Three-dimensionally Ordered Macroporous Phosphotungstic Acid/SiO_2 for Efficient Catalytic Oxidative Desulfurization

Three-dimensionally ordered(3DOM) macroporous phosphotungstic acid/SiO_2(HPW/SiO_2) materials were prepared by using colloidal crystal as templates and applied for oxidative desulfurization(ODS) of the model fuel oil. The obtained HPW/SiO_2 materials were characterized through scanning electron microscopy, powder X-ray diffraction, N_2 sorption, and Fourier transform infrared spectroscopy. The results indicated that 3 DOM HPW/SiO_2 possessed hierarchical pore architectures which contained ordered macropores and disordered mesopores, with the Keggin type HPW embedded in the framework of pore structure. The removal rate of dibenzothiophene(DBT) could reach 100% under the optimum conditions, moreover. The performance was only slightly decreased for the regenerated catalyst after 7 cycles.     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Mechanical characteristics of SiO<Subscript>2</Subscript> electrets

1μm SiO₂ layer was thermally grown on silicon wafer. Negative and positive charging of SiO₂ layer was performed by means of corona method at room temperature. By controlling grid voltage, we have obtained uniformly charged SiO₂ with surface potential from −500 to +200 V. With certain electric field, the electrostatic force between charged SiO₂ is investigated. Experimental results indicate that attraction not only exists between charged SiO₂ with different polarity, but also exists between charged SiO₂ with the same polarity, and no repulsion has been observed. The attractive force is related to both surface potential difference of charged SiO₂ and the uniformity of the electric field. Based on the experiment, the attractive force is supposed to be caused by polarization when two charged SiO₂ wafers are close.     

Optical and magnetic properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> nano-composite films

Fe₂O₃/SiO₂ nano-composite films were prepared by sol-gel technique combining heat treatment in the range of 100–900 °C. The particle size was observed by FE-SEM. Optical properties of the films were investigated by UV-visible spectra. Structural and magnetic characteristics were investigated through FT-IR and VSM. The transparency of the Fe₂O₃/SiO₂ nano-composite films decreased with the content of the Fe₂O₃. Water and organic solvent in the films were evaporated with heat treatment, so the transparency of the films was enhanced under high temperature. It is also found that the saturation magnetization (M _s) of the films increases with the temperature. As the content of the Fe₂O₃ increases, when the content of the Fe₂O₃ is around 30wt%, the M _s of the films has a maximum value.     

Rheological properties of konjac glucomannan/SiO<Subscript>2</Subscript>/organic-borate gels

A series of thermoreversible konjac glucomannan gels crosslinked by organic borate were prepared. Required amount of hydrophilic SiO₂ was added into the konjac glucomannan solutions before the crosslinking reaction. The gel network was formed through the crosslinking reaction between borate ions dissociated from organic borate and the cis-diol hydroxyl groups on the mannose units of polysaccharide chains. The rheological properties of the complex gels were studied by dynamic viscoelastic measurement. The gelation kinetics of the complex gels was studied and the critical gelation points of the gels were exactly determined by the Winter-Chambon criterion. The effects of temperature and composite ratio on the shear storage modulus (G′), the loss modulus (G″) and the sol-gel transition points were investigated. Funded by Chinese Natural Science Foundation Committee(No.50673080)     

Influences of heat treatments on crystallization in SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-K<Subscript>2</Subscript>O-F glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precip...     

Erosion Resistance of CaO-AI203-SiO2 System Glass-Ceramics

The erosion resistance tests were used to research the erosion wear behavior of CaO-Al2O3-SiO2 system glass-ceramic. With the orthogonal test method, the factors thai affect the erosion wear of CaO-Al2O3-SiO2 system galss-ceramic such as pacticles property, impact angle, impact time, size of particles were discussed. The results show that erosion rate rises along a straight line at the early period of erosion wear. With the impact time increased, the erosion rate deviates from original staight line, tendency of the erosion rate increases, With the size of paricle increased , it will have more kinetic energy, the erosion rate of the surface of glass-ceramics ploate rises.     

Investigation of one-dimensional Si/SiO<Subscript>2</Subscript> hotonic crystals for thermophotovoltaic filter

The spectral control is widely incorporated with the thermophotovoltaic (TPV) technology to improve the optical-electric conversion efficiency of the whole system. In order to match with GaSb photovoltaic cell, an 8-layer one-dimensional photonic crystals (PC) filter structure was designed as quarter-wave periodic structure by selecting silicon (Si) and silicon dioxide (SiO₂) as candidate materials. The multilayer Si/SiO₂ structure was developed for the matching filter to simultaneously realize the optimal matching with the spectral distribution of the high temperature emitter and the quantum efficiency of GaSb cell. The physical vapor deposition (PVD) method was used to fabricate the optical filter and the normal incidence optical property of the filter was measured within the spectral range from 0.7 to 3.3 μm. These experimental data were used to predict the spectral control performance in a TPV system. Finally, temperature performance experiments were carried out to establish its withstanding performance in high temperature environment. Supported by the National Natural Science Foundation of China (Grant No. 50776047) and Natural Science Foundation of Jiangsu Province (Grant No. BK2007726)     

Fabrication of Ordered Meso-macroporous HPW/TiO_2 Catalyst for Efficient Heterogeneous Oxidative Desulfurization

In order to reduce the emission of SO_x in the environment,sulfur compounds must be removed efficiently from fuels.Three-dimensional highly ordered meso-macroporous HPW/TiO₂ (3DO m/M HPW/TiO₂) materials were synthesized successfully by sol-gel method and applied as oxidative desulfurization catalyst for the model fuel.The characterization results displayed the existence of highly ordered meso-macroporous structures and the Keggin type of HPW was highly dispersed i...     

Properties of Nano SiO2 Modified PVF Adhesive

Some properties of nano SiO2 modified PVF adhesive were studied .the experimental results show that nano SiO2 can inprope the properties of PVF adhesive very well.Meanwhile the modification mechanism of nano SiO2 to PVF adhesire and the applications of this adhesire in paper-plastic composite ,conctete and fireproof paint were discussed by using IR and XRD determination.     

Effect of aluminum addition on microstructure and properties of SiO<Subscript>2</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO vitrified bond

Influence of aluminum addition on the structures and properties of SiO₂-B₂O₃-Al₂O₃-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10^-6 °C^-1, respectively.     

Microstructures and mechanism of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composites fabricated by the reaction between SiO<Subscript>2</Subscript> and molten aluminum

Al₂ O₃/Al composite was fabricated by the reaction between SiO₂ and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO₂. The morphologies of Al₂O₃ have different features, depending on the reaction temperature. The composite has equaxed Al₂O₃ grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al₂O₃ grains and aluninum. The composite has a frame-shaped Al₂O₃ microstructure at the reaction temperature of above 1250°C. CHENG Xiao-min: Born in 1964 Funded by the National Natural Science Foundation of China (No. 91522)     

Fabrication of high performance 3D SiO<Subscript>2</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite via perhydropolysilazane infiltration and pyrolysis

The continuous fiber reinforced ceramic matrix composites have received consider-able attention for structural applications because of their excellent thermal stability, light weight, and damage tolerance imparted by the reinforcing fibers. Silica fibers, with ex-cellent ablative resistance, thermal shock damage resistance, dielectric properties, chemical stability and flexibility, are suitable for fabricating high temperature antenna window materials to meet the requirements of communication, …     

Ordered mesoporous carbon/SnO<Subscript>2</Subscript> composites as the electrode material for supercapacitors

A series of composites as electrode materials for supercapacitors were prepared via incipient wetness impregnation method utilizing ordered mesoporous carbon (OMC) and tin (IV) oxide (SnO2) with different ratio.The structure and electrochemical properties of the OMC/SnO2 composites were characterized by XRD,TEM and cyclic voltammetry (CV).Pore characteristics were measured by nitrogen adsorption and desorption isotherms.The results show that the structure and electrochemical properties of the composites dep...     

Synthesis,characterization and catalytic properties of mesoporous HPMo/SiO<Subscript>2</Subscript> composite

A novel mesoporous HPMo/SiO2 composite was synthesized by the sol-gel method with triblock copolymer EO20PO70EO20 as template.The properties of the product were characterized by X-ray diffraction,transmission electron microscopy,N2 adsorption-desorption isotherms,Fourier transform infrared spectrometer and inductively-coupled plasma analysis.The experimental results show that the product has a very ordered hexagonal mesostructure,and the HPMo is immobilized into the framework of silica.The final mesoporous composite shows excellent stability in polar solvents.Results of catalytic tests indicate that the composite is an effective catalyst for oxidation of dibenzothiophen,and there are few activity losses even after the third cycle of uses.The high catalytic activity and good insolubility make it a promising catalyst in oxidative desulfurization process.     

Structural characteristics and photocatalytic activity of ambient pressure dried SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> aerogel composites by one-step solvent exchange/surface modification

An ambient pressure synthesis of SiO₂/TiO₂ binary aerogel was prepared through the low-cost precursors of titanium tetrachloride (TiCl₄) and sodium silicate (Na₂O·nSiO₂). After gelation, solvent exchange and surface modification were performed simultaneously and the modified gel was finally dried under ambient pressure. Microstructural analyses by transmission electron microscope (TEM) indicate that fabricated SiO₂/TiO₂ aerogel composite shows similar sponge-like nanostructure as silica aerogel, and the Brunauer–Emmett–Teller (BET) analysis shows that the specific surface area of the composite reaches 605 m²/g, and the average pore size is 9.7 nm. Such binary aerogel exhibits significant photocatalytic performance in this paper for treating model pollutant of methyl orange (MO), and the decolorizing efficiency of MO is detected as 84.9% after 210 mins exposure to UV light irradiation. Degraded gel suspends in the water so as to separate from solution for reuse, and after 4 times recycling, 70% degradation efficiency can be easily reached when composite catalyzed system is exposed for 210 mins under UV irradiation.     

Effect of water soluble PVA on the microstructure characteristics of C-S-H formed in Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript>-Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> solution system

The structure characteristics of hydrated calcium silicate synthesized by solution reaction method with the existing of water soluble polymer polyvinyl alcohol(PVA)are investigated.Using Na 2 SO 3 and Ca(NO 3 ) 2 as the main raw materials,in the condition of 2%(in weight)addition of PVA and the water to solid ratio of 20,hydrated calcium silicate samples(Ca/Si=1.0 and 1.5)were prepared with 60℃water bath.IR,BET,XRD and SEM methods were used to study the microstructure of the hydration products.The results s...     

Effect of Grain Size of CaCO3 and SiO2 on the Formation of C3S Under Different Conditions

The effect of grain size of CaCO3 and SiO2 on the formation of C3S under various conditions, such as rapid heating rate（800 ℃/min）, normal heating rate（30 ℃/min） and in the presence or absence of ZnO, was studied. The results show that the decomposition temperature of CaCO3, the temperature of appearance of liquid phase and the f-CaO content descend when the grain size of CaCO3 and SiO2 becomes smaller, which attributes to the reactive activity enhancement of powders due to the decrease of the particle size. When the grain size of CaCO3 and SiO2 is below 1 μm, the rate of the formation of C3S is greatly raised. A rapid sintering rate and the presence of ZnO have an important effect on the formation of C3S and can lower the temperature of the formation of C3S by about 50 ℃.     

Effect of diatomite additive on the mechanical and dielectric properties of porous SiO<Subscript>2</Subscript>-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite ceramics

Porous SiO₂-Si₃N₄ composite ceramics with high porosity and excellent mechanical properties were fabricated by pressureless-sintering at relatively low temperature of 1 500 °C using diatomite as pore forming agent. The effects of diatomite on flexural strength, fracture toughness, shrinkage, porosity and phase transformation of the porous ceramics were investigated in detail. Compared with that of the ceramic without adding diatomite, the porosity of the ceramic with 10% diatomite is increased by about 27.4%, the flexural strength and fracture toughness reaches 78.04 MPa and 1.25 MPa·m^1/2, respectively. As the porosity increases, the dielectric constant of porous SiO₂-Si₃N₄ ceramic decreases obviously from 3.65 to 2.95.     

Preparation and characteristics of Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgF<Subscript>2</Subscript>/Au tunnel junction

The fabrication process of Cu/Al₂O₃/MgF₂/Au double-barrier metal/insulator/metal junction (DMIMJ) was introduced, and more stable light emission from this junction was successfully observed. The light emission physical mechanism of the junction was discussed. Results show that light emission spectrum of this structure locates at wavelength of 250–700 nm with two peaks at around 460 nm and 640 nm, which moves towards shorter wavelength region in comparison with that of the Al/Al₂O₃/Au junction. The light emission efficiency of this junction ranges from 0.7×10⁻⁵–2.0×10⁻⁵, which is 1 to 2 orders higher than that of the single-barrier Al/Al₂O₃/Au junction. The improved properties of this structure should be due to the electrons resonant tunneling effect in the double-barrier.