Large-scale synthesis of hierarchical MnO2 for benzene catalytic oxidation

Hierarchical sea-urchin-shaped manganese oxide microspheres were synthesized via a tacile metnoa based on the reaction between KMnO_4 and MnSO_4 in HNO_3 solution at 50 C.The average diameter of the microspheres is ~850 nm.The microspheres consist of a core of diameter of ~800 nm and nanorods of width ~50 nm.The nanorods exist at the edge of the core.The Brunauer-Emmett-Teller surface area of the sea-urchin-shaped microspheres is 259.4 m~2/g.A possible formation mechanism of the hierarchical sea-urchin-shaped microspheres is proposed.The temperature for 90%conversion of benzene(T_(90)%) on the hierarchical urchin-shaped MnO_2 microspheres is about 218℃.     

In situ synthesis of CNTs/Fe-Ni/TiO2 nanocomposite by fluidized bed chemical vapor deposition and the synergistic effect in photocatalysis

Carbon nanotube(CNTs)/Fe-Ni/TiO_2 nanocomposite photocatalysts have been synthesized by an in situ fluidized bed chemical vapor deposition(FBCVD) method.The composite photocatalysts were characterized by XRD,Raman spectroscopy,BET,FESEM,TEM,UV-vis spectroscopy,and XPS.The results showed that the CNTs were grown in situ on the surface of TiO_2.Fe(lll) in TiO_2 showed no chemical changes in the growth of CNTs.Ni(Ⅱ) was partly reduced to metal Ni in the FBCVD process,and the metal Ni acted as a catalyst for the growth of CNTs.The photocatalytic activities of CNTs/Fe-Ni/TiO_2 decreased with the rise of the FBCVD reaction temperature.For the sample synthesized at low FBCVD temperature(500℃),more than 90% and nearly 50% of methylene blue were removed under UV irradiation in 180 min and under visible light irradiation in 300 min,respectively.The probable mechanism of synergistic enhancement of photocatalysis on the CNTs/Fe-Ni/TiO_2 nanocomposite is proposed.     

Fabrication and electrochemical performance of nanofibrous micro-frameworks of α-MnO_2

A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO_2 with a nanofibrous structure and high porosity.The fabrication is achieved by a three-step process using a preformed manganese tartrate with a rectangular framework as the precursor followed by thermal annealing and hydrothermal oxidation to form the final nanofibrous structure.Evolution of the phase and the morphology are characterized by FESEM,XRD,TG-DTA,and TEM measurements.The electrochemically active material α-MnO_2 exhibits both attractive stability of the Coulombic efficiency after long-term cyclic charging/discharging and acceptable specific capacitance.     

油酸/PS/TiO_2复合纳米微球对液体石蜡抗磨性能的影响研究

采用种子乳液聚合法制备了油酸 / PS/ Ti O2 复合纳米微球 ,在四球摩擦磨损试验机上考察了油酸 / PS/ Ti O2 复合纳米微球添加剂对液体石蜡抗磨性能的影响 ,采用 X射线光电子能谱分析了钢球磨斑表面边界膜元素的组成及化学状态 .结果表明 ,油酸 / PS/ Ti O2 复合微球作为润滑油添加剂具有良好的抗磨性能 ,能显著提高基础油的失效载荷 .表面分析结果表明 ,复合纳米微球的抗磨作用取决于其摩擦化学反应所生成的含有 Ti O2 及部分添加剂分解产物的复合膜 .     

油酸／PS／TiO2复合纳米微球对液体石蜡抗磨性能的影响研究

采用种子乳液聚合法制备了油酸／PS／TiO2复合纳米微球,在四球摩擦磨损试验机上考察了油酸／PS/TiO2复合纳米微球添加剂对液体石蜡抗磨性能的影响,采用X射线光电子能谱分析了钢球磨斑表面边界膜元素的组成及化学状态。结果表明,油酸／PS／TiO2复合微球作为润滑油添加剂具有良好的抗磨性能,能显著提高基础油的失效载荷。表明分析结果表明,复合纳米微球的抗磨作用取决于其摩擦化学反应所生成的含有TiO2及部分添加剂分解产物的复合膜。     

Synthesis of TiO2 nanoparticles by propane/air turbulent flame CVD process

Synthesis of TiO2 nanoparticles by the oxidation of titanium tetrachloride (TiCl4) in high-strength propane/air turbulent flame is investigated tentatively for mass production ofTiO2 nanoparticles. Effects of reactor heat flux varying from 247 to 627 kJ/m2 s, initial TiO2 number density from 2×1020> to 1 × 1021 m-3, and apparent residence time of TiO2 nanoparticles in reactor from 0.06 to 0.9 s, on particle morphology, phase composition, UV absorption and photoluminescence (PL) spectra are studied. The TiO2 nanoparti-cles synthesized, with mean size of 30-80 nm and rutile mass fraction from 0.155 up to 0.575, exhibited a strong PL signal at the wavelength of 370-450 nm, with a wide peak signal at 400-420 nm, reflecting significant oxygen vacancies on the surface of the TiO2 nanoparticles.     

Facile aqueous synthesis and thermal insulating properties of low-density glass/TiO2 core/shell composite hollow spheres

Anatase TiO2 shells assembled on hollow glass microspheres(HGM)with tunable morphologies were successfully prepared through a controllable chemical precipitation method with urea as the precipitator. Thus,glass/TiO2 core/shell composite hollow spheres with low particle density(0.40 g/cm3)were fabricated.The phase structures,morphologies,particle sizes,shell thicknesses,and chemical compositions of the composite microspheres were characterized by X-ray diffraction(XRD),scanning electron microscopy (SEM),and energy dispersive X-ray spectroscopy(EDS).The morphology of the TiO2 shell can be tailored by properly monitoring the reaction system component and parameters.The probable growth mechanism and fabrication process of the core/shell products involving the nucleation and oriented growth of TiO2 nanocrystals on hollow glass microspheres was proposed.A low infrared radiation study revealed that the radiation properties of the products are greatly influenced by the unique product shell structures. A thermal conductivity study showed that the TiO2/HGM possess low thermal conductivity that is similar to that of the pristine HGMs.This work provides an additional strategy to prepare low-density thermal insulating particles with tailored morphologies and properties.     

油酸修饰TiO2纳米微粒水溶液润滑下GCr15钢摩擦磨损性能研究

用四球摩擦磨损试验机考察了脂肪酸修饰TiO2纳米微粒水溶液润滑下GCr15钢的摩擦磨损性能,并用电子探针和X射线光电子能谱研究了钢球磨损表面边界润滑膜的化学组成和元素分布.摩擦磨损试验结果表明:脂肪酸修饰TiO2纳米微粒在水中具有较好的润滑性能、良好的极压性能及较高的承载能力.添加质量分数为0.1%～1.0%的油酸TiO2纳米微粒可使水的承载能力提高6～12倍,烧结负荷提高51～100%,抗磨减摩性能也有较大提高,卡咬负荷由150N提高至1000～1800N.磨损表面分析表明:油酸TiO2纳米微粒在较高负荷(>300N)下发生了摩擦化学反应,生成含TiO2及油酸复合物的边界润滑膜,从而起减摩抗磨作用     

PREPARATION OF TiO2 PHOTOCATALYST ANCHORED ON ACTIVATED CARBON FIBERS AND ITS PHOTODEGRADATION OF METHYLENE BLUE

TiO2 particulate photocatalyst anchored on activated carbon fibers (ACFs) was prepared by a molecular adsorption-deposition method. The TiO2 particles deposited on the carbon fibers formed a coating of about 100 nm in thickness. The photocatalyst prepared was characterized by means of SEM, EDS, XRD and UV-vis adsorption spectroscopy. Anatase-type TiO2 was uniquely developed, and the micrographic structure of ACFs was not damaged during preparation. The roomy space between adjacent carbon fibers could allow UV-light to penetrate into the felt-form photocatalyst to a certain depth, so that a three dimensional environment was formed for the photocatalytic reaction.Such TiO2/ACFs photocatalyst exhibited its photocatalytic reactivity in photodegradation of concentrated methylene blue(MB) solutions. The MB molecules in the bulk solutions was supposed to be condensed around TiO2 particles by adsorption by ACFs. Therefore, the photocatalyst possesses the combined effect of adsorption by activated carbon fibers and photocatalytic reactivity of anatase-type TiO2 on MB photodegradation.     

Photodegradation of benzene by TiO_2 nanoparticles prepared by flame CVD process

Photodegradation of benzene at ppb levels by mixed-phase TiO 2 nanoparticles, synthesized by the oxidation of TiCl 4 in propane/air turbulent flame chemical vapor deposition (CVD) process, is investigated experimentally by using a tubular photoreactor with thin TiO 2 films coated on the reactor wall by sedimentation. Effects of inlet benzene concentration from 10 to 300 g/m 3 , rutile mass fraction from about 20 to 50% and photoluminescence (PL) intensity of TiO 2 nanoparticles on degradation degree are exa...     

Immobilization of TiO2 nanoparticles on activated carbon fiber and its photodegradation performance for organic pollutants

The immobilization of titanium dioxide(TiO2) on activated carbon fiber(ACF),(TiO2/ACF),was accomplished by sol-gel-adsorption method followed by calcination at temperatures varying from 300 to 600℃ in an argon atmosphere.The material properties were determined by scanning electron microscope(SEM),X-ray diffraction(XRD) and nitrogen adsorption.The photodegradation behavior of TiO2/ACF was investigated in aqueous solutions using phenol and methyl orange(MO) as target pollutants.The effects of calcination temperature,photocatalyst dosage,initial solution pH and radiation time on the degradation of organic pollutants were studied.It was found that organic pollutants could be removed rapidly from water by the TiO2/ACF photocatalyst and the sample calcined at 500℃ exhibited the highest removal efficiency.Kinetics analysis showed that the photocatalytic degradation reaction can be described by a first-order rate equation.In addition,the possibility of cyclic usage of the photocatalyst was also confirmed.Moreover,TiO2 is tightly bound to ACF and can be easily handled and recovered from water.It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

The influence of nano-particle tracers on the slip length measurements by microPTV

Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry (microPIV/PTV) measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall (z = 0.25-1.5 μm) with two sizes of tracer particles (φ 50 nm and φ200 nm). The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.     

Uniform attractors for non-autonomous Klein-Gordon-Schr/Sdinger lattice systems

The existence of a compact uniform attractor for a family of processes corre- sponding to the dissipative non-autonomous Klein-Gordon-SchrSdinger lattice dynamical system is proved. An upper bound of the Kolmogorov entropy of the compact uniform attractor is obtained, and an upper semicontinuity of the compact uniform attractor is established.     

Preparation of polyacrylamide/silica composite capsules by inverse Picketing emulsion polymerization

Polyacrylamide/silica （PAM/SiO2） composite capsules were synthesized by inverse Pickering emulsion polymerization. Silica nanoparticles modified with methacryloxypropyltrimethoxysilane （MPS） were used as a stabilizer. Transmission electron microscopy （TEM）, scanning electron microscopy （SEM）. Fourier transform infrared （FTIR） spectroscopy, and thermal gravimetric analysis （TGA） were used to characterize the morphology and composition of the composite capsules. SEM and TEM images showed that capsules consisted of a particle shell and a polymer inner layer. The capsule size depends on the nanoparticle concentration in the continuous phase. The composite rigidity largely depends on the acrylamide concentration. FTIR and TGA results indicated the existence of polyacrylamide and SiO2 in the composite particles. Aqueous Hg（ll） removal testing by the PAM/SiO2 composite capsules indicated promising potential for removing heavy metal ions from wastewater.     

Nanohybrid TiO2/carbon black sensor for NO2 gas

A nanohybrid sensor of nanosized TiO2-coated carbon black particles, prepared by sol-gel technology for the detection of NO2 gas, has been developed. The response of the electric resistance of the hybrid sensor to NO2 concentration is investigated, showing that the sensitivity of the hybrid sensor is raised as certain ratio of the TiO2 content in the sensor. Easy and cheap to fabricate, the hybrid TiO2/carbon black promises to be a practical sensor for detecting NO2 gas.     

The vitiation effects of water vapor and carbon dioxide on the autoignition characteristics of kerosene

In ground tests of hypersonic scramjet, the highenthalpy airstream produced by burning hydrocarbon fuels often contains contaminants of water vapor and carbon dioxide. The contaminants may change the ignition characteristics of fuels between ground tests and real flights. In order to properly assess the influence of the contaminants on ignition characteristics of hydrocarbon fuels, the effect of water vapor and carbon dioxide on the ignition delay times of China RP-3 kerosene was studied behind reflected shock waves in a preheated shock tube. Experiments were conducted over a wider temperature range of 800–1 500 K, at a pressure of 0.3 MPa, equivalence ratios of 0.5 and 1, and oxygen concentration of 20%. Ignition delay times were determined from the onset of the excited radical OH emission together with the pressure profile. Ignition delay times were measured for four cases:(1) clean gas,(2) gas vitiated with10% and 20% water vapor in mole,(3) gas vitiated with 10%carbon dioxide in mole, and(4) gas vitiated with 10% water vapor and 10% carbon dioxide, 20% water vapor and 10%carbon dioxide in mole. The results show that carbon dioxide produces an inhibiting effect at temperatures below 1 300 K when φ = 0.5, whereas water vapor appears to accelerate the ignition process below a critical temperature of about1 000 K when φ = 0.5. When both water vapor and carbon dioxide exist together, a minor inhibiting effect is observed at φ = 0.5, while no effect is found at φ = 1.0. The results are also discussed preliminary by considering both the combustion reaction mechanism and the thermophysics properties of the fuel mixtures. The current measurements demonstrate vitiation effects of water vapor and carbon dioxide on the autoignition characteristics of China RP-3 kerosene at air-like O2 concentration. It is important to account for such effects when data are extrapolated from ground testing to real flight conditions.     

EFFECT OF POLYETHYLENEIMINE ON THE PROPERTIES OF CONCENTRATED SUSPENSIONS OF TITANIUM DIOXIDE MICROBEADS

The effect of polyethyleneimine (PEI) concentration on the properties of titanium dioxide (TiO2) suspensions is studied with or without the addition of an electrolyte (barium acetate). Measurements of the apparent viscosity and the stability of TiO2 suspensions showed that PEI is an effective dispersant for TiO2 particles in suspension in the absence of an electrolyte, not only reducing the viscosity of the suspension but also increasing its stability. In the presence of an electrolyte, however, small quantities of polyethyleneimine could neither disperse the TiO2 particles nor de-crease the viscosity of the TiO2 suspensions; only PEI concentrations beyond saturation adsorption could perceptively improve the stabilitv of TiO2 suspensions.     

PREPARATION AND MICROSTRUCTURE CHARACTERIZATION OF Ni／TiO2 NANOCOMPOSITE

Homogeneous Ni^2 -doped titania gel was synthesized by a sol-gel process,and the xerogel was then obtained through aging and drying,leading to the formation of Ni/TiO2 nanocomposite after heat treatment under a suitable reducing atmosphere.The resulting nanocomposite was characterized by TGA-DSC,TEM,XRD and BET methods.The results show that the structure and grain size of the nanocomposites could be manipulated by altering the heat-treatment conditions,and that the nanocomposite possesses a mesoporous structure with a pore radius of ca.28nm and a specific surface area of 49.1 m^2.g^-1.It is demonstrated that the nanosized Ni dispersion in the titania matrix significantly affects the anatase-rutile phase transformation.     

SYNTHESIS OF MESOPOROUS TiO_2 MATERIALS WITH HIGH SPECIFIC AREA USING INORGANIC ACIDS AS CATALYSTS

This paper presents a synthesis process for preparing mesoporous titanium dioxide materials in the absence of any templates and using inorganic acids as catalysts. Tetrabutyl titanate was used as the precursor at ambient temperature, and four different inorganic acids, i.e., hydrochloric, nitric, sulfuric and phosphoric, were used as catalysts. The as-prepared mesoporous TiO2 materials were characterized by SEM, XRD and nitrogen adsorption/desorption measurements. The influences of different inorganic acids on the properties of TiO2 were discussed and compared in details. Experiments showed that the inorganic acids have significant effects on the surface area, pore volume, pore size, and pore size distribution of the products. The mesoporous TiO2 materials catalyzed by phosphoric acid exhibited the largest specific surface area and largest pore volume with narrow pore size distribution. Vacuum and infrared drying methods tested in the process were found to have subtle impact on the structure of the TiO2 materials prepared.     

Development of a simulation model for dynamic derailment analysis of high-speed trains

The running safety of high-speed trains has become a major concern of the current railway research with the rapid development of high-speed railways around the world.The basic safety requirement is to prevent the derailment.The root causes of the dynamic derailment of highspeed trains operating in severe environments are not easy to identify using the field tests or laboratory experiments.Numerical simulation using an advanced train–track interaction model is a highly efficient and low-cost approach to investigate the dynamic derailment behavior and mechanism of high-speed trains.This paper presents a three-dimensional dynamic model of a high-speed train coupled with a ballast track for dynamic derailment analysis.The model considers a train composed of multiple vehicles and the nonlinear inter-vehicle connections.The ballast track model consists of rails,fastenings,sleepers,ballasts,and roadbed,which are modeled by Euler beams,nonlinear spring-damper elements,equivalent ballast bodies,and continuous viscoelastic elements,in which the modal superposition method was used to reduce the order of the partial differential equations of Euler beams.The commonly used derailment safety assessment criteria around the world are embedded in the simulation model.The train–track model was then used to investigate the dynamic derailment responses of a high-speed train passing over a buckled track,in which the derailmentmechanism and train running posture during the dynamic derailment process were analyzed in detail.The effects of train and track modelling on dynamic derailment analysis were also discussed.The numerical results indicate that the train and track modelling options have a significant effect on the dynamic derailment analysis.The inter-vehicle impacts and the track flexibility and nonlinearity should be considered in the dynamic derailment simulations.