Mixture Of SiO2 Research Articles

A Fourier Transform-Induced Data Process for Label-Free Selective Nanopore Analysis under Sinusoidal Voltage Excitations.

Nanopore analysis based on a resistive-pulse technique is an attractive tool for single-molecule detection in different fields, but it suffers a great drawback in selectivity. A common solution to this challenge is to add extra sensing aptamers and labels to analytes by improving the sensitivity of their pulses for distinguishing. Compared to the labeling methods, we alternatively develop and demonstrate a novel data process for label-free nanopore analysis that enables the conversion of resistive current signals to more specific frequency domain phase angle features with the contribution from both sinusoidal voltage excitation and Fourier transform. In particular, we find that the transmural capacitance induced by nanoparticle translocations under a sinusoidal voltage plays an important role in this process, making phase angle features more pronounced. In practical applications, the method is successfully applied to directly distinguish the translocation events through a nanopipette by their unique phase angles for similarly sized SiO2, Ag, and Au nanoparticles and soft living organisms of HeLa and LoVo and even in a more complicated case of a SiO2, Ag, and Au nanoparticle mixture.

Use of computational thermodynamics software to determine the influence of CaO, FeO and SiO2 on hot metal dephosphorization efficiency

The properties of the mixtures used in hot metal dephosphorization, such as solid and liquid fraction phases, CaO and FeO activity and viscosity, are determinant for the process efficiency. The influence of these properties on hot metal dephosphorization were studied for CaO–FeO–SiO2 mixtures. The experiments were carried out at 1400 °C, in MgO-C crucibles, where the mixtures were added to the hot metal. Metal samples were taken at different times to measure the variation of phosphorus (P) content over time. The initial mixtures and final slags properties were determined by computational thermodynamics software FactSage 7.2. A parameter named Dephosphorization Factor (FDeP), that measures the efficiency of the initial mixtures and final slag, in hot metal dephosphorization was used. It was found that the FDeP presents a high correlation (R2) with the dephosphorization efficiency and can be used to predict which slag will be the most efficient.

Interaction of Fluorocarbon with Silicon Monoxide and Processes of SiC Nanowire Formation

A study of the processes of the thermal carbonization of silicon monoxide in the presence of nonstoichiometric carbon monofluoride demonstrated that raising the annealing temperature of mixtures of SiO and CFx powders in a quasi-closed volume to 1000°C and higher leads to the formation of whisker-like SiC nanocrystals. It is found that, in parallel with the known crystallization of SiC nanowires as a result of the interaction of SiO vapor with carbon monoxide, the previously undescribed interaction of CO with gas-phase silicon difluoride SiF2 takes part in their formation. At temperatures below 1200°C, this reaction is dominant and makes the most pronounced contribution to the yield of SiC nanowires.

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.

Artefatos arqueológicos de cherte de Atapuerca (Burgos, Espanha): caracterização, causas de deterioração e seleção de produtos de consolidação compatíveis

Chert tools from Galería and Gran Dolina Caves, located in the Sierra de Atapuerca site complex (Burgos, Spain), were characterized (macro-visual inspection, mineralogical phases, degree of crystallinity, soluble salts, surface morphology and optical surface roughness) and compared to chert samples collected from the surrounding Atapuerca mountain range. The chert tools were studied to determine their causes of decay and for selecting the most compatible consolidation treatments. It was found that samples solely containing quartz were not significantly altered and required little conservation treatment compared to those that contained quartz and moganite, which were more weathered and powdery, requiring consolidation. The efficacy of the consolidating products traditionally used by conservators (acrylic resin and ethyl silicate) to preserve these chert remains, together with novel nanoparticle-based products (SiO2 and a mixture of SiO2 and Ca(OH)2 nanoparticles) were assessed in this study. Changes produced by these consolidating products in the physical (surface morphology and cohesion) and aesthetic properties of the chert tools were evaluated using non-destructive techniques (peeling test, spectrophotometry and optical surface roughness), followed by destructive techniques, such as SEM and XRD.

Processing of the Nd2O3:SiO2 system by Laser Floating Zone in air

Highly textured polycrystalline fibres of monoclinic P21/c Nd2SiO5 and hexagonal P63/m Nd9.33(SiO4)6O2 phases were obtained by Laser Floating Zone in air from stoichiometric mixtures of Nd2O3 and SiO2 changing the pulling rate from 10 to 400 mm/h. Distribution of phases barely varied due to the incongruent melt of the Nd2O3:SiO2 system, resulting in fibres adequate for microwave devices owing to the dielectric character of the Nd2SiO5 phase. Raman analysis was performed in this material for the first time.

Effect of hydrogen embrittlement and non-metallic inclusions on tensile fracture properties of 55CrSi spring steel

The tensile fracture behavior of 55CrSi spring steels were investigated. The results demonstrate that interior inclusion and hydrogen level has a significant effect on ductility and a minimal effect on tensile strength of the spring steel. It was due to the effect of cracking from MgO-Al2O3 spinel inclusion or the inclusions with a mixture of CaO, SiO2 and part of Al2O3 due to hydrogen. The results of SEM showed that the ductility reduction is connected with the formation of ‘fisheye’ which formed under the influence of mobile hydrogen. For the specimen containing MgO-Al2O3 spinel inclusion, the fracture surface in the ‘fisheye’ area is mainly composed of three regions including typical quasi-cleavage mixed intergranular fracture, dimple mixed transgranular fractures and ductile fracture from the interior to the edge, whereas there is no obvious transition zone from brittle fracture to dimple fracture in the ‘fisheye’ area of the specimen containing inclusions with a mixture of CaO, SiO2 and part of Al2O3.

Influence of the Mineral Content on the Emissivity of Hydrothermal Char

AbstractThe influence of minerals on solid fuel conversion is an important topic and has so far been addressed focusing mainly on the catalytic effects. Here, the impact of iron oxide on the emissivity of burning char particles was investigated. Synthetic, hydrothermally carbonized char was doped with SiO2 or with a mixture of SiO2 and Fe2O3. The sample was then exposed to an oxy‐fuel atmosphere in a laboratory reactor. An established pyrometer/infrared (IR) spectrometer setup was used to measure the size, temperature, and IR radiation of single burning particles. Based on these measurements, the spectral and total emissivity in the near‐IR (1.25–2.25 μm) and the total emissivity in the mid‐IR region (2.4–5.5 μm) were calculated. The results show that the iron content directly influences the emissivity of char during combustion.

Modeling of the Thermochemical Conversion of Biomass in Cement Rotary Kiln

Because of the depletion of fossil fuels and because of its increasing cost, waste has been used as alternative fuels in cement rotary kilns for several years. In order to fulfil the requirements of environmental protection and quality of the final product, it is necessary to understand and quantify the different processes occurring in the kiln. The aim of our work is to develop a mathematical model of the processes occurring in the kiln. This model will rely on the coupling between a CFD model and homemade software. More precisely, the CFD model, which will be fully three-dimensional will account for the homogeneous processes taking place in the freeboard of the bed of material being processed. This bed of material will be at the center of the second model which will represent it as a 1D plug flow reactor. In the present work, we focus on this 1D model. We first give insights on the main assumptions on which the model relies, and information on the reaction pathway leading to the production of cement. Indeed, it is considered that the bed is composed of a mixture of CaCO3, MgCO3, Al2O3, SiO2, Fe2O3, MgO, CaO, C2S, C3A, C4AF and C3S undergoing thermochemical transformation. The bed under consideration is also composed of biomass (agricultural residues). During its transformation (pyrolysis, combustion of volatiles, combustion of the pyrolysis residue), this material contributes to thermal equilibrium of the reactor, by carrying the energy associated to its complete combustion. In this paper, the different equations that translate into mathematical formalism the processes of transport of the bed as well as mass and energy balance are also presented. The results show that the cement obtained complies with the requirements of Portland cements (73.06% of Silicates and 18.76% of Aluminates), the conversion of the biomass is total (100%), and the specific energy consumption is almost in conformity with the values of literature.

Improving electrical properties of ZnO–Bi2O3–Sb2O3–MnO2 varistors by doping with pre-synthesized Bi–Si–O phase

Abstract The electric properties and microstructure of ZnO -Bi2O3– Sb2O3– MnO2 (ZBSM) varistor ceramics as a function of pre-synthesized mixture of 6Bi2O3 SiO2 (Bi–Si–O) were investigated. The introduction of Bi–Si–O increases liquid phase content during the sintering process, accelerating the solid solubility of MnO2, Sb2O3 and possibly partial Si ions towards ZnO grains. As results, the interface state density significantly increases to 16.43 × 1016/m2 in the 4 wt% Bi–Si–O ZBSM ceramic, which leads to the highest value of barrier height of 5.87 eV and nonlinear coefficient of 54.56. At the same time, the electric breakdown voltage and leakage current density decreases to 613.82 V/mm and 0.001 μA mm−2, respectively. Besides, grain boundary resistance gradually increases with increasing Bi–Si–O dopant (x ≤ 4 wt%) and then decreases sharply to a very low value when x = 6 wt%, which consists with the variation of leakage current density. Furthermore, only one relaxation occurred in ZBSM-xBi-Si-O varistors which can be confirmed by the Cole-Cole plot analysis. Oxygen absorption and ion migration mechanisms are used to explain the enhancement of nonlinear electrical properties.

Methane decomposition over strontium promoted iron catalyst: effect of different ratio of Al/Si support on hydrogen yield

The performance of a 5% Sr-promoted Fe catalyst on CH4 decomposition was investigated with the aid of catalysts to produce hydrogen gas and carbon. The catalysts consisted of 20% Fe and support mixtures of Al2O3 and SiO2 in various ratios (Al2O3/SiO2: 100/0.00, 90.0/10.0, 80.0/20.0, and 0.0/100.0). The catalysts were prepared via the impregnation method, calcination temperatures of 800 °C and 900 °C, and activation temperature at 800 °C. BET, XRD, H2-TPR, and TGA characterizations were employed to describe the physicochemical properties of the catalysts (SA-0, SA-10, SA-20, and SA-100). For the catalyst supported only with silica, no reaction was observed for all the considered temperatures. The Al/Si-20 catalyst calcined at 900 °C and reacted at 800 °C gave the optimal average hydrogen yield of about 80%. The Al/Si-20 sample promoted with 5% Sr provided a higher average H2 yield of around 84%. Moreover, the Sr-promoted catalyst improved stability by depressing the carbon deposition by 26%.

Synthesis and characterization of monophase CaO-TiO2-SiO2 (sphene) based glass-ceramics

Sphene based glass-ceramics (CaTiSiO5), an excellent candidate for a host lattice of ceramic materials and for nuclear waste immobilization, has been prepared from a powder mixture of CaCO3, TiO2 and SiO2 using vibro-milling for homogenization. Starting powders were melted at 1400?C for 2 h, cooled to room temperature, grounded again, then crystallized by thermal treatment yielding a sphene glass-ceramic. The evolution of the phase composition during thermal treatment was investigated by X-ray powder diffraction (XRPD), FT-IR, Raman and thermal analyses (TG-DTA). Pure synthetic single phase sphene was formed at 800?C for 4 h, even it is very hard to obtain monophase powder at such low temperature. Powder morphology was analyzed by scanning electron microscopy (SEM).

Взаимодействие фторуглерода с моноокисью кремния и процессы образования нанонитей SiC

When studying the processes of thermal carbonization of silicon monoxide in the presence of non-stoichiometric carbon monofluoride, it was found that increasing the annealing temperature of mixtures of SiO and CFx powders in a quasiclosed volume to 1000°C and higher leads to the release of whisker-like SiC nanocrystals. The studies showed that in parallel with the known crystallization of SiC nanowires as a result of the interaction of SiO vapors with carbon monoxide, previously undescribed interaction of CO with gas-phase silicon difluoride SiF2 takes part in their formation. At temperatures below 1200°C, this reaction is dominant, making the largest contribution to the yield of SiC nanowires.

Profound synergetic effect of metal oxide promoters and TiO2–SiO2 binary support in cobalt Fischer‐Tropsch catalyst

AbstractA series of cobalt catalysts supported on TiO2, SiO2, or a mixture of them, incorporated with some added oxides from Groups III, IV, and V of transition metals, were prepared using the incipient wetness impregnation method. For better evaluation of catalysts, the physicochemical properties of catalysts were investigated using brunauer‐emmett‐teller (BET), H2‐TPR, NH3‐TPD, X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy techniques. The performance of catalysts was studied in a fixed‐bed reactor at 220°C, 24 bar, gas hourly space velocity (GHSV) of 2 L/h/gcat., and H2 to CO ratio of 2. The results indicate that CeO2 and ZrO2 as promoters can enhance the CO conversion and catalyst activity and enhance the selectivities of higher‐molecular‐weight products. On the contrary, the presence of V2O5 as a promoter undesirably suppressed CO conversion and, consequently, catalytic performance. The results show that the catalyst included CeO2, was supported on a binary mixture of SiO2 and TiO2, and has significant improved activity and C5+ selectivity. From the reactor test, values of 156.48 mmol COconv./gCo/h activity, and 0.17 gC3+/(h.gcat.) productivity have been obtained for this catalyst.

Fabrication of Metal Powders for Energy-Intensive Combustible Compositions Using Mechanochemical Treatment: 2. Structure and Reactivity of Mechanically Activated Al–Modifier–SiO2 Mixtures

The results of studying the particles of the aluminum–modifier–quartz composites after mechanochemical treatment (MCT) in a planetary centrifugal mill by various physicochemical methods are presented. Graphite (C), polyvinyl alcohol (PVA), and stearic acid (SA) are used as modifiers. To increase the dispersive ability of plastic metallic powders (metal–modifier), MCT was performed in the presence of quartz, the weight fraction of which in the composite varies from 5 to 20%. The largest grinding of aluminum particles is observed with an increase in the graphite content from 5 to 20% and SiO2 content from 5 to 10% in the composition of aluminum–modifier–quartz composites. The particle decreases, while that of crystallites increases with the MCT of the Al–SA–SiO2 system with an increased quartz content in the composite. The maximal imperfection of aluminum after MCT is characteristic of the Al–SA–5%SiO2 samples. An increase in the particle size and, correspondingly, a decrease in the specific surface with rather small crystallite sizes are observed after MCT for the Al–PVA–SiO2 composition. It is shown that the imperfection of the crystalline structure of aluminum particles increases with an increase in the quartz content in the system. The synthesized powder material is a composite formation of aluminum and quartz particles bound by polymer formed based on polyvinyl alcohol in this case. The MCT of the Al–modifier–SiO2 mixtures results in an increase in the powder activity both due to the accumulation and redistribution of defects in aluminum particles and due to the change of the surface structure due to the incorporation of modifying additives into the destructed oxide layer. The conceptual model of transformation of the surface layer and subgrain structure of aluminum particles during MCT is presented.

Using mechanochemical treatment to obtain metal powders for energy-intensive combustible compositions. 2. Structure and reactivity of mechanically activated Al–modifier–SiО2 mixtures

The paper presents the results obtained when studying particles of aluminum-modifier-quartz composites by different physicochemical methods after mechanochemical treatment (MCT) in a planetary centrifugal mill. Graphite (C), polyvinyl alcohol (PVA) and stearic acid (SA) were used as modifiers. To increase the dispersibility of plastic metal powders in the composition (modifier metal), MCT was carried out in the presence of quartz with its mass fraction in the composite ranging from 5 to 20 %. The most significant grinding of aluminum particles was observed with an increase in the graphite content from 5 to 20 %, and SiO2 from 5 to 10 % in the composition of aluminum-modifier-quartz composites. The particle size decreases, while the crystallite size increases with an increase in the quartz content in the composite during the Al–SA–SiO2 system MCT. Al–SA–5%SiO2 showed the maximum defectiveness of aluminum after MCT. For the Al–PVA–SiO2 composition after MCT, an increase in the particle size and, accordingly, a decrease in the specific surface were observed at sufficiently low crystallite size values. It was shown that with an increase in the quartz content in the system, the defective crystal structure of aluminum particles increases as a result of MCT. In this case, the synthesized powder material is a composite formation of aluminum and quartz particles bound by a polymer obtained from polyvinyl alcohol. As a result of Al–modifier–SiO2 mixture MCT, powder activity increases due to the accumulation and redistribution of defects in aluminum particles, as well as changes in the surface structure occurring after modifying additives penetration into the oxide layer to be destroyed. A conceptual model for the transformation of the surface layer and subgrain structure of aluminum particles as a result of MCT is presented.

Effect of Iron-Compound Additives on Self-Propagating High-Temperature Synthesis of Si2N2O

The effects of iron-containing compounds on Si2N2O production during burning in N2 of an Si + SiO2 mixture were studied. It was established that the phase composition and morphology of the crystalline combustion products depended on the iron-containing compound. Si2N2O powder without impurity phases was obtained in the presence of FeCl3·6H2O and formed polycrystalline fibers consisting of ultrafine crystals.

Role of hybrid nanoparticles in thermal performance of Sutterby fluid, the ethylene glycol

This articles analyses the thermal performance of mixture of ethylene glycol and hybrid nanoparticles (MoS2 and SiO2). Three dimensional heat transfer in the mixture of ethylene glycol liquid (the Sutterby rheology) and hybrid nanoparticles is modeled and obtained highly complex mathematical models are solved by finite element method (FEM). Numerical experiments are carried out to compare thermal performances of working hybrid Sutterby nanofluid (mixture of Sutterby fluid, MoS2 and SiO2) and working Sutterby nanofluid (mixture of Sutterby fluid and SiO2). The effectiveness of thermal conductivity of hybrid nano-Sutterby fluid is more than the effectiveness of thermal conductivity of nanofluid. Therefore, the usage of hybrid nanofluid in thermal and cooling systems is recommended. As in this work, it is proven that the thermal performance of hybrid nanofluid is greater than the thermal performance of nanofluid. Therefore, hybrid nanoparticles are recommended to enhance thermal performance of working fluid. Surprisingly, the momentum boundary layer thickness in hybrid Sutterby liquid is greater than in conventional working fluid or nanofluid. Eventually, a significant reduction in thermal resistance of hybrid Sutterby nano-liquid is observed. Surface heat flux for the case of hybrid nanofluid is greater than that for the case of nanofluid or base fluid.

The Effects of Catalyst Support and Temperature on the Hydrotreating of Waste Cooking Oil (WCO) over CoMo Sulfided Catalysts

Waste cooking oil (WCO) hydrotreating to produce green diesel is good for both the environmental protection and energy recovery problems. The roles of catalyst support and reaction temperature on reactions during WCO hydrotreating process were evaluated over an unsupported and a commercial sulfided cobalt and molybdenum (CoMoS) catalyst supported by a mixture of Al2O3, TiO2, and SiO2. The presence of catalyst support helped to improve the dispersion and enlarge the surface area of CoMoS, and was found to be a key factor in reducing reaction temperature, in enhancing the hydrodeoxygenation (HDO) and hydrogenation capabilities, and in decreasing polymerization capability. The increase of reaction temperature strongly improved the deoxygenation, hydrogenation, and cracking reaction activities. Compared to the unsupported CoMoS, the supported one exhibited good deoxygenation and hydrogenation capabilities at 340 °C in WCO hydrotreating to produce diesel fraction; however, high temperature operation needs to be carefully controlled because it may cause overcracking and dehydrogenation.

Physical Properties of Encapsulated Iron Oxide

The size effect of magnetic nanoparticles provides a various magnetic characteristic as a change of domain size. We report, synthesis of core-shell iron oxide and magnetic properties. Iron oxide particles were synthesized by co-precipitation method of iron (III) FeCl3.6H2O, iron (II) FeCl2.4H2O, in the mixture of with or without TEOS to investigated the physical properties. From XRD measurement, it was observed that all iron oxide particles with or without mixture of SiO2 has a hematite phase of a-Fe2O3. From M-H loop measurement, it was observed that the iron oxide without SiO2 has a ferromagnetic characteristic, while the iron oxide with SiO2 showed a medium state as a contribution of superparamagnetic and ferromagnetic properties.