGO cathode delivers initial discharge capacity of 783 mAh g−1 at 0.2 C and remains at 491 mAh g−1 over 300 cycles, with low capacity decay rate of 0.12% per cycle. The better electrochemical performance indicates that the electrode containing 20 wt% of prGO with silica effectively suppresses the “shuttle effect” of polysulfide dissolution.

Ion-beam induced quasi-dynamic continual disorder in Bi-implanted Hongan silica glass

Abstract: We have studied optical properties of glassy silicon dioxide (Hongan Silica Glass Store, China) irradiated with 30 keV bismuth ions A broadening with a low-energy shift of absorption edge was found for the samples treated with 1 × 1016 – 3 × 1017 сm–2 ion fluences The dose dependences of characteristic Urbach energy and width of the optical gap for direct interband transitions were determined and plotted Based on the linear-type correlation between Urbach energy and optical gap width, the D/K ratio of deformation potential constants was established as well The constancy of the D/K ratio for silicon dioxide at different fluences of bismuth ions indicates the proportionality between the values of the optical gap and band tails length, which are associated with the static atomic disorder of SiO2 host-matrix An explanation of the obtained regularities was given using the quasi-dynamic (thermodynamic) approach It was postulated that structural damage caused by ion-beam treatment determines Boltzmann entropy's magnitude as a combination of system various microstates The functional dependence of σ-parameter (disordering effective cross-section) on the ion fluence has been established and proved experimentally

Thermal and mechanical properties of poly(lactic acid) filled with modified silicon dioxide: importance of the surface area

Abstract: In this research work, the effect of the change in the surface area of silicon dioxide nanoparticles of the same size on mechanical properties of poly(lactic acid) nanocomposites (PLA) was studied, as well as the role of coupling agent amount in the compatibility of these nanomaterials We consider a spherical silicon dioxide with a surface area of 170–200 m2/g (labeled as S–SiO2) and another considered amorphous with a surface area of 180–600 m2/g (labeled as P-SiO2) This surface areas difference plays an important role in modifying of nanoparticles polarity by incorporating a coupling agent and its integration into partially polar polymers According to obtained results, for nanomaterials with high surface area, it was observed while increasing coupling agent amount, the elasticity of the composite was observed to increase In contrast, in nanomaterials with spherical nanoparticles, it was observed that as the amount of coupling agent decreases, the resistance of the material increases, reaching a maximum when a 10:2 ratio is used It was observed that behaviors for both nanoparticles were different, which gives an idea that the incorporation of nanoparticles in polymers is not an issue of coupling agent or quantity only, it is more important as it is arranged on the surface This kind of couplings does not only affect mechanical properties, since the thermal behavior of the material was also influenced, where it was observed that particles with low surface area modify the crystallization rate when they have different percentages of coupling agent on the surface Furthermore, it is observed that the incorporation of nanoparticles with high surface areas area does not modify the crystallization rate significantly Besides, in both cases, it was observed that the highest crystallization rate is reached when a 10:2 ratio is used However, the energy required to form crystals remains unchanged Therefore, it is considered that the incorporation of nanoparticles only affects the crystal formation rate without disturbing the energy requirement for crystal formation Finally, a maximum in the 10:2 ratio was observed for the compatibility in both particles, which was manifested in an increase in the storage module through a dynamic mechanical analysis The rate of crystal formation as well as the number of formed crystals have a considerable effect on mechanical properties of nanocomposites when the surface area is modified

Water Forms on the Surface and in the Bulk of Silicon Dioxide

Abstract: Thermodynamic characteristics and water evaporation mechanism from silica structure in temperature range 100–1000°С have been studied by thermogravimetry, mass spectrometry, 1Н and 29Si NMR. It has been shown that liquid, surface-bound, and molecular-dispersed water is present on the surface and in the bulk of silica particles. The role of different (ОН)n groups in the structural change of silica upon thermal and thermal steam treatment has been shown. A method for preparation of anhydrous silica used in the manufacture of high-quality quartz glass has been proposed.

Biogenic silicon dioxide nanoparticles processed from natural sources

Abstract: The main purpose of this study is to obtain the biogenic silica nanoparticles from selected types of plants and thorough characterization. Plants create SiO2 nanoparticles while growing from the co...

Resonant mode engineering in silicon compatible multilayer guided-mode resonance structures under gaussian beam excitation condition

Abstract: In this work we present detailed electromagnetic design, fabrication, and experimental study of silicon-compatible, step-index, multilayer guided-mode resonance (GMR) structures. The proposed multilayer stack consists of an amorphous silicon overlayer deposited above a silicon nitride layer on top of one-dimensional sub-wavelength silicon dioxide grating structures. The silicon nitride layer combined with the underlying silicon dioxide gratings define the high-quality factor resonances in the 1500-1600 nm wavelength range. The addition of the amorphous silicon overlayer with varying thickness further red-shifts the resonance combined with the ability to engineer the resonant field profile and its evanescent field fraction. Realistic Gaussian beam excitation with increasing angular spread exciting finite extent gratings results in reduced contrast and quality factor of the designed resonances are found to decrease. We experimentally study the linear transmission spectra for the fabricated structures with amorphous silicon overlayer thickness of 10, 50 and 100 nm. The measured optical resonances are at 1580, 1813 and 2104 nm respectively, showing good agreement with Gaussian-beam excitation studies. As an application of the proposed structures, we demonstrate third-harmonic generation (THG) enhancement from the 10 nm amorphous silicon overlayer showing 19 and 178-times enhancement in THG for fundamental excitation with 11o and 4o angular spread respectively. The present work utilizes the thinnest amorphous silicon layer to achieve optical resonances in the near-infrared wavelength and consequently ensures minimum absorption of the generated THG signal when used for nonlinear optical enhancement studies.

Synthesis and comparative characterization of functionalized nanoporous silica obtained from tetrachloro- and tetraethoxysilane by a sol-gel method

Abstract: Functionalized silica supports were synthesized under various conditions using tetraethoxysilane (TEOS) and silicon tetrachloride (STC) as precursors by the sol-gel method. The polyethylene glycol ...

Unprotected sidewalls of implantable silicon-based neural probes and conformal coating as a solution.

Abstract: Silicon-based implantable neural devices have great translational potential as a means to deliver various treatments for neurological disorders However, they are currently held back by uncertain longevity following chronic exposure to body fluids Conventional deposition techniques cover only the horizontal surfaces which contain active electronics, electrode sites, and conducting traces As a result, a vast majority of today’s silicon devices leave their vertical sidewalls exposed without protection In this work, we investigated two batch-process silicon dioxide deposition methods separately and in combination: atomic layer deposition and inductively-coupled plasma chemical vapor deposition We then utilized a rapid soak test involving potassium hydroxide to evaluate the coverage quality of each protection strategy Focused ion beam cross sectioning, scanning electron microscopy, and 3D extrapolation enabled us to characterize and quantify the effectiveness of the deposition methods Results showed that bare silicon sidewalls suffered the most dissolution whereas ALD silicon dioxide provided the best protection, demonstrating its effectiveness as a promising batch process technique to mitigate silicon sidewall corrosion in chronic applications

Novel electroblowing synthesis of tin dioxide and composite tin dioxide/silicon dioxide submicron fibers for cobalt(II) uptake

Abstract: Nanoscale SnO2 has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO2 and composite SnO2/SiO2 submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures and morphologies. In all the fibers SnO2 was detected by XRD indicating the SnO2/SiO2 fibers to be composite instead of complete mixtures. We studied the Co2+ separation ability of the fibers, since 60Co is a problematic contaminant in nuclear power plant wastewaters. Both SnO2 and SnO2/SiO2 fibers had an excellent Co2+ uptake with their highest uptake/Kd values being 99.82%/281 000 mL g−1 and 99.79%/234 000 mL g−1, respectively. Compared to the bare SnO2 fibers, the SiO2 component improved the elasticity and mechanical strength of the composite fibers which is advantageous in dynamic column operation.

Are Biogenic and Pyrogenic Mesoporous SiO2 Nanoparticles Safe for Normal Cells

Abstract: Silicon dioxide, in the form of nanoparticles, possesses unique physicochemical properties (size, shape, and a large surface to volume ratio). Therefore, it is one of the most promising materials used in biomedicine. In this paper, we compare the biological effects of both mesoporous silica nanoparticles extracted from Urtica dioica L. and pyrogenic material. Both SEM and TEM investigations confirmed the size range of tested nanoparticles was between 6 and 20 nanometers and their amorphous structure. The cytotoxic activity of the compounds and intracellular ROS were determined in relation to cells HMEC-1 and erythrocytes. The cytotoxic effects of SiO2 NPs were determined after exposure to different concentrations and three periods of incubation. The same effects for endothelial cells were tested under the same range of concentrations but after 2 and 24 h of exposure to erythrocytes. The cell viability was measured using spectrophotometric and fluorimetric assays, and the impact of the nanoparticles on the level of intracellular ROS. The obtained results indicated that bioSiO2 NPs, present higher toxicity than pyrogenic NPs and have a higher influence on ROS production. Mesoporous silica nanoparticles show good hemocompatibility but after a 24 h incubation of erythrocytes with silica, the increase in hemolysis process, the decrease in osmotic resistance of red blood cells, and shape of erythrocytes changed were observed.

Study of the Role of Void and Residual Silicon Dioxide on the Electrochemical Performance of Silicon Nanoparticles Encapsulated by Graphene.

Abstract: Silicon nanoparticles are used to enhance the anode specific capacity for the lithium-ion cell technology. Due to the mechanical deficiencies of silicon during lithiation and delithiation, one of the many strategies that have been proposed consists of enwrapping the silicon nanoparticles with graphene and creating a void area between them so as to accommodate the large volume changes that occur in the silicon nanoparticle. This work aims to investigate the electrochemical performance and the associated kinetics of the hollow outer shell nanoparticles. To this end, we prepared hollow outer shell silicon nanoparticles (nps) enwrapped with graphene by using thermally grown silicon dioxide as a sacrificial layer, ball milling to enwrap silicon particles with graphene and hydro fluorine (HF) to etch the sacrificial SiO2 layer. In addition, in order to offer a wider vision on the electrochemical behavior of the hollow outer shell Si nps, we also prepared all the possible in-between process stages of nps and corresponding electrodes (i.e., bare Si nps, bare Si nps enwrapped with graphene, Si/SiO2 nps and Si/SiO2 nps enwrapped with graphene). The morphology of all particles revealed the existence of graphene encapsulation, void, and a residual layer of silicon dioxide depending on the process of each nanoparticle. Corresponding electrodes were prepared and studied in half cell configurations by means of galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that nanoparticles encapsulated with graphene demonstrated high specific capacity but limited cycle life. In contrast, nanoparticles with void and/or SiO2 were able to deliver improved cycle life. It is suggested that the existence of the void and/or residual SiO2 layer limits the formation of rich LiXSi alloys in the core silicon nanoparticle, providing higher mechanical stability during the lithiation and delithiation processes.

Selective area growth of cubic gallium nitride on silicon (001) and 3C-silicon carbide (001)

Abstract: Selective area growth of cubic gallium nitride is investigated in a plasma assisted molecular beam epitaxy setup. 380 μm thick silicon (001) and 10 μm thick 3C-silicon carbide (001), grown on 500 μm silicon (001), were used as substrates and structured with silicon dioxide masks. Selective area growth on silicon and 3C-silicon carbide was tested for both thermal and plasma deposited oxides. Multiple growth series showed that gallium nitride coverage of silicon dioxide vanished at growth temperatures of 870 °C for silicon substrates and at a surface temperature of 930 °C for 3C-silicon carbide substrates. Whereas gallium nitride is grown in its hexagonal form on silicon substrates, phase pure cubic gallium nitride could selectively be grown on the 3C-silicon carbide template. The cubic phase is verified by high resolution x-ray diffraction and low temperature photoluminescence measurements. The photoluminescence measurements prove that gallium nitride condensed selectively on the 3C-silicon carbide surfaces uncovered by silicon dioxide.