Nucleation of Ethylene Glycol Vapor and Growth of Sub-10-nm Particles in Nanoparticle Size Magnifier

We investigated the rates of heterogeneous and homogeneous nucleation of ethylene glycol vapor onto sub-10-nm particles in a newly developed condensation device called nanoparticle size magnifier (NanoPSM). The saturation ratio in the NanoPSM is precisely controlled by vapor-feeding system and mixing section, which are designed based on an earlier particle size magnifier (PSM) developed by Okuyama et al. (1984). Size-classified NaCl nanoparticles smaller than 10 nm in mobility diameter are used as heterogeneous nuclei for the condensation of ethylene glycol vapor. The activation efficiency and growth rate of the activated nuclei are determined by a pulse height analysis using an optical particle counter (OPC). A computer fluid dynamics (CFD) simulation is employed to calculate the profiles of the gas velocity, temperature, vapor concentration, and resulting supersaturation in the NanoPSM. Annular high-supersaturation region is generated around the mixing boundary between cold aerosol and hot vapor. The experimental activation efficiency is 50% for 4.5-nm and 0.8% for 2 nm NaCl particles, through the subsequent growth of droplets to 2 μm in diameter. The experimental data are in fairly good agreement with the predicted activation efficiencies based on the classical Kelvin-Thomson theory when the local profiles of supersaturation are taken into account.     

The Effect of Water Vapor on the Particle Structure and Size of Silica Nanoparticles During Sintering

In this article, the influence of the water vapor concentration on structural changes of SiO₂ aerosol nanoparticle agglomerates during tempering was studied. The presence of water vapor in the carrier gas was shown to strongly accelerate the kinetics of sintering. While dry sintering at temperatures between 1100°C and 1500°C generated aggregates only, the addition of water to the process yields individual, completely coalesced nanoparticles at a temperature of 1300°C. Furthermore, depending on the water vapor concentration and temperature of the process, evaporation and condensation processes could be observed, leading to bimodal size distributions. The results prove the significant role of the water concentration in high temperature synthesis of silica and may be used to improve the control over morphology and specific surface area in these processes.     

The Effect of Temperature on Silicon Nucleation from Melt in Seed-assisted Growth — a Molecular Dynamics Study

Silicon - Based on the Tersoff potential, we investigated the process of silicon nucleation and crystal growth from melt assisted by silicon carbide seed through molecular dynamics simulations. The...     

砂粒和氯离子对P110钢冲刷与腐蚀性能的影响

采用旋转圆盘冲蚀仪并辅以腐蚀电化学工作站分别测试了P110钢(26CrMo4)在含不同砂粒粒径和氯离子浓度溶液中的冲刷腐蚀行为。借助扫描电镜形貌观察,分析了不同氯离子浓度与砂粒粒径对P110钢冲蚀速率和腐蚀行为的影响规律。结果表明:砂粒粒径和氯离子浓度对P110钢冲刷和腐蚀过程有着重要影响,均为腐蚀和机械的协同作用所致。粒径较大的砂粒在冲刷时加速了传质过程,引起腐蚀作用的增加,最终导致整个冲刷腐蚀失重率的增加。氯离子的存在致使腐蚀过程中大量点蚀坑的形成,引起局部冲刷作用的加剧,最终导致P110钢的整个冲刷腐蚀失重速率增加。     

Effect of Polymer Particle Size and Inlet Gas Temperature on Industrial Fluidized Bed Polyethylene Reactors

Static and dynamic bifurcation behaviors dominate the operation of fluidized bed catalytic reactors for the production of polyethylene (UNIPOL Process) and have important implications on the safe operating temperature and polyethylene production rate. The investigations show that the multiplicity of the steady state phenomenon covers a wide range of parameters together with the phenomenon of periodic oscillations with sharply changing amplitudes with a change of the chosen bifurcation parameter. In some cases, the periodic branches terminate through periodic limit point (PLPs), while in other cases it terminates homoclinically. A detailed parameteric investigation using two-parameter continuation diagrams for the loci of static and Hopf bifurcation points as well as one parameter bifurcation diagrams shows that it is possible to increase the productivity of the unit considerably without exceeding the constraints of the polymer melting point. Gas feed temperature, catalyst feed rate, and polymer particle size distribution are important operating parameters in polyethylene fluidized bed reactors. Gas velocity plays a significant role in keeping the fluidized bed bubbling in addition to the fact that it acts as a cooling media by removing excess heat generated from the polymerization reaction. The kinetic behavior of the catalyst and effect of reactor temperature on product properties require, in some cases, operating just below the softening point of the polymer which requires a suitable controller to avoid polymer melting.     

Influence of Dose on Particle Size and Optical Properties of Colloidal Platinum Nanoparticles

Attempts to produce colloidal platinum nanoparticles by using steady absorption spectra with various chemical-based reduction methods often resulted in the fast disappearance of the absorption maxima leaving reduced platinum nanoparticles with little information on their optical properties. We synthesized colloidal platinum nanoparticles in an aqueous solution of polyvinyl pyrrolidone by gamma radiolytic reduction method, which produced steady absorption spectra of fully reduced and highly pure platinum nanoparticles free from by-product impurities or reducing agent contamination. The average particle size was found to be in the range of 3.4–5.3 nm and decreased with increasing dose due to the domination of nucleation over ion association in the formation of metal nanoparticles by the gamma radiolytic reduction method. The platinum nanoparticles exhibit optical absorption spectra with two absorption peaks centered at about 216 and 264 nm and the peaks blue shifted to lower wavelengths with decreasing particle size. The absorption spectra of platinum nanoparticles were also calculated using quantum mechanical treatment and coincidently a good agreement was obtained between the calculated and measured absorption peaks at various particle sizes. This indicates that the 216 and 264-nm absorption peaks of platinum nanoparticles conceivably originated from the intra-band transitions of conduction electrons of (n = 5, l = 2) and (n = 6, l = 0) energy states respectively to higher energy states. The absorption energies, i.e., conduction band energies of platinum nanoparticles derived from the absorption peaks increased with increasing dose and decreased with increasing particle size.     

Effect of Particle Shape on Inline Particle Size Measurement Techniques

The influence of the particle shape on the results of different measuring techniques was investigated. Considered were single‐frequency ultrasound technique, 3D optical reflectance measurement (advanced particle analyzing system with multi capture signal technology), and focused‐beam reflectance measurement probes as techniques which are usable inline and in suspension density ranges usually present in industrial crystallization processes. Advantages and shortcomings of these techniques are compared and discussed.     

离子液体对超声法制备硫化锌粒径及光催化性能的影响

以醋酸锌和硫代乙酰胺为原料,分别以水、离子液以及两者的混合液为溶剂,用超声法成功合成了不同粒径的ZnS纳米粒子。用X射线衍射、扫描电子显微镜、红外光谱以及紫外–可见吸收光谱等对所制备样品的晶型、形貌和光学特性进行表征;以紫外光为光源、甲基橙为目标降解物质评价了ZnS纳米粒子的光催化活性。结果表明：离子液体的引入使ZnS纳米粒子的粒径明显变小,带隙能量变大,离子液介质中合成的ZnS纳米粒子具有更高的光催化活性。     

Sludge Bio-drying Process at Low Ambient Temperature: Effect of Bulking Agent Particle Size and Controlled Temperature

Sludge bio-drying is an aeration process for the removal of water. The drying process utilizes the bio-heat generated from aerobic degradation of organic matter in sludge. In this study, four trials were run in the winter season at ambient temperatures of between 3°C and 9°C. The physical and chemical changes that occurred during the process were investigated and the impacts of the particle sizes of bulking agents and the controlled-matrix temperature were assessed. Results indicated that the process can start up in winter with a three-day lag, while the total duration was only seven days. The highest water removal rate (of 31.0%) with the least organic matter loss (of 12.2%) was obtained at a lower controlled matrix temperature (of 43°C) with a bulking agent of mixed particle size. As a common bulking agent, straw, which has a small particle size of 2–5 mm, was beneficial for organic matter degradation, while it had a negative effect on water removal. The use of different types of straw (with larger particle size of 20–30 mm) as the bulking agent gave poor performance, in which the organic matter degradation rate was 9.75% and the water removal rate was 25.9%. Higher controlled temperature (53°C) resulted in less aeration but degradation rates were enhanced to 16.8%. The using of lower temperatures (43°C) resulted in lower water removal rate (of 29.2%) and relatively lower biodegradation rate.     

催化剂粒径对水合异丁烯反应的影响

在半连续浆态搅拌釜中,使用NKC-9离子交换树脂细粉作为催化剂,考察了颗粒粒径对异丁烯水合反应速率的影响。试验结果表明,催化剂颗粒在105μm以上时内扩散影响较严重。在30μm以下,速率随颗粒粒径减小而加快的趋势较为明显。     

颗粒粒径和膜孔径对陶瓷膜微滤微米级颗粒悬浮液的影响

通过测定颗粒悬浮液通过陶瓷微滤膜时的参透通量及污染阻力,确定了陶瓷膜处理微米级颗粒悬浮液时,颗粒粒径和膜孔径对微滤过程的影响和膜污染机理,获得了微米级颗粒悬浮液微滤过程中膜孔径的选择方法。     

利用激光粒度仪测定城市池塘水体的悬浮物粒度分布

使用激光粒度仪测定城市池塘水体中悬浮物颗粒的粒度分布,并探索最适宜的测量参数。测定结果表明,在泵速为1800r／min,遮光度为5％,15％的测量条件下,测量结果有较好的重现性,并且与显微镜测定结果基本符合。     

Effect of Pore Size and Particle Size Distribution on Granular Bed Filtration and Microfiltration

Abstract

The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.     

The Synthesis and Evaluation of Up-scalable Molybdenum Based Ultra Dispersed Catalysts: Effect of Temperature on Particle Size

Unsupported molybdenum (Mo) micro/nanoparticle size range catalysts have been synthesized via precursor salts dissolved within a water-in-oil emulsion and online injected to a decomposition zone simulating processing conditions. The particles were characterized via DLS, reactivity tests and SEM. The effect of decomposition temperature on particle sizes was studied in both a horizontal reactor and vertical reactor configuration.     

RDX粒度对机械感度的影响

系统研究了RDX粒度对撞击感度和摩擦感度的影响．实验测试的RDX平均粒径为1．5～124μm,并在此粒度范围内分为5个粒度等级。其中撞击感度用特性落高法表示,摩擦感度用特性正压力表示。结果表明：炸药的撞击感度、摩擦感度均随粒度的减小而降低。从理论上分析了炸药粒度变化对机械感度影响的机理。     

粒径对褐煤煤粉流动性影响研究

为了给工业制备流动性好的煤粉提供技术支撑,采用工业分析仪、扫描电子显微镜和超声衰减粒度仪对6种不同粒径的褐煤进行了分析,并采用流动性指数法研究了粒径对煤粉流动性的影响规律,分析表明6种不同粒径褐煤的工业分析组分相近,褐煤颗粒表面粗糙、结构疏松且具有丰富的孔隙结构.研究发现采用休止角、平板角、压缩度或流动性指数获得褐煤煤粉流动性的结论存在差异,流动性指数法用于评判煤粉流动性具有较高的可靠性.流动性指数法表明124～1000μm的煤粉流动性良好,74～124μm的褐煤流动性相当良好,45～74μm的褐煤流动性一般,小于45μm的褐煤流动性不大好,褐煤的流动性随粒径减小而变差.