Types Of SiO Research Articles

Preparation and properties of silica/hydroxyapatite whiskers porous ceramics scaffold

To investigate the preparation and properties of the novel silica (SiO 2)/hydroxyapatite (HAP) whiskers porous ceramics scaffold. The HAP whiskers were modified by the SiO 2 microspheres using the Stöber method. Three types of SiO 2/HAP whiskers were fabricated under different factors (for the No.1 samples, the content of tetraethoxysilane, stirring time, calcination temperature, and soaking time were 10 mL, 12 hours, 560℃, and 0.5 hours, respectively; and in the No.2 samples, those were 15 mL, 24 hours, 650℃, and 2 hours, respectively; while those in the No.3 samples were 20 mL, 48 hours, 750℃, and 4 hours, respectively). The phase and morphology of the self-made HAP whisker and 3 types of SiO 2/HAP whiskers were detected by the X-ray diffraction analysis and scanning electron microscopy. Taken the self-made HAP whisker and 3 types of SiO 2/HAP whiskers as raw materials, various porous ceramic materials were prepared using the mechanical foaming method combined with extrusion molding method, and the low-temperature heat treatment. The pore structure of porous ceramics was observed by scanning electron microscopy. Its porosity and pore size distribution were measured. And further the axial compressive strength was measured, and the biodegradability was detected by simulated body fluid. Cell counting kit 8 method was used to conduct cytotoxicity experiments on the extract of porous ceramics. The SiO 2 microspheres modified HAP whiskers and its porous ceramic materials were prepared successfully, respectively. In the SiO 2/HAP whiskers, the amorphous SiO 2 microspheres with a diameter of 200 nm, uniform distribution and good adhesion were attached to the surface of the whiskers, and the number of microspheres was controllable. The apparent porosity of the porous ceramic scaffold was about 78%, and its pore structure was composed of neatly arranged longitudinal through-holes and a large number of micro/nano through-holes. Compared with HAP whisker porous ceramic, the axial compressive strength of the SiO 2/HAP whisker porous ceramics could reach 1.0 MPa, which increased the strength by nearly 4 times. Among them, the axial compressive strength of the No.2 SiO 2/HAP whisker porous ceramic was the highest. The SiO 2 microspheres attached to the surface of the whiskers could provide sites for the deposition of apatite. With the content of SiO 2 microspheres increased, the deposition rate of apatite accelerated. The cytotoxicity level of the prepared porous ceramics ranged from 0 to 1, without cytotoxicity. SiO 2/HAP whisker porous ceramics have good biological activity, high porosity, three-dimensional complex pore structure, good axial compressive strength, and no cytotoxicity, which make it a promising scaffold material for bone tissue engineering.

Design of Highly Efficient Catalyst for Rational Way of Direct Conversion of Methane

<p>Effects of composition and preparation method of MnNaW/SiO<sub>2</sub> and LaSr/CaO catalysts on their physical-chemical properties and performance in oxidative coupling of methane (OCM) have been studied. For MnNaW/SiO<sub>2</sub> catalysts the synthesis method and type of SiO<sub>2</sub> have a significant effect on the texture, while the Na/W ratio determines the phase composition. The variation of preparation method and temperature of catalyst calcination allows regulation of the metal surface concentration and mode of metal distribution across the SiO<sub>2</sub> support. For LaSr/CaO catalysts the synthesis method determines the specific surface area, surface and phase composition. Correlations between catalyst performance, preparation method and state of the catalyst were established. The rational preparation procedure and perspective composition of OCM catalyst have been developed. The 20La/CaO catalysts prepared by citrate sol-gel method were shown to provide ~20% C<sub>2</sub> yield and ~40% methane conversion at 800 °C.</p>

Electrical and magnetoelectronic properties of La 0.7Sr 0. 3MnO 3/SiO 2/p-Si heterostructure for spintronics application

An experimental study of p-silicon (Si)/La 0.7Sr 0.3MnO 3 (LSMO) junction in which the LSMO and silicon are separated by a thin interfacial silicon dioxide (SiO 2) layer has been fabricated. Two type of SiO 2 layer has been discussed here – one is native oxide and another one is thermal oxide. The thermal SiO 2 film is grown on Si by annealing it at 800 °C in oxygen atmosphere. The LSMO film of about 64 nm thick has been grown on SiO 2 at 800 °C substrate temperature in 10 −1 mbar oxygen pressure by Pulsed Laser Deposition technique. The LSMO/SiO 2/Si heterostructure exhibits MOS diode-like behavior with all type of possible current flow mechanisms (such as thermionic emission, tunneling, recombination degeneration, etc.) through the heterojunction. The high field Fowler-Nordheim [ln(J FN/E 2) vs 1/E] plot at different temperatures confirms that the dominating transport mechanism across the heterostructure is tunneling. The junction resistance changes under magnetic field and the junction magnetoresistance is found to be ∼31% with 1T applied magnetic field at room temperature at a bias voltage of 2.2 V. The capacitor-voltage characteristics confirm the presence of trap charges.

Computational simulations of the structure of Japan twin boundaries in quartz

The structures of Japan twin boundaries in quartz are studied through molecular dynamics simulations and energy minimization calculations. Four types of twinning are grouped under the Japan twin law, comprising 10 subtypes of geometrical configurations based on the structural handedness and composition plane. For each subtype, the twin displacement vector is determined and the structures of the twin boundaries with {11 22} or {TT22} composition plane are simulated. It is shown that six subtypes composed of two crystals with same-handed structure have the same type of SiO 4 tetrahedral linkage at twin boundaries. The twin boundary structures of these six subtypes can be further divided into two enantiomorphic structures composed of right- or left-handed quartz. The other four subtypes are composed of combinations of right- and left-handed quartz, and are structurally distinct from the same-handed group. The twin boundary energies of the same-handed group are lower than for the opposite-handed group. The Si-O bond lengths in the region of the twin boundary differ by no more than 0.05 A from those in the bulk quartz for all subtypes. The differences between the Si-O-Si angles at the twin boundaries and in the bulk exceed 20°, whereas the differences in O-Si-O angles are less than 10°. The present calculations demonstrate that SiO 4 tetrahedra at Japan twin boundaries are very stiff in comparison with inter-tetrahedral forces, consistent with previous reports for silica polymorphs, and that structural matching of twin individuals is primarily achieved through the rotation of SiO 4 tetrahedra.

Combined effect of noble metals (Pd, Au) and support properties on HDS activity of Co/SiO2 catalysts

Abstract Cobalt-based catalysts supported on different types of SiO 2 are studied in the hydrodesulfurization of thiophene. Amorphous silica and siliceous MCM-41 and HMS, characterized by different texture and surface acidity are used as carriers. The effects due to the modification of the support by impregnation with palladium precursor and to the co-impregnation of cobalt and gold are considered. The catalysts are characterized by N 2 physisorption (BET), XRD, TPR and XPS techniques. The use as supports of the ordered mesoporous silica with higher surface area with respect to amorphous silica, produces a better dispersion of the cobalt oxides particles. Moreover, the addition of palladium to the supports inhibits the interaction between cobalt and silica and favors the reducibility of the cobalt oxide. Co-impregnation of gold and cobalt decreases the Co 3 O 4 crystallite size. Due to the combination of these effects an increase in the cobalt activity is observed. The extent of the improvement is highly dependent on the support characteristics. As compared to the monometallic Co catalysts, the monometallic Pd catalysts supported on amorphous SiO 2 and on MCM-41 are less active. However quite unexpectedly the Pd/HMS exhibits the best performance among all the studied samples. Catalytic tests of HDS of tetrahydrothiophene (THT) support the direct route of the C–S bond cleavage as the rate-determining step of the reaction.

Water-Retention Effect of Composite Membranes with Different Types of Nanometer Silicon Dioxide

Four kinds of composite membranes were prepared by the solution-cast method with Nafion resin, poly(tetrafluoroethylene), and different types of SiO(2). They are SiO(2) sulfonated by 1,3-propane sultone (denoted as SiO(2)-1,3PS), SiO(2) sulfonated by H(2)SO(4) (denoted as SiO(2)-SO(3)H), and pure SiO(2). The SiO(2) content was controlled at 5% in the composite membranes. Combined with the results of the electrochemical impedance spectroscopy, water uptake, and fuel cell performance of different membranes, it suggested the organically modified SiO(2) has a weak water uptake ability due to the organic molecule chain. (C) 2008 The Electrochemical Society.

Controlling particle size distribution for preparing multi-layer structure compacts

Ceramic compacts which have a self-arrangement characteristic according to surface properties in moulding process were made. Two types of SiO 2 powder, of which particle sizes are different from each other in average, went through the surface treatment through stearic acid and ABDM (alkyl benzyl dimethyl ammonium chloride) to have hydrophobic and hydrophilic features, respectively. This process is to induce diverse movements to several directions by surface properties in a slip. In gypsum mould, it is shown that different kinds of particles have relatively different movements in the process of squeeze casting to make compacts, that is, particles with hydrophobic features on the surface tend to move to the surface of the gypsum and particles with hydrophilic features on its surface show a tendency to be distributed evenly in the slip. Finally, on the surface of the compact are mainly hydrophobic particles, and hydrophilic particles come to exist mainly in the inside of the compact, and this demonstrates the fact that by modifying surface properties the particles distribution can be controlled artificially, and this study observed the fact through based on the experimental results above.

Crystal structure and structural disorder of (Ba 0.65Ca 0.35) 2SiO 4

Crystal structure and structural disorder of (Ba 0.65Ca 0.35) 2SiO 4 were investigated by laboratory X-ray powder diffraction (Cu Kα 1). The initial structural model with eleven independent atoms in the unit cell was determined using direct methods, and it was further modified to a split-atom model, in which the two types of Ba/Ca atoms and two types of SiO 4 tetrahedra were, respectively, positionally and orientationally disordered. The crystal structure is trigonal (space group P 3 ¯ m 1 , Z=4) with lattice dimensions a=0.57505(1) nm, c=1.46706(2) nm and V=0.42014(1) nm 3. The validity of the structural model was verified by the three-dimensional electron density distribution, the structural bias of which was reduced as much as possible using the maximum-entropy methods-based pattern fitting (MPF). The final reliability indices calculated from the MPF were R wp=9.56% ( S=1.48), R p=7.29%, R B=1.82% and R F=0.88%. This compound is most probably homeotypic to glaserite.

Nature of cobalt active species in hydrodesulfurization catalysts: Combined support and preparation method effects

Co/γ-Al 2O 3, Co/SiO 2, Co/MCM-41, Co/ASA and Co/S2 (amorphous aluminosilicate with Al/Si = 0.13 and with Al/Si ≈ 2, respectively) were prepared by the method of wet impregnation and by the method of precipitation in the presence of sodium carbonate. The samples were characterised by XPS, XRD and TPR. The catalytic activity was tested in the hydrodesulfurization of thiophene using a continuous flow reactor. Among the wet impregnated catalysts those supported on the amorphous and ordered mesoporous silica exhibited higher HDS activity as compared to the alumina containing supports. Particularly, the use of the mesoporous, high surface area MCM-41 support, determined the best performing cobalt catalyst. Quite surprisingly, the catalytic performance of the cobalt catalysts was completely reversed by using the method of precipitation with sodium carbonate. In this case the alumina supported catalyst was the most active. For the wet impregnated samples, the positive influence of SiO 2, as compared to the aluminosilicates, was related to the formation of Co 3O 4 which on the other supports was hindered by the interaction with alumina. On the contrary, using the method of precipitation with sodium carbonate, Co 3O 4 formed on the alumina containing supports, whereas cobalt-support interacting species formed over the two types of SiO 2. Increased cobalt reducibility and cobalt dispersion accounted for the different catalytic behaviour.

Direct electrolytic reduction of solid SiO 2 in molten CaCl 2 for the production of solar grade silicon

The direct electrolytic reduction of solid SiO 2 has been investigated in molten CaCl 2 at 1123 K aiming at the production of solar grade silicon (SOG-Si). A new type of SiO 2 contacting electrode was prepared to prevent the metal contamination from a conducting wire; the top end of an SiO 2 glass plate was put between two single crystal silicon plates and they were wound by a molybdenum wire. A silicon ingot was successfully produced from the electrochemically reduced samples by separating the silicon from the unreduced SiO 2 by means of a melting process under vacuum at 1773 K. The purity of the silicon ingot was 99.80 at.% at this stage, due to the metal contamination from the stainless vessel. However, the concentrations of boron and phosphorus were very low in the ingot, which verifies the applicability of this electrochemical process for the SOG-Si production.

Agglomerate size in an acoustic fluidized bed with sound assistance

Three types of SiO 2 ultrafine particles were used to investigate the fluidization behavior in a fluidized bed with sound excitation. It has been shown that agglomerate size tends to reduce with an increase in sound pressure level. At a given sound pressure level, there exists a critical sound frequency ( f c). Agglomerate size is decreased with increasing sound frequency as sound frequency less than f c. Whereas, agglomerate size intends to grow with an increase in sound frequency as sound frequency exceeds f c. A mathematic model to predict the agglomerate size has been developed based on energy balance between the agglomerate collision energy, the energy arising from sound wave, and cohesive energy. The model can predict qualitatively the effects of sound frequency and sound pressure level on agglomerate size.

Encapsulation of titanium dioxide particles by polystyrene via radical polymerization

The paper describes the preparation and characterization of a novel type of SiO 2-and-Al 2O 3-coated-TiO 2 particle encapsulated by polystyrene via radical polymerization. SiO 2-and-Al 2O 3-coated-TiO 2 particle was modified by 3-(trimethoxysilyl)propylmethacrylate (MPS) coupling agent, followed by free radical copolymerization of styrene with the methacrylate group of MPS at the particle surface. The inorganic particle/polystyrene core-shell composites were characterized by means of FTIR spectroscopy, transmission electron microscopy (TEM), elemental analysis, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). TEM and FTIR investigation provided direct and clear evidence for the presence of polystyrene shell on SiO 2-and-Al 2O 3-coated-TiO 2 core particles, and TGA showed quantitative evidence of the presence of polystyrene shell on SiO 2-and-Al 2O 3-coated-TiO 2 core particles. It was demonstrated that polystyrene shell was chemically bonded to inorganic core surface, leading to more stable core-shell microspheres.

Characterization of ion-induced sodium migration in various kinds of silicon oxide films

The migration behavior of Na in SiO 2 films during SIMS depth profiling was characterized, and effects of the chemical structure and defects in the film on Na migration were investigated. Several types of SiO x N y samples were prepared and the relationship between Na migration behavior and the type of the films was determined. It is clarified that not only defects formed by ion-implantation but also porousness of the film accelerate the Na migration during SIMS analysis and it is suggested that reducing Na migration in such low-density SiO 2 film is quite difficult. On the other hand, it was shown that Si–N bonds in the film are effective in suppressing the migration of Na. Thus the Na migration during SIMS analysis is affected by the structure of the film, and there is the possibility of obtaining information on the chemical structure of the films.

Oxygen and lattice distortions in multicrystalline silicon

Oxygen is one of the main impurities in multicrystalline silicon for photovoltaic applications. Precipitation of oxygen occurs during crystal growth and solar cell processing. It is shown that dislocations enhance the oxygen precipitation. Depending on the thermal conditions and the initial oxygen content various types of SiO 2+precipitates and oxygen related defects are observed and investigated by fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy. The large area distribution of oxygen decorated dislocations is studied by scanning infrared microscopy (SIRM). Both inhomogeneous distributions of dislocations and oxygen precipitates occur and can lead to internal stresses. The internal stresses of multicrystalline-silicon wafers are investigated by an optical method using polarized infrared light. The results are compared with the dislocation microstructure and the oxygen distribution in wafers produced by different growth techniques.

Ab initio study of MgSiO3 low-clinoenstatite at high pressure

We investigated the athermal high-pressure behavior of the structural properties of MgSiO 3 low clinoenstatite using the plane wave pseudopotential method within the local density approximation. The experimental zero pressure structure and pressure variations of the lattice parameters were reasonably well reproduced. The calculated atomic positions vary slightly and monotonically with pressure. Our results showed that MgO 6 octahedra are three times more compressible than SiO 4 tetrahedra, consistent with the general observation that the SiO 4 tetrahedra are nearly incompressible in silicates. Mg2O 6 octahedra (the larger of two Mg sites) remain most distorted over the pressure regime studied while Mg1O 6 octahedra and both types of SiO 4 tetrahedra show similar level of distortions. The tetrahedral chain angles were shown to slightly vary with pressure indicating that the structure under compression always remains highly distorted away from the ideal close-packing of O atoms.

Radiation induced optical absorption and radioluminescence in electron irradiated SiO 2

Optical absorption and radioluminescence spectra from 2000 to 8000 Å have been measured for two different types of SiO 2 (Anhydroguide silica and KU1 quartz glass) irradiated at ionizing and displacement dose rates, and temperatures of relevance for ITER optical diagnostic components. Radioluminescence intensity has been quantified in terms of photon emission and shown to be up to two orders of magnitude less than that found earlier for high purity sapphire. Cherenkov radiation sets a lower limit on the radioluminescence intensity for these SiO 2 materials. On the other hand optical absorption is considerably higher for the SiO 2 materials than for sapphire. Considerable advantage may be obtained by operating these materials at about 300°C.

Silicon nanoparticles embedded in SiO 2 films with visible photoluminescence

Applying laser ablation technique, we have synthesized two types of SiO 2 films that included nanometer-sized Si particles. One is synthesized by alternative deposition of Si nanoparticle layers and SiO 2 layers. The synthesized film exhibits red photoluminescence (PL) with a peak energy below 1.5 eV. The other is a SiO 2 film in which Si nanocrystallites precipitate. The films were synthesized by annealing at 1000°C of SiO x films which are formed by laser ablation in diluted O 2 gas. The films exhibit PL with peak energies of 1.5 eV, 2.2 eV and 2.7 eV. We find that there is a narrow range of composition for efficient 1.5-eV PL.

New measurement of the orthopositronium decay rate

The orthopositronium decay rate is measured with an entirely new method, in which the pickoff annihilation rate is directly measured as a function of time with a high-resolution germanium detector. The decay rate can be determined without the ambiguities of the thermalization nor of the extrapolation, which might have been sources of the main systematic errors in all the previous experiments. Two independent measurements are carried out with two different types of SiO 2 powder, resulting in decay rate values consistent with each other. The combined result is λ 0 = 7.0398 ± 0.0025 (stat.) ± 0.0015 (sys.) μs −1, which is consistent with the QED prediction, and differs by 2.9–4.1Φ from three recent measurements.

On the validity of the elastic model for temperature induced surface transitions

Temperature induced surface alignment transitions in nematic liquid crystals are analysed by means of an elastic model in which the effective splay-bend surface-like elastic constant is taken into account. Experimental data in hybrid cells are analysed and the value of the effective splay-bend elastic constant is found to be in good agreement with that obtained in homogeneous samples for the same liquid crystal. The validity of the model is successfully checked on data from the literature, for such different temperature dependences as those of MBBA at the free surface and on two types of SiO x deposited surfaces, and for E7 on a fluoropolymeric surface, exhibiting a temperature induced surface alignment transition from planar to homeotropic.

Phosphorescence and thermally stimulated luminescence of amorphous SiO 2

Thermally Stimulated Luminescence (TSL) and phosphorescence measurements excited by X- and beta rays have been performed above room temperature on fused quartz and on thin SiO 2 films deposited on a silicon substrate by the technique of chemical vapour deposition. Although in these types of SiO 2 the basic TSL features, noticeably the prominent glow peak at 60 < T < 120°C, are similar to those already studied in quartz, some behaviours are different. Specifically, the maximum temperature of the glow peak shifts linearly to higher temperatures as a consequence of partial pre-heating treatments and the phosphorescence decay shows a t −1 power law. The implications of these results are discussed also in comparison with the corresponding ones of crystalline quartz and with preliminary data on thermally stimulated currents measurements.