Amorphous SiO2 Research Articles

<i>In Situ</i> Synthesis of SiO<sub>2</sub> Nanoparticles by Sol-Gel Method on Cotton Fabrics and Investigation of their Physical and Chemical Properties

In this paper, the sol-gel method was used for in-situ synthesis of SiO2nanoparticles (NPs) on cotton fabrics with tetraethyl orthosilicate (TEOS) in the presence of acid and alkaline indicators. The samples were characterized using by(X-ray diffraction)XRD,(scanning electron Microscopy)SEM,(Inductively coupled plasma)ICP, water drop test and also the flame retardant properties were studied by char yield. The SEM images showed that the nanoparticles are spherical in shape and the acidity or alkalinity of the medium has an effect on the formation of particles. The XRD patterns showed the typical diffraction of amorphous SiO2(Si-O short-order structure), also ICP analysis showed that by washing the fabrics, the nanoparticles are still present on the fabric, and this indicated the stability of the washing of the fabrics impregnated with the nanoparticles. By in-situ synthesis of SiO2nanoparticles, the flame retardant properties have been improved significantly and the amount of residual char was increased and samples were observed to be hydrophilic.

The formation mechanism and effect of amorphous SiO2 on the corrosion behaviour of Fe-Cr-Si ODS alloy in LBE at 550 °C

The corrosion behaviour of the newly developed Fe-Cr-Si oxide-dispersion-strengthened alloys in liquid lead–bismuth eutectic at 550 °C was microstructurally studied. The corrosion resistance was enhanced with increasing Si content, attributing to the preferred formation of amorphous SiO2 during the inward diffusion of oxygen. SiO2 promoted the formation of Cr-rich oxides that were uniformly distributed in the inner-oxide layer and matrix, thereby reducing the Fe and O diffusion coefficients and ultimately delaying the formation of the outer magnetite layer and the growth of the inner Cr-rich oxide layer while reducing interfacial defects.

Improved Hygroscopicity and Bioavailability of Solid Dispersion of Red Ginseng Extract with Silicon Dioxide.

This study aims to develop a powder formulation for the Korean red ginseng extract (RGE) and to evaluate its in vitro and in vivo formulation characteristics. The solid dispersion of RGE was prepared with hydrophilic carriers using a freeze-drying method. After conducting the water sorption–desorption isothermogram (relative humidity between 30 and 70% RH), differential scanning calorimetry thermal behavior, dissolution test, and intestinal permeation study, a solid dispersion formulation of RGE and silicon dioxide (RGE-SiO2) was selected. RGE-SiO2 formulation increased intestinal permeability of ginsenoside Rb1 (GRb1), GRb2, GRc, and GRd by 1.6-fold in rat jejunal segments as measured by the Ussing chamber system. A 1.6- to 1.8-fold increase in plasma exposure of GRb1, GRb2, GRc, and GRd in rats was observed following oral administration of RGE-SiO2 (375 mg/kg as RGE). No significant difference was observed in the time to reach maximum concentration (Tmax) and half-life in comparison to those in RGE administered rats (375 mg/kg). In conclusion, formulating solid dispersion of RGE with amorphous SiO2, the powder formulation of RGE was successfully formulated with improved hygroscopicity, increased intestinal permeability, and enhanced oral bioavailability and is therefore suitable for processing solid formulations of RGE product.

LaFeO3 films on SiO2 for supported-Pt catalysts

ABSTRACT LaFeO3 films were deposited to a thickness of 0.5 nm onto amorphous SiO2 by Atomic Layer Deposition and used as supports for Pt. Uniform coverage of the SiO2 was demonstrated by Scanning Transmission Electron Microscopy (STEM) and Temperature Programmed Desorption (TPD) of 2-propanol. The films were found to be amorphous to X-Ray Diffraction, but the reducibility of the Fe in the films and the ability of the films to maintain high Pt dispersions following harsh redox treatments suggested that the perovskite phase was formed on a short length scale. Similar to results found on Pt/LaFeO3/MgAl2O4, Pt/LaFeO3/SiO2 catalysts maintained a high Pt dispersion following redox cycling at 1073 K and showed high activity for CO oxidation following high-temperature reduction. The implications for using these materials is discussed.

Porous SiC–Si3N4 composite ceramics with excellent EMW absorption property prepared by gelcasting using DMAA

The porous SiC–Si3N4 composite ceramics with good EMW absorption properties were prepared by combination of gelcasting and carbothermal reduction. The pre-oxidation of Si3N4 powders significantly improved the rheological properties of slurries (0.06 Pa s at 103.92 s−1) and also suppressed the generation of NH3 and N2 from Si3N4 hydrolysis and reaction between Si3N4 and initiator APS, thereby reducing the pore defects in green bodies and enhancing mechanical properties with a maximum value of 42.88 MPa. With the extension of oxidation time from 0 h to 10 h, the porosity and pore size of porous SiC–Si3N4 composite ceramics increased from approximately 41.86% and 1.0–1.5 μm to 46.33% and ~200 μm due to the production of CO, N2 and gaseous SiO, while the sintering shrinkage decreased from 16.24% to 10.50%. With oxidation time of 2 h, the Si2N2O fibers formed in situ by the reaction of Si3N4 and amorphous SiO2 effectively enhanced the mechanical properties, achieving the highest flexural strength of 129.37 MPa and fracture toughness of 4.25 MPa m1/2. Compared with monolithic Si3N4 ceramics, the electrical conductivity, relative permittivity and dielectric loss were significantly improved by the in-situ introduced PyC from the pyrolysis of three-dimensional network DMAA-MBAM gel in green bodies and the SiC from the carbothermal reduction reaction between PyC and SiO2 and Si3N4. The porous SiC–Si3N4 composite ceramics prepared by the unoxidized Si3N4 powders demonstrated the optimal EMW absorption properties with reflection loss of −22.35 dB at 8.37 GHz and 2 mm thickness, corresponding to the effective bandwidth of 8.20–9.29 GHz, displaying great application potential in EMW absorption fields.

Tunable Adhesive Self-Cleaning Coating with Superhydrophobicity and Photocatalytic Activity.

Superhydrophobic coatings with intelligent properties have attracted much attention because of their wide application in many fields. However, there is a limited amount of literature on superhydrophobic coatings whose wettability and adhesion can be adjusted by UV irradiation and calcination at the same time. In this study, amorphous SiO2 microspheres (A-SiO2) and nano-TiO2 particles (N-TiO2) were used to fabricate A-SiO2/N-TiO2 composites by wet grinding, and then, they were modified with polydimethylsiloxane (PDMS) and sprayed onto substrate surfaces to obtain a tunable adhesive superhydrophobic A-SiO2/N-TiO2@PDMS coating. It is worth noting that the wettability and adhesion of the coating to water droplets could be adjusted by UV irradiation and calcination. The mechanisms of the aforementioned phenomena were studied. Moreover, methyl orange solution could be degraded by the coating due to its photocatalysis. The as-prepared coating had good adaptation to different substrates and outdoor environments. Moreover, the surfaces of these coatings exhibited the same liquid repellency towards different droplets. This research provides an environmental strategy to prepare advanced self-cleaning coatings.

Self-healing improvement strategy of thermally sprayed MoSi2 coating at 1773 K: From calculation to experiment

To improve the limited oxidation resistance of thermally sprayed MoSi2 coating at 1773 K, multiple and multiscale simulation methods as well as experiments verification were adopted to design appropriate modification strategy. Based on viscosity calculation, MoSi2-mullite system which could form aluminosilicate glass, was considered. Compared with MoSi2 coating (80 h, −2.1 wt.%), mullite modified MoSi2 coating exhibit improved self-healing ability and anti-oxidation performance (+2.6 wt.%). The improvement of self-healing ability was concerned with the deconstruction of Al atoms on the SiO rings in the amorphous SiO2 and the formation of AlSiO glass with lower viscosity (104.0 Pa·s).

Preparation and Properties of Rice Hull Ash as the catalysis supporter in the fluidized-bed reactor

This research focuses on the preparation and properties of rice hull ash(RHA). We prepared RHA from combustion of rice husk in the fluidized-bed reactor. The temperature field of the furnace was steady and bellow 850°C to keep SiO2 amorphous. XRD, BET and SEM were applied in the characterization tests to investigate the effect of flow rate(u), the higher primary-secondary wind ratio(i) and relative height of bed material. The optimal combustion condition for preparing RHA was discussed. RHA obtained from rice hull contains abundant amorphous SiO2 (>90%) and the characterization results of RHA show its potential to be a good catalyst supporter.

Optical properties of a low-temperature bioactive glass powders

The bioactive glass powders have been synthesis by sol-gel method at low temperature. The silica used as the starting material in this study is silica purified from natural sand with mass variations for amorphous silica and phase variations (Quartz, amorphous). Analysis of the FTIR curves in samples BA1, BA2, BA3 and BQ showed that a lot of group bonds on Bioactive Glass had been formed for all samples. There are Si-O symmetric stretching functional groups (823-825 cm−1), Si-O-Si symmetric stretching functional groups (1047-1050 cm−1), PO4 functional groups (579-606 cm−1), as well as OH symmetry and asymmetry functional groups (3414-3435 cm−1). Meanwhile, the UV-Vis curve reveals the absorption of ultraviolet wavelengths in the range of 230-300 nm for all samples. Although the trend of sample density (BA1, BA2 and BA3) with the SiO2-amorphous starting material was indicated to decrease with the increase in mass, respectively 0.555 gram/cm3, 0.553 gram/cm3 and 0.543 gram/cm3, the highest density was achieved by the BQ sample of 0.563 gram/cm3. This density value is still higher than the density of bone tissue so that further synthesis is needed by adding an amorphous SiO2 starting material.

Strength degradation of alumina fiber: Irreversible phase transition after high-temperature treatment

The mechanical properties of alumina AF17-20 fiber after high-temperature treatment have been evaluated through tensile tests on single fiber and bundle. The tensile test on single fibers shows that the temperature has little effect on the elastic modulus of the fibers, which stables around 140 GPa. The test on bundles minimizes the personal errors thus giving a more reliable value of tensile strength. In general, as temperature increases, both the Weibull modulus and the tensile strength decrease gradually. De-sized fibers have the highest tensile strength, but inherent defects like pores still cause slight dispersion of the strength. Further, the strength maintains about 90% after treating below 1200 °C, and this insignificant decline is caused by the decrease of amorphous SiO2 and the formation of aluminum silicate. In addition, the severe degradation in strength over 1200 °C is mainly attributed to the appearance and growth of mullite grains, which is only about 60% of the initial value.

Titanosilicate zeolite supported Pt nanoparticles with electronic metal-support interactions for efficient methanol steam reforming

In situ release of hydrogen from liquid organic hydrogen carriers―such as methanol by steam reforming, offers a feasible way to potentially solve the problem of hydrogen storage and transport. Here we report that the titanosilicalite-1 (TS-1) zeolite support efficiently accelerates the Pt catalyzed methanol steam reforming (MSR), giving the hydrogen productivity at 639.7 molH2 molPt−1 h−1 at 250 °C, which steadily outperforms the Pt nanoparticles supported on other carriers, including ZSM-5 zeolite, amorphous SiO2, and TiO2 anatase. Further studies reveal that the electronic metal-support interactions (EMSIs) between Pt and TS-1 zeolite occurs, which modifies Pt nanoparticles surface charge state to accelerate the reaction. More importantly, the interactions could stabilize the Pt nanoparticles, achieving sinter-resistant Pt/TS-1 catalyst in the continuous MSR tests. This finding indicates the important role of heteroatoms in the zeolite framework for supported metal nanoparticles, which open a new way to guide the design of highly efficient heterogeneous catalysts in the future.

Hydrolytic Modification of SiO2 Microspheres with Na2SiO3 and the Performance of Supported Nano-TiO2 Composite Photocatalyst.

Modified microspheres (SiO2-M) were obtained by the hydrolytic modification of silicon dioxide (SiO2) microspheres with Na2SiO3, and then, SiO2-M was used as a carrier to prepare a composite photocatalyst (SiO2-M/TiO2) using the sol-gel method; i.e., nano-TiO2 was loaded on the surface of SiO2-M. The structure, morphology, and photocatalytic properties of SiO2-M/TiO2 were investigated. Besides, the mechanism of the effect of SiO2-M was also explored. The results show that the hydrolytic modification of Na2SiO3 coated the surface of SiO2 microspheres with an amorphous SiO2 shell layer and increased the quantity of hydroxyl groups. The photocatalytic performance of the composite photocatalyst was slightly better than that of pure nano-TiO2 and significantly better than that of the composite photocatalyst supported by unmodified SiO2. Thus, increasing the loading capacity of nano-TiO2, improving the dispersion of TiO2, and increasing the active surface sites are essential factors for improving the functional efficiency of nano-TiO2. This work provides a new concept for the design of composite photocatalysts by optimizing the performance of the carrier.

Micro-mesoporous TiO2/SiO2 nanocomposites: Sol-gel synthesis, characterization, and enhanced photodegradation of quinoline

Micro-mesoporous TiO2/SiO2 nanocomposite powders have been successfully synthesized by the sol-gel process with different TiO2/SiO2 molar ratios and were applied in the UV-photodegradation of quinoline (λ = 254 nm). The structural, morphological, and textural characterization of the powders showed a homogeneous distribution of TiO2 nanoparticles within a porous amorphous SiO2 matrix. Due to the micro-mesoporous character of the materials, their textural characteristics were evaluated by the N2 adsorption method, by comparing BET, DR, Langmuir, and DFT theories. Si60Ti40 powders (60%SiO2/40%TiO2) presented the highest specific surface area (SSA) obtained from BET (SSA = 363 m2g-1), DR (SSA = 482 m2g-1), and Langmuir (SSA = 492 m2g-1) due to the adequate particle size of TiO2 and its high dispersion in the porous matrix. A higher degradation of quinoline in the presence of H2O2 (66%) was achieved using Si80Ti20 powders (80%SiO2/20%TiO2), as compared to pure sol-gel TiO2 powders, (51%) under the same reaction conditions (1 UVC lamp - 250W, t = 180 min). The better performance of the Si80Ti20 nanocomposite could be attributed to the small TiO2 anatase crystallite size (<5.7 nm), high dispersion of these crystallites in the SiO2 matrix, great specific surface area (DR SSA = 342 m2 g−1), and the formation of Ti–O–Si bond, which is associated with new catalytic sites in TiO2/SiO2 composite.

First-principles XANES simulation for oxygen-related defects in Si-O amorphous materials

To understand the chemical reaction during the initial charging in an amorphous negative SiO (a-SiO) electrode for Li-ion batteries, we simulated the O K-edge X-ray absorption near-edge structure (XANES) spectra for oxygen-excess defects in silicon oxide crystals and glasses using the first-principles projector augmented-wave (PAW) method. Oxygen-excess defects, including the oxygen bridge-bonded (OBB) and peroxy linkage (POL) configurations, reproduce the pre-edge peak observed in the experimental spectrum of the as-prepared a-SiO material. It was found that the electronic states contributing to the pre-edge peaks are the σ∗ state of the O-O bond for the OBB and POL configurations, and the π∗ state of the O-O bond for an O2 molecule. The formation energy of these defects is distributed within the amorphous structure, and POL configurations with small formation energies were found in a-SiO. In addition, O2 molecules can exist in a-SiO2, whereas those in a-SiO are incorporated into the bond network. Through the insertion of Li+ ions, the pre-edge peak disappears, and weak peaks appear in the higher-energy region. These correspond to the experimental results in which the pre-edge peak in the O K-edge XANES of the as-prepared a-SiO disappeared during the initial charging. The chemical reaction between POL configurations in a-SiO and Li+ ions during the initial charging is thought to play an important role in improving cycle characteristics.

Temperature Effects on Properties of Rice Husk Biochar and Calcinated Burkina Phosphate Rock

Rice husk biochar (RHB) and phosphate rock (PR) are locally accessible resources that poor farmers in Sub-Saharan Africa (SSA) can utilize to increase rice productivity. However, biochars are variable depending on feedstock, pyrolysis temperature, and duration. Phosphate rocks from SSA are of low solubility. The goal of this study was to determine whether pyrolysis of rice husk (RH), calcination of PR, and the calcination/pyrolysis of a RHB-PR mixture at 300 °C, 500 °C, and 700 °C can increase formic acid (FA)- extractable phosphorous (P). The properties of these RHBs were compared to the properties of RHB produced through a simple farmer-friendly pyrolysis technique termed “Kun-tan”. Properties of calcinated PR were also compared to the raw PR. Quartz formed from amorphous SiO2 during RH pyrolysis and was the dominant mineral phase in the biochars, irrespective of the pyrolysis temperature. Formic acid-extractable P content, pH, and ash content of the biochars increased with increasing pyrolysis temperature. At 700 °C, FA-extractable P content of the RHB was 219% more than the feedstock. Hydroxyapatite and quartz were the dominant minerals in the PR irrespective of calcination temperature, indicating that hydroxyapatite and quartz were stable to at least 700 °C. Rather, calcination decreased the FA-extractable P content of the PR.

Core‐shell structured BaTiO3@SiO2@PDA for high dielectric property nanocomposites with ultrahigh energy density

AbstractFlexible nanocomposite dielectrics with high dielectric constant and discharge energy density have broad application prospects in the field of energy storage. However, dielectrics with high dielectric constant tend to have a high dielectric loss. Herein, we prepared a dielectric composite material with ultra‐high discharge energy density by modifying the interface between nanoparticles and poly(vinylidene fluoride‐co‐hexafluoropropylene) (P[VDF‐HFP]). After coating a shell of insulating amorphous SiO2 (~7 nm) outside the barium titanate (BT), the electric field concentration and current density inside BT particles can be significantly reduced. In addition, coating the SiO2 shell with a polydopamine (PDA) shell (~7 nm) not only enhances the interface interaction between the nanoparticles and the polymer matrix, but also can form lots of microcapacitors in the composite. As a result, an ultra‐high discharge energy density of 13.78 J/cm3 at the expense of relatively inconspicuous efficiency (~59.8%) in the BT@SiO2@PDA/P (VDF‐HFP) with 2.5 wt% loading has been achieved under 460 kV/mm. This is mainly attributed to the increases of dielectric constant from 12.1 to 14.2 and the relatively low dielectric loss (0.086) at 100 Hz. Moreover, compared with the pure P (VDF‐HFP) (400 kV/mm), the breakdown voltage of the composite with 2.5 wt% loading is surged to 460 kV/mm, which benefited from the hindrance of nanoparticles on carrier migration at low content. This work has realized a thin‐film dielectric with ultra‐high discharge energy density through a novel design of the nanoparticle structure, providing a theoretical direction for the development of polymer dielectric capacitors.

Coherence in the Ferroelectric A3ClO (A = Li, Na) Family of Electrolytes.

Coherence is a major caveat in quantum computing. While phonons and electrons are weakly coupled in a glass, topological insulators strongly depend on the electron-phonon coupling. Knowledge of the electron−phonon interaction at conducting surfaces is relevant from a fundamental point of view as well as for various applications, such as two-dimensional and quasi-1D superconductivity in nanotechnology. Similarly, the electron−phonon interaction plays a relevant role in other transport properties e.g., thermoelectricity, low-dimensional systems as layered Bi and Sb chalcogenides, and quasi-crystalline materials. Glass-electrolyte ferroelectric energy storage cells exhibit self-charge and self-cycling related to topological superconductivity and electron-phonon coupling; phonon coherence is therefore important. By recurring to ab initio molecular dynamics, it was demonstrated the tendency of the Li3ClO, Li2.92Ba0.04ClO, Na3ClO, and Na2.92Ba0.04ClO ferroelectric-electrolytes to keep phonon oscillation coherence for a short lapse of time in ps. Double-well energy potentials were obtained while the electrolyte systems were thermostatted in a heat bath at a constant temperature. The latter occurrences indicate ferroelectric type behavior but do not justify the coherent self-oscillations observed in all types of cells containing these families of electrolytes and, therefore, an emergent type phenomenon where the full cell works as a feedback system allowing oscillations coherence must be realized. A comparison with amorphous SiO2 was performed and the specific heats for the various species were calculated.

Preparation of Synthetic β-Wollastonite Produced from Amorphous SiO&lt;sub&gt;2&lt;/sub&gt; Bamboo Leaf Ash and &lt;i&gt;Meretix meretix&lt;/i&gt; Shell

The objective of this study is to produce b-wollastonite from amorphous SiO2 obtained from bamboo leaf ash (BLA) and CaO derived from meretix meretix shell (MMS) using solid state reaction. Amorphous SiO2 utilization in this work obtained by precipitation of BLA and calcined at 700 °C for 3 h, whereas CaO MMS was generated by calcination of MMS at 1000 °C for 5 h. High purity amorphous SiO2 obtained was 99.325 wt % and CaO purity obtained was 97.531 wt %. Single phase of b-wollastonite found in this study as confirmed by XRD results. The vibrations at 933.42 , 904.49, and 890.99 cm-1 were caused by the Si-O-Ca bond, which shows the bonding of b-wollastonite obtained from the FTIR. The acicular morphology of b-wollastonite with average grains size of 0.28,0.33 and 0.71 mm was obtained for the samples calcined at 900 , 1000 , and 1100 °C respectively.

Investigations on continuous-wave laser and pulsed laser induced controllable ablation of SiCf/SiC composites

To lay a foundation for the feasibility exploration of laser-induced ablation-assisted machining for SiCf/SiC composites, combined with numerical simulation and experiments, the laser-induced ablation mechanism of SiCf/SiC composites was studied, and the relationship between laser parameters and ablation depth was analyzed. The laser-induced ablation products of SiCf/SiC composites mainly consisted of recrystallized 3C-SiC and amorphous SiO2, which were powdery and porous. According to the stratification characteristic, the ablation products were divided into attached smoke dust layer, sublimate recrystallization layer, heat-affected layer, and unaffected layer from the surface to the inside of the material. By adjusting the laser parameters (significant factors were the scanning speed and the scanning spacing), the depth of laser-induced ablation was adjustable and controllable. The ablation depth was greater in continuous-wave (CW) mode due to the continuous energy input. Therefore, CW laser is more suitable for generating larger and various ablation depths to match various cutting allowances.

Improvement High Purity Biogenic Amorphous SiO&lt;sub&gt;2&lt;/sub&gt; Derived from Rice Husk Ash: Synthesis and its Characterization

In this work a simple process for the production of high purity biogenic amorphous SiO2 derived from rice husk ash have been studied. Rice husk ash obtained from heat treatment of rice husk and citric acid leaching of rice husk at 700 o C for 6 h. Improvement of purity SiO2 from rice husk ash conducted by precipitation technique. The precipitated SiO2 particles obtained were characterized by x-ray fluorescence (XRF) analysis, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction analysis (XRD). The XRF result shows that the high purity of biogenic amorphous SiO2 obtained is 99.258 %. The XRD result shows the silica have amorphous phase and for the FTIR results shows bending and stretching vibration of Si-O and Si-O-Si.