CuO/H2O纳米流体的池沸腾传热及预测

通过络合-沉淀法合成氧化铜纳米颗粒,制备铜颗粒的直径在40～100 nm,晶型为正六面体。利用“两步法”制备水基氧化铜纳米流体。考察了不同质量分数纳米流体的热导率、接触角变化和加热表面颗粒沉积对核沸腾传热性能的影响,并利用可视化记录沸腾过程气泡行为。结果表明：在测试质量分数范围内,传热系数随热通量增加而增大,当质量分数达到0.1%时,强化率最大为146.1%。经过分析可知纳米流体的接触角度、热导率、颗粒沉积以及颗粒扰动对水基氧化铜纳米流体强化传热作用均有影响。通过高速摄像采集质量分数0.07%纳米流体沸腾过程验证结论的可靠性。并对纳米流体核沸腾传热过程建立气泡动力学经验模型,模型计算结果与实测值相对偏差在±10%以内。     

Densification and Grain Growth of Fe-Doped and Fe/Y Codoped Alumina: Effect of Fe Valency

The effect of iron and iron/yttrium codoping on the densification and grain growth of ultra high-purity (99.995%) fine-grained alumina has been studied. The experiments were carried out under both oxidizing (flowing air) and reducing conditions (N₂/H₂ mixture, p O₂∼5.1 × 10⁻¹⁴). For studies carried out in air, relative to undoped alumina, the addition of 1000 ppm Fe was found to reduce the densification rate by a factor of 5 and also retard the grain growth rate. This result, which was consistent with tensile creep data obtained in a separate study, was attributed to the retardation of grain-boundary diffusive processes by segregating Fe(III) ions. In contrast, under reducing conditions the 1000 ppm Fe- doped samples exhibited an increase in the densification rate of 2.5 orders of magnitude over that of the undoped samples. In the case of the codoped compositions (1000 ppm Fe/1000 ppm Y), for heat treatment in air, the densification behavior did not differ significantly from that of samples singly doped with Y (1000 ppm). However, under reducing conditions, the presence of the Fe²⁺ in the samples appeared to compensate for the retarding effect of the yttrium, such that the densification rate of the codoped samples was comparable with that of the undoped material. A mechanism based on compensating point defects is invoked to rationalize the more rapid kinetics under reducing conditions.     

Structural features of copper halide phase in CuBr-containing glasses

The structural changes in copper halide phase regions upon secondary heat treatments of copper halide aluminosilicate glasses at temperatures in the range 20–520°C have been studied by the small-angle X-ray scattering (SAXS) technique. It is revealed that regions of copper halide phase are characterized by the degree of internal dispersion due to the separation of drops of this phase upon cooling and its crystallization. Upon heat treatment at temperatures above the melting point of copper halide phase, the drops within the phase regions coalesce into larger drops, which, in particular, brings about the change in the melting and crystallization temperatures of nanoparticles. It is demonstrated that, upon low-temperature heat treatments (T< T _g), copper enters into the regions of copper halide phase, which leads to the change in its composition (enrichment with CuBr) and also to the precipitation of particles of new phase (presumably, amorphous copper) in the free volume (vacuum pore) of copper halide phase regions. The crystallization processes caused by the change in composition and the catalyzing effect of copper particles are observed at temperatures above the liquidus point of copper halide phase precipitated upon the primary heat treatment.     

Structural features of copper halide phase in CuBr-containing glasses

The structural changes in copper halide phase regions upon secondary heat treatments of copper halide aluminosilicate glasses at temperatures in the range 20–520°C have been studied by the small-angle X-ray scattering (SAXS) technique. It is revealed that regions of copper halide phase are characterized by the degree of internal dispersion due to the separation of drops of this phase upon cooling and its crystallization. Upon heat treatment at temperatures above the melting point of copper halide phase, the drops within the phase regions coalesce into larger drops, which, in particular, brings about the change in the melting and crystallization temperatures of nanoparticles. It is demonstrated that, upon low-temperature heat treatments (T< T _g), copper enters into the regions of copper halide phase, which leads to the change in its composition (enrichment with CuBr) and also to the precipitation of particles of new phase (presumably, amorphous copper) in the free volume (vacuum pore) of copper halide phase regions. The crystallization processes caused by the change in composition and the catalyzing effect of copper particles are observed at temperatures above the liquidus point of copper halide phase precipitated upon the primary heat treatment.     

Preparation,characterizations, and antibacterial properties of Cu/SnO<Subscript>2</Subscript> nanocomposite bilayer coatings

A nano-bilayer structure consisting of copper and SnO₂ nanocomposites was prepared by a magnetron sputtering method. A nano-SnO₂ thin layer with a thickness of 52 nm was achieved on quartz glass. A nano-copper layer was then deposited on top of the SnO₂ thin layer by the sputtering method. The thickness of the nano-copper layer was approximately 7 nm, such that the SnO₂ layer was not only completely covered by the copper layer but it also resulted in transparent bilayer films. Post-annealing was carried out at 400°C in air for 1 h to obtain a crystalline SnO₂ phase and simultaneously the copper layer was oxidized to CuO. Sputtered nanocomposites of CuO/SnO₂ bilayer films showed a synergistic effect toward E. coli inactivation under indoor light exposure. A possible mechanism for the synergistic effect with respect to the antibacterial properties of CuO/SnO₂ bilayer nanocomposites has been proposed. Incorporating CuO onto the SnO₂ layer achieves photocatalyst works under indoor light and provides an antimicrobial function even under a dark environment by the antimicrobial property of CuO itself. Reported CuO/SnO₂ sputter coating can be useful to apply, for instance, to electric devices such as touch panel displays in a hospital in order to reduce hospital-acquired infections (HAIs).     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

Purification and particle size control of β-SiC powder using thermocycling process

Abstract

Recently, SiC single crystal growth has been of interest for the development of an alternative semiconducting material. The aim of this study was to purify and grow β-SiC particles for use as a single crystal source. First, a β-SiC powder with a particle size of about 10 μm and a purity of 99·5% was prepared from a phenyl-containing silica sol. Then, three different of heat treatment process were applied to grow the β-SiC particles and evaluate the effects of heat-treatment time and temperature. After three thermocycling processes carried out from 1850 to 2000°C in 1 h, the β-SiC particles had diameters over 100 μm because of a vaporisation–recrystallisation process that accelerated the β-SiC particle growth. Moreover, the thermocycling process improved the purity of β-SiC by eliminating metallic impurities.     

Effect of nanodiamond surface functionalization using oleylamine on the scratch behavior of polyacrylic/nanodiamond nanocomposite

Addition of hard particles such as nanodiamonds to polymers to improve their physical and mechanical properties is very common. However, nanodiamonds are usually hydrophilic so their tendency to form agglomerates in a polymeric matrix is quite strong. In this study, the effect of nanodiamond surface modification on its uniform dispersion in a polymeric matrix such as polyacrylic-base polymer clear coat was investigated. For this purpose, detonation nanodiamond (DND) with an average particle diameter of 4–6 nm was used. To improve dispersion of as-received DND (AR-DND) in the polymeric matrix, the surfaces of the particles were modified by heat treatment (oxidation) in air and followed by functionalization using oleylamine (OLA) as surfactant. So, nanocomposites with different contents of AR-DND, HT-DND and OLA treated HT- DND (OLA-HT-DND) particles were produced. Their characterizations were investigated by employing many analytical methods such as: Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermo-gravimetry analysis (TGA). Scratch resistance test and study of coating surfaces, using scanning tunneling microscopy (STM), were carried out on the polymeric nanocomposites. The results showed that the surface-functionalized nanodiamonds are highly dispersive and stable in the polymeric matrix. In addition, scratch resistance was increased with the addition of nanoparticles.     

Detection of Phase Separation by FTIR in a Liquid-Crystal-Display Substrate Aluminoborosilicate Glass

The effect of heat treatment on the Fourier transform infrared spectrometry (FTIR) reflection peak position of the Si–O structural band near 1087 cm⁻¹ of a liquid-crystal-display substrate glass was investigated. The FTIR peak position shifted more slowly with heat-treatment time, and to a greater extent than expected, for the fictive temperature change. The isochronal shift of the FTIR peak as a function of the heat-treatment temperature exhibited a good correlation with the change of chemical durability in an HCl solution, suggesting that the infrared peak shift was the result of the phase separation induced by the heat treatment. The separated phase, with spherical particles ∼50 nm in diameter, was observed by scanning electron microscopy in a glass sample heat-treated at 750°C for 2500 h. The FTIR peak shift measurement appears to be a sensitive method for detecting the early stage of the glass-in-glass phase separation for borosilicate glasses.     

Metal copper films coated on microparticle substrates using an ultrasonic-assisted magnetron sputtering system

Metal copper films were coated on micrometer silicon carbide (SiC) and polymer particles with different sizes using the ultrasonic-assisted magnetron sputtering system. The surface morphology, the chemical composition and the crystallization of the SiC and the polymer particles were characterized by the field emission scanning electron microscopy (FE-SEM), energy dispersive analysis of X-rays (EDAX) and X-ray diffraction (XRD) analysis before and after film deposition. The experiment results indicate that the copper films were successfully coated on SiC and polymer particles. The XRD results show that the copper films have a face centred cubic structure. It was found from the FE-SEM results that film growth of copper films is a three-dimensional island growth mode.     

显色工艺对纳米CdSexS1-x微晶玻璃光吸收曲线性能的影响

采用不同的热处理显色工艺对掺杂Se和CdS着色剂的硼硅酸盐玻璃进行热处理,制备出一系列的纳米硒硫化镉颜色玻璃,研究了热处理显色工艺对玻璃光透过性能的影响。结果表明,玻璃的截止吸收波长位置取决于热处理条件;采用低温长时间热处理工艺,使所制备的玻璃具有较高的光透过率和完整的吸收边界。微观结构分析表明,热处理后玻璃中出现的纳米微晶等结构变化是导致玻璃着色、出现光截止吸收的根本原因。     

Effect of Heat Treatment on Rapidly Quenched AgI-Based Silver Orthoborate Glasses Containing Large Amounts of AgI

The effect of heat treatment on the twin-roller rapidly quenched 75AgI·18.7Ag₂O6.3B₂O₃ glass was investigated by differential scanning calorimetry (DSC), high-temperature X-ray diffraction (XRD), and field-emission-type scanning electron microscopy. The glass had an inhomogeneous microstructure with dispersed particles 40-60 nm in diameter at room temperature. On the other hand, island regions of several hundred nanometers with fine dispersed particles about 20-30 nm in diameter were observed in the glass after heating to 120°C. DSC and high-temperature XRD measurements revealed that crystallization occurred at around 120°C, which is lower than the α-β phase transformation temperature (147°C), to form α-AgI in the glass. The crystallization of α-AgI from the glass below the α-ß phase transformation temperature strongly supports the possibility of the existence of α-AgI nuclei in AgI-based silver orthoborate glasses. Validating the existence of AgI microcrystals supports the microdomain model for superionic AgI-based glasses.     

Synthesis and Application of Stable Copper Oxide Nanoparticle Suspensions for Nanoparticulate Film Fabrication

Colloidal suspensions of copper oxide (CuO) nanoparticles were prepared by an alcothermal method, in which copper acetate was reacted with sodium hydroxide in the presence of acetic acid in ethanol at 78°C. The prepared suspension was stable for up to 1 month without stabilizers such as surfactants. Transmission electron microscopy analyses revealed that the suspension contained nanosized CuO particles of 5–10 nm size with a narrow size distribution. Nanoparticulate CuO films packed with grains smaller than 60 nm were fabricated on Si substrates by spin coating a suspension of CuO nanoparticles and subsequent heat treatment at 500°C.     

Properties of BaTiO3 synthesized from barium titanyl oxalate

In order to enhance the tetragonality of BaTiO₃ derived from barium titanyl oxalate (BTO), various treatments were carried out by considering the thermal decomposition mechanism of BTO in air. A multi-step heat treatment process and the addition of carbon black, as a particle growth inhibitor, were effective in increasing the tetragonality, whilst maintaining a particle size smaller than 200 nm. The synthesized BaTiO₃ powder with a mean particle size of 177 nm showed a tetragonality and K-factor of 1.0064 and approximately 3, respectively.     

Synthesis and characterization of sol-gel bioactive glass nanoparticles doped with boron and copper

In this work the sol-gel synthesis of bioactive glass nanoparticles containing both boron and copper oxides is reported for the first time in the literature. Two acid/base co-catalysed methods were compared. The obtained glasses have been characterized in terms of morphology, composition, particle surface area, phase analysis and bioactivity in acellular simulated body fluids. The almost spherical nanoparticles (<100 nm diameter) obtained are characterized by a certain degree of aggregation and have compositions, which are coherent with the theoretical ones. Each glass revealed the ability to promote the growth of hydroxyapatite on its surface during soaking in simulated body fluid, thus we can assume that the addition of boron and copper did not negatively affect the bioactivity of the sol-gel derived glasses. Future investigations will be devoted to biological characterizations for cytotoxicity, antibacterial properties and pro-angiogenetic abilities.     

New Particle Formation and Growth in an Isoprene-Dominated Ozark Forest: From Sub-5 nm to CCN-Active Sizes

Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT NOIR) were conducted in a Missouri forest dominated by isoprene emissions from May to October 2012. This study presents results of new particle formation (NPF) and the growth of new particles to cloud condensation nuclei (CCN)-active sizes (～100 nm) observed during this field campaign. The measured sub-5 nm particles were up to ～20,000 cm^?3 during a typical NPF event. Nucleation rates J₁ were relatively high (11.0 ± 10.6 cm^?3 s^?1), and one order of magnitude higher than formation rates of 5 nm particles (J₅). Sub-5 nm particle formation events were observed during 64% of measurement days, with a high preference in biogenic volatile organic compounds (BVOCs)- and SO₂-poor northwesterly (90%) air masses than in BVOCs-rich southerly air masses (13%). About 80% of sub-5 nm particle events led to the further growth. While high temperatures and high aerosol loadings in the southerly air masses were not favorable for nucleation, high BVOCs in the southerly air masses facilitated the growth of new particles to CCN-active sizes. In overall, 0.4–9.4% of the sub-5 nm particles grew to CCN-active sizes within each single NPF event. During a regional NPF event period that took place consecutively over several days, concentrations of CCN size particles increased by a factor of 4.7 in average. This enhanced production of CCN particles from new particles was commonly observed during all 13 regional NPF events during the campaign period.

Copyright 2014 American Association for Aerosol Research     

Dense Nanostructured Hydroxyapatite Coating on Titanium by Aerosol Deposition

In order to improve biocompatibility of Ti metal substrates, 1-μm-thick nanostructured hydroxyapatite (HAp) coatings were deposited on the substrates through aerosol deposition, which sprays HAp powder with an average particle size of 3.2 μm at room temperature in vacuum. The original HAp particles were fractured into nanoscale fragments to form highly dense coating during the deposition process. Density of the HAp coating was 98.5% theoretical density (TD). Transmission electron microscopy observation revealed that the as-deposited coating consisted of HAp crystallites with average grain size of 16.2 nm and amorphous phase. Tensile adhesion strength between the coating and the substrate was 30.5±1.2 MPa. Annealing up to 500°C in air increased crystallinity and grain size in the coating without any delamination or crack according to X-ray diffraction analysis and electron microscopy. MTS assay and alkaline phosphatase activity measurements with MC3T3-E1 preosteoblast cell revealed that the biocompatibility was greatly improved by postdeposition heat treatment at 400°C in air due to well-crystallized HAp with average grain size of 29.3 nm. However, further heat treatment at 500°C deteriorated biocompatibility due to rapid growth of HAp grains to average size of 99 nm. Cross section of the coating on a commercially available Ti dental implant revealed full coverage of the surface with HAp.     

Characterization of media mills based on mechanical energy applied to particles

This paper deals with the evaluation of characteristics of media mills having a different milling mechanism based on the mechanical energy applied to the particles to be processed during a milling treatment. Spherical copper powder was used as a stress-sensitive material and the milling treatment of the copper powder was carried out under various operating conditions using three types of media mills, a horizontal tumbling ball mill, vertical agitating ball mill and bead mill. The size distributions of copper powder before and after the milling treatment were measured and the deformation of copper particles was determined experimentally. The net energy applied to the copper powder was estimated from the plastic deformation of copper particles. It has been clarified that the applied energy depends strongly on the motion of media in the mill. By introducing two dimensionless parameters, which express the energy transfer efficiency from the kinetic energy of media to the particles and the motion of media in the mill, respectively, the media mills could be characterized on a uniform scale based on the applied energy regardless of milling mechanism.