Facile Chemical Synthesis and Characterization of Copper Tungstate Nanoparticles

Copper tungstate nanoparticles were synthesized by a chemical precipitation reaction in aqueous ambient involving direct addition of copper ion solution to the solution of tungstate reagent. Optimization of the synthesis procedure was carried out using Taguchi robust design as a statistical method. In order to controllable, simple and fast synthesis of copper tungstate nanoparticles, effects of some synthesis conditions such as reagents concentrations (i.e., copper and tungstate ions), flow rate of copper feeding and temperature of the reactor on the particle size of synthesized copper tungstate were investigated by the aid of an orthogonal array. The results of optimization process showed that copper tungstate nanoparticles could be prepared by controlling the effective parameters and at optimum conditions of synthesis procedure, the size of prepared copper tungstate particles was about 56 nm. Chemical composition and microstructure of the prepared copper tungstate nanoparticles were characterized by means of X-ray diffraction, scanning electron microscopy, UV–Vis spectrophotometry, FT-IR spectroscopy and Photoluminescence.     

火焰合成法制备TiO2的燃烧发生器研究进展

火焰合成法是指前驱物在燃烧器中经过一系列复杂的物理化学反应过程得到产物纳米颗粒的方法,具有一步合成的优点,是现代工业规模化制备高性能材料的一种重要方法。火焰合成过程机理涉及物质的相态变化、颗粒生长团聚和热量质量交换等复杂过程,探究火焰合成过程是实现产物颗粒调控的关键。本文对火焰合成过程中的关键部分,如前驱物、为合成过程提供高温氧化环境的燃烧器、产物颗粒等进行分析,阐述了火焰气溶胶技术中颗粒的生长及转变路径、不同燃烧器的结构及其温度场、流场特点,并分析了不同燃烧器合成的纳米TiO₂进行了粒径及晶型特点的研究进展。指出火焰合成TiO₂生长机理和形态调控的基础研究对工业制备钛白粉具有指导意义。     

Surfactant-free synthesis of poly (styrene-co-acrylamide) monodisperse nanoparticles using hybrid flow-to-batch chemistry

We have demonstrated a hybrid flow-to-batch process for synthesizing monodisperse poly(styrene-co-acrylamide) nanoparticles via a surfactant-free emulsion radical polymerization. The flow-to-batch synthesized nanoparticles have a smaller average particle size, tighter particle size distribution, higher molecular weight, and lower molecular weight distribution compared to conventionally batch-synthesized nanoparticles. Our results also indicate that the flow-to-batch synthesized nanoparticles have more hydrophilic acrylamide segments on the particle surface than the batch-synthesized nanoparticles. These results demonstrate that a flow synthesis process can improve the quality of nanoparticles due to the efficient mixing and heat transfer in a flow reactor and simplify the scale up of nanoparticle synthesis in a conventional chemistry lab.     

12-磷钨酸体系水热法制备金颗粒及其表征

利用Keggin结构的12-磷钨酸作为软模板,采用水热法还原氯金酸制备金颗粒. 考察了AuCl4-离子与12-磷钨酸的摩尔比、反应时间及反应温度对Au颗粒的影响. 用TEM, UV-Vis, FESEM, XPS, XRD等手段对所制金纳米颗粒的形貌、组分、粒径和结构进行了表征. 结果表明,HAuCl4与磷钨酸反应速率较快,可获得尺寸范围较大的球形、三角形、多孪晶和六边形等不同形貌的Au颗粒. 对Au颗粒的形成机理进行了探讨.     

Continuous synthesis of monodispersed silver nanoparticles using a homogeneous heating microwave reactor system

Continuous synthesis of silver nanoparticles based on a polyol process was conducted using a microwave-assisted flow reactor installed in a cylindrical resonance cavity. Silver nitrate (AgNO(3)) and poly(N-vinylpyrrolidone) (PVP) dissolved in ethylene glycol were used respectively as a silver metal precursor and as a capping agent of nanoparticles. Ethylene glycol worked as the solvent and simultaneously as the reductant. Silver nanoparticles of narrow size distributions were synthesized steadily for 5 h, maintaining almost constant yield (>93%) and quality. The reaction was achieved within 2.8 s of residence time, although nanoparticles were not formed under this flow rate by conventional heating. A narrower particle size distribution was realized by the increased flow rate of the reaction solution. Nanoparticles of 9.8 nm average size with a standard deviation of 0.9 nm were synthesized at the rate of 100 ml h(-l).     

Rapid quenching by supersonic expansion and injection of water

Gaseous components or gasborne particles in flows are often sensitive to mid range temperatures, whereby unintended side products or aggregated particles develop during cooling processes. Supersonic quenching combines high gasdynamic cooling rates of dT/dt<−10⁶ K/s with a total enthalpy reduction through evaporation of an injected liquid. In this manner the residence time at critical temperatures is minimized. Up to now there are no publications covering this particular application. Preliminary test results regarding the massive water injection into a supersonic laval nozzle flow are presented as well as the developed supersonic quench concept and corresponding design rules. Essential is the suppression of an anew temperature rise downstream of the supersonic domain when the gas is compressed and decelerated again. Therefore liquid injection into the supersonic domain and its partial evaporation within it is a key feature. Despite the massive water injection the gas flow must remain in a supersonic regime. In addition to water injection from the wall a moveable slender cone equipped with water jets is extending into the divergent nozzle from the exit to enhance the coverage of the cross-sectional area with dispersed water. Presented experimental results in form of pressure and temperature profiles prove the functional efficiency of the supersonic quench. Pressure profiles attest the supersonic conditions downstream of the water injection and define the supersonic domain length. Two dimensional temperature plots demonstrate the sufficient water distribution, the suppression of hot subsonic zones and the total evaporation of the injected water within the quench domain. Applied to “Gasdynamically induced nanoparticle synthesis” spherical non-aggregated nanoparticles are obtained.     

火焰法合成纳米TiO2颗粒生长过程

在新型火焰反应器生产纳米TiO2的过程中使用TEM微栅在不同火焰高度位置处进行原位取样分析,得到生长过程中纳米TiO2颗粒的粒径和形态. TiO2颗粒经历了成核、生长、聚并、烧结的过程. 调节反应物浓度为7.9×10-5~5.7×10-3 mol/L,研究了不同反应物浓度对纳米颗粒生长过程的影响,高前驱体浓度形成较高的单体浓度,使颗粒间碰撞几率增加,从而得到粒径较大的颗粒,产物粒径17~85 nm. 调节CH4和O2流量,改变温度场,研究温度对颗粒生长过程的影响,在相同反应物浓度条件下,较高的温度下形成分散性好、一次粒径为63 nm的颗粒,而在较低的温度下形成的颗粒一次粒径为35 nm,但颈部烧结严重;增加喷嘴气流速度减小了反应停留时间,颗粒粒径从63 nm减小到36 nm.     

Operation characteristics of a new liquid-solid circulating moving bed reactor

The liquid-solid circulating moving bed reactor is a novel one, which consists of two or more reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through an upper conduit and to the particle transport system through a lower conduit, and then are conveyed into the upper reaction chamber through a riser. The circulating rate of particles and the flow of liquid in the two conduits are key factors to the continuous steady operation of the reactor; they can be controlled by varying operating conditions: the outlet liquid flow rate in the regeneration chamber, the outlet liquid flow rate in the reaction chamber, the inlet liquid flow rate of the reactants, and the flow rate of driving flow. A flow model has been proposed to quantify the operation characteristics of the reactor. The results predicted by the model show satisfactory agreement with the experimental data.     

A molecular simulation study on the sintering mechanism of TiO2

The sintering process of TiO₂ nanoparticles with different particle sizes and temperatures was studied thoroughly using equilibrium molecular dynamics simulations. The results show that when two nanoparticles contact, the sintering process was initiated by the merge of surface atoms of nanoparticles, and the process subsequently drives the internal atom to merge until two particles being merged homogeneously. There is mutual attraction between atoms and the particles gain kinetic energy to migrate due to the heating at high temperatures, leading to a faster sintering reaction. Moreover, there is a large difference in the sintering speed between 1600 and 1800 K. In the vicinity of the melting point, a small change in temperature makes a great impact on the sintering rate of TiO₂ nanoparticles. Furthermore, by using the Lindemann index, it can be found that the larger particles have higher lattice structure stability compared to the smaller ones. The larger particle has a greater effect on the sintering behaviors when particles with different sizes’ contact. As a consequence, the sintering of two particles with different sizes is mainly initiated by the smaller particles moving toward the larger particle and is ended up with the atoms of smaller particle spreading around the larger particle. Therefore, the large nanoparticle size reduces the overall sintering rate.     

A Novel Porous Tube Reactor for Nanoparticle Synthesis with Simultaneous Gas-Phase Reaction and Dilution

A novel porous tube reactor that combines simultaneous reactions and continuous dilution in a single-stage gas-phase process was designed for nanoparticle synthesis. The design is based on the atmospheric pressure chemical vapor synthesis (APCVS) method. In comparison to the conventional hot wall chemical vapor synthesis reactor, the APCVS method offers an effective process for the synthesis of ultrafine metal particles with controlled oxidation. In this study, magnetic iron and maghemite were synthesized using iron pentacarbonyl as a precursor. Morphology, size, and magnetic properties of the synthesized nanoparticles were determined. The X-ray diffraction results show that the porous tube reactor produced nearly pure iron or maghemite nanoparticles with crystallite sizes of 24 and 29 nm, respectively. According to the scanning mobility particle sizer data, the geometric number mean diameter was 110 nm for iron and 150 nm for the maghemite agglomerates. The saturation magnetization value of iron was 150 emu/g and that of maghemite was 12 emu/g, measured with superconducting quantum interference device (SQUID) magnetometry. A computational fluid dynamics (CFD) simulation was used to model the temperature and flow fields and the decomposition of the precursor as well as the mixing of the precursor vapor and the reaction gas in the reactor. An in-house CFD model was used to predict the extent of nucleation, coagulation, sintering, and agglomeration of the iron nanoparticles. CFD simulations predicted a primary particle size of 36 nm and an agglomerate size of 134 nm for the iron nanoparticles, which agreed well with the experimental data.

Copyright 2015 American Association for Aerosol Research     

OPERATION CHARACTERISTICS OF A NEW LIQUID-SOLID CIRCULATING MOVING BED REACTOR

The liquid-solid circulating moving bed reactor is a novel one, which consists of two or more reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through an upper conduit and to the particle transport system through a lower conduit, and then are conveyed into the upper reaction chamber through a riser. The circulating rate of particles and the flow of liquid in the two conduits are key factors to the continuous steady operation of the reactor; they can be controlled by varying operating conditions: the outlet liquid flow rate in the regeneration chamber, the outlet liquid flow rate in the reaction chamber, the inlet liquid flow rate of the reactants, and the flow rate of driving flow. A flow model has been proposed to quantify the operation characteristics of the reactor. The results predicted by the model show satisfactory agreement with the experimental data.     

液固循环移动床反应器操作规律和模拟

液固循环移动床反应 -再生系统由上下两个或两个以上的反应室、再生室、连通管和颗粒提升管组成 .颗粒经再生室、反应室向下移动 ,进入输送管后被向上输送返回至再生室 .颗粒循环能力和各流股间的窜液行为是循环移动床连续操作的关键 .通过实验对该液固循环移动床的颗粒循环、斜管窜液和连接段窜液的规律进行了研究 ,同时建立了循环移动床的液固流动模型 ,并进行了模拟计算     

基于CFD⁃DEM的水下切粒装置水室内颗粒流动过程数值模拟

基于CFD?DEM耦合方法,研究了颗粒在水室内的流动状态,分析了不同刀盘转速、粒子水通入量和水室出口角度对造粒过程的影响,发现提高刀盘转速、增加粒子水通入量和水室出口倾斜一定的角度都有利于水室内颗粒的排出。进一步研究了颗粒与碎屑在水室内的流动,发现在水室出口处二者的流动基本呈现出一定的分离角度。     

Parameter studies of the synthesis of titanium dioxide nanoparticles: Effect on particle formation and size

The large scale synthesis of TiO₂ nanoparticles in the nonaqueous benzyl alcohol route was investigated with respect to the influence of process parameters, like temperature, pressure, reactor filling ratio, agitator speed and precursor concentration, on the induction time of particle formation and particle size. A coherence of the varied process parameters and the molecular reaction mechanism was found that supports the suggested mechanism of particle formation, representing an important step toward a controllable and predictable particle synthesis.     

Process intensification of synthesis of magnetite using spinning disc reactor

An instantaneous co‐precipitation reaction for the synthesis of magnetite particles has been investigated in conventional mechanically agitated reactor and novel spinning disc reactor (SDR) with an objective of process intensification. Characteristics of the particles have been analysed using Coulter Counter particle analyser. It has been observed that the particle size distribution is more uniform with overall lower power consumption in the SDR as compared to the conventional reactors. With a viewpoint of improving the synthesis process in terms of the obtained conversion levels in the SDR, effect of different operating parameters viz. rotational speed, diameter and type of the disc, flow rate of the reactants and the operating temperature on the synthesis process has also been investigated. It has been observed that the flow rate of the reactants as well as disc characteristics have a significant influence on the extent of conversion. Overall, it has been established that the SDR gives excellent particle size distribution characteristics as compared to the conventional approaches and hence results in process improvement/intensification for magnetite synthesis process at comparatively lower energy inputs.     

H2 production by steam-quenching of Zn vapor in a hot-wall aerosol flow reactor

Hydrogen production by steam-hydrolysis of zinc is investigated as part of a two-step water-splitting thermochemical cycle based on ZnO/Zn redox reactions. The hydrolysis reactor consists of a hot-wall tube containing a flow of Zn(g) that is steam-quenched to co-produce H₂ and Zn/ZnO nanoparticles. The effects of the quenching gas flow rate and reactor wall temperature on the Zn-to-ZnO chemical conversion and particle yield are examined. Solid products are characterized by X-ray diffraction, N₂ adsorption, and SEM microscopy. Quench rates of 2-6×10⁴ K/s yielded conversions of up to 95% at the expense of low particle yield due to significant wall deposition with subsequent hydrolysis. Aerosol particles with hexagonal structure were formed by Zn evaporation-condensation containing low ZnO mass fraction. In contrast, operation at quench rates up to 10⁶ K/s led to increased particle yield but lower conversion. Filamentary and rod-like particles were formed with high ZnO content by surface reaction and coagulation.     

Synthesis of Lithium-Cobalt Oxide Nanoparticles by Flame Spray Pyrolysis

Crystalline LiCoO2nanoparticles were synthesized from an aqueous solution of acetate compounds of lithium and cobalt by a flame spray pyrolysis, and characterized by TEM, XRD, and BET method. We investigated the evolution of LiCoO2nanoparticles from liquid droplets sprayed along the flame and observed disintegration of aqueous precursor droplets about 10μm into smaller fragments around 50 nm in the high temperature flame, as well as decomposition/oxidation of the precursor and coalescence/coagulation. We also examined effects of process variables such as molar concentrations of the precursors and flow rates of combustible gases on the particle size and crystal structure. The average particle diameter increased with an increase in the molar concentration of the precursor. Raising the maximum flame temperature by controlling the gas flow rates also led to an increase in the average diameter of the particles. The crystalline nanoparticles synthesized were nearly spherical, and their average primary particle diameters ranged from 11 to 35 nm.     

Facile synthesis of tetrapodal ZnO nanoparticles by modified French process and its photoluminescence

Facile synthesis of tetrapodal ZnO nanoparticles was conducted using a modified French process in which oxygen and nitrogen flow rates were controlled. The synthesized ZnO nanoparticles exhibit photoluminescent characteristics depending on the synthesis conditions. Electron microscopic analysis revealed that the tetrapodal nanostructure of ZnO with high crystallinity which was confirmed by XRD analyses could be controlled by a variation of O₂/N₂ feed ratio. Typical photoluminescence with UV and blue emission of the tetrapodal ZnO nanoparticles was influenced by the particle size and crystallinity, which is manipulated by the oxidation condition.