HYDROTHERMAL SYNTHESIS OF NANO-METER MICROPOROUS ZINC FERRITE

Nano-meter microporous zinc ferrite was prepared by a hydrothermal method,using triethylamine as a template.Adsorption curves showed that the product had a microporous structure.The effects of precursor pH.reaction temperature and reaction time on the preparation were studied,yielding optimal conditions:pH=11.448K,360mm,The morphology of zinc ferrite as observed by TEM,showed that zinc ferrite was well-crystallized and well-dispersed with little conglomeration.     

Synthesis of Mg–Al–carbonate layered double hydroxide by an atom-economic reaction

A clean method for preparing layered double hydroxides (LDHs) has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reaction. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester. The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps (SNAS) method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment.     

Li2SiO3 fast microwave-assisted hydrothermal synthesis and evaluation of its water vapor and CO2 absorption properties

A series of lithium metasilicate (Li₂SiO₃) powder materials has been successfully synthesized by the microwave-assisted hydrothermal route using lithium hydroxide and tetraethyl-orthosilicate-derived sol precursors. Ceramic powders were obtained under hydrothermal conditions of autogenous pressure in the presence of a nonionic surfactant. The production of pure and well-crystallized Li₂SiO₃ using very short reaction times at low temperatures was shown by X-ray diffraction, scanning electron microscopy, and N₂ adsorption-desorption analyses. Synthesized Li₂SiO₃ particles were nanocrystalline and exhibited different morphologies and specific surface areas depending on the synthesis conditions. Additionally, the capability of selected Li₂SiO₃ samples to absorb H₂O and CO₂ was evaluated via thermogravimetric analyses by varying the temperature, carrier gas, and water vapor concentration. Li₂SiO₃ particles exhibited interesting textural and morphological characteristics that make them suitable for use as a CO₂ absorbent and which suggest that they also have the potential to be used in other applications.     

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.     

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.     

A novel preparation of nanosized hexagonal Mg(OH)2 as a flame retardant

Nanosized dispersive hexagonal magnesium hydroxide (Mg(OH)₂) has been prepared using an ammonia-hydrothermal method. Citric acid and monoethanolamine (MEA) were added to the reaction system during the ammonia precipitation and hydrothermal processes, respectively, to improve the crystallinity and dispersion of the (Mg(OH)₂) particles. The resulting Mg(OH)₂ samples obtained under the optimum preparation conditions were characterized by scanning electron microscopy, X-ray diffraction and thermal gravity analysis, which showed that this newly developed procedure afforded well-dispersed hexagonal nanoplates of Mg(OH)₂ with a mean diameter of 246 nm.     

Synthesis of Mg-Al-carbonate layered double hydroxide by an atom-economic reaction

A clean method for preparing layered double hydroxides (LDHs) has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reactions. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester.The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps (SNAS) method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment.     

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4–NaCl–H2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization (FGD) gypsum. When purified FGD gypsum was used as raw material, the morphology and phase structure of the hydrothermal products grown in pure water, H₂SO₄–H₂O, NaCl–H₂O, and H₂SO₄–NaCl–H₂O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated. The results indicate that calcium sulfate whiskers grow favorably in the H₂SO₄–NaCl–H₂O system. When prepared using 10–70 g NaCl/kg gypsum −0.01 M H₂SO₄–H₂O at 130 °C for 60 min, the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 μm and lengths from 200 to 600 μm, and their phase structure was calcium sulfate hemihydrate (HH). Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed. With the co-presence of sulfuric acid and sodium chloride in the reaction solution, the concentrations of Ca²⁺ and SO₄²⁻ can be kept relatively stable, which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.     

45~#钢表面纳米晶层的高温磨损特性

通过增压喷丸方式使45#钢实现表面纳米化,采用MMU-5G高温材料端面磨损试验机进行45#钢纳米晶层摩擦磨损性能随温度变化的试验,利用TEM表征喷丸后表层的组织,DSC与显微硬度研究纳米层的热稳定性,XPS和SEM表征磨损表面的成分及形貌.结果发现:当温度低于200℃时,喷丸样品表面硬度高,有效减少实际接触面积,耐磨性能优于未喷丸样品;在200～400℃之间时,纳米化样品表层组织结构中存在大量的晶界、位错、空位等缺陷为氧原子与金属原子提供更多的扩散通道,加速疏松的Fe2O3氧化物的形成与脱落,耐磨性能低于未喷丸样品;在400～550℃之间时,喷丸样品由于回复与再结晶,与未喷丸的耐磨性能基本一致.     

Elastic and Dielectric Properties of Active Ag/BaTiO<Subscript>3</Subscript> Composites

This study examines the elastic and dielectric properties of active composites consisting of barium titanate (BaTiO₃) and silver (Ag) constituents using experimental and numerical approaches. The elastic constants including Young’s modulus, shear modulus and Poisson’s ratio were measured by resonant ultrasound spectroscopy (RUS), a nondestructive dynamic technique, while a dielectric (impedance) spectroscopy was used to measure the relative permittivity and dielectric loss at different frequencies. The dielectric tests were also conducted at temperature ranges from ?50 to 200 °C where the two phase transformations of barium titanate at around 0 °C and 120 °C were examined. The experimental results in this study were compared to data available in the literature. In addition to the experimental work, a numerical method is also considered in order to study the effects of blending silver into barium titanate on the effective elastic and dielectric properties of the composite and the local field fluctuations. For this purpose, two micromechanics models describing the detailed composite microstructures were constructed. The first model is based on two dimensional (2D) images of realistic microstructures obtained by the scanning electronic microscopy (SEM), while the second model is based on randomly generated three-dimensional (3D) microstructures with spherical particles. The effects of loading direction, porosity, particle shape and dispersion were examined using the micromechanics models. Numerical predictions of the effective elastic and dielectric constants were compared to the experiment results.     

Residual strain measurement in composites using the cure-referencing method

This paper describes the details of a novel procedure called the cure-referencing method (CRM) to measure the strains associated with residual stresses on the surface of composite panels. The CRM involves the replication of diffraction gratings onto the surface of composite specimens during the autoclave during cycle. Residual strains associated with the curing process are measured using moiré interferometry at room temperature after the specimens have been taken out of the autoclave. The procedures for both the grating replication and the moiré interferometry experiment are described in detail. A method of high-temperature moiré interferometry was developed to resolve the residual strains due to thermal expansion from those due to chemical matrix shrinkage and stress relaxation. These procedures are demonstrated on unidirectional and multidirectional laminates and on woven textile composites.     

Controllable magnetic properties of cobalt ferrite particles derived from layered double hydroxide precursors

Cobalt ferrite CoxNi1-xFe2O4 (x=0, 0.5, 1) particles with controllable magnetic properties have been pre-pared by calcination of co-substituted NiFe2+Fe3+-layered double hydroxide (NiFe2+Fe3+-LDH) precursors prepared via a scalable method involving separate nucleation and aging steps (SNAS). Their structural and magnetic characteristics were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). Measurements of magnetic properties show that the saturation magnetization (Ms) and coercivity (Hc) of the calcined products increased with increasing cobalt content. The LDH precursor-based product obtained by calcination of a mixture of CoFe2+Fe3+-LDH and NiFe2+Fe3+-LDH powders with a Co/Ni molar ratio of 1:1, exhibits a moderate value of Ms and an increased value of Hc compared to the corresponding values for an Ni0.5Co0.5Fe2O4 material prepared by calcination of a Co0.5Ni0.5Fe2+Fe3+-LDH precursor, and a physical mixture of CoFe2O4 and NiFe2O4 with a Co/Ni molar ratio of 1 : 1. These results may provide a way to regulate magnetic anisotrupy of ferrite spinels by varying the composition of the LDH precursors.     

Insight into the interaction between water and surfactant aerosol particles based on molecular dynamics simulations

The ubiquitous surfactant significantly influences the hygroscopic growth of atmospheric aerosol particles. However, knowledge on the morphology of surfactant particles after the adsorption of water is insufficient. In this study, the interaction between water and particles composed of surface active malonic acid (MA) or adipic acid (AA) are simulated based on the molecular dynamics method. The key point is the combined effect of temperature and water content on the structural properties of particles and the surface propensity of surfactants at the equilibrium state. Results show that demixed structure 1 with the adsorption of water clusters on acid grain, mixed structure and demixed structure 2 with acids coating on water droplet can be observed. With temperature increasing from 160 K to 330 K the surface propensity of MA and AA increases first and then weakens. Near the standard atmospheric temperature (280–330 K), the surface propensity of MA and AA increases with increasing water content and alkyl group, and its sensitivity to temperature and water content varies regularly. Moreover, all surfactants at the particle surface orient their hydrophobic groups toward the gas. These findings improve our insight into the surfactant partitioning and further assist in more accurate prediction of the particle hygroscopic growth.     

水平流动边界层内气固相间作用的试验研究

应用三维粒子动态分析仪（threedimensionalparticledynamicsanalyzer）,测量了含有230μm颗粒的气固两相水平流的特性,特别是壁面边界层内的两相流动特性．结果表明颗粒载荷比（质量流率）对相间作用有较大影响,随颗粒流率的增加颗粒对气流平均速度和湍流的影响增大,颗粒使气流速度边界展变薄．颗粒和气流相互作用在不同方向上呈各向异性,颗粒对气流垂直方向的脉动影响较大．颗粒与湍流边界层气流的作用行为大致可以分成三个区域：贴壁区、中间区和外流区．     

Melting of horizontal ice layer from above by combined effect of temperature and concentration of aqua-solvent

This paper is concerned with the melting of horizontal ice layer from above by aqua-solvent with low solidification point. The solute used in this experiment are Sodium chloride NaCl, Calcium chloride CaCl₂, Magnesium chloride MgCl₂, and Urea CO(NH₂)₂- The upper surface of aqua-solvent melt layer is heated by an infrared lamp, whose temperature is in the range of about 8 ?C to 40 ?C. The ice layer located under the aqua-solvent melt layer melts greatly by a combined effect of both thermal energy and chemical reaction, and the typical temperature distribution in both aqua-solvent and ice layer is examined. The relation between melt amount of ice layer per unit temperature gradient and mean concentration in aqua-solvent melt layer was obtained.     

Micromechanical modeling of the effect of particle size difference in dual phase steels

Dual phase (DP) steels having a microstructure consisting of martensite islands, referred to as particles, dispersed in a ferrite matrix have received a great deal of attention due to their useful combination of high strength, high work hardening rate and ductility, all of which are favorable properties for forming processes. The martensite particles display two distinct deformation mechanisms, depending on their size. Small particles are reported in the literature to undergo no measurable plastic deformation and thus can be described as rigid particles dispersed in a matrix of ferrite. On the other hand, large particles reportedly experience a small degree of plastic deformation, which has a significant influence on the mechanism of deformation of such materials. Although most micromechanical models assume a uniform particle size, a distribution of sizes in DP-steels is a more realistic assumption. In this work, a micromechanical model is developed to capture the effect of particle size differences on the mechanical behavior of DP-steels. It is shown that the difference becomes most significant when the ratio of the small to large particle size is approximately 1/2. At low volume fractions of martensite, the effect of a distribution of particle sizes is negligible, but at intermediate and high volume fractions of martensite the interaction due to the size difference becomes quite important. The model displays the intrinsic ability of capturing the steep rise in the strain-hardening rate observed in DP-steels. The model also successfully predicts the mechanisms involved in the deformation process in the DP-steels in agreement with experimental observations reported in the literature.     

LSCF材料氧化还原过程的力化学耦合瞬态三维模拟

镧锶钴铁氧体(LSCF)具有良好的化学催化性能和导电性能,未来有望被应用于能源工程领域.在周围环境氧气浓度变化时,LSCF会通过化学反应与周围环境交换氧.这一过程往往会引起化学应力并可能危害设备安全.本文对LSCF棒在氧化还原循环过程中的反应-扩散过程进行了力化学耦合建模.表面处的化学反应动力学考虑了浓度、应力和温度的影响.通过有限元方法分别求解出三种给定的不同表面化学反应速率下棒伸长量和棒端部附近第一主应力的瞬态解.     

Development and characterization of orthotropic-birefringent materials

Materials were selected and fabrication procedures developed for orthotropic-birefringent materials. An epoxy resin (Maraset 658/558 system) was selected as the matrix material. Fibers obtained from Style 3733 glass cloth and Type 1062 glass roving were used as reinforcement. Two different fabrication procedures were used. In the first one, layers of unidirectional fibers removed from the glass cloth were stacked, impregnated with resin, bagged and cured in an autoclave at elevated temperature. In the second procedure, the glass roving was dry-wound over metal frames, impregnated with resin and cured at room temperature under vacuum and pressure in the autoclave. Unidirectional, angleply, and quasi-isotropic laminates of two thicknesses were fabricated. The matrix and the unidirectional glass/epoxy material were fully characterized. The density, fiber-volume ratio, mechanical, and optical properties were determined. The fiber-volume ratio was over 0.50. Birefringent properties were in good agreement with predictions, based on a stress-proportioning concept and also, with one exception, with properties predicted by a finite-element analysis.     

Hydrothermal synthesis and physicochemical characterization of CuO/ZnO/Al2O3 nanopowder. Part I: Effect of crystallization time

A hydrothermal method was successfully used for synthesis of CuO/ZnO/Al₂O₃ (CZA) nanopowder with atomic ratio of 6:3:1. The effect of crystallization time (3, 6, 9, and 12 h) on physicochemical properties of nanopowder was investigated. Nanopowders were characterized using XRD, FESEM, EDX, FTIR, TG, and BET techniques. The XRD patterns confirmed metal oxides formation and their good crystallinity with average crystallite size of 20 nm as obtained by the Scherrer equation. Relative crystallinity was shown to increase with increasing crystallization time. In agreement with XRD results, FESEM images also illustrated nanosized particles. EDX mapping indicated homogenous dispersion of elements. BET specific surface area analysis showed acceptable surface area for CZA nanopowder. FTIR spectroscopy confirmed metal oxides formation during hydrothermal and calcination processing. TG results illustrated high thermal stability of the synthesized nanopowders. TG-DTG and FTIR analyses were used to propose a reaction mechanism for nanopowder formation during processing. Physicochemical characterization showed optimal crystallization time to be 6 h.     

INTERPARTICLE FORCES IN HIGH TEMPERATURE FLUIDIZATION OF GELDART A PARTICLES

Previous reports and current studies show that fluidization of some Geldart A particles is enhanced by in-creasing bed temperature.Both the averaged local particle concentration and the particle concentration in the dense phase decrease with increasing bed temperature,at constant superficial gas velocities.However,conventional models fail to predict these changes,because the role of interparticle forces is usually neglected at different bed temperatures.Here.the temperature increases,the interparticle attractive forces decrease while the interparticle repulsive forces increase.Consequently.fluidization behaviors of some Geldart A particles seem to increasingly shift from typical Geldart A towards B with increasing temperature.