Functionalized TiO2@ZrO2@Y2O3 ：Eu3＋ core-multishell microspheres and their photoluminescence properties

TiO2@ZrO2@Y2O3 ：Eu3＋ composite particles with a core-multishell structure were synthesized through the combination of a layer-by-layer （LBL） self-assembly method and a sol-gel process. The obtained sam- ples were characterized with scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and fluorescence spectropho- tometry. The results showed that the composite particles had a core-multishell structure, spherical morphology, and a narrow size distribution. The presence of a ZrO2 layer on the TiO2 core can effec- tively prevent the reaction between the TiO2 core and a Y203 shell; the temperature for the reaction between the TiO2 core and the Y203 shell in the TiO2@ZrO2@Y2O3 ：Eu core-multishell phosphor can be elevated by 300 ℃ compared to that for TiO2@ZrO2：Eu. Upon excitation of the core-multishell particles in the ultraviolet （254 nm）, the Eu3＋ ion in the Y2O3 ：Eu3＋ shell shows its characteristic red emission （611 nm, 5D0→7F2）, and the photoluminescence （PL） intensity of the phosphor with the core-multishell structure was obviously greater than that of the core-shell TiO2@Y2O3 ：Eu phosphor.     

High-frequency dielectric properties of BSTO ceramic prepared with hydrothermal synthesized SrTiO3 and BaTiO3 powders

BSTO dielectric ceramic was prepared from SrTi03 and BaTi03 powders synthesized by hydrothermal method, as well as from Bao.sSro.4TiO3 powder synthesized by conventional solid-state reaction. The former can be sintered at a relatively low temperature of 1120 ℃. Characterization by SEM showed that the grain shapes of both ceramics are cubical, though the grain size of the former is much smaller. Dielectric constants measured at 20℃ were shown to vary with frequency in the range from I kHz to 2 MHz and dc bias field, and further that the dielectric loss of the former to be less than 2 × 10^- 3 in the frequency range of 20 kHz to 1 MHz, much smaller than that of the latter sample. For the former, temperature dependence of dielectric constant is much flatter and there exists an extended phase transition diffusion covering a wide temperature range of Curie temperature To. The smaller grain size of the former depresses the dc bias electrical field dependence of dielectric constant. The tunability is 7% under a bias field of 0.6 kV/mm dc.     

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.     

SYNTHESIS OF MESOPOROUS TiOz 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,     

FORMATION OF MICRO-POROUS SPHERICAL PARTICLES OF CALCIUM SILICATE （XONOTLITE）IN DYNAMIC HYDROTHERMAL PROCESS

Stiming during hydrothermal synthesis plays an important role in the formation of porous spherical xonotlite particles.The size of spherical particles formed during dynamic hydrothermal process is related to the size of minimum vortices in the reaction slurry,which is determined by stirring speed.The kinetics of growth of xonotlite particless is de-termined by measuring the apparent viscosity of the reactant slurry at various reaction time and reaction temperatures.It is found that the growth of particles follows the contracting-volume equation.and the activation energies for nucleation and growth are 104 and 123 kJ-mol,respectively.     

AEROSOL BEHAVIOR IN CHROMIUM WASTE INCINERATION

Cr2O3 is considered as the dominant incineration product during the combustion disposal of chromium waste. A hydrogen/air diffusion flame was employed to simulate the industrial process of incineration. Cr2O3 aerosols were generated inside the flame by the gas phase reaction of chromium and oxygen. Chromium came from the rapid decomposition of chromium hexacarbonyl (Cr(CO)6) at room temperature and was carried into the combustion chamber by hydrogen. Aerosol and clusters can then be easily formed in the flame by nucleation and coagulation. A two dimensional Discrete-Sectional Model (DSM) was adopted to calculate the Cr2O3 aerosol behavior. The experimental measurement method was Dynamic Light Scattering. The numerically predicted results agreed well with those of the experimental measurement. Both results show that the Cr2O3 aerosol size reached about 70 nanometers at the flame top.     

Solid-state synthesis of Li[Li0.2Mn.56Ni0.6Co0.08]O2 cathode materials for lithium-ion batteries

Layered Li[Li0.2Mn.56Ni0.6Co0.08]O2 cathode materials were synthesized via a solid-state reaction for Liion batteries, in which lithium hydroxide monohydrate, manganese dioxide, nickel monoxide, and cobalt monoxide were employed as metal precursors. To uncover the relationship between the structure and electrochemical properties of the materials, synthesis conditions such as calcination temperature and time as well as quenching methods were investigated. For the synthesized Li[Li0.2Mn.56Ni0.6Co0.08]O2 materials, the metal components were found to be in the form of Mn4＋, Ni2＋, and Co3＋, and their molar ratio was in good agreement with stoichiometric ratio of 0.56：0.16：0.08. Among them, the one synthesized at 800 ℃ for 12 h and subsequently quenched in air showed the best electrochemical performances, which had an initial discharge specific capacity and coulombic efficiency of 265.6 mAh/g and 84.0%, respectively, and when cycled at 0.5, 1, and 2 C, the corresponding discharge specific capacities were 237.3, 212.6, and 178.6 mAh/g, respectively. After recovered to 0.1 C rate, the discharge specific capacity became 259.5 mAh/g and the capacity loss was only 2.3% of the initial value at 0.1 C. This work suggests that the solid-state synthesis route is easy for preparing high performance Li[Li0.2Mn0.56Ni0.16Co0.08]O2 cathode materials for Li-ion batteries.     

Comparison of schemes for preparing magnetic Fe3O4 nanoparticles

Magnetic Fe3O4 nanoparticles were prepared by means of coprecipitation using NH3·H2O in water and in alcohol, and using NaOH in water. A series of instruments such as SEM, TEM, HRTEM, FT-IR, XRD and VSM were used to characterize the properties of the magnetic nanoparticles.was the longest. The process using NaOH in water was the simplest and the reaction time was the shortest, but the particle characteristics were inferior to those of the other two methods. The mean size of magnetic Fe3O4 nanoparticles prepared by coprecipitation in alcohol was the smallest among the three, but the nanoparticles aggregated severely. The magnetic Fe3O4 nanoparticles were coated with oleic acid using saturated sodium coated successfully and thoroughly.     

A three-dimensional numerical study on instability of sinusoidal flame induced by multiple shock waves

The instabilities of a three-dimensional sinusoidally premixed flame induced by an incident shock wave with Mach = 1.7 and its reshock waves were studied by using the Navier–Stokes(NS) equations with a single-step chemical reaction and a high resolution, 9th-order weighted essentially non-oscillatory scheme. The computational results were validated by the grid independence test and the experimental results in the literature. The computational results show that after the passage of incident shock wave the flame interface develops in symmetric structure accompanied by large-scale transverse vortex structures. After the interactions by successive reshock waves, the flame interface is gradually destabilized and broken up, and the large-scale vortex structures are gradually transformed into small-scale vortex structures. The small-scale vortices tend to be isotropic later.The results also reveal that the evolution of the flame interface is affected by both mixing process and chemical reaction. In order to identify the relationship between the mixing and the chemical reaction, a dimensionless parameter, η, that is defined as the ratio of mixing time scale to chemical reaction time scale, is introduced. It is found that at each interaction stage the effect of chemical reaction is enhanced with time.The enhanced effect of chemical reaction at the interaction stage by incident shock wave is greater than that at the interaction stages by reshock waves. The result suggests that the parameter η can reasonably character the features of flame interface development induced by the multiple shock waves.     

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.     

DEA/TEAOH templated synthesis and characterization of nanostructured NiAPSO-34 particles:Effect of single and mixed templates on catalyst properties and performance in the methanol to olefin reaction

A nanostructured NiAPSO-34 catalyst was hydrothermally synthesized and the effect of the template（diethylamine（DEA）,tetraethylammonium hydroxide（TEAOH） and DEA/TEAOH） on the physicochemical properties and catalytic performance in the methanol to olefin（MTO） reaction was investigated.The samples were characterized by X-ray diffraction,field emission scanning electron microscopy（FESEM）,particle size distribution analysis,energy-dispersive X-ray spectroscopy,Brunauer-Emmett-Teller analysis and Fourier transform infrared spectroscopy.The X-ray diffraction patterns indicated a higher crystallinity and larger crystallite size for the catalyst synthesized using the DEA template.The FESEM results indicated that the nature of the template could affect the morphology of the nanostructured NiAPSO-34 catalyst because of its effect on the rate of crystal growth.The catalytic performance of the samples was studied in the MTO reaction at atmospheric pressure and a space velocity of 4200 cm³/(g h^-1)in a fixed bed reactor.The stability and activity of the NiAPSO-34 catalyst were improved using the DEA template because of its higher crystallinity,surface area and the greater extent of Ni incorporation into its framework.The possible stages of synthesis and the reaction mechanism for the MTO process over NiAPSO-34 are discussed in detail.     

SYNTHESIS OF SnO2 NANOCRYSTALS BY SOLID STATE REACTION FOLLOWED BY CALCINATION

Nanocrystalline SnO2 was synthesized by direct mixing and grinding of SnCI4-5H2O and NaOH at room temperature, followed by calcination at different temperatures for different times in air. Product samples were characterized by X-ray diffraction and transmission electron microscope, revealing that the amorphous precursor SnO2 was transformed to crystals at 200℃ for 3h, and that the average particle size increased upon raising the calcining temperature or prolonging the calcining time. The mechanism of the phase transformation of the products is discussed.     

Influence of phase and microstructure on the rate of hydrochloric acid leaching in pretreated Panzhihua ilmenite

The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate of Panzhihua ilmenite.The as-pretreated ilmenite was leached with 20%HCl at 105℃.The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes.The leaching kinetics of pure hematite,ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate;the rate of iron leaching occurs in the following order in the HCl solution:hematite(ferric iron) ilmenite(ferrous iron)pseudobrookite(ferric iron).Therefore,the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate.Moreover,the oxidation pretreatment(at 600-1000℃ for 4 h)cannot destroy the dense structure of the Panzhihua ilmenite.Therefore,the influence exerted by the oxidation on the leaching process is primarily determined by the phase change;oxidation at 600 and 700℃slightly increased the rate of iron leaching because the ilmenite was transformed into hematite,while the oxidation at 900-1000℃ significantly reduced the rate of iron leaching because a pseudobrookite phase formed.The reduction effect was subsequently investigated;the as-oxidized ilmenite was reduced under H_2 at 750℃ for 30 min.The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2h in 20%HCl at 105℃.This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.     

DEM simulations of die filling during pharmaceutical tabletting

The flow behaviour of powders from a stationary shoe into a moving die, which mimics the die filling process in a rotary tablet press, was analysed using a discrete element method （DEM）, in which 2D irregular shaped particles were considered. The influence of the particle shape, size and size distribution, the number of particles used in the simulation, the initial height of powder bed in the shoe, and the filling speed on the average mass flow rate and the critical filling speed （the highest speed at which the die can be completely filled） were explored. It has been found that a maximum flow rate is obtained at the critical filling speed for all systems investigated and poly-disperse systems have higher mass flow rates and higher critical filling speeds than mono-disperse systems. In addition, the powder with particles which can tessellate generally has a lower filling rate and a lower critical titling speed.     

A mild one-step solvothermal route to truncated octahedral magnetite crystals

Perfect truncated octahedral magnetite crystals were successfully synthesized from FeCl_3·6H_2O and poly(acrylic acid)(PAA)in an alkaline ethylene glycol solution via a mild one-step solvothermal process.The structure and morphologies of the obtained products were characterized by powder X-ray diffraction(XRD),Raman spectroscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM).The effects of synthetic parameters including reaction temperature,reaction time,and the amount of alkali on the morphological evolution of the truncated octahedral magnetite crystals were systematically explored.160℃ was found to be the optimum temperature for the formation of truncated octahedral magnetite crystals.Below 160 ℃,little magnetite was formed.Above 160 ℃,the truncated octahedrons were gradually transformed into irregular-shaped polyhedrons.Alkali is indispensable in promoting the formation of magnetite at mild temperatures.The truncated octahedral magnetite crystals were found to be ferromagnetic and had a saturation magnetization of about 83 emu/g.     

Direct transformation of FGD gypsum to calcium sulfate hemihydrate whiskers:Preparation,simulations,and process analysis

Calcium sulfate hemihydrate（CSH） whiskers were synthesized by phase transition in CaCl₂ solution under atmospheric pressure.Analytical-grade calcium sulfate dihydrate（AR CSD） was used as the raw material for the synthesis of CSH whiskers,according to orthogonal experiments.The effects of reaction temperature,AR CSD content,H₂SO₄ content,and reaction time were investigated,and the crystallization conditions were optimized.The as-prepared CSH whiskers displayed a regular morphology and a highly uniform size,with an aspect ratio of 105.A simulation system was also established by blending various sulfates with AR CSD,to evaluate the effects of impurities in flue gas desulfurization（FGD） gypsum.The main aim was to prepare CSH whiskers directly from FGD gypsum,without any purification,using the optimized conditions.This is a facile potential alternative process for large-scale production of CSH whiskers using abundant FGD gypsum as source materials.     

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core-shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO3·2Ni(OH)2·2H2O-and Fe2O3·nH2O-coated alumina,graphite and cenosphere were synthesized by precipitation using ferrous sulfate,nickel sulfate,ammonium bicarbonate,alumina,graphite and cenosphere as the main starting materials.Magnetic γ-FeNi-coated alumina,graphite and cenosphere core-shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600℃ for 2h.Precipitation parameters,e.g.concentration of ceramic micropowders(10g/L),sulfate solution(0.2mol/L),rate of adding reactants(3mL/min)and pH value were optimized by a trial-and-error method.Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40nm on alumina,graphite and cenosphere microspheres were characterized by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The magnetic properties of the nanosize γ-FeNi-coated alumina,graphite and cenosphere microspheres were measured by vibrating sample magnetometer(VSM).The results show that the core-shell structuralγ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders,indicating that these materials can be used for high-performance functional materials and devices.     

Influence of suspension stability on wet grinding for production of mineral nanoparticles

Grinding behavior of nanoparticles in an attritor mill and the minimum achievable particle size are strongly influenced by the suspension stability. In the present work, suspension stability （i.e. ξ-potential） of nanoparticles was studied by measuring pH as a function of grinding time in the wet milling process. It was found that after a certain time in an attritor mill, there is no further size reduction and the average product particle size increases monotonically. One of the reasons is that the production of submicron particles leads to more particle-particle interactions and consequently pH of the suspension decreases with grinding time. Usually pH value is related to suspension stability and it can be enhanced by addition of NaOH solution. The maximum negative ξ-potential of -51.2 mV was obtained at pH of 12 for silica. The higher the ξ-potential with the same polarity, higher will be the electrostatic repulsion between the particles. Hence, the maximum electrostatic repulsion force was maintained by the adjustment ofpH value in wet milling. The experiments were conducted at different pH conditions which were maintained constant throughout the experiments and nanosized particles were obtained consequently.     

BUBBLE CHARACTERISTICS IN A TWO-DIMENSIONAL VERTICALLY VIBRO-FLUIDIZED BED

Measurement of bubble size and local average bubble rise velocity was carried out in a vertically sinusoidal vibro-fluidized bed. Glass beads of Geldart group B particles were fluidized at different gas velocities, while the bed was vibrated at different frequencies and amplitudes to study their effects on the bubble behavior. This is compared with the case of no vibration in a two-dimensional bed and it is concluded that with vibration the local average bubble size, dbav, decreases significantly, especially at minimum bubbling velocity. The average bubble size increases slightly with increasing vibration frequency and amplitude. The local average bubble rise velocity is higher than that with no vibration, though with increasing vibration frequency and amplitude, it does not change significantly.     

CFB cyclones at high temperature: Operational results and design assessment

Pressure drop and cut size measurements are reported for a full scale cyclone operating within a 58 MWth CFB-combustor unit at 775 ℃.
The paper reviews the vast number of equations to calculate the pressure drop and separation efficiency of cyclones, generally for operation at ambient temperature and at low Cs [〈0.5]. None of the literature correlations predicts the pressure drop with a fair accuracy within the range of experimental operating conditions. The cut size d50 can be estimated using direct empirical methods or using the Stokes number, Stk50. Both methods were used to compare measured and predicted values of d50. With the exception of Muschelknautz and Krambrock, none of the equations made accurate predictions.
Finally, an alternative method to determine the friction factor of the pressure drop equation （Euler number, Eu） and of the cut size is proposed. The Eu number is determined from the geometry of common cyclones, and the derived value of Stk50 defines more accurate cut sizes. The remaining discrepancy of less than 5%, when compared with the measured values, is tentatively explained in terms of a reduced cyclone diameter due to the solids layer formed near its wall. Further measurements, mostly using positron emission particle tracking, elucidate the particle motion in the cyclone and both tracking results and the influence of the particle movement on Eu and Stk50 will be discussed in a follow-up paper.