Size Measurements of Latex Particles by Laser Aerosol Spectrometer

Size measurements of PSL (polystyrene latex) particles in a size range from 0.109 to 0.330 μm were made by laser aerosol spectrometer (PMS, LAS-X). The results were compared with those by electron microscopy. For example, the geometric standard deviation, σ_g, of nominally 0.176-μm PSL particles was measured as 1.05, assuming that their sizes distribute log-normally. The value of 1.05 was very close to 1.02 measured by electron microscopy. It was found that the spectrometer had very high size resolution, although the size resolution of the light scattering type spectrometer has been said to be poor. For some samples of PSL particles, however, there were large differences between particle sizes measured by LAS-X and those by electron microscopy. It was also found that LAS-X had a problem in calibration of size response curve.     

气溶胶单粒子成分和粒径的实时测量

利用气溶胶飞行时间激光质谱仪测定了两种芳香烃气溶胶的质谱,发现芳香族化合物产生的气溶胶粒子容易形成分子离子峰,对苯二酚还发生分子离子反应.对室内外空气中的气溶胶粒子的粒径进行实时检测的结果表明,室内外空气中的气溶胶粒子多以细粒子为主.实验结果表明,该仪器在大气气溶胶污染监测及相关研究领域具有重要的实用价值.     

浑善达克沙地沙尘气溶胶物理特性的观测分析

浑善达克沙地是我国主要沙尘气溶胶源地之一,但对其沙尘气溶胶特征一直缺乏研究.2001年4月末到5月初,在内蒙古浑善达克沙地利用PMS Fssp--100型激光粒谱仪进行了大气气溶胶的外场观测,取得了晴天、扬沙和沙尘暴天气条件下沙尘粒子的采样资料,通过统计分析研究,总结出浑善达克沙地不同天气条件下近地面沙尘气溶胶的粒谱分布规律.结果显示,沙尘粒谱分布在沙尘天为双峰对数正态函数,晴天和扬沙天为单峰对数正态函数,此结论为沙尘气溶胶辐射气候效应的数值模拟提供了新的实测依据.     

The Effect of Humidity on the Size of Particles Delivered from Metered-Dose Inhalers

The presence of humidity in air supplied to intubated patients has long been identified as a limiting factor in the delivery of therapeutic aerosols during mechanical ventilation. In this work, the well-known reduction in drug delivery to the lung observed when metered-dose inhalers (MDIs) are actuated into warm, humid airflow was investigated through examination of the evolution of particle size distributions delivered from two commercial hydrofluoroalkane (HFA) MDIs actuated through a standard mechanical ventilation holding chamber. Aerosol deposition in the holding chamber and mass median aerodynamic diameter (MMAD) increased significantly with humidity for both MDIs, regardless of the presence of cosolvent and surfactant in one MDI formulation but not the other. However, in humid air MMAD decreased with distance downstream from the holding chamber, again for both MDIs studied. A modification to the popular assumption of MDI particle growth by condensation is proposed, in which condensed water evaporates back into the supplied airflow subsequent to an initial transient, nucleated condensation. It is anticipated that the present improved understanding of MDI aerosol behavior in humid air may lead to the development of enhanced techniques of drug delivery to mechanically ventilated patients.     

操作参数对煤泥脱水效果的影响

探究不同操作参数对煤泥脱水效果的影响,通过改变操作参数进行单因素试验,分别探究入料浓度、入料流量、转鼓转速对煤泥脱水效果的影响,并通过正交试验确定三者的主次序列.结果表明,随着入料浓度的增加,煤泥的脱水效果越来越好,产品的含水率逐渐降低;在一定的入料流量范围内,随着入料流量的增加,产品的含水率降低,但是超过某一流量后,含水率会有所增加;在转鼓最大允许范围内,产品水分随着转速的增加而降低.通过正交试验可以得知影响脱水效果的主次因素依次为转鼓转速、入料流量、入料浓度.     

Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles

The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH₄ NO₃ aerosol. The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle flash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection efficiency measurements. The capability to measure aerosol size and mass distributions is compared to simultaneous measurements using a differential mobility analyzer (DMA) and condensation particle counter (CPC). Quantitative size classification is demonstrated for pure component NH₄ NO₃ aerosols having mass concentrations 0.25_mu g m -3. Results of fluid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and field portable instrument is discussed.     

Effect of Operating Parameters on the Separation of Sugars by Nanofiltration

ABSTRACT

Due to the complexity of fermentation mixtures, separation of solutes and secondary substrates has a special importance. Membrane processes such as nanofiltration may offer good alternatives for the separation of fermentation products or recovery of substrates. For an efficient separation, the membrane type and operating parameters such as feed flow rate, operating pressure, and feed should be optimized. In this study the separation and recovery of sugars were targeted. It was found that with an increase of the feed flow rate, permeate flux increased since the effect of concentration polarization was minimized. As a result, experiments were carried out at the highest possible flow rate. The effect of pressure was studied at five pressures (10–50 bar). It was found that there is a linear relationship between the pressure and permeate flux up to 30 bars. Beyond 30 bars the effect of pressure became less significant. Thus, 30 bars was chosen as the operating pressure. To investigate the effect of concentration, 1 to 10 weight percentage sucrose and glucose solutions were utilized. It was observed that with an increase in concentration, permeate flux decreased and rejections increased, finally reaching a limiting value. Binary solutions of sucrose and glucose were also studied. It was seen that the separation factor slightly decreased, probably due to a glucose–sucrose interaction. Experimental data were used with a mathematical model to predict the permeate flux and rejection. Good agreement of the predicted results was obtained with the experimental data for a 500 MWCO membrane     

Effect of Operating Parameters on the Effectiveness of Electric Field-Enhanced Separations

The purpose of this work is to summarize our latest research results about constant-current electroosmotic dewatering (EOD). The Terzaghi-Voigt combined model is used for the analysis of EOD of various solid-liquid systems by considering the creep deformation of the material. Bentonite clay, KC-flock, zinc oxide, and some of their mixtures are used as experimental materials. It is assumed that the electroosmotic pressure gradient E _pg and modified consolidation coefficient C _e of the materials are constant. The relation between the ratio of creep deformation to total deformation B and the modified consolidation coefficient C _e is determined and compared with previous observations for the case of mechanical expression. The effectiveness of dewatering is described depending on operating parameters such as preconsolidation pressure, material composition, electric current density, and total solid volume per unit cross-sectional area. The model is verified by comparing the calculations with experimental data.     

Size Control and Surface Modification of Colloidal Semiconductor Particles

Several methods for the control of semiconductor particle sizes, in particular in the quantum size regime, are surveyed. Rational choice of solvent polarity, reaction temperature, concentration of reactants, solution pH, and counterions will determine the size and size distribution of the particles. Sizes of colloidal particles formed in microheterogeneous environments will often be predetermined by the dimensions of the micropores and cavities within the network of the medium. This is the situation in zeolite and clay cavities, and in polymer networks. Self-aggregation of amphiphillic molecules often generates microdomains which may be utilized to direct the particle precursors or the particles themselves into these domains and thus limit their growth. Finally, complexation at the surface of the particles may limit and control the growth processes of the particles. The latter approach also allows functional modification of the particles' surface.     

Effect of Operating Parameters on the Condensation of Ammonium Sulfate by Electrodialysis

The separation of ammonium sulfate from dilute solution by electrodialysis was investigated. From the results obtained, it is suggested that it is feasible to separate ammonium sulfate from aqueous solution by electrodialysis. The removal performance of ammonium sulfate obtained was very satisfactory. The optimal cation and anion membranes were found. The removal efficiencies were influenced by voltage, initial concentration, flow rate and temperature. High voltage and high temperature are beneficial to this separation process, but high fluid flow rate and concentrated initial concentration prolong the operation time required to achieve the target value. It was found that the optimal outlet concentration is 1 g/L, since the operation time is prolonged almost two‐fold if the outlet concentration is decreased from 1 g/L to 0.5 g/L.     

Measurement of the Aerodynamic Drag Force on Single Aerosol Particles

The “picobalance” (quadrupole) was used to measure the aerodynamic drag force on individual solid particles and droplets by suspending the object in a laminar jet of gas introduced through the bottom electrode. Particles ranging in diameters from about 1 to 150 μm can be studied in this manner. The DC voltage required to maintain the particle position against the opposing forces of aerodynamic drag and gravity was measured to determine the drag force. The flow velocity at which the aerodynamic drag force balances the gravitational force yields information on the aerodynamic size, and the DC voltage required to suspend the particle against gravity with no flow provides a measure of the particle mass. Particle mobilities for spherical and irregularly shaped solids are presented. Light-scattering measurements for spherical particles provide an independent determination of size; the results are generally in good agreement with the aerodynamic size. It is shown that the electrodynamic balance can be used to measure drag forces much larger than the particle weight.     

Electrodynamic Focusing of Charged Aerosol Particles

An electrodynamic screen for focusing charged particles carried by an airflow stream has been constructed and tested. The screen has the shape of a cone frustum with half-angle of 8° and is 17 cm long. Entrance and exit diameters are 7.0 and 2.5 cm, respectively. Electrodes forming the screen are three 0.71-mm diameter stainless-steel wires configured as a triple-start helix with 2.0-mm pitch. A three-phase power supply drives each wire with a line-to-ground voltage of 2300 V at 350 Hz with a phase difference of 120° between adjacent wires. Test particles of 5.2-μm aerodynamic diameter with electric charge of 1850–6080 elementary units per particle in an aerosol having a mean flow velocity of 4.3×10^?2 m/s parallel to the vertically oriented cone axis are confined and focused with essentially no particle loss. Minimum distance of approach of the test particles to the screen, as found from computer simulation of particle trajectories, solution of the particle equations of motion by linear approximation, and experimental observation, are in good agreement.     

The Effect of Porous Support Composition and Operating Parameters on the Performance of Supported Liquid Membranes

Abstract

Factors, such as porous support composition and operating parameters, that influence the performance of supported liquid membranes (SLMs) were investigated. SLMs of varying porous support compositions and structures were studied for the transport of metal ions. A microporous polybenzimidazole support was synthesized and prepared in the form of an SLM. This SLM, containing the selective extractant di-(2-ethylhexyl)phosphoric acid, was evaluated for the transport of copper and neodymium. Dramatically improved performance over that of commercially available membranes was found in tests for removing the metal ions from solution. Metal ion transport reaches near completion in less than 3 h, whereas Celgard-polypropylene and Nuclepore-polycarbonate reaches only 50% completion even after 15 h. The transport driving force for acidic extractants is a pH gradient between the feed and strip solutions. Polybenzimidazole, an acid- and radiation-resistant polymer, has two protonatable tertiary nitrogens per repeat unit that may help sustain the pH driving force. Another factor may be the ability of the polybenzimidazole to hydrogen bond with the extractant. Transport through the flat-sheet SLMs was tested by using a unique cell design. Countercurrent flow of the feed and strip solutions was established through machined channels in half-cell faceplates that are in a spiral, mirror-image pattern with respect to each other, with the flat-sheet SLM interposed between the two channeled solutions. Advantages comprised in the design of the two clamped half-cells (tangential entry, zero primary pressure, zero pressure differential, controlled flow regimes, no sharp turns, and channeled flow) give operating parameters that will not physically dislodge the liquid membrane from the porous support; consequently, the lifetime of the support is increased. Permeability coefficients remained unchanged after a month of daily use versus 20 to 100% declines for membranes in other cell configurations.     

Bipolar Charging of Ultrafine Aerosol Particles

The stationary bipolar charging characteristics of aerosol particles in the size range between 4.5 and 40 nm have been studied using a new technique whereby the particles neutralized by a ²⁴¹Am radioactive source are enlarged and directly observed in an electric field. The number ratio of charged particles to total particles obtained in this study was found to deviate from the charge distribution obtained from Boltzmann's law and to agree well with that calculated with the bipolar charging theory of Fuchs using his values for the ion properties. The ratio of positively charged to negatively charged particles was found to be approximately 0.35:0.65.

     

反应体系组成对纳米SiO2/PS复合粒子粒径及分布的影响

研究了在纳米SiO2粒子表面的苯乙烯原位聚合反应中,反应体系的组成(单体、引发剂、稳定剂及纳米SiO2粒子用量)对纳米SiO2/PS复合粒子的形态、粒径大小及分布的影响。结果表明,当纳米SiO2粒子与单体质量比为5%,苯乙烯质量分数为25%,引发剂及稳定剂用量分别为单体用量(质量比)的0.15%和1.5%时,制备出的纳米SiO2/PS复合粒子呈球形,表面光滑无明显缺陷,颗粒之间分散性很好,粒径为0.923μm,分散系数为0.108。     

浅谈重灰粒度的控制与大颗粒的消除方法

影响重灰粒度的因素很多,在实际生产过程中化合水温度的控制,粗盐中钙、镁离子的含量等对重灰粒度都有影响,如何保证一水碱的结晶显得尤为关键。通过重灰生产过程中出现一水碱结晶的粗、细情况以及在生产过程中采取的措施进行相应的探讨,对稳定重灰生产有一定的指导意义。     

Rheological Control of the Coffee Stain Effect for Inkjet Printing of Ceramics

The rheology of inkjet printing inks must be well controlled in order to be able to form small droplets. One solution is to use low volume fraction dispersed suspensions, but this leads to a common problem during drying called the coffee stain effect. It is caused by particle migration from the center to the edge of a drying drop and leads to nonuniform printed structures. This article describes an approach, to suppress the coffee stain effect by a sufficiently fast increase in viscosity after deposition. Due to the viscosity limitations during printing, inks with tailored rheology and drying behavior need to be developed. Ceramic inks were prepared and printed. First, a binder was added to study the influence of viscosity on printability and the coffee stain effect. Second, the use of a high vapor pressure solvent for faster drying was investigated. Eventually, an ink with the combination of binder and fast drying agent was prepared. This ink showed a considerable decrease in drying time as well as a rapid increase in viscosity after deposition and was suitable to completely suppress the coffee stain effect. Plateau‐like structures were achieved by adapting the drying temperature to permit particle movement to a certain degree.     

调酸介质对二甲戊灵微胶囊囊形及粒径的影响

[目的]优选出原位聚合法制备二甲戊灵微胶囊的较佳调酸介质,为二甲戊灵的微胶囊化提供一定的理论指导.[方法]以脲醛树脂为壁材采用原位聚合法制备了二甲戊灵微胶囊,研究了不同调酸介质对二甲戊灵微胶囊囊形及粒径的影响.[结果]5％盐酸溶液作为调酸介质形成的微胶囊囊形粗糙,产生粘连,粒径分布较宽;5％硝酸铵溶液、5％硫酸氢铵溶液作为调酸介质形成的微胶囊囊形松散,容易破裂,产生粘连,粒径分布较窄;5％氯化铵溶液作为调酸介质形的微胶囊囊形光滑致密且坚固,粒径分布较窄.[结论]调酸介质对原位聚合法制备的微胶囊囊形及粒径影响很大,选择合适的调酸介质能获得囊形致密、粒径分布窄的微胶囊.     

Effect of the Size of Titanium Particles Released from Dental Implants on Immunological Response

The techniques used in oral implantology to remove bacterial biofilm from the surface of implants by machining the titanium surface (implantoplasty) or by placing rough dental implants through friction with the cortical bone generate a large release of particles. In this work, we performed a simulation of particle generation following clinical protocols. The particles were characterized for commercially pure titanium with particle sizes of 5, 10, 15, and 30 μm. The aim was to determine the effect of particle size and chemical composition of the implant on the immune response. For this purpose, their morphology and possible contamination were characterized by scanning electron microscopy and X-ray microanalysis. In addition, the granulometry, specific surface area, release of metal ions into the medium, and studies of cytocompatibility, gene expression, and cytokine release linked to the inflammatory process were studied. The release of ions for titanium particles showed levels below 800 ppb for all sizes. Smaller particle sizes showed less cytotoxicity, although particles of 15 μm presented higher levels of cytocompatibility. In addition, inflammatory markers (TNFα and Il-1β) were higher compared to larger titanium. Specifically, particles of 15 μm presented a lower proinflammatory and higher anti-inflammatory response as characterized by gene expression and cytokine release, compared to control or smaller particles. Therefore, in general, there is a greater tendency for smaller particles to produce greater toxicity and a greater proinflammatory response.     

影响纳米碳酸钙制备过程的因素分析

Cubic shaped CaCO3 particles with mean size of 30-40 nm were prepared by intermittent carbonation process without any additives. It was found that the flow rate of CO2 has no distinct influence on the particle size in the range of 30-120ml·min-1 under conditions of 13℃ and stirring rate of 680r·min-1. A further increase of flow rate makes the particles larger. When CO2 flow rate is 70ml·min-1, a high agitation rate is in favor of the reduction of the crystal size in the range of 70-680 r·min-1. When flow rate is 120 ml·min-1, the particles prepared at agitation rates of 680r·min-1 and 280r·min-1 have similar sizes, while products prepared at 90r·min-1 have larger size.