Displacement of Ammonium from Aerosol Particles by Uptake of Triethylamine

The displacement of ammonium by triethylammonium (TEAH) in aerosol particles of about 15–35 μm in diameter was investigated using an electrodynamic balance (EDB) coupled with in situ Raman spectroscopy. The phase state of particles played a crucial role in the extent of triethylamine (TEA) uptake. At 50 or 75% relative humidity (RH), the heterogenous uptake of about 40-ppm TEA by aqueous ammonium salts of sulfate [(NH₄)₂SO₄], bisulfate (NH₄HSO₄), nitrate (NH₄NO₃), chloride (NH₄Cl), and oxalate [(NH₄)₂C₂O₄] led to increases in particle mass of over 90%. A complete displacement of ammonium by TEAH was confirmed by direct EDB mass measurements and the Raman spectra obtained. TEAH sulfate was formed during the exposure of aqueous droplets of (NH₄)₂SO₄ and NH₄HSO₄ to TEA vapor at 50% RH; but a fraction of it decomposed to TEAH bisulfate when the TEA supply was removed. Crystalline solid particles of (NH₄)₂SO₄ and (NH₄)₂C₂O₄ experienced small mass increases of <5%, both of which were attributed to the hindered mass transfer of TEA in crystalline solids. However, TEA reacted with the amorphous solid NH₄NO₃ particle at <3% RH as effectively as if it was in the aqueous NH₄NO₃ droplet (50% RH) and formed TEAH nitrate. On the other hand, the amorphous NH₄HSO₄ solid particle reacted with TEA at <3% RH to form crystalline (NH₄)₂SO₄ and liquid TEAH bisulfate and sulfate. The formation of rather inert crystalline (NH₄)₂SO₄ suppressed the ammonium exchange.

Copyright 2012 American Association for Aerosol Research     

高压二氧化碳电镀钴薄膜颗粒形貌

本文研究了高压二氧化碳电镀钴薄膜颗粒形貌的影响。实验高压二氧化碳分别为液态((15 MPa,25℃),亚临界态((15 MPa,30℃),超临界态((15 MPa,40℃)。高压二氧化碳电镀在高压釜中进行电镀,电镀液使用20%体积分数的高压二氧化碳和80%体积分数的钴电镀液。本文同时研究了温度和电流密度的影响。钴薄膜颗粒形貌随着温度的下降和电流密度的上升由片状转变为棱锥状以及半球状结构。     

Hydrated Binders and Preserving Agents for Lime Refractories

Basically new binding and preserving agents for refractories containing free CaO are described. The efficiency of these hydrated agents comes from the specific properties of supersaturated phosphate solutions used for their preparation.     

Indentation Creep of Hydrated Soda–Lime Silicate Glass Determined by Nanoindentation

Time-dependent deformation behavior was investigated for soda–lime silicate glass with various water contents, using a nanoindentation technique. The complete indentation curve, loading and unloading part, is analyzed. It is shown that this deformation behavior may be represented in terms of a simple mechanical model analogous to a viscoelastic system. Values for Young's modulus were derived, a retardation spectrum was deduced, and apparent viscosity values were calculated. Structural rearrangements of the glass appear to be responsible for the observed changes of the viscoelastic properties. Water in the glass reduces Young's modulus and yield stress and thus promotes viscous flow.     

Scattering and Absorption by Elongated Aerosol Particles

Recently we developed a new technique, the iterative extended boundary condition method, which is suitable for calculating the scattering and absorption by elongated particles in a broad frequency range, including at resonance. This paper briefly describes this technique, illustrates its capabilities, and presents the results of its most recent extensions. This includes the implementation of a sectioning procedure and the use of a new segmentation method for calculating scattering by very long oriented chains of aerosols. Results of absorption cross sections in two different frequency ranges, visible and infrared, and for two different polarizations, parallel and end-fire polarizations, will be presented. The range of validity of some reported relationships between scattering from a single particle and from coagulated particles are discussed. It is shown that in the end-fire polarization case the sum of the absorption by separate n particles (P _sum) is more than the absorption by a chain of n coagulated particles (P _end-fire), while in the parallel polarization case, the ratio between P _parallel/P _end-fire may be as high as a factor of 4. This observation emphasizes the importance of taking the polarization into account in calculating light scattering by elongated chains of aerosols.     

以水合二氧化锰混凝去除原水中的污染物

以高锰酸钾还原法制备的水合MnO2对模拟原水进行了混凝实验,探讨了水合MnO2作为新型净水剂在给水处理中应用的可行性;并对水合MnO2粒子的结构及界面性质进行了表征,探讨了其除污染的可能机制。结果表明：该水合二氧化锰具有丰富的表面羟基、晶型为δ-MnO2、比表面积为151．422m^2／g。在较低投量时（2～3mg／L）即表现出对原水的优良的混凝效能,可使滤后水浊度降至1NTU以下。     

Controlled Synthesis of Nanosized Particles by Aerosol Processes

Solid particles in the 1 nm < d_p < 100 nm size range form in gases as a result of gas phase condensation, particle collision processes, and solid-state processes. The relative rates of sintering and collision determine the size and morphology of the spheroidal primary particles. Rapid sintering is equivalent to the classical theory of coagulation with instantaneous coalescence. When the sintering rate is slow compared with the collision rate, fine primary particles form and aggregate into irregularly shaped agglomerates. The growth of primary particles in an aerosol generator that is cooling at a constant rate was studied theoretically. The most important process parameter determining particle diameter is the maximum gas temperature, because the rate of sintering is a sensitive function of temperature. Aerosol volume loading and cooling rate are important when the rate of particle growth is limited by collision processes. Experiments on the formation of alumina particles were made to study these effects. Predictions of primary particle size did not agree well with experimental measurements, which is attributed to an inadequate understanding of solid-state diffusion processes in nanosized particles. Other experiments showed that low concentrations of sodium and potassium additives reduce the primary particle size of silica.     

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.     

Field Charging of Fine Aerosol Particles by Unipolar Ions

Unipolar charging of fine aerosol particles by gaseous ions has been investigated in the presence of an electric field with a strength of E ≤ 4 kV/cm. It has been found that, when the ion conductivity of the medium in the charging zone is kept constant, variation of the ion mobility spectrum caused by change in the ion polarity or by addition of vapor of various liquids does not affect the particle charging. The measured mean particle charge for the particle radii, ranging from 0.05 to 1.5 μm, is shown to be in agreement with the theoretical data calculated as a sum of charges acquired by the particles owing to the diffusion and field charging mechanisms.     

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.

     

Transport Phenomena with Single Aerosol Particles

This is a review of theory and experiments related to single aerosol particle transport processes. The theories of mass, heat, momentum, and charge transfer are outlined, with emphasis on mass transport in the continuum and noncontinuum regimes. Included in the discussion of mass transfer are single and multicomponent droplet evaporation, a comparison of the results of solutions of the Boltzman equations for Knudsen aerosol evaporation and growth and experimental methods for the study of single droplet evaporation or growth. Of particular concern here are the experimental apparati and techniques developed for single particle measurements. These range from the Millikan oil drop experiment through the electrostatic balance (the Millikan condenser with automatic stabilization of the particle) to the electrodynamic balance. The principles and applications of these instruments are reviewed.     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

Electrostatic and Inertial Collection of Aerosol Particles by Water Droplets

Inertial impaction and electrostatic attraction are generally the two most important mechanisms for the collection of charged micron-sized particles by charged droplets. An experiment was carried out to determine the collision efficiencies of charged 142-μm-radius water droplets for charged micron-sized particles under different values of the electrostatic force. Experimental results agree well with a trajectory model that used a numerically derived flow field for the 142-μm-radius droplets.     

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.     

Detection of Spatial Correlations among Aerosol Particles

Most approaches for evaluating rates of fundamental processes in aerosol science depend upon the implicit assumption that aerosol particles are independently and identically distributed in space. The validity of this assumption has not been examined in several decades, despite the fact that the presence of correlations can be shown to alter theoretical expressions significantly for such phenomena as attenuation of electromagnetic radiation and coagulation rate. Here, we provide evidence that the classification of the positions of aerosol particles as a Poisson process--even under stationary conditions--is often in error. In particular, small-scale aerosol clustering is experimentally demonstrated. Some consequences of these findings are discussed.     

Synthesis of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Using a Carbon Dioxide Laser

The synthesis and the structure of silicon carbide-silicon nitride (SiC─Si₃N₄) composite ultrafine particles have been studied. SiC─Si₃N₄ composite ultrafine particles were prepared by irradiating a SiH₄, C₂H₄, and NH₃ gas mixture with a CO₂ laser at atmospheric pressure. The composition of composite powders changed with the reactant gas flow rate. The carbon and nitrogen content of the powder could be controlled in a wide range from 0 to 30 wt%. The composite powder, which contained 25.3 wt%. carbon and 5.8 wt% nitrogen, had a (β-SiC structure. As the nitrogen con- tent increased, SiC decreased and amorphous phase, Si₃N₄, Si appeared. The results of XPS and lattice constant measurements suggested that Si, C, and N atoms were intimately mixed in the composite particles.     

Filtration of Multi-Walled Carbon Nanotube Aerosol by Fibrous Filters

Filtration efficiency of multi-walled carbon nanotube (MWCNT) aerosol by fibrous filter was evaluated experimentally. Mono-mobility test aerosols with electrical mobility diameter of 100, 200, and 300 nm were generated by the atomization of MWCNT aqueous suspension followed by mobility classification with a differential mobility analyzer (DMA). By analyzing the shape of classified aerosol particles under a scanning electron microscope, it was found that the DMA-classified 300 nm particles were fibrous in shape and had uniform diameter of about 60 nm and length of 2.1 micrometer. On the other hand, 100 nm and 200 nm particles contained a fairly large amount of multiply charged fibrous particles with a larger diameter. These test aerosols were challenged to a medium performance fibrous filter at various filtration velocities. As a result, fibrous particles were captured by fibrous filter at a higher collection efficiency than the spherical particles with the same mobility. By analyzing the single fiber capturing efficiency, interception incorporating the rotation of fibrous particles is found to be the dominant capturing mechanism for the fibrous particles in the studied size range.     

Regeneration of Activated Carbon Loaded with Toluene by Supercritical Carbon Dioxide

Abstract

Activated carbon loaded with toluene was regenerated by supercritical carbon dioxide. The adsorptive capacities after several regeneration cycles were still close to that of virgin carbon and remained stable. The effects of temperature, pressure, and flow rate on regeneration efficiency were studied. It was found that the operations at higher pressures were more favorable for regeneration, but the optimal operating temperature depended on pressure. The interphase mass transfer resistance was insignificant during regeneration. A one-parameter mathematic model assuming linear desorption kinetics is proposed which agrees well with the experimental data. The adsorption rates of activated carbon regenerated by the supercritical regeneration method and the steam regeneration method are compared in this study. It was found that the supercritical regeneration method is superior to the steam regeneration method.     

二氧化碳法制备纳米级氧化锌

研究了以锌泥为原料,采用二氧化碳法制备纳米级氧化锌的生产工艺,考察了乳化、合成、干燥、煅烧等工艺过程,结果表明：锌浆固液比为1／4,反应温度为80℃,反应压力为0．8MPa,搅拌速度1000μm,碳化时间90min,煅烧温度400℃,煅烧时间120min,得到的纳米级氧化锌产品粒径小于50m,比表面积在50m。幢以L,应用该工艺建成了一套1000t／a的生产装置。     

微米级气溶胶粒子在滤层中的收集效率研究

采用颗粒床过滤系统对含气溶胶气体进行过滤实验,研究微米级气溶胶粒子在滤层中过滤效率的变化规律,并建立滤层模型计算过滤效率理论值.结果表明,在低风速(u0≤0.2m/s)范围内,过滤风速的提高有利于大粒径气溶胶粒子(dP=2.5 μm)的收集,而对中小粒径气溶胶粒子(dp≤1.0μm)的过滤效率没有明显帮助;滤料材质相同时,滤料粒径越小、比表面积越大,过滤效率越高;材质不同时,Hamaker 常数越大,越有利于捕集气溶胶粒子.由颗粒床层模型分析得出,当dp<0.1μm时,扩散效应起主导作用,颗粒粒径越小,扩散效率越高;当dp>1.0μm时,惯性碰撞效应起主导作用,粒径越大,惯性碰撞和拦截效应越显著.